Astrophysics


astro-ph new abstracts, Wed, 18 Jan 06 01:00:09 GMT
0601346 -- 0601375 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0601357 [abs, ps, pdf, other] :
Title: Pulsar rotation measures and the large-scale structure of Galactic magnetic field
Authors: J.L. Han (NAOC), R.N. Manchester (ATNF), A.G. Lyne (Jodrell Obs), G.J. Qiao (PKU), W. van Straten (UTB)
Comments: ApJ accepted. 16 pages, 14 figures, 2 tables, 223 pulsar RMs

The large-scale magnetic field of our Galaxy can be probed in three dimensions using Faraday rotation of pulsar signals. We report on the determination of 223 rotation measures from polarization observations of relatively distant southern pulsars made using the Parkes radio telescope. Combined with previously published observations these data give clear evidence for large-scale counterclockwise fields (viewed from the north Galactic pole) in the spiral arms interior to the Sun and weaker evidence for a counterclockwise field in the Perseus arm. However, in interarm regions, including the Solar neighbourhood, we present evidence that suggests that large-scale fields are clockwise. We propose that the large-scale Galactic magnetic field has a bisymmetric structure with reversals on the boundaries of the spiral arms. Streaming motions associated with spiral density waves can directly generate such a structure from an initial inwardly directed radial field. Large-scale fields increase toward the Galactic Center, with a mean value of about 2~$\mu$G in the Solar neighbourhood and 4~$\mu$G at a Galactocentric radius of 3 kpc.

 
astro-ph/0601368 [abs, ps, pdf, other] :
Title: Bistable Profile Illumination in Pulsars B0919+06 & B1859+07
Authors: Joanna M. Rankin (University of Vermont), Cameron Rodriguez (University of Vermont), Geoffrey A.E. Wright (University of Sussex)
Comments: 9 pages, 4 figures, submitted to MNRAS

A new single pulse behaviour has been identified in two pulsars, B0919+06 and B1859+07. Normally both starts emit bright subpulses in a region near the trailing edge of heir profile. However, occasionally these stars exhibit "events" wherein the emission longitude gradually decreases by about their profile width, remains in this position for typically tens of pulses and then gradually returns over a few pulses to the usual longitude. The effect bears some resemblance to a profile "mode change", but here the effect is gradual and episodic. When the separated profiles of the normal and "event" emission, they reveal a broad and complex profile structure in each pulsar - but one which can probably be understood correctly in terms of a single conical beam. Possibly the effect entails an extreme example of "absorption"-induced profile asymmetry, as suspected in other pulsars. Alternatively, shifting sources of illumination within the pulsar beam may be responsible.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0601061 [abs, ps, pdf, other] :
Title: Gravitational field energy contribution to the neutron star mass
Authors: M.Dyrda, B.Kinasiewicz, M.Kutschera, A. Szmaglinski
Comments: 19 pages, 18 figures

Neutron stars are discussed as laboratories of physics of strong gravitational fields. The mass of a neutron star is split into matter energy and gravitational field energy contributions. The energy of the gravitational field of neutron stars is calculated with three different approaches which give the same result. It is found that up to one half of the gravitational mass of maximum mass neutron stars is comprised by the gravitational field energy. Results are shown for a number of realistic equations of state of neutron star matter.

 

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Astrophysics


astro-ph new abstracts, Thu, 19 Jan 06 01:00:11 GMT
0601376 -- 0601399 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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Astrophysics


astro-ph new abstracts, Fri, 20 Jan 06 01:00:08 GMT
0601400 -- 0601453 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0601410 [abs, ps, pdf, other] :
Title: General Relativistic Force-Free Electrodynamics: A New Code and Applications to Black Hole Magnetospheres
Authors: Jonathan C. McKinney (Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics)
Comments: 14 pages, 4 figures, accepted for publication in MNRAS Main Journal

The force-free limit of magnetohydrodynamics (MHD) is often a reasonable approximation to model black hole and neutron star magnetospheres. We describe a general relativistic force-free (GRFFE) formulation that allows general relativistic magnetohydrodynamic (GRMHD) codes to directly evolve the GRFFE equations of motion. Established, accurate, and well-tested conservative GRMHD codes can simply add a new inversion piece of code to their existing code, while continuing to use all the already-developed facilities present in their GRMHD code. We show how to enforce the $\mathbf{E}\cdot\mathbf{B}=0$ constraint and energy conservation, and we introduce a simplified general model of the dissipation of the electric field to enforce the $B^2-E^2>0$ constraint. We also introduce a simplified yet general method to resolve current sheets, without much reconnection, over many dynamical times. This formulation is incorporated into an existing GRMHD code (HARM), which is demonstrated to give accurate and robust GRFFE results for Minkowski and black hole space-times.

 
astro-ph/0601411 [abs, ps, pdf, other] :
Title: Relativistic Force-Free Electrodynamic Simulations of Neutron Star Magnetospheres
Authors: Jonathan C. McKinney (Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics)
Comments: 5 pages, 5 figures, accepted for publication in MNRAS LETTERS

The luminosity and structure of neutron star magnetospheres are crucial to our understanding of pulsar and plerion emission. A solution found using the force-free approximation would be an interesting standard with which any model with more physics could be compared. Prior quasi-analytic force-free solutions may not be stable, while prior time-dependent magnetohydrodynamic models used unphysical model parameters. We use a time-dependent relativistic force-free electrodynamics code with no free parameters to find a unique stationary solution for the axisymmetric rotating pulsar magnetosphere in a Minkowski space-time in the case of no surface currents on the star. The solution is similar to the force-free quasi-analytic solution of \citet{cont99} and the numerical magnetohydrodynamic solution of \citet{kom05}. The magnetosphere structure and the usefulness of the classical y-point in the general dissipative regime are discussed. The pulsar luminosity is found to be $L \approx 0.99\pm 0.01 \mu^2\Omega_\star^4/c^3$ for a dipole moment $\mu$ and stellar angular frequency $\Omega_\star$.

 

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Astrophysics


astro-ph new abstracts, Mon, 23 Jan 06 01:00:09 GMT
0601454 -- 0601487 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0601458 [abs, ps, pdf, other] :
Title: A Study of Compact Object Mergers as Short Gamma-ray Burst Progenitors
Authors: Krzysztof Belczynski, Rosalba Perna, Tomasz Bulik, Vassiliki Kalogera, Natalia Ivanova, Donald Q. Lamb
Comments: submitted to ApJ

We present a theoretical study of double compact objects as potential short/hard gamma-ray burst (GRB) progenitors. An updated population synthesis code StarTrack is used to calculate properties of double neutron stars and black-hole neutron star binaries. We obtain their formation rates, estimate merger times and finally predict their most likely merger locations and afterglow properties for different types of host galaxies. Our results serve for a direct comparison with the recent HETE-II and SWIFT observations of several short bursts, for which afterglows and host galaxies were detected. We also discuss the possible constraints these observations put on the evolutionary models of double compact object formation. We emphasize that our double compact object models can successfully reproduce at the same time short GRBs within both young, star-forming galaxies (e.g., GRB 050709 and GRB 051221A), as well as within old, elliptical hosts (e.g., GRB 050724 and probably GRB 050509B)

 
astro-ph/0601476 [abs, ps, pdf, other] :
Title: The Hamburg/ESO R-process Enhanced Star survey (HERES) III. HE 0338-3945 and the formation of the r+s stars
Authors: K. Jonsell (1), P. S. Barklem (1), B. Gustafsson (1), N. Christlieb (2), V. Hill (3), T. C. Beers (4), J. Holmberg (5) ((1) Uppsala, (2) Hamburg, (3) Paris Meudon, (4) Michigan State, (5) Tuorla)
Comments: Accepted for A&A; 22 pages, 9 figures, 2 tables. Table 2 is in electronic form and available at this http URL with description at this http URL)

We have derived abundances of 33 elements and upper limits for 6 additional elements for the metal-poor ([Fe/H] = -2.42) turn-off star HE 0338-3945 from high-quality VLT-UVES spectra. The star is heavily enriched, by about a factor of 100 relative to iron and the Sun, in the heavy s-elements (Ba, La, ..). It is also heavily enriched in Eu, which is generally considered an r-element, and in other similar elements. It is less enriched, by about a factor of 10, in the lighter s-elements (Sr, Y and Zr). C is also strongly enhanced and, to a somewhat lesser degree, N and O. These abundance estimates are subject to severe uncertainties due to NLTE and thermal inhomogeneities which are not taken into detailed consideration. However, an interesting result, which is most probably robust in spite of these uncertainties, emerges: the abundances derived for this star are very similar to those of other stars with an overall enhancement of all elements beyond the iron peak.
We have defined criteria for this class of stars, r+s stars, and discuss nine different scenarios to explain their origin. None of these explanations is found to be entirely convincing. The most plausible hypotheses involve a binary system in which the primary component goes through its giant branch and asymptotic giant branch phases and produces CNO and s-elements which are dumped onto the observed star. Whether the r-element Eu is produced by supernovae before the star was formed (perhaps triggering the formation of a low-mass binary), by a companion as it explodes as a supernova (possibly triggered by mass transfer), or whether it is possibly produced in a high-neutron-density version of the s-process is still unclear. Several suggestions are made on how to clarify this situation.

 

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astro-ph/0601189 [abs, ps, pdf, other] :
Title: Searches for diffuse X-ray emission around millisecond pulsars: An X-ray nebula associated with PSR J2124-3358
Authors: C. Y. Hui, W. Becker (MPE)
Comments: Accepted by A&A letter
Note: replaced with revised version Fri, 20 Jan 2006 17:26:16 GMT (167kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 24 Jan 06 01:00:10 GMT
0601488 -- 0601516 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0601491 [abs, ps, pdf, other] :
Title: A Further Study of the Luminosity-Dependent Cyclotron Resonance Energies of the Binary X-ray Pulsar 4U0115+63 with RXTE
Authors: Motoki Nakajima (1 and 2), Tatehiro Mihara (2), Kazuo Makishima (2 and 3), Hisako Niko (3) ((1) College of Science and Technology, Nihon University, (2) Cosmic Radiation, The Institute of Physical and Chemical Research, (3) Department of Physics, University of Tokyo)
Comments: 33 pages, 12 figures, 4 tables. Accepted for publication in Astrophysical Journal

The present paper reports on the RXTE observations of the binary X-ray pulsar 4U0115+63, covering an outburst in 1999 March-April with 44 pointings. The 3-30 keV PCA spectra and the 15-50 keV HEXTE spectra were analyzed jointly for the cyclotron resonance features. When the 3-50 keV luminosity at an assumed distance of 7 kpc was in the range (5-13)x10^{37} erg s^{-1}, harmonic double cyclotron features were observed in absorption at ~11 and ~22 keV, as was measured previously during typical outbursts. As the luminosity decreased below \~5x10^{37} erg s^{-1}, the second resonance disappeared, and the fundamental resonance energy gradually increased, up to $\sim$16 keV at 0.16x10^{37} erg s^{-1}. These results reconfirm the report by Mihara et al. (2004) using Ginga, who observed a single absorption at ~16 keV in a minor (~10^{37} erg s^{-1}) outburst of this object. The luminosity-dependent cyclotron resonance energy may be understood as a result of a decrease in the accretion column height, in response to a decrease in the mass accretion rate.

 

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Astrophysics


astro-ph new abstracts, Wed, 25 Jan 06 01:00:08 GMT
0601517 -- 0601555 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0601521 [abs, ps, pdf, other] :
Title: The Parallax and Proper Motion of PSR J0030+0451
Authors: Andrea N. Lommen (1), Richard A. Kipphorn (1), David J. Nice (2), Eric M. Splaver (3), Ingrid H. Stairs (4), Donald C. Backer (5) ((1) Franklin and Marshall College, (2) Bryn Mawr College, (3) Princeton University, (4) University of British Columbia, (5) University of California Berkeley)
Comments: accepted by ApJ, 6 pages, 3 figures, 2 tables

We report the parallax and proper motion of millisecond pulsar J0030+0451, one of thirteen known isolated millisecond pulsars in the disk of the Galaxy. We obtained more than 6 years of monthly data from the 305 m Arecibo telescope at 430 MHz and 1410 MHz. We measure the parallax of PSR J0030+0451 to be 3.3 +/- 0.9 mas, corresponding to a distance of 300 +/- 90 pc. The Cordes and Lazio (2002) model of galactic electron distribution yields a dispersion measure derived distance of 317 pc which agrees with our measurement. We place the pulsar's transverse space velocity in the range of 8 to 17 km/s, making this pulsar one of the slowest known. We perform a brief census of velocities of isolated versus binary millisecond pulsars. We find the velocities of the two populations are indistinguishable. However, the scale height of the binary population is twice that of the isolated population and the luminosity functions of the two populations are different. We suggest that the scale height difference may be an artifact of the luminosity difference.

 
astro-ph/0601530 [abs, ps, pdf, other] :
Title: A Braking Index for the Young Pulsar at the Center of the Supernova Remnant Kes 75
Authors: Margaret A. Livingstone, Victoria M. Kaspi, Eric V. Gotthelf
Comments: 16 pages, 4 figures. ApJ submitted

We present the first phase-coherent measurement of a braking index for the young, energetic and high magnetic field pulsar, PSR J1846-0258, located at the center of the supernova remnant Kes 75. We present two consistent timing solutions from a phase-coherent timing analysis over 2 yr and a partially phase-coherent timing analysis of 6 yr of widely spaced data obtained with the Rossi X-ray Timing Explorer. Our measured value of the braking index, n=2.18+/-0.07, is significantly less than 3, the value expected from magnetic dipole radiation, implying another physical process must contribute to the pulsar's rotational evolution. Based on the new braking index measurement we place an upper limit on the spin-down age of PSR J1846-0258 of <1200 yr. If PSR J1846-0258 was born with a spin frequency comparable to its present value, its true age could be significantly smaller than this estimate.

 
astro-ph/0601543 [abs, ps, pdf, other] :
Title: Optical Structure and Proper-Motion Age of the Oxygen-rich Supernova Remnant 1E 0102-7219 in the Small Magellanic Cloud
Authors: Steven L. Finkelstein (Arizona State University), Jon A. Morse (Arizona State University), James C. Green (University of Colorado - Boulder), Jeffrey L. Linsky, J. Michael Shull, Theodore P. Snow, John T. Stocke, Kenneth R. Brownsberger, Dennis C. Ebbets, Erik Wilkinson, Sara R. Heap, Claus Leitherer, Blair D. Savage, Oswald H. Siegmund, Alan Stern
Comments: 28 pages, 8 figures. Accepted to the Astrophysical Journal, to appear in 20 April 2006 issue. Full resolution figures are posted at: this http URL

We present new optical emission-line images of the young SNR 1E 0102-7219 (E0102) in the SMC obtained with the HST Advanced Camera for Surveys (ACS). E0102 is a member of the oxygen-rich class of SNRs showing strong oxygen, neon , and other metal-line emissions in its optical and X-ray spectra, and an absence of H and He. The progenitor of E0102 may have been a Wolf-Rayet star that underwent considerable mass loss prior to exploding as a Type Ib/c or IIL/b SN. The ejecta in this SNR are fast-moving (V > 1000 km/s) and emit as they are compressed and heated in the reverse shock. In 2003, we obtained optical [O III], H-alpha, and continuum images with the ACS Wide Field Camera. The [O III] image captures the full velocity range of the ejecta, and shows considerable high-velocity emission projected in the middle of the SNR that was Doppler-shifted out of the narrow F502N bandpass of a previous Wide Field and Planetary Camera 2 image from 1995. Using these two epochs separated by ~8.5 years, we measure the transverse expansion of the ejecta around the outer rim in this SNR for the first time at visible wavelengths. From proper-motion measurements of 12 ejecta filaments, we estimate a mean expansion velocity for the bright ejecta of ~2000 km/s and an inferred kinematic age for the SNR of \~2050 +/- 600 years. The age we derive from HST data is about twice that inferred by Hughes et al.(2000) from X-ray data, though our 1-sigma error bars overlap. Our proper-motion age is consistent with an independent optical kinematic age derived by Eriksen et al.(2003) using spatially resolved [O III] radial-velocity data. We derive an expansion center that lies very close to X-ray and radio hotspots, which could indicate the presence of a compact remnant (neutron star or black hole).

 

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astro-ph/0601020 [abs, ps, pdf, other] :
Title: QPOs during magnetar flares are not driven by mechanical normal modes of the crust
Authors: Yuri Levin (Leiden Observatory and Lorentz Institute)
Comments: 4 pages, accepted to MNRAS letters. Important references on oscillations of magnetic stars are added, comment on the 625Hz QPO is added, the conclusions are strengthened
Note: replaced with revised version Tue, 24 Jan 2006 13:56:35 GMT (36kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 26 Jan 06 01:00:11 GMT
0601556 -- 0601578 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0601575 [abs, ps, pdf, other] :
Title: First detection of a VHE gamma-ray spectral maximum from a Cosmic source: H.E.S.S. discovery of the Vela X nebula
Authors: Aharonian et al. (H.E.S.S. Collaboration)
Comments: 5 pages, 4 figures, accepted for publication in Astronomy and Astrophysics letters

The Vela supernova remnant (SNR) is a complex region containing a number of sources of non-thermal radiation. The inner section of this SNR, within 2 degrees of the pulsar PSR B0833-45, has been observed by the H.E.S.S. gamma-ray atmospheric Cherenkov detector in 2004 and 2005. A strong signal is seen from an extended region to the south of the pulsar, within an integration region of radius 0.8 deg. around the position (RA = 08h 35m 00s, dec = -45 deg. 36' J2000.0). The excess coincides with a region of hard X-ray emission seen by the ROSAT and ASCA satellites. The observed energy spectrum of the source between 550 GeV and 65 TeV is well fit by a power law function with photon index = 1.45 +/- 0.09(stat) +/- 0.2(sys) and an exponential cutoff at an energy of 13.8 +/- 2.3(stat) +/- 4.1(sys) TeV. The integral flux above 1 TeV is (1.28 +/- 0.17 (stat) +/- 0.38(sys)) x 10^{-11} cm^{-2} s^{-1}. This result is the first clear measurement of a peak in the spectral energy distribution from a VHE gamma-ray source, likely related to inverse Compton emission. A fit of an Inverse Compton model to the H.E.S.S. spectral energy distribution gives a total energy in non-thermal electrons of ~2 x 10^{45} erg between 5 TeV and 100 TeV, assuming a distance of 290 parsec to the pulsar. The best fit electron power law index is 2.0, with a spectral break at 67 TeV.

 

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astro-ph/0509806 [abs, ps, pdf, other] :
Title: Phase transitions in rotating neutron stars cores: back bending, stability, corequakes and pulsar timing
Authors: J. L. Zdunik, M. Bejger, P. Haensel, E. Gourgoulhon
Comments: 13 pages, 15 figures, accepted by A&A
Note: replaced with revised version Wed, 25 Jan 2006 11:54:56 GMT (88kb)
 
astro-ph/0512107 [abs, ps, pdf, other] :
Title: Frequency dependence of orthogonal polarisation modes in pulsars
Authors: J.M. Smits, B.W. Stappers, R. T. Edwards, J. Kuijpers, R. Ramachandran
Comments: 31 pages, 24 figures, 1 table, accepted by A&A; added references in introduction
Note: replaced with revised version Wed, 25 Jan 2006 12:51:50 GMT (685kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 27 Jan 06 01:00:09 GMT
0601579 -- 0601617 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0601603 [abs, ps, pdf, other] :
Title: Multi-Dimensional Simulations of the Accretion-Induced Collapse of White Dwarfs to Neutron Stars
Authors: Luc Dessart, Adam Burrows, Christian Ott, Eli Livne, Sung-Chul Yoon, Norbert Langer
Comments: 25 pages, 19 figures, submitted to ApJ, high resolution of the paper available at this http URL

We present 2.5D radiation-hydrodynamics simulations of the accretion-induced collapse (AIC) of white dwarfs, starting from 2D rotational equilibrium configurations. Electron capture leads to the collapse to nuclear densities of these cores within a few tens of milliseconds. The shock generated at bounce moves slowly, but steadily, outwards. Within 50-100ms, the stalled shock breaks out of the white dwarf along the poles. The blast is followed by a neutrino-driven wind that develops within the white dwarf, in a cone of ~40deg opening angle about the poles, with a Mdot of 5-8 x 10^{-3} Msun/s. The ejecta have an entropy on the order of 20-50 k_B/baryon, and an electron fraction distribution that is bimodal. By the end of the simulations, at >600ms after bounce, the explosion energy has reached 3-4 x 10^49 erg and the outflowing mass has reached a few times 0.001Msun. We estimate the asymptotic explosion energies to be lower than 10^50 ergs, significantly lower than those inferred in the core collapse of massive progenitors. AIC of WDs thus represents one instance where a neutrino mechanism leads undoubtedly to a successful, albeit weak, explosion. We document in detail the numerous effects of the fast rotation of the progenitors: the neutron stars are aspherical; the ``\nu_{\mu}'' and \bar{\nu}_e luminosities are reduced compared to the \nu_e luminosity; the deleptonized region has a butterfly shape; the neutrino flux and electron fraction depend strongly upon latitude (a la von Zeipel); and a quasi-Keplerian 0.1-0.5Msun accretion disk is formed [abridged].

 
astro-ph/0601612 [abs, ps, pdf, other] :
Title: Two-body problem with the cosmological constant and observational constraints
Authors: Ph. Jetzer (Uni. Zurich) M. Sereno (Uni. Zurich)
Comments: 8 pages, accepted for publication in Phys. Rev. D

We discuss the influence of the cosmological constant on the gravitational equations of motion of bodies with arbitrary masses and eventually solve the two-body problem. Observational constraints are derived from measurements of the periastron advance in stellar systems, in particular binary pulsars and the solar system. Up to now, Earth and Mars data give the best constraint, Lambda < 10^{-36} km^{-2}; bounds from binary pulsars are potentially competitive with limits from interplanetary measurements. If properly accounting for the gravito-magnetic effect, this upper limit on $\Lambda$ could greatly improve in the near future thanks to new data from planned or already operating space-missions.

 
astro-ph/0601613 [abs, ps, pdf, other] :
Title: Formation of a partially-screened inner acceleration region in radio pulsars: drifting subpulses and thermal X-ray emission from polar cap surface
Authors: Janusz Gil, George Melikidze, Bing Zhang

Formation of a partially-screened inner acceleration region in 102 pulsars with drifting subpulses is considered. This is motivated by that spark discharges leading to drifting subpulses cannot be produced in a steady polar cap flow and thus the inner accelerator should be intermittent in nature, that the traditional pure vacuum gap model predicts too fast a sub-pulse drifting rate, and that recent X-ray observations as well as the radio drifting data are both consistent with the inner gap being partially screened. By means of the condition $T_{\rm c}/T_{\rm s}>1$ (where $T_{\rm c}$ is the critical temperature above which the surface delivers a thermal flow to adequately supply the corotation charge density, and $T_{\rm s}$ is the actual surface temperature), it is found that a partially-screened acceleration region can be formed given that the near surface magnetic fields are very strong and curved. We consider both curvature radiation (CR) and resonant inverse Compton scattering (ICS) to produce seed photons for pair production. It is found that the ICS mechanism is unlikely to develop a partially screened gap, while the CR mechanism can naturally drive the sparking discharge of such a gap. Observational signatures of thermal radiation from the spark-heated polar caps are consistent with the model that invokes a partially screened gap formed in strong nondipolar surface magnetic fields.

 

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astro-ph/0503602 [abs, ps, pdf, other] :
Title: On the nature of the radio quiet X-ray neutron star 1E 1207.4-5209
Authors: Biping Gong, G.F. Bignami
Comments: 6 pages, submitted to A&A
Note: replaced with revised version Thu, 26 Jan 2006 08:12:41 GMT (12kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 30 Jan 06 01:00:09 GMT
0601618 -- 0601653 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0601627 [abs, ps, pdf, other] :
Title: A Chandra Catalog of X-ray Sources in the Central 150 pc of the Galaxy
Authors: M. P. Muno (UCLA), F. E. Bauer (Columbia), R. M. Bandyopadhyay (U Florida), Q. D. Wang (UMass Amherst)
Comments: 16 pages, incl. 9 figures, 3 in color. Submitted to ApJ. An electronic catalog of X-ray point sources is located at this http URL . A high-resolution version of figure 1 will be available when the manuscript is published

We present the catalog of X-ray sources detected in a shallow Chandra survey of the inner 2 by 0.8 degrees of the Galaxy, and in two deeper observations of the Radio Arches and Sgr B2. The catalog contains 1352 objects that are highly-absorbed (N_H > 4e22 cm^-2 and are therefore likely to lie near the Galactic center (D~8 kpc), and 549 less-absorbed sources that lie within <6 kc of Earth. Based on the inferred luminosities of the X-ray sources and the expected numbers of various classes of objects, we suggest that the sources with L_X < 1e33 erg/s that comprise ~90% of the catalog are cataclysmic variables, and that the ~100 brighter objects are accreting neutron stars and black holes, young isolated pulsars, and Wolf-Rayet and O stars in colliding-wind binaries. We find that the spatial distribution of X-ray sources matches that of the old stellar population observed in the infrared, which supports our suggestion that most of the X-ray sources are old cataclysmic variables. However, we find that there is an apparent excess of ~10 bright sources in the Radio Arches region. That region is already known to be the site of recent star formation, so we suggest that the bright sources in this region are young high-mass X-ray binaries, pulsars, or WR/O star binaries. We briefly discuss some astrophysical questions that this catalog can be used to address.

 
astro-ph/0601641 [abs, ps, pdf, other] :
Title: INTEGRAL observations of the Crab pulsar
Authors: T.Mineo, C.Ferrigno, L.Foschini, A.Segreto, G.Cusumano, G.Malaguti, G.Di Cocco, C.Labanti
Comments: 10 pages, 7 figures, accepted by Astronomy and Astrophysics

The paper presents the timing and spectral analysis of several observations of the Crab pulsar performed with INTEGRAL in the energy range 3-500 keV. All these observations, when summed together provide a high statistics data set which can be used for accurate phase resolved spectroscopy. A detailed study of the pulsed emission at different phase intervals is performed. The spectral distribution changes with phase showing a characteristic reverse S shape of the photon index. Moreover the spectrum softens with energy, in each phase interval, and this behavior is adequately modeled over the whole energy range 3-500 keV with a single curved law with a slope variable with Log(E), confirming the BeppoSAX results on the curvature of the pulsed emission. The bending parameter of the log-parabolic model is compatible with a single value of 0.14+/-0.02 over all phase intervals. Results are discussed within the three-dimensional outer gap model.

 
astro-ph/0601644 [abs, ps, pdf, other] :
Title: INTEGRAL survey of the Cassiopeia region in hard X rays
Authors: P.R. den Hartog (1), W. Hermsen (1,2), L. Kuiper (1), J. Vink (3,1), J.J.M. in 't Zand (1,3), W. Collmar (4) ((1) SRON Netherlands Institute for Space Research (2) University of Amsterdam (3) University of Utrecht (4) MPE)
Comments: 16 pages, 13 figures, accepted for publication in A&A

We report on the results of a deep 1.6 Ms INTEGRAL observation of the Cassiopeia region performed from December 2003 to February 2004. Eleven sources were detected with the imager IBIS-ISGRI at energies above 20 keV, including three new hard X-ray sources. Most remarkable is the discovery of hard X-ray emission from the anomalous X-ray pulsar 4U 0142+61, which shows emission up to \~150 keV with a very hard power-law spectrum with photon index Gamma = 0.73 +/- 0.17. We derived flux upper limits for energies between 0.75 MeV and 30 MeV using archival data from the Compton telescope COMPTEL. In order to reconcile the very hard spectrum of 4U 0142+61 measured by INTEGRAL with the COMPTEL upper limits, the spectrum has to bend or break between ~75 keV and ~750 keV. 1E 2259+586, another anomalous X-ray pulsar in this region, was not detected. INTEGRAL and COMPTEL upper limits are provided. The new INTEGRAL sources are IGR J00370+6122 and IGR J00234+6144. IGR J00370+6122 is a new supergiant X-ray binary with an orbital period of 15.665 +/- 0.006 days, derived from RXTE All-Sky Monitor data. Archival BeppoSAX Wide-Field Camera data yielded four more detections. IGR J00234+6144 still requires a proper identification. Other sources for which INTEGRAL results are presented are high-mass X-ray binaries 2S 0114+650, Gamma~Cas, RX J0146.9+6121 and 4U 2206+54, intermediate polar V709 Cas and 1ES 0033+595, an AGN of the BL-Lac type. For each of these sources the hard X-ray spectra are fitted with different models and compared with earlier published results.

 
astro-ph/0601652 [abs, ps, pdf, other] :
Title: MeV-GeV emission from neutron-loaded short gamma-ray burst jets
Authors: Soebur Razzaque, Peter Meszaros
Comments: 10 pages, 1 figure

Recent discovery of the afterglow emission from short gamma-ray bursts suggests that binary neutron star or black hole-neutron star binary mergers are the likely progenitors of these short bursts. The accretion of neutron star material and its subsequent ejection by the central engine implies a neutron-rich outflow. We consider here a neutron-rich relativistic jet model of short bursts, and investigate the high energy neutrino and photon emission as neutrons and protons decouple from each other. We find that upcoming neutrino telescopes are unlikley to detect the 50 GeV neutrinos expected in this model. For bursts at z~0.1, we find that GLAST and ground-based Cherenkov telescopes should be able to detect prompt 100 MeV and 100 GeV photon signatures, respectively, which may help test the neutron star merger progenitor identification.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0509408 [abs, ps, pdf, other] :
Title: A Neutron Star with a Massive Progenitor in Westerlund 1
Authors: M. P. Muno, J. S. Clark, P. A. Crowther, S. M. Dougherty, R. de Grijs, C. Law, S. L. W. McMillan, M. R. Morris, I. Negueruela, D. Pooley, S. Portegies Zwart, F. Yusef-Zadeh
Comments: 4 pages, 5 figures. Final version to match ApJL (added one figure since v2)
Note: replaced with revised version Thu, 26 Jan 2006 22:38:44 GMT (127kb)
 

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astro-ph new abstracts, Tue, 31 Jan 06 01:00:12 GMT
0601654 -- 0601692 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0601658 [abs, ps, pdf, other] :
Title: Newtonian mechanics of neutron superfluid in elastic star crust
Authors: Brandon Carter, Elie Chachoua
Comments: 31 pages Latex

To account for pulsar frequency glitches, it is necessary to use a neutron star crust model allowing not only for neutron superfluidity but also for elastic solidity. These features have been treated separarately in previous treatments of crust matter, but are combined here in a unified treatment that is based on the use of a Lagrangian master functon, so that the coherence the system is ensured by the relevant Noether identities. As well as the model obtained directly from the variation principle, the same master function can provide other conservative alternatives, allowing in particular for the effect of perfect vortex pinning. It is also shown how such models can be generalised to allow for dissipative effects, including that of imperfect pinning, meaning vortex drag or creep.

 
astro-ph/0601666 [abs, ps, pdf, other] :
Title: QPOs: Einstein's gravity non-linear resonances
Authors: Paola Rebusco, Marek A. Abramowicz
Comments: Proceeding of the Einstein's Legacy, Munich 2005

There is strong evidence that the observed kHz Quasi Periodic Oscillations (QPOs) in the X-ray flux of neutron star and black hole sources in LMXRBs are linked to Einstein's General Relativity. Abramowicz&Klu\'zniak (2001) suggested a non-linear resonance model to explain the QPOs origin: here we summarize their idea and the development of a mathematical toy-model which begins to throw light on the nature of Einstein's gravity non-linear oscillations.

 
astro-ph/0601670 [abs, ps, pdf, other] :
Title: Tail emission from a ring-like jet: its application to shallow decays of early afterglows and to GRB 050709
Authors: Y. C. Zou, Z. G. Dai
Comments: 6 pages, 2 figures. Summitted to ChJAA

Similar to the pulsar, the magnetic axis and the spin axis of the gamma-ray burst source may not lie on the same line. This may cause a ring-like jet. We analyze the tail emission from such a jet, and find that it has a shallow decay phase with temporal index equal to -1/2 if the Lorentz factor of the ejecta is not very high. This phase is consistent with the shallow decay phase of early X-ray afterglow detected by {\it{swift}}. The ring-like jet has a tail cusp with sharp rising and very sharp decay. This effect can provide an explanation to the brightening and sharp decay of the X-ray afterglow of GRB 050709.

 
astro-ph/0601689 [abs, ps, pdf, other] :
Title: Spectra of the spreading layers on the neutron star surface and constraints on the neutron star equation of state
Authors: Valery Suleimanov, Juri Poutanen
Comments: 13 pages, 13 figures, submitted to MNRAS

Spectra of the spreading layers on the neutron star surface are calculated on the basis of the Inogamov-Sunyaev model taking into account general relativity correction to the surface gravity and considering various chemical composition of the accreting matter. Local (at a given latitude) spectra are similar to the X-ray burst spectra and are described by a diluted black body. Total spreading layer spectra are integrated accounting for the light bending, gravitational redshift, and the relativistic Doppler effect and aberration. They depend slightly on the inclination angle of the neutron star and on the luminosity. These spectra also can be fitted by a diluted black body with the color temperature depending mainly on a neutron star compactness. Constraints on the neutron star compactness were obtained by comparing the theoretical spreading layer spectra with the observed boundary layer spectrum described by a black body of color temperature 2.4 +- 0.1 keV. We obtain the neutron star radius R=15+-1.5 km (for a 1.4 solar mass star and solar composition of the accreting matter), which corresponds to the hard equation of state.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0601086 [abs, ps, pdf, other] :
Title: The physics of dense hadronic matter and compact stars
Authors: Armen Sedrakian
Comments: 84 pages, 30 figures, to apper in Prog. Part. Nucl. Phys

This review describes the properties of hadronic phases of dense matter in compact stars. The theory is developed within the method of real-time Green's functions and is applied to study of baryonic matter at and above the saturation density. The non-relativistic and covariant theories based on continuum Green's functions and the T-matrix and related approximations to the self-energies are reviewed. The effects of symmetry energy, onset of hyperons and meson condensation on the properties of stellar configurations are demonstrated on specific examples. Neutrino interactions with baryonic matter are introduced within a kinetic theory. We concentrate on the classification, analysis and first principle derivation of neutrino radiation processes from unpaired and superfluid hadronic phases. We then demonstrate how neutrino radiation rates from various microscopic processes affect the macroscopic cooling of neutron stars and how the observed X-ray fluxes from pulsars constrain the properties of dense hadronic matter.

 

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astro-ph/0408083 [abs, ps, pdf, other] :
Title: Entrainment coefficient and effective mass for conduction neutrons in neutron star crust: II Macroscopic treatment
Authors: Brandon Carter, Nicolas Chamel, Pawel Haensel
Comments: 21 pages Latex. Part II of article whose Part I (Simple microscopic models) is given by nucl-th/0402057. New version extended to include figures
Note: replaced with revised version Mon, 30 Jan 2006 13:01:47 GMT (49kb)
 

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astro-ph new abstracts, Wed, 1 Feb 06 01:00:20 GMT
0601693 -- 0601718 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0212062 [abs, ps, pdf, other] :
Title: Equation of state and opacities for hydrogen atmospheres of neutron stars with strong magnetic fields
Authors: A. Y. Potekhin (Ioffe Inst., St.-Petersburg), G. Chabrier (CRAL, ENS-Lyon)
Comments: 20 pages, 12 figures, 1 table. Compared to v1 and to the jourrnal version, the bibliography updated and a typo corrected. Compared to v.1 and v.2, accidental typos are corrected in eqs.(B6) and (B7) for an effective potential
Journal-ref: Astrophys.J. 585 (2003) 955-974
Note: replaced with revised version Mon, 30 Jan 2006 21:41:00 GMT (105kb)
 

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astro-ph new abstracts, Thu, 2 Feb 06 01:00:11 GMT
0602001 -- 0602028 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602024 [abs, ps, pdf, other] :
Title: On the Formation and Progenitor of PSR J0737-3039: New Constraints on the Supernova Explosion Forming Pulsar B
Authors: B. Willems, J. Kaplan, T. Fragos, V. Kalogera, K. Belczynski
Comments: Submitted to Physical Review D

We revisit the formation of PSR J0737-3039, taking into account the most recent observational constraints. We show that the most likely kick velocity and progenitor parameters depend strongly on the consideration of the full five-dimensional PDF for the magnitude and direction of the kick velocity imparted to pulsar B at birth, the mass of pulsar B's pre-supernova helium star progenitor, and the pre-supernova orbital separation, and on the adopted prior assumptions. The priors consist of the transverse systemic velocity, the age of the system, and the treatment of the unknown radial velocity. Since the latter cannot be determined from observation, we adopt a statistical approach and use theoretical radial-velocity distributions obtained from population synthesis calculations for coalescing double neutron stars. We find that the prior assumptions about the pre-supernova helium star mass affect the derived most likely parameters significantly: when the minimum helium star mass required for neutron star formation is assumed to be 2.1Msun, the most likely kick velocity ranges from 70-180km/s; when masses lower than 2.1Msun are assumed to allow neutron star formation, the most likely kick velocity can be as low as a few km/s, although the majority of the considered models still yield most likely kick velocities of 50-170km/s. We also show that the proximity of the double pulsar to the Galactic plane and the small proper motion do not pose stringent constraints on the kick velocity and progenitor mass of pulsar B. Instead, the constraints imposed by the orbital dynamics of asymmetric supernova explosions turn out to be much more restrictive. We conclude that the currently available observational constraints cannot be used to favor a specific core-collapse and neutron star formation mechanism. (abridged)

 

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astro-ph/0509325 [abs, ps, pdf, other] :
Title: The outer crust of non-accreting cold neutron stars
Authors: Stefan B. Ruster, Matthias Hempel, Jurgen Schaffner-Bielich
Comments: 20 pages, 10 figures, accepted for publication in Phys. Rev. C
Note: replaced with revised version Wed, 1 Feb 2006 10:55:38 GMT (538kb)
 

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astro-ph new abstracts, Fri, 3 Feb 06 01:00:11 GMT
0602029 -- 0602055 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602047 [abs, ps, pdf, other] :
Title: Strangeness in Compact Stars
Authors: Fridolin Weber (San Diego State University), Andreu Torres i Cuadrat (Universitat Autonoma de Barcelona), Alexander Ho (San Diego State University), Philip Rosenfield (San Diego State University)
Comments: 26 pages, 13 figures, 29th Johns Hopkins Workshop on current problems in particle theory: Strong Matter in the Heavens

Astrophysicists distinguish between three different types of compact stars. These are white dwarfs, neutron stars, and black holes. The former contain matter in one of the densest forms found in the Universe. This feature, together with the unprecedented progress in observational astronomy, makes such stars superb astrophysical laboratories for a broad range of exciting physical studies. This article studies the role of strangeness for compact star phenomenology. Strangeness is carried by hyperons, mesons, H-dibaryons, and strange quark matter, and may leave its mark in the masses, radii, cooling behavior, surface composition and the spin evolution of compact stars.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0602004 [abs, ps, pdf, other] :
Title: Radiation Damping in Einstein-Aether Theory
Authors: Brendan Z. Foster
Comments: 23 pages, 1 figure

This work concerns the loss of energy of a material system due to gravitational radiation in Einstein-aether theory-an alternative theory of gravity in which the metric couples to a dynamical, timelike, unit-norm vector field. Derived to lowest post-Newtonian-order are waveforms for the metric and vector fields far from a nearly-Newtonian system and the rate of energy radiated by the system. The expressions depend on the quadrupole moment of the source, as in standard general relativity, but also contain monopolar and dipolar terms. There exists a one-parameter family of Einstein-aether theories for which only the quadrupolar contribution is present, and for which the expression for the damping rate is identical to that of general relativity to lowest order. Because observations from binary pulsar systems already test the damping rate beyond this order, this family cannot yet be declared observationally viable.

 

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astro-ph new abstracts, Mon, 6 Feb 06 01:00:09 GMT
0602056 -- 0602087 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602078 [abs, ps, pdf, other] :
Title: HESS Observations of Pulsar Wind Nebulae
Authors: Ocker C. de Jager
Comments: 6 pages, 3 figures, appeared in the proceedings of "Astrophysical Sources of High Energy Particles and Radiation", held in Torun, Poland, eds. T. Bulik, B. Rudak, and G. Madejski

The high resolution capabilities of the High Energy Stereoscopic System (HESS) introduced a new era in Gamma-Ray Astronomy, and opens a new window on pulsar wind nebula (PWN) research. A rotationally induced jet (associated with PSR B1509-58) is resolved for the first time in gamma-rays, allowing us to trace the particle transport directly, without having the complicating effect of spatially varying field distributions on the synchrotron emissivity. For PWN older or more extended than Crab (i.e. those with lower field strengths), HESS also reveals the properties of electrons contributing to the EUV/soft X-ray synchrotron bands, whereas EUV/soft X-rays suffer from severe interstellar absorption effects. Finally, HESS morphological studies of evovled PWN also allow us to directly measure the effects of assymetric reverse shock interactions due to SNR forward shock expansion into the inhomogeneous interstellar medium.

 

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astro-ph new abstracts, Tue, 7 Feb 06 01:00:14 GMT
0602088 -- 0602132 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602104 [abs, ps, pdf, other] :
Title: Nuclear Astrophysics of Worlds in the String Landscape
Authors: Craig J. Hogan
Comments: 27 pages, Latex, 2 figures

Motivated by landscape models in string theory, the cosmic behavior of matter is analyzed allowing the Standard Model Higgs expectation value $w$ to take values different from that in our world ($w\equiv 1$), while holding the Yukawa couplings fixed. Astrophysical consequences are described, and thresholds in $w$ are estimated, associated with changes in nuclear stability and reactions. A new lower limit on $w$ is derived, corresponding to the threshold where the neutron and not the proton becomes the ground state of an isolated baryon, in terms of the mass difference of the up and down quarks in our world. The effect of a stable neutron on nuclear evolution in the Big Bang and stars is shown to lead to radical differences from our world, such as a predominance of heavy r-process and s-process nuclei and a lack of normal stars and planets, which justify using the threshold as a possible anthropic constraint. Estimates are made of upper limits on $w$ deriving from thresholds for pp and pep reactions, the stability of deuterons, helium, and heavier nuclei, and changes in carbon and oxygen production during stellar nucleosynthesis. Although the thresholds and the astrophysical consequences are not evaluated rigorously, estimates suggest that significant changes in behavior occur with changes in $w$ of order ten percent. It is shown that $w$ is more finely tuned for some effects near the upper end of the currently allowed range for the down quark mass than it is at the lower end, which may allow some landscape models to make testable predictions for the real-world quark masses.

 
astro-ph/0602107 [abs, ps, pdf, other] :
Title: Neutron-capture elements in the very metal-poor star HD122563
Authors: S. Honda, W. Aoki, Y. Ishimaru, S. Wanajo, S. G. Ryan
Comments: 29 pages, 7 figures, Accepted for publication in ApJ

We obtained high resolution, high S/N spectroscopy for the very metal-poor star HD122563 with the Subaru Telescope High Dispersion Spectrograph. Previous studies have shown that this object has excesses of light neutron-capture elements, while its abundances of heavy ones are very low. In our spectrum covering 3070 - 4780 A of this object, 19 neutron-capture elements have been detected, including seven for the first time in this star (Nb, Mo, Ru, Pd, Ag, Pr, and Sm). Upper limits are given for five other elements including Th. The abundance pattern shows a gradually decreasing trend, as a function of atomic number, from Sr to Yb, which is quite different from those in stars with excesses of r-process elements. This abundance pattern of neutron-capture elements provides new strong constraints on the models of nucleosynthesis responsible for the very metal-poor stars with excesses of light neutron-capture elements but without enhancement of heavy ones.

 
astro-ph/0602113 [abs, ps, pdf, other] :
Title: Study of the cyclotron feature in MXB 0656-072
Authors: V.A. McBride (1), J. Wilms (2), M.J. Coe (1), I. Kreykenbohm (3,4), R.E. Rothschild (5), W. Coburn (6), J.L. Galache (1), P. Kretschmar (7), W.R.T. Edge (1), R. Staubert (3) ((1) Southampton, (2) Warwick, (3) IAA Tuebingen, (4) ISDC, (5) CASS-UCSD, (6) SSL-UCB, (7) ESAC Madrid)
Comments: 7 pages, 6 figures, accepted for publication in A&A

We have monitored a Type II outburst of the Be/X-ray binary MXB 0656-072 in a series of pointed RXTE observations during October through December 2003. The source spectrum shows a cyclotron resonance scattering feature at 32.8 +/- 0.5 keV, corresponding to a magnetic field strength of (3.67 +/- 0.06) x 10^12 G and is stable through the outburst and over the pulsar spin phase. The pulsar, with an average pulse period of 160.4 +/- 0.4 s, shows a spin-up of 0.45 s over the duration of the outburst. From optical data, the source distance is estimated to be 3.9 +/- 0.1 kpc and this is used to estimate the X-ray luminosity and a theoretical prediction of the pulsar spin-up during the outburst.

 
astro-ph/0602115 [abs, ps, pdf, other] :
Title: A 0535+26: Back in business
Authors: M J Coe (Southampton), P Reig (Crete), V A McBride (Southampton), J L Galache (Southampton), J Fabregat (Valencia)
Comments: Accepted for publication in MNRAS

In May/June 2005, after 10 years of inactivity, the Be/X-ray binary system A 0535+26 underwent a major X-ray outburst. In this paper data are presented from 10 years of optical, IR and X-ray monitoring showing the behaviour of the system during the quiescent epoch and the lead up to the new outburst. The results show the system going through a period when the Be star in the system had a minimal circumstellar disk and then a dramatic disk recovery leading, presumably, to the latest flare up of X-ray emission. The data are interpreted in terms of the state of the disk and its interaction with the neutron star companion.

 

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astro-ph new abstracts, Wed, 8 Feb 06 01:00:09 GMT
0602133 -- 0602168 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602138 [abs, ps, pdf, other] :
Title: Recent Developments in Neutron Star Thermal Evolution Theories and Observation
Authors: Sachiko Tsuruta
Comments: Invited Paper presented in International Symposium on Origin of Matter and Evolution of Galaxies (OMEG05), November 8-11 2005, University of Tokyo, Tokyo, Japan; in press in the proceedings of this symposium, eds. Kubono, et al. (AIP), 2006

Recent years have seen some significant progress in theoretical studies of physics of dense matter. Combined with the observational data now available from the successful launch of Chandra and XMM/Newton X-ray space missions as well as various lower-energy band observations, these developments now offer the hope for distinguishing various competing neutron star thermal evolution models. For instance, the latest theoretical and observational developments may already exclude both nucleon and kaon direct Urca cooling. In this way we can now have a realistic hope for determining various important properties, such as the composition, superfluidity, the equation of state and stellar radius. These developments should help us obtain deeper insight into the properties of dense matter.

 

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astro-ph new abstracts, Thu, 9 Feb 06 01:00:11 GMT
0602169 -- 0602197 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0503044 [abs, ps, pdf, other] :
Title: Effect of entrainment on stress and pulsar glitches in neutron star crust
Authors: Nicolas Chamel, Brandon Carter
Comments: 17 pages Latex. Revised version has been extended to include generalised Proudman theorem
Note: replaced with revised version Wed, 8 Feb 2006 17:06:38 GMT (91kb)
 

Astrophysics authors/titles "new"

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astro-ph new abstracts, Fri, 10 Feb 06 01:00:09 GMT
0602198 -- 0602212 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602200 [abs, ps, pdf, other] :
Title: Stochastic modeling of kHz QPO light curves
Authors: R. Vio, P. Rebusco, P. Andreani, H. Madsen, R.V. Overgaard
Comments: Accepted for Pubblication in A&A

The Kluzniak & Abramowicz model explains high frequency, double peak, "3:2" QPOs observed in neutron star and black hole sources in terms of a non-linear parametric resonance between radial and vertical epicyclic oscillations of an almost Keplerian accretion disk. The 3:2 ratio of epicyclic frequencies occurs only in strong gravity. Rebusco (2004) and Horak (2004) studied the model analytically: they proved that a small forcing may indeed excite the parametric 3:2 resonance, but they have not explained the physical nature of the forcing. Here we integrate their equations numerically, dropping the ad hoc forcing, and adding instead a stochastic term to mimic the action of the very complex processes that occur in disks as, for example,
MRI turbulence. We demonstrate that the presence of the stochastic term triggers the resonance in epicyclic oscillations of nearly Keplerian disks, and influences their pattern.

 
astro-ph/0602208 [abs, ps, pdf, other] :
Title: The rate and luminosity function of Short GRBs
Authors: Tsvi Piran, Dafne Guetta
Comments: Proceedings of the conference on "Gamma Ray Bursts in the Swift Era", November 29,-December 2, Washington, DC

We compare the luminosity function and rate inferred from the BATSE short hard bursts (SHBs) peak flux distribution with the redshift and luminosity distributions of SHBs observed by Swift/HETE II. The Swift/HETE II SHB sample is incompatible with SHB population that follows the star formation rate. However, it is compatible with a distribution of delay times after the SFR. This would be the case if SHBs are associated with binary neutron star mergers. The implied SHB rates that we find range from \sim 8 to \sim 30h_{70}^3 Gpc^{-3}yr^{-1}. This rate is a much higher than what was previously estimated and it is comparable to the rate of neutron star mergers estimated from statistics of binary pulsars. If GRBs are produced in mergers the implied rate practically guarantees detection by LIGO II and possibly even by LIGO I, if we are lucky. Our analysis, which is based on observed short hard burst is limited to bursts with luminosities above 10^{49}erg/sec. Weaker bursts may exist but if so they are hardly detected by BATSE or Swift and hence their rate is very weakly constrained by current observations. Thus the rate of mergers that lead to a detection of a gravitational radiation signal might be even higher.

 

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astro-ph new abstracts, Mon, 13 Feb 06 01:00:10 GMT
0602213 -- 0602248 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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astro-ph new abstracts, Tue, 14 Feb 06 01:00:13 GMT
0602249 -- 0602288 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602255 [abs, ps, pdf, other] :
Title: Proper Motion of the Crab Pulsar Revisited
Authors: C.-Y. Ng, Roger W. Romani
Comments: 10 pages, 3 figures, accepted for publication in ApJ

It has been suggested that the Crab pulsar's proper motion is well aligned with the symmetry axis of the pulsar wind nebula. We have re-visited this question, examining over 6 years of F547M WFPC2 chip 3 images to obtain a best-fit value of $\mu_\ast = 14.9 \pm 0.8$mas/yr at PA $278\arcdeg \pm 3\arcdeg$. At $26\arcdeg\pm 3\arcdeg$ to the nebula axis, this substantially relaxes constraints on the birth kick of this pulsar. Such misalignment allows the momentum to be imparted over $\sim$1s timescales.

 
astro-ph/0602275 [abs, ps, pdf, other] :
Title: Quasi-Periodic Oscillations from Magnetorotational Turbulence
Authors: Phil Arras, Omer Blaes, Neal J. Turner
Comments: 4 pages, 2 figures. submitted to apj

Quasi-periodic oscillations (QPOs) in the X-ray lightcurves of accreting neutron star and black hole binaries have been widely interpreted as being due to standing wave modes in accretion disks. These disks are thought to be highly turbulent due to the magnetorotational instability (MRI). We study wave excitation by MRI turbulence in the shearing box geometry. We demonstrate that axisymmetric sound waves and radial epicyclic motions driven by MRI turbulence give rise to narrow, distinct peaks in the temporal power spectrum. Inertial waves, on the other hand, do not give rise to distinct peaks which rise significantly above the continuum noise spectrum set by MRI turbulence, even when the fluid motions are projected onto the eigenfunctions of the modes. This is a serious problem for QPO models based on inertial waves.

 
astro-ph/0602277 [abs, pdf] :
Title: Do the Solitary Cooled-Down Neutron Stars Spontaneously Disintegrate?
Authors: Ivan V. Anicin
Comments: 7 pages

We discuss the possibility for a cooled down and otherwise stable solitary neutron star to make a spontaneous transition to its potential black hole ground state. This fundamental process would mimic a precursorless explosion in which the emitted radiations consisting of the statistical mass spectrum of high-energy neutron-rich nuclei, gamma rays and (anti) neutrinos, would carry away some mass of the star, leaving behind the core of the star in the form of a black hole.

 
astro-ph/0602281 [abs, ps, pdf, other] :
Title: Properties of localized protons in neutron star matter for realistic nuclear models
Authors: A. Szmaglinski, W. Wojcik, M. Kutschera
Comments: 6 pages, 3 figures, Presented at the XXIX Mazurian Lakes Conference on Physics, Piaski, Poland, August 30 - Septenber 6, 2005
Journal-ref: Acta Phys. Pol. B 37, 277 (2006)

We study the localization of protons in the core of neutron stars for ten realistic nuclear models that share a common behaviour of nuclear symmetry energy which saturates and eventually decreases at high densities. This results in the low proton fraction of beta-stable neutron star matter. Protons form a small admixture in the neutron star core, which is localized at sufficiently high densities. For every model we calculate the density $n_{loc}$ above which the localization effect is present. Our results indicate that localization occurs at densities above $0.5-1.0 fm^{-3}$. The phase with localized protons occupies a spherical shell or a core region inside neutron stars which contains significant fraction of all nucleons. Proton localization is of great importance for astrophysical properties of neutron stars as it strongly affects transport coefficients of neutron star matter and can produce spontaneous magnetization in neutron stars.

 
astro-ph/0602282 [abs, ps, pdf, other] :
Title: Temperature dependent pulsations of superfluid neutron stars
Authors: M.E. Gusakov (1,2), N. Andersson (2) ((1) Ioffe Institute, (2) University of Southampton)
Comments: 28 pages, 4 figures, submitted to MNRAS

We examine radial oscillations of superfluid neutron stars at finite internal temperatures. For this purpose we generalize the description of relativistic superfluid hydrodynamics to the case of superfluid mixtures. We show that in a neutron star at hydrostatic and beta-equilibrium the red-shifted temperature gradient is smoothed out by neutron superfluidity (but not by proton superfluidity). We calculate radial oscillation modes of neutron stars assuming "frozen" nuclear composition in the pulsating matter. The resulting pulsation frequencies show a strong temperature dependence in the temperature range (0.1-1) T_cn, where T_cn is the critical temperature of neutron superfluidity. Combining our results with thermal evolution, we obtain a significant evolution of the pulsation spectrum, associated with highly efficient Cooper pairing neutrino emission, for 20 years after superfluidity onset.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0507557 [abs, ps, pdf, other] :
Title: Resonant Cyclotron Scattering and Comptonization in Neutron Star Magnetospheres
Authors: Maxim Lyutikov (1,2), Fotis P. Gavriil (3), ((1) UBC, (2) University of Rochester, (3) McGill University)
Comments: 37 pages, 10 figures, accepted by MNRAS, minor changes
Note: replaced with revised version Fri, 10 Feb 2006 21:20:05 GMT (90kb)
 
astro-ph/0512646 [abs, ps, pdf, other] :
Title: Short-living supermassive magnetar model for the early X-ray flares following short GRBs
Authors: W. H. Gao, Y. Z. Fan
Comments: 7 pages
Note: replaced with revised version Mon, 13 Feb 2006 14:53:28 GMT (6kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 15 Feb 06 01:00:10 GMT
0602289 -- 0602317 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602295 [abs, ps, pdf, other] :
Title: Anisotropic weak turbulence of Alfven waves in collisionless astrophysical plasmas
Authors: Q. Luo, D. B. Melrose
Comments: 9 pages, accepted for publication in MNRAS

The evolution of Alfven turbulence due to three-wave interactions is discussed using kinetic theory for a collisionless, thermal plasma. There are three low-frequency modes, analogous to the three modes of compressible MHD. When only Alfven waves are considered, the known anisotropy of turbulence in incompressible MHD theory is reproduced. Inclusion of a fast mode wave leads to separation of turbulence into two regimes: small wave numbers where three-wave processes involving a fast mode is dominant, and large wave numbers where the three Alfven wave process is dominant. Possible application of the anisotropic Alfven turbulence to the interstellar medium and dissipation of magnetic energy in magnetars is discussed.

 
astro-ph/0602301 [abs, ps, pdf, other] :
Title: Contribution of a nearby Pulsar to Cosmic Rays observed at Earth
Authors: A. Bhadra
Comments: 14 pages, 2 figures, Accepted in Astropart. Phys

Contribution of nearby pulsars to the cosmic rays observed at Earth has been studied. It is found that the experimental bound on amplitude of cosmic ray anisotropy may produce significant constraint on the efficiency of converting pulsar rotational energy to emitted particles kinetic energy. Cosmic ray fluxes from two well known nearby gamma ray pulsars, namely the Vela and Geminga pulsars, are estimated. The analysis suggests that observed bound on cosmic ray anisotropy restricts the contributions of the Vela and the Geminga pulsars to at most 1 % of the observed cosmic rays below the knee.

 
astro-ph/0602312 [abs, ps, pdf, other] :
Title: An X-ray Search for Compact Central Sources in Supernova Remnants II: Six Large Diameter SNRs
Authors: D. L. Kaplan, B. M. Gaensler, S. R. Kulkarni, P. O. Slane
Comments: 32 pages, 30 figures; uses emulateapj.cls and hyperref.sty. Accepted for publication in ApJS

We present the second in a series of results in which we have searched for undiscovered neutron stars in supernova remnants (SNRs). This paper deals with the largest six SNRs in our sample, too large for Chandra or XMM-Newton to cover in a single pointing. These SNRs are nearby, with typical distances of <1 kpc. We therefore used the ROSAT Bright Source Catalog and past observations in the literature to identify X-ray point sources in and near the SNRs. Out of 54 sources, we were immediately able to identify optical/IR counterparts to 41 from existing data. We obtained Chandra snap-shot images of the remaining 13 sources. Of these, 10 were point sources with readily identified counterparts, two were extended, and one was not detected in the Chandra observation but is likely a flare star. One of the extended sources may be a pulsar wind nebula, but if so it is probably not associated with the nearby SNR. We are then left with no identified neutron stars in these six SNRs down to luminosity limits of \~1e32 ergs/s. These limits are generally less than the luminosities of typical neutron stars of the same ages, but are compatible with some lower-luminosity sources such as the neutron stars in the SNRs CTA 1 and IC 443.

 
astro-ph/0602314 [abs, ps, pdf, other] :
Title: Scattering of magnetosonic waves in a relativistic and an-isotropic magnetised plasma
Authors: Joachim Moortgat, Jan Kuijpers
Comments: 13 pages, 6 figures (2 color). Accepted for publication in Monthly Notices of the Royal Astronomical Society, MNRAS, to appear on-line mid March

Gravitational waves (GW) propagating through a magnetised plasma excite low-frequency magnetohydrodynamic (MHD) waves. In this paper we investigate whether these waves can produce observable radio emission at higher frequencies by scattering on an an-isotropic intrinsically relativistic distribution of electrons and positrons in the force-free wind surrounding a double neutron star binary merger. The relativistic particle distribution is assumed to be strictly along the magnetic field lines, while the magneto-plasma streams out at a relativistic speed from the neutron stars. In the case of Compton scattering of an incident MHD wave transverse to the magnetic field, we find that the probability of scattering to both a transverse x-mode and a quasi-transverse Langmuir-o mode is suppressed when the scattered frequency is below the local relativistic gyro-frequency, i.e. when the magnetic field is very strong.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0602038 [abs, ps, pdf, other] :
Title: Constraints on the high-density nuclear equation of state from the phenomenology of compact stars and heavy-ion collisions
Authors: T. Klahn, D. Blaschke, S. Typel, E.N.E. van Dalen, A. Faessler, C. Fuchs, T. Gaitanos, H. Grigorian, A. Ho, E.E. Kolomeitsev, M.C. Miller, G. Ropke, J. Trumper, D.N. Voskresensky, F. Weber, H.H. Wolter
Comments: 15 pages, 8 figures, 5 tables

A new scheme for testing nuclear matter equations of state (EsoS) at high densities using constraints from neutron star phenomenology and a flow data analysis of heavy-ion collisions is suggested. An acceptable EoS shall not allow the direct Urca process to occur in neutron stars with masses below $1.5~M_{\odot}$, and also shall not contradict flow and kaon production data of heavy-ion collisions. Compact star constraints include the mass measurements of 2.1 +/- 0.2 M_sun (1 sigma level) for PSR J0751+1807, of 2.0 +/- 0.1 M_sun from the innermost stable circular orbit for 4U 1636-536, the baryon mass - gravitational mass relationships from Pulsar B in J0737-3039 and the mass-radius relationships from quasiperiodic brightness oscillations in 4U 0614+09 and from the thermal emission of RX J1856-3754. This scheme is applied to a set of relativistic EsoS constrained otherwise from nuclear matter saturation properties with the result that no EoS can satisfy all constraints simultaneously, but those with density-dependent masses and coupling constants appear most promising.

 

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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 16 Feb 06 01:00:08 GMT
0602318 -- 0602349 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602330 [abs, ps, pdf, other] :
Title: High-Energy Activity in the Unusually Soft TeV Source HESS J1804-216 toward the Galactic Center
Authors: M. Fatuzzo, F. Melia, R. M. Crocker

In recent years, apparent anisotropies in the ~EeV cosmic ray (CR) flux arriving at Earth from the general direction of the galactic center have been reported from the analysis of AGASA and SUGAR data. The more recently commissioned Auger Observatory has not confirmed these results. HESS has now detected an unusually soft TeV source roughly coincident with the location of the previously claimed CR anisotropy. In this paper, we develop a model for the TeV emission from this object, consistent with observations at other wavelengths, and examine the circumstances under which it might have contributed to the $\sim$ EeV cosmic ray spectrum. We find that the supernova remnant G8.7-0.1 can plausibly account for all the known radiative characteristics of HESS J1804-216, but that it can accelerate cosmic rays only up to an energy $\sim 10^5$ GeV. On the other hand, the pulsar (PSR J1803-2137) embedded within this remnant can in principle inject EeV protons into the surrounding medium, but it cannot account for the broadband spectrum of HESS J1804-216. We therefore conclude that although G8.7-0.1 is probably the source of TeV photons originating from this direction, there is no compelling theoretical motivation for expecting a cosmic ray anisotropy at this location. However, if G8.7-0.1 is indeed correctly identified with HESS J1804-216, it should also produce a $\sim$ GeV flux detectable in a one-year all sky survey by GLAST.

 
astro-ph/0602345 [abs, ps, pdf, other] :
Title: Cosmological Gravitational Wave Background from Phase Transitions in Neutron Stars
Authors: Guenter Sigl (APC and GReCO, IAP, Paris)
Comments: 12 latex pages, 4 ps figures included

It has recently been suggested that collapse of neutron stars induced by a phase transition to quark matter can be a considerable source of gravitational waves with kHz frequencies. We demonstrate that if about one percent of all neutron stars undergo this process, the resulting cosmological gravitational wave background would reach about 10^-10 times the critical density. The background would peak at kHz frequencies and could have an observationally significant tail down to Hz frequencies. It would be comparable or higher than other astrophysical backgrounds, for example, from ordinary core collapse supernovae, from r-mode instabilities in rapidly rotating neutron stars, or from magnetars. The scenario is consistent with cosmological backgrounds in neutrinos and photons.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 17 Feb 06 01:00:09 GMT
0602350 -- 0602376 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602354 [abs, ps, pdf, other] :
Title: A transient I band excess in the optical spectrum of the accreting millisecond pulsar SAX J1808.4-3658
Authors: J. G. Greenhill (1), A. B. Giles (1 and 2), C. Coutures (3) ((1) University of Tasmania (2) Spurion Technology (3) CEA / Saclay)
Comments: 7 pages, 5 figures, submitted to MNRAS

The optical counterpart of the transient, millisecond X-ray pulsar SAX J1808.4-3658 was observed in four colours (BVRI) for five weeks during the 2005 June-July outburst. The optical fluxes declined by ~2 magnitudes during the first 16 days and then commenced quasi-periodic secondary outbursts, with time-scales of several days, similar to those seen in 2000 and 2002. The broadband spectra derived from these measurements were generally consistent with emission from an X-ray heated accretion disc. During the first 16 days decline in intensity the spectrum became redder. We suggest that the primary outburst was initiated by a viscosity change driven instability in the inner disc and note the contrast with another accreting millisecond pulsar, XTE J0929-314, for which the spectrum becomes bluer during outburst. Several significant short duration changes in V-I were detected. One occurred at about HJD 2453546 in the early phase of the first secondary outburst and may be due to a mass transfer instability. On the night of 2005 June 5 (HJD 2453527) the I band flux was ~0.45 magnitudes brighter than on the preceding or following nights whereas the BVR bands showed no obvious enhancement. A Type I X-ray burst was detected by the RXTE spacecraft during this I band integration. It seems unlikely that reprocessed radiation from the burst was sufficient to explain the observed increase. We suggest that a major part of the I band excess was due to synchrotron emission triggered by the X-ray burst.

 
astro-ph/0602359 [abs, ps, pdf, other] :
Title: Magnetars as persistent hard X-ray sources: INTEGRAL discovery of a hard tail in SGR 1900+14
Authors: D. Gotz, S. Mereghetti, A. Tiengo, P. Esposito
Comments: 5 pages, 2 figures, submitted to A&A Letters

Using 2.5 Ms of data obtained by the INTEGRAL satellite in 2003-2004, we discovered persistent hard X-ray emission from the soft gamma-ray repeater SGR 1900+14. Its 20-100 keV spectrum is well described by a steep power law with photon index Gamma=3.1+/-0.5 and flux 1.5E-11 erg/cmsq/s. Contrary to SGR 1806-20, the only other soft gamma-ray repeater for which persistent emission above 20 keV was reported, SGR 1900+14 has been detected in the hard X-ray range while it was in a quiescent state (the last bursts from this source were observed in 2002). By comparing the broad band spectra (1-100 keV) of all the magnetars detected by INTEGRAL (the two SGRs and three anomalous X-ray pulsars) we find evidence for a different spectral behaviour of these two classes of sources.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0507312 [abs, ps, pdf, other] :
Title: Observational constraints on hyperons in neutron stars
Authors: Benjamin D. Lackey, Mohit Nayyar, Benjamin J. Owen (Penn State)
Comments: 8 pages, 5 figures; corrected error in equation three, corrected minor typos, new tables of equations of state added; final version as appearing in PRD
Journal-ref: Phys.Rev. D73 (2006) 024021
Note: replaced with revised version Wed, 15 Feb 2006 21:42:20 GMT (85kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 20 Feb 06 01:00:09 GMT
0602377 -- 0602406 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602402 [abs, ps, pdf, other] :
Title: The Prelude to and Aftermath of the Giant Flare of 2004 December 27: Persistent and Pulsed X-ray Properties of SGR 1806-20 from 1993 to 2005
Authors: Peter M. Woods (Dynetics/Usra/NSSTC), Chryssa Kouveliotou (NASA/MSFC/NSSTC), Mark H. Finger (USRA/NSSTC), Ersin Gogus (Sabanci Univ/Usra/NSSTC), Colleen A. Wilson (NASA/MSFC/NSSTC), Sandeep K. Patel (USRA/NSSTC), Kevin Hurley (UCB), Jean H. Swank (NASA/GSFC)
Comments: 34 pages, 7 figures, 8 tables. Submitted to ApJ

On 2004 December 27, a highly-energetic giant flare was recorded from the magnetar candidate SGR 1806-20. In the months preceding this flare, the persistent X-ray emission from this object began to undergo significant changes. Here, we report on the evolution of key spectral and temporal parameters prior to and following this giant flare. Using the Rossi X-ray Timing Explorer, we track the pulse frequency of SGR 1806-20 and find that the spin-down rate of this SGR varied erratically in the months before and after the flare. Contrary to the giant flare in SGR 1900+14, we find no evidence for a discrete jump in spin frequency at the time of the December 27th flare (|dnu/nu| < 5 X 10^-6). In the months surrounding the flare, we find a strong correlation between pulsed flux and torque consistent with the model for magnetar magnetosphere electrodynamics proposed by Thompson, Lyutikov & Kulkarni (2002). As with the flare in SGR 1900+14, the pulse morphology of SGR 1806-20 changes drastically following the flare. Using the Chandra X-ray Observatory and other publicly available imaging X-ray detector observations, we construct a spectral history of SGR 1806-20 from 1993 to 2005. The usual magnetar persistent emission spectral model of a power-law plus a blackbody provides an excellent fit to the data. We confirm the earlier finding by Mereghetti et al. (2005) of increasing spectral hardness of SGR 1806-20 between 1993 and 2004. Contrary to the direct correlation between torque and spectral hardness proposed by Mereghetti et al., we find evidence for a sudden torque change that triggered a gradual hardening of the energy spectrum on a timescale of years. Interestingly, the spectral hardness, spin-down rate, pulsed, and phase-averaged of SGR 1806-20 all peak months before the flare epoch.

 

Cross-listings


2 abstracts or titles contain neutron star, magnetar or pulsar


hep-ph/0602150 [abs, ps, pdf, other] :
Title: Opening a new window for warm dark matter
Authors: Takehiko Asaka, Alexander Kusenko, Mikhail Shaposhnikov
Comments: 5 pages

We explore the range of parameters for dark-matter sterile neutrinos in an extention of the Minimal Standard Model by three singlet fermions with masses below the electroweak scale (the $\nu$MSM). This simple model, which can explain a wide range of phenomena, including neutrino oscillations, baryogenesis, the pulsar velocities, and the early reionization, allows for the dark-matter sterile neutrinos to have masses as small as 0.5 keV. The presence of two heavier sterile neutrinos and the possibility of entropy production in their decays broadens the allowed range of parameters for the dark-matter sterile neutrinos (or other types of dark matter, for example, the gravitino). Of particular interest is the possibility of large mixing angles between active and sterile neutrinos, which may be accessible to laboratory experiments.

 
nucl-th/0602042 [abs, ps, pdf, other] :
Title: Links Between Heavy Ion and Astrophysics
Authors: C. J. Horowitz
Comments: 8 pages, 6 figures. To be published in "Dynamics and Thermodynamics with Nucleon Degrees of Freedom", eds. P. Chomaz, F. Gulminelli, J. Natowitz, and S. Yennello, this http URL

Heavy ion experiments provide important data to test astrophysical models. The high density equation of state can be probed in HI collisions and applied to the hot protoneutron star formed in core collapse supernovae. The Parity Radius Experiment (PREX) aims to accurately measure the neutron radius of $^{208}$Pb with parity violating electron scattering. This determines the pressure of neutron rich matter and the density dependence of the symmetry energy. Competition between nuclear attraction and coulomb repulsion can form exotic shapes called nuclear pasta in neutron star crusts and supernovae. This competition can be probed with multifragmentation HI reactions. We use large scale semiclassical simulations to study nonuniform neutron rich matter in supernovae. We find that the coulomb interactions in astrophysical systems suppress density fluctuations. As a result, there is no first order liquid vapor phase transition. Finally, the virial expansion for low density matter shows that the nuclear vapor phase is complex with significant concentrations of alpha particles and other light nuclei in addition to free nucleons.

 

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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 21 Feb 06 01:00:18 GMT
0602407 -- 0602441 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602417 [abs, ps, pdf, other] :
Title: Corona of Magnetars
Authors: Andrei M. Beloborodov, Christopher Thompson
Comments: 72 pages, 14 figures, submitted to ApJ

We develop a theoretical model that explains the formation of hot coronae around strongly magnetized neutron stars -- magnetars. The starquakes of a magnetar shear its external magnetic field, which becomes non-potential and is threaded by an electric current. Once twisted, the magnetosphere cannot untwist immediately because of its self-induction. The induced electric field lifts particles from the stellar surface, accelerates them, and initiates avalanches of pair creation in the magnetosphere. The created plasma corona maintains the electric current demanded by curl(B) and regulates the self-induction e.m.f. by screening. This corona persists in dynamic equilibrium: it is continually lost to the stellar surface on the light-crossing time of 10^{-4} s and replenished with new particles. In essence, the twisted magnetosphere acts as an accelerator that converts the toroidal field energy to particle kinetic energy. Using a direct numerical experiment, we show that the corona self-organizes quickly (on a millisecond timescale) into a quasi-steady state, with voltage ~1 GeV along the magnetic lines. The heating rate of the corona is 10^{36}-10^{37} erg/s, in agreement with the observed persistent, high-energy output of magnetars. We deduce that a static twist that is suddenly implanted into the magnetosphere will decay on a timescale of 1-10 yrs. The particles accelerated in the corona impact the solid crust, knock out protons, and regulate the column density of the hydrostatic atmosphere of the star. The transition layer between the atmosphere and the corona is the likely source of the observed 100-keV emission from magnetars. The corona emits curvature radiation and can supply the observed IR-optical luminosity. (Abridged)

 
astro-ph/0602419 [abs, ps, pdf, other] :
Title: Stellar Explosions by Magnetic Towers
Authors: Dmitri A. Uzdensky, Andrew I. MacFadyen
Comments: 18 pages, 8 figures, submitted to ApJ

We propose a magnetic mechanism for the collimated explosion of a massive star relevant for GRBs, XRFs and asymmetric supernovae. We apply Lynden-Bell's magnetic tower scenario to the interior of a massive rotating star after the core has collapsed to form a black hole with an accretion disk or a millisecond magnetar acting as a central engine. We solve the force-free Grad-Shafranov equation to calculate the magnetic structure and growth of a tower embedded in a stellar environment. The pressure of the toroidal magnetic field, continuously generated by differential rotation of the central engine, drives a rapid expansion which becomes vertically collimated after lateral force balance with the surrounding gas pressure is reached. The collimation naturally occurs because hoop stress concentrates magnetic field toward the rotation axis and inhibits lateral expansion. This leads to the growth of a self-collimated magnetic tower. When embedded in a massive star, the supersonic expansion of the tower drives a strong bow shock behind which an over-pressured cocoon forms. The cocoon confines the tower by supplying collimating pressure and provides stabilization against disruption due to MHD instabilities. Because the tower consists of closed field lines starting and ending on the central engine, mixing of baryons from the cocoon into the tower is suppressed. The channel cleared by the growing tower is thus plausibly free of baryons and allows the escape of magnetic energy from the central engine through the star. While propagating down the stellar density gradient, the tower accelerates and becomes relativistic. During the expansion, fast collisionless reconnection becomes possible resulting in dissipation of magnetic energy which may be responsible for GRB prompt emission.

 
astro-ph/0602438 [abs, ps, pdf, other] :
Title: Solar and stellar system tests of the cosmological constant
Authors: M. Sereno (Univ. Zurich), Ph. Jetzer (Univ. Zurich)
Comments: 4 pages; this is a preprint of an article accepted for publication in Physical Review D

Some tests of gravity theories - periastron shift, geodetic precession, change in mean motion and gravitational redshift - are applied in solar and stellar systems to constrain the cosmological constant. We thus consider a length scale range from 10^8 to 10^{15} km. Best bounds from the solar system come from perihelion advance and change in mean motion of Earth and Mars, Lambda < 10^{-36} km^{-2}. Such a limit falls very short to estimates from observational cosmology analyses but a future experiment performing radio ranging observations of outer planets could improve it by four orders of magnitude. Beyond the solar system, together with future measurements of periastron advance in wide binary pulsars, gravitational redshift of white dwarfs can provide bounds competitive with Mars data.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0410548 [abs, ps, pdf, other] :
Title: Magnetospheric Birefringence Induces Unique Polarization Signatures in Neutron-Star Spectra
Authors: R. M. Shannon, Jeremy S. Heyl (UBC)
Comments: 4 pages, 5 figures, changes to reflect accepted version
Note: replaced with revised version Sat, 18 Feb 2006 19:48:49 GMT (462kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 22 Feb 06 01:00:12 GMT
0602442 -- 0602472 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602453 [abs, ps, pdf, other] :
Title: The Magnetospheric Eternally Collapsing Object (MECO) Model of Galactic Black Hole Candidates and Active Galactic Nuclei
Authors: Stanley L. Robertson, Darryl J. Leiter
Comments: Synopsis of three previously published papers plus new results., 48 pages
Journal-ref: in `New Developments in Black Hole Research', Nova Science Publishers, 2005, ed. P. V, Kreitler, ISBN 1-59454-460-3

The spectral, timing, and jet formation properties of neutron stars in low mass x-ray binary systems are influenced by the presence of central magnetic moments. Similar features shown by the galactic black hole candidates (GBHC) strongly suggest that their compact cores might be intrinsically magnetic as well. We show that the existence of intrinsically magnetic GBHC is consistent with a new class of solutions of the Einstein field equations of General Relativity. These solutions are based on a strict adherence to the Strong Principle of Equivalence (SPOE) requirement that the world lines of physical matter must remain timelike in all regions of spacetime. The new solutions emerge when the structure and radiation transfer properties of the energy momentum tensor on the right hand side of the Einstein field equations are appropriately chosen to dynamically enforce this SPOE requirement of timelike world line completeness. In this context, we find that the Einstein field equations allow the existence of highly red shifted, Magnetospheric, Eternally Collapsing Objects (MECO). MECO necessarily possess intrinsic magnetic moments and they do not have trapped surfaces that lead to event horizons and curvature singularities. Their most striking features are equipartition magnetic fields, pair plasma atmospheres and extreme gravitational redshifts. Since MECO lifetimes are orders of magnitude greater than a Hubble time, they provide an elegant and unified framework for understanding a broad range of observations of GBHC and active galactic nuclei. We examine their spectral, timing and jet formation properties and discuss characteristics that might lead to their confirmation.

 
astro-ph/0602460 [abs, ps, pdf, other] :
Title: Heavy element nucleosynthesis in a collapsar
Authors: Shin-ichirou Fujimoto, Masa-aki Hashimoto, Kei Kotake, Shoichi Yamada
Comments: 16 pages, 19 figures, submitted to the Astrophysical Journal

We investigate synthesis of heavy elements in a collapsar. We have calculated detailed composition of magnetically driven jets ejected from a collapsar, which is based on long-term, magneto-hydrodynamic simulations of a rapidly rotating massive star of 40Msun during core collapse. We follow evolution of abundances of about 4000 nuclides from the collapse phase to the ejection phase through the jet generation phase with use of two large nuclear reaction networks. We find that the r-process successfully operates in the jets, so that U and Th are synthesized abundantly when the progenitor has large magnetic field of 10^{12} G and rapidly rotating core. Abundance pattern inside the jets is similar compared to that of r-elements in the solar system. Heavy neutron-rich nuclei \sim 0.01Msun can be ejected from the collapsar. The detailed abundances depend on nuclear properties of mass model, beta-decay rate, and fission, for nuclei near the neutron drip line. Furthermore, we find that p-nuclei are produced without seed nuclei: not only light p-nuclei, such as Se74, Kr78, Sr84, and Mo92, but also heavy p-nuclei, In113, Sn115, and La138, can be abundantly synthesized in the jets. The amounts of p-nuclei in the ejecta are much greater than those in core-collapse supernovae (SNe). In particular, Mo92, In113, Sn115, and La138 deficient in the SNe, are significantly produced in the ejecta.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 22 Feb 06 01:00:12 GMT
0602442 -- 0602472 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602453 [abs, ps, pdf, other] :
Title: The Magnetospheric Eternally Collapsing Object (MECO) Model of Galactic Black Hole Candidates and Active Galactic Nuclei
Authors: Stanley L. Robertson, Darryl J. Leiter
Comments: Synopsis of three previously published papers plus new results., 48 pages
Journal-ref: in `New Developments in Black Hole Research', Nova Science Publishers, 2005, ed. P. V, Kreitler, ISBN 1-59454-460-3

The spectral, timing, and jet formation properties of neutron stars in low mass x-ray binary systems are influenced by the presence of central magnetic moments. Similar features shown by the galactic black hole candidates (GBHC) strongly suggest that their compact cores might be intrinsically magnetic as well. We show that the existence of intrinsically magnetic GBHC is consistent with a new class of solutions of the Einstein field equations of General Relativity. These solutions are based on a strict adherence to the Strong Principle of Equivalence (SPOE) requirement that the world lines of physical matter must remain timelike in all regions of spacetime. The new solutions emerge when the structure and radiation transfer properties of the energy momentum tensor on the right hand side of the Einstein field equations are appropriately chosen to dynamically enforce this SPOE requirement of timelike world line completeness. In this context, we find that the Einstein field equations allow the existence of highly red shifted, Magnetospheric, Eternally Collapsing Objects (MECO). MECO necessarily possess intrinsic magnetic moments and they do not have trapped surfaces that lead to event horizons and curvature singularities. Their most striking features are equipartition magnetic fields, pair plasma atmospheres and extreme gravitational redshifts. Since MECO lifetimes are orders of magnitude greater than a Hubble time, they provide an elegant and unified framework for understanding a broad range of observations of GBHC and active galactic nuclei. We examine their spectral, timing and jet formation properties and discuss characteristics that might lead to their confirmation.

 
astro-ph/0602460 [abs, ps, pdf, other] :
Title: Heavy element nucleosynthesis in a collapsar
Authors: Shin-ichirou Fujimoto, Masa-aki Hashimoto, Kei Kotake, Shoichi Yamada
Comments: 16 pages, 19 figures, submitted to the Astrophysical Journal

We investigate synthesis of heavy elements in a collapsar. We have calculated detailed composition of magnetically driven jets ejected from a collapsar, which is based on long-term, magneto-hydrodynamic simulations of a rapidly rotating massive star of 40Msun during core collapse. We follow evolution of abundances of about 4000 nuclides from the collapse phase to the ejection phase through the jet generation phase with use of two large nuclear reaction networks. We find that the r-process successfully operates in the jets, so that U and Th are synthesized abundantly when the progenitor has large magnetic field of 10^{12} G and rapidly rotating core. Abundance pattern inside the jets is similar compared to that of r-elements in the solar system. Heavy neutron-rich nuclei \sim 0.01Msun can be ejected from the collapsar. The detailed abundances depend on nuclear properties of mass model, beta-decay rate, and fission, for nuclei near the neutron drip line. Furthermore, we find that p-nuclei are produced without seed nuclei: not only light p-nuclei, such as Se74, Kr78, Sr84, and Mo92, but also heavy p-nuclei, In113, Sn115, and La138, can be abundantly synthesized in the jets. The amounts of p-nuclei in the ejecta are much greater than those in core-collapse supernovae (SNe). In particular, Mo92, In113, Sn115, and La138 deficient in the SNe, are significantly produced in the ejecta.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 23 Feb 06 01:00:14 GMT
0602473 -- 0602494 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602475 [abs, ps, pdf, other] :
Title: Relativistic MHD Winds from Rotating Neutron Stars
Authors: N. Bucciantini (1), Todd. A. Thompson (2), J. Arons (1), E. Quataert (1), L. Del Zanna (3). ((1) Astronomy Dep. U.C. Berkeley, (2) Dep. Astrophysical Science Princeton, (3) Dip. Astronomia Univ. Firenze)
Comments: Accepted for publication in MNRAS. 19 pages, 21 figures

We solve for the time-dependent dynamics of axisymmetric, general relativistic magnetohydrodynamic winds from rotating neutron stars. The mass loss rate is obtained self-consistently as a solution to the MHD equations, subject to a finite thermal pressure at the stellar surface. We consider both monopole and dipole magnetic field geometries and we explore the parameter regime extending from low magnetization (low-sigma_o), almost thermally-driven winds to high magnetization (high-sigma_o), relativistic Poynting-flux dominated outflows. We compute the angular momentum and rotational energy loss rates as a function of sigma_o and compare with analytic expectations from the classical theory of pulsars and magnetized stellar winds. In the case of the monopole, our high-sigma_o calculations asymptotically approach the analytic force-free limit. If we define the spindown rate in terms of the open magnetic flux, we similarly reproduce the spindown rate from recent force-free calculations of the aligned dipole. However, even for sigma_o as high as ~20, we find that the location of the Y-type point (r_Y), which specifies the radius of the last closed field line in the equatorial plane, is not the radius of the light cylinder R_L = c/omega (R = cylindrical radius), as has previously been assumed in most estimates and force-free calculations. Instead, although the Alfven radius at intermediate latitudes quickly approaches R_L as sigma_o exceeds unity, r_Y remains significantly less than R_L. Because r_Y < R_L, our calculated spindown rates thus exceed the classic ``vacuum dipole'' rate. We discussthe implications of our results for models of rotation-powered pulsars and magnetars, both in their observed states and in their hypothesized rapidly rotating initial state.

 
astro-ph/0602488 [abs, ps, pdf, other] :
Title: The rp-Process in Neutrino-driven Winds
Authors: Shinya Wanajo (Univ. of Tokyo)
Comments: 28 pages, 17 figures, submitted to ApJ

Recent hydrodynamic simulations of core-collapse supernovae with accurate neutrino transport suggest that the bulk of the early neutrino-heated ejecta is proton rich, in which the production of some interesting proton-rich nuclei is expected. As suggested in recent nucleosynthesis studies, the rapid proton-capture (rp) process takes place in such proton-rich environments by bypassing the waiting point nuclei with the beta-lives of a few minutes via the faster capture of neutrons continuously supplied from the neutrino absorption by protons. In this study, the nucleosynthesis calculations are performed with the wide ranges of the neutrino luminosities and the electron fractions (Ye), using the semi-analytic models of proto-neutron star winds. The masses of proto-neutron stars are taken to be 1.4 Msun and 2.0 Msun, where the latter is regarded as the test for somewhat high entropy winds (about a factor of two). For Ye > 0.52, the neutrino-induced rp-process takes place in many wind trajectories, and the p-nuclei up to A = 130 are synthesized with interesting amounts. However, 92Mo is somewhat underproduced compared to those with similar mass numbers. For 0.46 < Y < 0.49, on the other hand, 92Mo is significantly enhanced by the nuclear flows in the vicinity of the abundant 90Zr that originates from the alpha-process at higher temperature. The nucleosynthetic yields are averaged over the ejected masses of winds, and further the Ye distribution predicted by the recent hydrodynamic simulation of a core-collapse supernova. Comparison of the mass-Ye-averaged yields to the solar compositions implies that the neutrino-driven winds can be potentially the origin of light p-nuclei up to A = 110, including 92,94Mo and 96,98Ru that cannot be explained by other astrophysical sites.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0503461 [abs, ps, pdf, other] :
Title: Effects of Pulsar Rotation on Timing Measurements of the Double Pulsar System J0737-3039
Authors: Roman R. Rafikov (IAS), Dong Lai (Cornell)
Comments: Minor changes, accepted to ApJ
Note: replaced with revised version Tue, 21 Feb 2006 23:22:08 GMT (56kb)
 
astro-ph/0507099 [abs, ps, pdf, other] :
Title: Torus Formation in Neutron Star Mergers and Well-Localized Short Gamma-Ray Bursts
Authors: R. Oechslin, H.-Th. Janka (MPI for Astrophysics, Garching)
Comments: 12 pages, 9 figures, high-resolution color figures available on request; accepted by MNRAS
Note: replaced with revised version Wed, 22 Feb 2006 19:23:59 GMT (903kb)
 
astro-ph/0508372 [abs, ps, pdf, other] :
Title: QCD phase transition in rotaing neutron star, Neutrino beaming and Gamma-ray bursters
Authors: Abhijit Bhattacharyya, Sanjay K. Ghosh, Sibaji Raha
Comments: Modified manuscript with 9 pages including 3 ps figures, Accepted for publication in Phys. Lett. B
Note: replaced with revised version Wed, 22 Feb 2006 06:15:21 GMT (13kb)
 
astro-ph/0512417 [abs, ps, pdf, other] :
Title: Effects of Gravitational Lensing and Companion Motion on the Binary Pulsar Timing
Authors: Roman R. Rafikov (CITA), Dong Lai (Cornell)
Comments: Minor changes, accepted to Phys. Rev. D
Note: replaced with revised version Tue, 21 Feb 2006 23:19:16 GMT (26kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 24 Feb 06 01:00:10 GMT
0602495 -- 0602521 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602501 [abs, ps, pdf, other] :
Title: Optical Detection of Two Intermediate Mass Binary Pulsar Companions
Authors: B. A. Jacoby, D. Chakrabarty, M. H. van Kerkwijk, S. R. Kulkarni, D. L. Kaplan
Comments: 9 pages, 2 figures, accepted for publication in ApJL

We report the detection of probable optical counterparts for two Intermediate Mass Binary Pulsar (IMBP) systems, PSR J1528-3146 and PSR J1757-5322. Recent radio pulsar surveys have uncovered a handful of these systems with putative massive white dwarf companions, thought to have an evolutionary history different from that of the more numerous class of Low Mass Binary Pulsars (LMBPs) with He white dwarf companions. The study of IMBP companions via optical observations offers us several new diagnostics: the evolution of main sequence stars near the white-dwarf-neutron star boundary, the physics of white dwarfs close to the Chandrasekhar limit, and insights into the recycling process by which old pulsars are spun up to high rotation frequencies. We were unsuccessful in our attempt to detect optical counterparts of PSR J1141-6545, PSR J1157-5112, PSR J1435-6100, and PSR J1454-5846.

 
astro-ph/0602510 [abs, ps, pdf, other] :
Title: Double-core evolution and the formation of neutron-star binaries with compact companions
Authors: J. D. M. Dewi (Cambridge), Ph. Podsiadlowski (Oxford), A. Sena (Oxford)
Comments: MNRAS, accepted

We present the results of a systematic exploration of an alternative evolutionary scenario to form double neutron-star binaries, first proposed by Brown (1995), which does not involve a neutron star passing through a common envelope. In this scenario, the initial binary components have very similar masses, and both components have left the main sequence before they evolve into contact; preferably the primary has already developed a CO core. We have performed population synthesis simulations to study the formation of double neutron star binaries via this channel and to predict the orbital properties and system velocities of such systems. We obtain a merger rate for DNSs in this channel in the range of 0.1 - 12/Myr. These rates are still subject to substantial uncertainties such as the modelling of the contact phase.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 27 Feb 06 01:00:09 GMT
0602522 -- 0602547 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602522 [abs, ps, pdf, other] :
Title: Chandra Observations of the Transient 7-s X-ray Pulsar AX J1845.0-0258
Authors: C. R. Tam (1), V. M. Kaspi (1), B. M. Gaensler (2), E. V. Gotthelf (3) ((1) McGill University, (2) Harvard CfA, (3) Columbia University)
Comments: 6 pages, 2 figures, submitted to ApJ

We present the results of Chandra X-ray Observatory observations of the transient anomalous X-ray pulsar (AXP) candidate AX J1845.0-0258 in apparent quiescence. Within the source's error circle, we find a point source and possible counterpart, which we designate CXOU J184454.6-025653. No coherent pulsations are detected, and no extended emission is seen. The source's spectrum is equally well described by a blackbody model of temperature kT~2.0 keV or a power law model with photon index Gamma~1.0. This is considerably harder than was seen for AX J1845.0-0258 during its period of brightening in 1993 (kT~0.6 keV) despite being at least ~13 times fainter. This behavior is opposite to that observed in the case of another transient AXP, XTE J1810-197. We therefore explore the possibility that CXOU J184454.6-025653 is an unrelated source, and that AX J1845.0-0258 remains undetected since 1993, with flux 260-430 times fainter than at that epoch. If so, this would represent an unprecedented range of variability in AXPs.

 
astro-ph/0602525 [abs, ps, pdf, other] :
Title: X-Ray Flares from Postmerger Millisecond Pulsars
Authors: Z. G. Dai, X. Y. Wang, X. F. Wu, B. Zhang
Comments: 10 pages, published in Science
Journal-ref: Science, 311 (2006) 1127-1129

Recent observations support the suggestion that short-duration gamma-ray bursts are produced by compact star mergers. The X-ray flares discovered in two short gamma-ray bursts last much longer than the previously proposed postmerger energy release time scales. Here we show that they can be produced by differentially rotating, millisecond pulsars after the mergers of binary neutron stars. The differential rotation leads to windup of interior poloidal magnetic fields and the resulting toroidal fields are strong enough to float up and break through the stellar surface. Magnetic reconnection--driven explosive events then occur, leading to multiple X-ray flares minutes after the original gamma-ray burst.

 
astro-ph/0602529 [abs, ps, pdf, other] :
Title: Timing Features of the Accretion--driven Millisecond X-Ray Pulsar XTE J1807--294 in 2003 March Outburst
Authors: Fan Zhang (1), J.L. Qu (1), C. M. Zhang (2), W. Chen (1), T. P. Li (1,3) ((1)Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, CAS, Beijing, PR. China (2)National Astronomical Observatories, CAS (3)Tsinghua University, PR. China)
Comments: Accepted by ApJ, 23 pages, 7 figures, 3 tables

In order to probe the activity of the inner disk flow and its effect on the neutron star surface emissions, we carried out the timing analysis of the Rossi X-Ray Timing Explorer (RXTE) observations of the millisecond X-ray pulsar XTE J1807--294, focusing on its correlated behaviors in X-ray intensities, hardness ratios, pulse profiles and power density spectra. The source was observed to have a serial of broad "puny" flares on a timescale of hours to days on the top of a decaying outburst in March 2003. In the flares, the spectra are softened and the pulse profiles become more sinusoidal. The frequency of kilohertz quasi-periodic oscillation (kHz QPO) is found to be positively related to the X-ray count rate in the flares. These features observed in the flares could be due to the accreting flow inhomogeneities. It is noticed that the fractional pulse amplitude increases with the flare intensities in a range of $\sim 2%-14%$, comparable to those observed in the thermonuclear bursts of the millisecond X-ray pulsar XTE J1814--338, whereas it remains at about 6.5% in the normal state. Such a significant variation of the pulse profile in the "puny" flares may reflect the changes of physical parameters in the inner disk accretion region. Furthermore, we noticed an overall positive correlation between the kHz QPO frequency and the fractional pulse amplitude, which could be the first evidence representing that the neutron-star surface emission properties are very sensitive to the disk flow inhomogeneities. This effect should be cautiously considered in the burst oscillation studies.

 
astro-ph/0602538 [abs, ps, pdf, other] :
Title: Effect of hyperon-hyperon interaction on bulk viscosity and r-mode instability in neutron stars
Authors: Debarati Chatterjee, Debades Bandyopadhyay, (Saha Institute of Nuclear Physics, India)
Comments: 26 pages, 9 figures

We investigate the effect of hyperon matter including hyperon-hyperon interaction on bulk viscosity. Equations of state are constructed within the framework of a relativistic field theoretical model where baryon-baryon interaction is mediated by the exchange of scalar and vector mesons. Hyperon-hyperon interaction is also taken into account by the exchange of two strange mesons. This interaction results in a smaller maximum mass neutron star compared with the case without the interaction. The coefficient of bulk viscosity due to the non-leptonic weak process is determined by these equations of state. The interacting hyperon matter enhances the bulk viscosity coefficient in a neutron star interior compared with the no interaction case. The r-mode instability is more effectively suppressed in hyperon-hyperon interaction case than that without the interaction.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0510684 [abs, ps, pdf, other] :
Title: Anisotropic thermal emission from magnetized neutron stars
Authors: J.F. Perez-Azorin, J.A. Miralles, J.A. Pons
Comments: 18 pages, 19 figures, version accepted for publication in A&A
Note: replaced with revised version Fri, 24 Feb 2006 08:47:32 GMT (724kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 28 Feb 06 01:00:11 GMT
0602548 -- 0602595 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602558 [abs, ps, pdf, other] :
Title: Luminosity dependent study of the High Mass X-ray Binary Pulsar 4U~0114+65 with ASCA
Authors: U. Mukherjee, B. Paul
Comments: 14 pages, 4 figures and 2 tables. Accepted in Journal of Astrophysics and Astronomy

Here we report the spectral characteristics of the high and low states of the pulsar 4U~0114+65 and examine the change in the parameters of the spectral model. A power law and a photoelectric absorption by material along the line of sight together with a high energy cut-off suffice to describe the continuum spectrum in both the states. A fluorescence iron line at $\sim$6.4 keV is present in the high as well as in the low state, though it is less intense in the latter. The photon index, cut-off energy and e-folding energy values hardly show any discernible change over the states. We compare these spectral characteristics as observed with ASCA to that with other satellites. We also compare the spectral characteristics of 4U~0114+650 with other X-ray sources which show intensity variation at different time scales.

 
astro-ph/0602559 [abs, ps, pdf, other] :
Title: Variable Quasi Periodic Oscillations during an outburst of the transient X-ray pulsar XTE J1858+034
Authors: U. Mukherjee, S. Bapna, H. Raichur, B. Paul, S. N. A. Jaaffrey
Comments: 17 pages, 8 figures and 1 table. Accepted in Journal of Astrophysics and Astronomy

We have investigated the Quasi Periodic Oscillation (QPO) properties of the transient accreting X-ray pulsar XTE J1858+034 during the second outburst of this source in April-May 2004. We have used observations made with the Proportional Counter Array (PCA) of the Rossi X-ray Timing Explorer (RXTE) during May 14-18 2004, in the declining phase of the outburst. We detected the presence of low frequency QPOs in the frequency range of 140--185 mHz in all the RXTE-PCA observations. We report evolution of the QPO parameters with the time, X-ray flux, and X-ray photon energy. Though a correlation between the QPO centroid frequency and the instantaneous X-ray flux is not very clear from the data, we point out that the QPO frequency and the one day averaged X-ray flux decreased with time during these observations. We have obtained a clear energy dependence of the RMS variation in the QPOs, increasing from about 3% at 3 keV to 6% at 25 keV. The X-ray pulse profile is a single peaked sinusoidal, with pulse fraction increasing from 20% at 3 keV to 45% at 30 keV. We found that, similar to the previous outburst, the energy spectrum is well fitted with a model consisting of a cut-off power law along with an iron emission line.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0512646 [abs, ps, pdf, other] :
Title: Short-living supermassive magnetar model for the early X-ray flares following short GRBs
Authors: W. H. Gao, Y. Z. Fan
Comments: 7 pages
Note: replaced with revised version Mon, 27 Feb 2006 09:32:37 GMT (6kb)
 
gr-qc/0511072 [abs, ps, pdf, other] :
Title: Checking the variability of the gravitational constant with binary pulsars
Authors: G.S. Bisnovatyi-Kogan
Comments: Submitted to Journal
Subj-class: General Relativity and Quantum Cosmology; Space Physics
Note: replaced with revised version Sun, 26 Feb 2006 10:53:35 GMT (5kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 1 Mar 06 01:00:12 GMT
0602596 -- 0602633 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602609 [abs, ps, pdf, other] :
Title: Pulsar Wind Nebulae and the Non-thermal X-Ray Emission of Millisecond Pulsars
Authors: K. S. Cheng, Ronald E. Taam, W. Wang
Comments: To be appeared in ApJ April 2006

The non-thermal, non-pulsed X-ray emission of MSPs is investigated. As in young pulsars, MSPs emit a relativistic wind, which interacting with the interstellar medium and/or a binary companion can significantly contribute to the non-pulsed emission of these pulsars. An application and extension of a simple model developed for young pulsars is applied to the old recycled MSP B1957+20. It is found that the pulsar wind can, indeed, contribute to both the resolved and unresolved X-ray emission. For other MSP in the Galactic field where the spectral index of the non-pulsed component has been measured (i.e., PSR B1937+21, J0218+4232) the contribution of the pulsar wind to the non-pulsed X-ray luminosity is estimated. For the MSPs in the core regions of globular clusters, the pulsar wind nebula is likely affected by its interaction with the dense stellar environment, possibly leading to a diminished contribution to the total X-ray emission. In this case, the existence of non-thermal non-pulsed X-ray emission is more likely for binary rather than isolated MSPs with the emission arising from the interaction of the relativistic pulsar wind with a binary companion. Our study suggests that the magnetization parameter in the pulsar wind nebulae of MSPs is significantly larger than that of the Crab nebula by about a factor of 10. The emission from MSPs moving at high velocities may appear spatially extended with a tail-like morphology, which may contribute to the faint filamentary X-ray source subpopulation in the Galaxy.

 
astro-ph/0602625 [abs, ps, pdf, other] :
Title: The neutron star soft X-ray transient 1H1905+000 in quiescence
Authors: P.G. Jonker, C.G. Bassa, G. Nelemans, A.M. Juett, E.F. Brown, D. Chakrabarty
Comments: 10 pages, 5 figures, accepted for publication in MNRAS

In this Paper we report on our analysis of a ~25 ksec. Chandra X-ray observation of the neutron star soft X-ray transient (SXT) 1H1905+000 in quiescence. Furthermore, we discuss our findings of the analysis of optical photometric observations which we obtained using the Magellan telescope and photometric and spectroscopic observations which we obtained using the Very Large Telescope at Paranal. The X-ray counterpart of 1H1905+000 was not detected in our Chandra data, with a 95 per cent confidence limit to the source count rate of 1.2x10^-4 counts s^-1. For different spectral models this yields an upper limit on the luminosity of 1.8x10^31 erg s^-1 (for an upper limit on the distance of 10 kpc.) This luminosity limit makes 1H1905+000 the faintest neutron star SXT in quiescence observed to date. The neutron star luminosity is so low that it is similar to the lowest luminosities derived for black hole SXTs in quiescence. This low luminosity for a neutron star SXT challanges the hypothesis presented in the literature that black hole SXTs in quiescence have lower luminosities than neutron star SXTs as a result of the presence of a black hole event horizon. Furthermore, the limit on the neutron star luminosity obtained less than 20 years after the outburst has ceased, constrains the thermal conductivity of the neutron star crust. Finally, the neutron star core must be so cold that unless the time averaged mass accretion rate is lower than 2x10^-12 M_sun yr^-1, core cooling has to proceed via enhanced neutrino emission processes. We derive a limit on the absolute I-band magnitude of the quiescent counterpart of M_I>7.8 assuming the source is at 10 kpc. This is in line with 1H1905+000 being an ultra-compact X-ray binary, as has been proposed based on the low outburst V-band absolute magnitude.

 

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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 2 Mar 06 01:00:08 GMT
0603001 -- 0603030 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603008 [abs, ps, pdf, other] :
Title: Evolution of the periodicities in 2S 0114+650
Authors: Ravi Sood, Sean Farrell, Paul O'Neill, Ravi Manchanda, N. M. Ashok
Comments: 4 pages, 3 figures. Presented at 2005 COSPAR Colloquium on Spectra and Timing of Compact X-ray Binaries in Mumbai, India. Accepted for publication by Advances in Space Research, 14th February 2006

We have analysed nine years of data from the All Sky Monitor on the Rossi X-ray Timing Explorer for 2S 0114+650 to study the evolution of its spin, binary and super-orbital periods. The spin history of the neutron star in this system exhibits torque reversals lasting ~1 yr. The newly discovered super-orbital period has remained stable over the 9-yr span, making 2S 0114+650 the fourth known system to exhibit stable super-orbital modulation. We compare its super-orbital period evolution with those of the other three such systems.

 
astro-ph/0603012 [abs, ps, pdf, other] :
Title: Why the braking indices of young pulsars are less than 3?
Authors: W. C. Chen, X. D. Li
Comments: 4 pages, 3 figures, accepted for publication in A&A Letters

In this letter we discuss two possible reasons which cause the observed braking indices n of young radio pulsars to be smaller than 3: (a) the evolving spin-down model of the magnetic field component $B_{\perp}$ increases with time; (b) the extrinsic braking torque model in which the tidal torques exerted on the pulsar by the fallback disk, and carries away the spin angular momentum from the pulsar. Based on some simple assumptions, we derive the expression of the braking indices, and calculate the spin-down evolutionary tracks of pulsars for different input parameters.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0506563 [abs, ps, pdf, other] :
Title: A Hydrogen Atmosphere Spectral Model Applied to the Neutron Star X7 in the Globular Cluster 47 Tucanae
Authors: Craig O. Heinke (Northwestern), George B. Rybicki (CfA), Ramesh Narayan (CfA), Jonathan E. Grindlay (CfA)
Comments: 14 pages, 6 figures, ApJ in press (replaced with accepted version)
Note: replaced with revised version Wed, 1 Mar 2006 20:28:47 GMT (113kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 3 Mar 06 01:00:10 GMT
0603031 -- 0603060 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603034 [abs, ps, pdf, other] :
Title: Protoneutron star dynamos: pulsars, magnetars, and radio-silent X-ray emitting neutron stars
Authors: A.Bonanno, V.Urpin, G.Belvedere
Comments: 4 pages, 2 figures, to appear on A&A

We discuss the mean-field dynamo action in protoneutron stars that are subject to instabilities during the early evolutionary phase. The mean field is generated in the neutron-finger unstable region where the Rossby number is $\sim 1$ and mean-field dynamo is efficient. Depending on the rotation rate, the mean-field dynamo can lead to the formation of three different types of pulsars. If the initial period of the protoneutron star is short, then the generated large-scale field is very strong ($> 3 \times 10^{13}$G) and exceeds the small-scale field at the neutron star surface. If rotation is moderate, then the pulsars are formed with more or less standard dipole fields ($< 3 \times 10^{13}$G) but with surface small-scale magnetic fields stronger than the dipole field. If rotation is very slow, then the mean-field dynamo does not operate, and the neutron star has no global field. Nevertheless, strong small-scale fields are generated in such pulsars, and they can manifest themselves as objects with very low spin-down rate but with a strong magnetic field inferred from the spectral features.

 
astro-ph/0603037 [abs, ps, pdf, other] :
Title: Profile morphology and polarization of young pulsars
Authors: Simon Johnston, Joel M. Weisberg
Comments: Accepted for publication in MNRAS. 16 pages

We present polarization profiles at 1.4 and 3.1 GHz for 14 young pulsars with characteristic ages less than 75 kyr. Careful calibration ensures that the absolute position angle of the linearly polarized radiation at the pulsar is obtained. In combination with previously published data we draw three main conclusions about the pulse profiles of young pulsars. (1) Pulse profiles are simple and consist of either one or two prominent components. (2) The linearly polarized fraction is nearly always in excess of 70 per cent. (3) In profiles with two components the trailing component nearly always dominates, only the trailing component shows circular polarization and the position angle swing is generally flat across the leading component and steep across the trailing component.
Based on these results we can make the following generalisations about the emission beams of young pulsars. (1) There is a single, relatively wide cone of emission from near the last open field lines. (2) Core emission is absent or rather weak. (3) The height of the emission is between 1 and 10 per cent of the light cylinder radius.

 
astro-ph/0603039 [abs, ps, pdf, other] :
Title: The origin of the lead-rich stars in Galactic halo: investigation of the model parameters for the s-process
Authors: Wenyuan Cui (1,2), Bo Zhang (1,2) ((1) NAOC, China; (2) Department of Physics, Hebei Normal University, China)
Comments: 5 pages, 7 EPS figures. Accepted for publication in MNRAS

Several stars at the low-metallicity extreme of the Galactic halo show large spreads of [Pb/hs]. Theoretically, a s-process pattern should be obtained from an AGB star with fixed metallicity and initial mass. For the third dredge-up and the s-process model, several important properties depend primarily on the core mass of AGB stars. Zijlstra (2004) reported that the initial-final-mass relation steepens at low metallicity, due to low mass-loss efficiency. This perhaps affects the model parameters of the AGB stars, e.g. the overlap factor and the neutron irradiation time, in particular at low metallicity. The calculated results show indeed that the overlap factor and the neutron irradiation time are significantly small at low metallicities, especially for 3.0Msun AGB stars. The scatter of [Pb/hs] found in low metallicities can therefore be explained naturally when varying the initial mass of the low-mass AGB stars.

 

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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 6 Mar 06 01:00:09 GMT
0603061 -- 0603099 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603080 [abs, ps, pdf, other] :
Title: Simulated synchrotron emission from Pulsar Wind Nebulae
Authors: Luca Del Zanna, Delia Volpi, Elena Amato, Niccolo' Bucciantini
Comments: 14 pages, submitted to A&A

A complete set of diagnostic tools aimed at producing synthetic synchrotron emissivity, polarization, and spectral index maps from relativistic MHD simulations is presented. As a first application we consider here the case of the emission from Pulsar Wind Nebulae (PWNe). The proposed method is based on the addition, on top of the basic set of MHD equations, of an extra equation describing the evolution of the maximum energy of the emitting particles. This equation takes into account adiabatic and synchrotron losses along streamlines for the distribution of emitting particles and its formulation is such that it is easily implemented in any numerical scheme for relativistic MHD. Application to the axisymmetric simulations of PWNe, analogous to those described by Del Zanna et al. (2004, A&A, 421, 1063), allows direct comparison between the numerical results and observations of the inner structure of the Crab Nebula, and similar objects, in the optical and X-ray bands. We are able to match most of the observed features typical of PWNe, like the equatorial torus and the polar jets, with velocities in the correct range, as well as finer emission details, like arcs, rings and the bright knot, that turn out to arise mainly from Doppler boosting effects. Spectral properties appear to be well reproduced too: detailed spectral index maps are produced for the first time and show softening towards the PWN outer borders, whereas spectral breaks appear in integrated spectra. The emission details are found to strongly depend on both the average wind magnetization (here approximately 2%), and on the magnetic field shape.

 
astro-ph/0603081 [abs, ps, pdf, other] :
Title: IGR J11215-5952: a hard X-ray transient displaying recurrent outbursts
Authors: L. Sidoli, A. Paizis, S. Mereghetti (INAF/IASF Milano, Italy)
Comments: 4 pages, 4 figures, accepted for publication in Astronomy and Astrophysics Letters

The hard X-ray source IGRJ11215-5952 has been discovered with INTEGRAL during a short outburst in 2005 and proposed as a new member of the class of supergiant fast X-ray transients. We analysed INTEGRAL public observations of the source field in order to search for previous outbursts from this transient, not reported in literature.Our results are based on a systematic re-analysis of INTEGRAL archival observations, using the latest analysis software and instrument calibrations. We report the discovery of two previously unnoticed outbursts, spaced by intervals of ~330 days, that occurred in July 2003 and May 2004. The 5-100keV spectrum is well described by a cut-off power law, with a photon index of 0.5, and a cut-off energy ~15-20keV, typical of High Mass X-ray Binaries hosting a neutron star. A 5-100keV luminosity of 3E36 erg/s has been derived (assuming 6.2kpc, the distance of the likely optical counterpart). The 5-100keV spectral properties, the recurrent nature of the outbursts,together with the reduced error region containing the blue supergiant star HD306414,support the hypothesis that IGRJ11215-5952 is a member of the class of the Supergiant Fast X-ray Transients.

 
astro-ph/0603089 [abs, ps, pdf, other] :
Title: Giant Pulses -- the Main Component of the Radio Emission of the Crab Pulsar
Authors: M.V. Popov (ASC Lpi), V.A. Soglasnov (ASC Lpi), V.I. Kondratiev (ASC Lpi), S.V. Kostyuk (ASC Lpi), Yu.P. Ilyasov (PRAO Asc Lpi), V.V. Oreshko (PRAO Asc Lpi)
Comments: 13 pages, 6 figures (originally published in Russian in Astronomicheskii Zhurnal, 2006, vol. 83, No. 1, pp. 62-69) translated by Denise Gabuzda
Journal-ref: Astronomy Reports, 2006, vol. 50, No. 1, pp. 55-61

The paper presents an analysis of dual-polarization observations of the Crab pulsar obtained on the 64-m Kalyazin radio telescope at 600 MHz with a time resolution of 250 ns. A lower limit for the intensities of giant pulses is estimated by assuming that the pulsar radio emission in the main pulse and interpulse consists entirely of giant radio pulses; this yields estimates of 100 Jy and 35 Jy for the peak flux densities of giant pulses arising in the main pulse and interpulse, respectively. This assumes that the normal radio emission of the pulse occurs in the precursor pulse. In this case, the longitudes of the giant radio pulses relative to the profile of the normal radio emission turn out to be the same for the Crab pulsar and the millisecond pulsar B1937+21, namely, the giant pulses arise at the trailing edge of the profile of the normal radio emission. Analysis of the distribution of the degree of circular polarization for the giant pulses suggests that they can consist of a random mixture of nanopulses with 100% circular polarization of either sign, with, on average, hundreds of such nanopulses within a single giant pulse.

 
astro-ph/0603098 [abs, ps, pdf, other] :
Title: New Gamma Cas-like objects: X-ray and optical observations of SAO49725 and HD161103
Authors: Raimundo Lopes de Oliveira, Christian Motch, Frank Haberl, Ignacio Negueruela, Eduardo Janot-Pacheco
Comments: 14 pages, 9 figs, accepted for publication in A&A

A growing number of early Be stars exhibit unusually hard X-ray spectra and luminosities intermediate between those typical of early type stars and those emitted by most Be/X-ray binaries in quiescence. We report on XMM-Newton and optical observations of two such Be stars, SAO 49725 and HD 161103. The nature of the hard-thermal X-ray emission is discussed in the light of the models proposed for Gamma Cas, magnetic disc-star interaction or accretion onto a compact companion object - neutron star or white dwarf. These two new objects added to similar cases discovered in XMM-Newton surveys point at the emergence of a new class of Gamma Cas analogs.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603012 [abs, ps, pdf, other] :
Title: Why the braking indices of young pulsars are less than 3?
Authors: W. C. Chen, X. D. Li
Comments: 4 pages, 3 figures, accepted for publication in A&A Letters
Note: replaced with revised version Fri, 3 Mar 2006 04:05:52 GMT (81kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 7 Mar 06 01:00:10 GMT
0603100 -- 0603143 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603102 [abs, ps, pdf, other] :
Title: The radio SNR G65.1+0.6 and its associated pulsar J1957+2831
Authors: W.W. Tian, D.A. Leahy
Comments: 11 pages, 4 pictures and tables, submitted to A&A

New images of the radio Supernova Remnant (SNR) G65.1+0.6 are presented, based on the 408 MHz and 1420 MHz continuum emission and the HI-line emission data of the Canadian Galactic Plane Survey (CGPS). HI observations show structures associated with the SNR G65.1+0.6 in the radial velocity range of -20 to -26 km/s and suggest a distance of 9.2 kpc for the SNR. The estimated Sedov age for G65.1+0.6 is 4 - 14$\times10^{4}$yr. The pulsar (PSR) J1957+2831 is associated with the SNR G65.1+0.6 due to their consistent distances and ages. The EGRET source 3EG J1958+2909 and $\gamma$-ray source 2CG 065+00 are also near the eastern edge of the SNR but do not agree in position with the pulsar and are likely not associated with the SNR. The SNR's flux densities at 408 MHz (8.6$\pm$0.8 Jy), 1420 MHz (4.9$\pm$0.5 Jy) and 2695 MHz (3.3$\pm$0.5 Jy) have been corrected for flux densities from compact sources within the SNR. The integrated flux density based spectral index (S$_{\nu}$$\propto$$\nu$$^{-\alpha}$) between 1420 MHz and 408 MHz is 0.45$\pm$0.11 and agrees with the T-T plot spectral index of 0.34 $\pm$0.20. The nearby SNR DA495 has a T-T plot spectral index of 0.50$\pm$0.01.

 
astro-ph/0603123 [abs, ps, pdf, other] :
Title: CHANDRA ACIS Spectroscopy of N157B -- A Young Composite Supernova Remnant in a Superbubble
Authors: Yang Chen (NJU), Q. Daniel Wang (UMass), Eric V. Gotthelf (Columbia), Bing Jiang (NJU), You-Hua Chu (UIUC), Robert Gruendl (UIUC)
Comments: 12 pages (emulateapj), submitted to ApJ, Fig.1 of high resolution available at this http URL

We present Chandra ACIS observations of N157B, a young supernova remnant located in the 30 Doradus star-formation region of the LMC. This remnant contains the most energetic pulsar known (PSR J0537-6910), which is surrounded by a bright nonthermal nebula that likely represents a toroidal pulsar wind terminal shock observed edge-on. We confirm the non-thermal nature of the comet-shaped X-ray emission feature and show that the spectral steepening of this feature away from the pulsar is quantitatively consistent with synchrotron cooling of shocked pulsar wind particles flowing downstream at a bulk velocity close to the speed of light. Around the cometary nebula we unambiguously detect a thermal component, which accounts for about 1/3 of the total 0.5 - 10 keV flux from the remnant. This thermal component is distributed among various clumps of metal-enriched plasma embedded in the low surface brightness X-ray-emitting diffuse gas. The relative metal enrichment pattern suggests that the mass of the supernova progenitor is >~ 20M_sun. A comparison of the X-ray data with HST optical images suggests that the explosion site is close to a dense cloud, against which a reflection shock is launched. The interaction between this reflection shock and the nebula has likely produced both its cometary shape and the surrounding thermal emission enhancement. SNR N157B is apparently expanding into the hot low-density interior of a nearby superbubble formed by the young OB association LH99, as revealed by Spitzer mid-infrared images. This scenario naturally explains the exceptionally large sizes of both the thermal and nonthermal components as well as the lack of an outer shell of the SNR. These results provide a rare glimpse into the SNR structure and evolution of a recent star-formation region.

 
astro-ph/0603126 [abs, ps, pdf, other] :
Title: Analysing the atolls: X-ray spectral transitions of accreting neutron stars
Authors: Jeanette Gladstone, Chris Done, Marek Gierlinski

We systematically analyse all the available X-ray spectra of disc accreting neutron stars (atolls and millisecond pulsars) from the RXTE database. We show that while these all show similar spectral evolution as a function of mass accretion rate, there are also subtle differences. There are two different types of hard/soft transition, those where the spectrum softens at all energies, leading to a diagonal track on a colour-colour diagram, and those where only the higher energy spectrum softens, giving a vertical track. The luminosity at which the transition occurs is correlated with this spectral behaviour, with the vertical transition at L/LEdd ~ 0.02 while the diagonal one is at ~ 0.1. Superimposed on this is the well known hysteresis effect, but we show that classic, large scale hysteresis occurs only in the outbursting sources, indicating that its origin is in the dramatic rate of change of mass accretion rate during the disc instability. We show that the long term mass accretion rate correlates with the transition behaviour, and speculate that this is due to the magnetic field being able to emerge from the neutron star surface for low average mass accretion rates. While this is not strong enough to collimate the flow except in the millisecond pulsars, its presence may affect the inner accretion flow through changing the jet properties.

 
astro-ph/0603130 [abs, ps, pdf, other] :
Title: The INTEGRAL Galactic Bulge monitoring program
Authors: E. Kuulkers (ESA/ESAC, Spain), S. Shaw (Univ. of Southampton, UK/ ISDC, Switzerland), S. Brandt, J. Chenevez (DNSC, Denmark), T.J.-L. Courvoisier (ISDC, Switzerland), K. Ebisawa (ISAS, Japan), P. Kretschmar (ESA/ESAC, Spain), C. Markwardt (Univ.of Maryland, USA/ NASA/GSFC, USA), N. Mowlavi (ISDC, Switzerland), T. Oosterbroek, A. Orr (ESA/ESTEC, Netherlands), A. Paizis (INAF-IASF, Italy), C. Sanchez-Fernandez (ESA/ESAC, Spain), R. Wijnands (Univ. of Amsterdam, The Netherlands)
Comments: 5 pages, 2 figures, to be published in: "The Transient Milky Way: a perspective for MIRAX", eds. F. D'Amico, J. Braga & R. Rothschild, AIP Conf. Proc

The Galactic Bulge region is a rich host of variable high-energy point sources. These sources include bright and relatively faint X-ray transients, X-ray bursters, persistent neutron star and black-hole candidate binaries, X-ray pulsars, etc.. We have a program to monitor the Galactic Bulge region regularly and frequently with the gamma-ray observatory INTEGRAL. As a service to the scientific community the high-energy light curves of all the active sources as well as images of the region are made available through the WWW. We show the first results of this exciting new program.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0602028 [abs, ps, pdf, other] :
Title: Quantum calculation of vortices in the inner crust of neutron stars
Authors: P. Avogadro, F. Barranco, R.A. Broglia, E. Vigezzi

We study, within a quantum mechanical framework based on self-consistent mean field theory, the interaction between a vortex and a nucleus immersed in a sea of free neutrons, a scenario representative of the inner crust of neutron stars. Quantal finite size effects force the vortex core outside the nucleus, influencing vortex pinning in an important way.

 

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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 8 Mar 06 01:00:12 GMT
0603144 -- 0603175 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603145 [abs, ps, pdf, other] :
Title: Merger of binary neutron stars to a black hole: Disk mass, short gamma-ray bursts, and quasinormal mode ringing
Authors: Masaru Shibata, Keisuke Taniguchi
Comments: 28 pages, 21 figures, accepted for publication in Phys.Rev.D

Three-dimensional simulations for the merger of binary neutron stars (BNSs) are performed in the framework of full general relativity. We pay particular attention to the black hole (BH) formation case and to the resulting mass of the surrounding disk for exploring possibility for formation of the central engine of short-duration gamma-ray bursts. Hybrid equations of state (EOSs) are adopted mimicking realistic, stiff nuclear EOSs, for which the maximum allowed gravitational mass of cold and spherical neutron stars (NSs), M_sph, is larger than 2M_sun. For the simulations, we focus on BNSs of the ADM mass M>2.6M_sun. For M>M_thr, the merger results in prompt formation of a BH irrespective of the mass ratio Q_M with 0.65<Q_M<1. The value of M_thr is approximately written as 1.3-1.35M_sph for the chosen EOSs. For the BH formation case, we evolve the spacetime using a BH excision technique and determine the mass of a quasistationary disk surrounding the BH. The disk mass steeply increases with decreasing the value of Q_M for given ADM mass and EOS. For M<M_thr, the outcome is a hypermassive neutron star (HMNS) of a large ellipticity. If the HMNS collapses to a BH after the longterm angular momentum transport, the disk mass may be >0.01M_sun. Gravitational waves (GWs) are computed in terms of a gauge-invariant wave extraction technique. In the formation of the HMNS, quasiperiodic GWs of frequency (3-3.5kHz) are emitted. The effective amplitude of GWs can be >5x10^{-21} at a distance of 50 Mpc. For the BH formation case, the BH excision technique enables a longterm computation and extraction of ring-down GWs associated with a BH quasinormal mode. It is found that the frequency and amplitude are 6.5-7kHz and 10^{-22} at a distance of 50Mpc for M=2.7-2.9M_sun.

 
astro-ph/0603147 [abs, ps, pdf, other] :
Title: Time-dependent force-free pulsar magnetospheres: axisymmetric and oblique rotators
Authors: Anatoly Spitkovsky (KIPAC, Stanford University)
Comments: Submitted to ApJ Letters; version with higher resolution figures available at this http URL (900kb)

Magnetospheres of many astrophysical objects can be accurately described by the low-inertia (or "force-free") limit of MHD. We present a new numerical method for solution of equations of force-free relativistic MHD based on the finite-difference time-domain (FDTD) approach with a prescription for handling spontaneous formation of current sheets. We use this method to study the time-dependent evolution of pulsar magnetospheres in both aligned and oblique magnetic geometries. For the aligned rotator we confirm the general properties of the time-independent solution of Contopoulos et al. (1999). For the oblique rotator we present the 3D structure of the magnetosphere and compute, for the first time, the spindown power of pulsars as a function of inclination of the magnetic axis. We find the pulsar spindown luminosity to be L = (mu^2 Omega^4/c^3) (1+ sin^2(alpha)) for a star with the dipole moment "mu", rotation frequency "Omega", and magnetic inclination angle "alpha". We also discuss the effects of current sheet resistivity and reconnection on the structure and evolution of the magnetosphere.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 9 Mar 06 01:00:08 GMT
0603176 -- 0603204 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603188 [abs, ps, pdf, other] :
Title: Implications of the metallicity dependence of Wolf-Rayet winds
Authors: John J. Eldridge, Jorick S. Vink
Comments: 8 pages, 9 figures, accepted by Astronomy & Astrophysics

Aims: Recent theoretical predictions for the winds of Wolf-Rayet stars indicate that their mass-loss rates scale with the initial stellar metallicity in the local Universe.We aim to investigate how this predicted dependence affects the models of Wolf-Rayet stars and their progeny in different chemical environments. Methods: We compute models of stellar structure and evolution for Wolf-Rayet stars for different initial metallicities, and investigate how the scaling of the Wolf-Rayet mass-loss rates affects the final masses, the lifetimes of the WN and WC subtypes, and how the ratio of the two populations vary with metallicity. Results: We find significant effects of metallicity dependent mass-loss rates for Wolf-Rayet stars. For models that include the scaling of the mass-loss rate with initial metallicity, all WR stars become neutron stars rather than black holes at twice the solar metallicity; at lower $Z$, black holes have larger masses. We also show that our models that include the mass-loss metallicity scaling closely reproduce the observed decrease of the relative population of WC over WN stars at low metallicities.

 
astro-ph/0603197 [abs, ps, pdf, other] :
Title: Radio Images of 3C 58: Expansion and Motion of its Wisp
Authors: M. F. Bietenholz
Comments: 12 pages; accepted for publication in the Astrophysical Journal

New 1.4 GHz VLA observations of the pulsar-powered supernova remnant 3C 58 have resulted in the highest-quality radio images of this object to date. The images show filamentary structure over the body of the nebula. The present observations were combined with earlier ones from 1984 and 1991 to investigate the variability of the radio emission on a variety of time-scales. No significant changes are seen over a 110 day interval. In particular, the upper limit on the apparent projected velocity of the wisp is 0.05c. The expansion rate of the radio nebula was determined between 1984 and 2004, and is 0.014+/-0.003%/year, corresponding to a velocity of 630+/-70 km/s along the major axis. If 3C 58 is the remnant of SN 1181, it must have been strongly decelerated, which is unlikely given the absence of emission from the supernova shell. Alternatively, the low expansion speed and a number of other arguments suggest that 3C 58 may be several thousand years old and not be the remnant of SN 1181.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0603018 [abs, ps, pdf, other] :
Title: Entrainment parameters in cold superfluid neutron star core
Authors: Nicolas Chamel, Pawel Haensel
Comments: 10 pages, 7 figures. Accepted for publication in Phys. Rev. C

Hydrodynamical simulations of neutron star cores, based on a two fluid description in terms of a neutron-proton superfluid mixture, require the knowledge of the Andreev-Bashkin entrainment matrix which relates the momentum of one constituent to the currents of both constituents. This matrix is derived for arbitrary nuclear asymmetry at zero temperature and in the limits of small relative currents in the framework of the energy density functional theory. The Skyrme energy density functional is considered as a particular case. General analytic formulae for the entrainment parameters and various corresponding effective masses are obtained. These formulae are applied to the liquid core of a neutron star, composed of an homogeneous plasma of nucleons, electrons and possibly muons in beta equilibrium.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 10 Mar 06 01:00:07 GMT
0603205 -- 0603250 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603211 [abs, ps, pdf, other] :
Title: Simulations of relativistic collisionless shocks: shock structure and particle acceleration
Authors: Anatoly Spitkovsky (KIPAC, Stanford University)
Comments: 6 pages, invited talk at "Astrophysical Sources of High Energy Particles and Radiation," Torun, June 20 - 24, 2005
Journal-ref: AIP Conf. Proc. 801 (2005), 345-350

We discuss 3D simulations of relativistic collisionless shocks in electron-positron pair plasmas using the particle-in-cell (PIC) method. The shock structure is mainly controlled by the shock's magnetization ("sigma" parameter). We demonstrate how the structure of the shock varies as a function of sigma for perpendicular shocks. At low magnetizations the shock is mediated mainly by the Weibel instability which generates transient magnetic fields that can exceed the initial field. At larger magnetizations the shock is dominated by magnetic reflections. We demonstrate where the transition occurs and argue that it is impossible to have very low magnetization collisionless shocks in nature (in more than one spatial dimension). We further discuss the acceleration properties of these shocks, and show that higher magnetization perpendicular shocks do not efficiently accelerate nonthermal particles in 3D. Among other astrophysical applications, this may pose a restriction on the structure and composition of gamma-ray bursts and pulsar wind outflows.

 
astro-ph/0603212 [abs, ps, pdf, other] :
Title: Pulsar electrodynamics: a time-dependent view
Authors: Anatoly Spitkovsky (KIPAC, Stanford University)
Comments: 6 pages, invited talk at "Astrophysical Sources of High Energy Particles and Radiation," Torun, June 20 - 24, 2005
Journal-ref: AIP Conf. Proc. 801 (2005), 253-258

Pulsar spindown forms a reliable yet enigmatic prototype for the energy loss processes in many astrophysical objects including accretion disks and back holes. In this paper we review the physics of pulsar magnetospheres, concentrating on recent developments in force-free modeling of the magnetospheric structure. In particular, we discuss a new method for solving the equations of time-dependent force-free relativistic MHD in application to pulsars. This method allows to dynamically study the formation of the magnetosphere and its response to perturbations, opening a qualitatively new window on pulsar phenomena. Applications of the method to other magnetized rotators, such as magnetars and accretion disks, are also discussed.

 
astro-ph/0603227 [abs, ps, pdf, other] :
Title: M-type giants as optical counterparts of X-ray sources 4U 1700+24 and 4U 1954+319
Authors: N. Masetti, M. Orlandini, E. Palazzi, L. Amati, F. Frontera
Comments: 6 pages, 3 figures, 2 tables, accepted for publication on A&A, main journal

We observed with Chandra two peculiar galactic X-ray sources, 4U 1700+24 and 4U 1954+319, which are suspected to have a M-type giant star as optical counterpart, in order to get an high-precision astrometric position for both of them. The peculiarity of these sources lies in the fact that these are the only two cases among low-mass X-ray binaries (LMXBs), besides the confirmed case of GX 1+4, for which the companion can possibly be a M-type giant. We found that in both cases the field M-type giant star is indeed the counterpart of these X-ray sources. We also determined the distance to 4U 1954+319 to be about 1.7 kpc. This result suggests that a number of faint (L_X around 10^32-10^34 erg s-1) Galactic X-ray sources are `symbiotic X-ray binaries', that is, wide-orbit LMXBs composed of a compact object, most likely a neutron star, accreting from the wind of a M-type giant.

 
astro-ph/0603249 [abs, ps, pdf, other] :
Title: "Propeller" Regime of Disk Accretion to Rapidly Rotating Stars
Authors: G.V. Ustyugova, A.V. Koldoba, M.M. Romanova, R.V.E. Lovelace
Comments: 19 pages, 16 figures, ApJ (accepted), see animation at this http URL

We present results of axisymmetic magnetohydrodynamic simulations of the interaction of a rapidly-rotating, magnetized star with an accretion disk. The disk is considered to have a finite viscosity and magnetic diffusivity. The main parameters of the system are the star's angular velocity and magnetic moment, and the disk's viscosity, diffusivity. We focus on the "propeller" regime where the inner radius of the disk is larger than the corotation radius. Two types of magnetohydrodynamic flows have been found as a result of simulations: "weak" and "strong" propellers. The strong propeller is characterized by a powerful disk wind and a collimated magnetically dominated outflow or jet from the star. The weak propeller have only weak outflows. We investigated the time-averaged characteristics of the interaction between the main elements of the system, the star, the disk, the wind from the disk, and the jet. Rates of exchange of mass and angular momentum between the elements of the system are derived as a function of the main parameters. The propeller mechanism may be responsible for the fast spinning-down of the classical T Tauri stars in the initial stages of their evolution, and for the spinning-down of accreting millisecond pulsars.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 13 Mar 06 01:00:09 GMT
0603251 -- 0603275 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603251 [abs, ps, pdf, other] :
Title: Solving the Transfer Equation for Arbitrary Flows in Stationary Spacetimes
Authors: B. Chen, R. Kantowski, E. Baron, S. Knop, P. H. Hauschildt
Comments: 22 pages, 2 figures, submitted to PRD15

We derive the radiative transfer equation for arbitrary stationary relativistic flows in stationary spacetimes, i.e. for steady-state transfer problems. We show that the standard characteristics method of solution developed by Mihalas and used throughout the radiative transfer community can be significantly simplified in multi-dimensional applications because the characteristics always coincide with geodesics and can always be specified by constants. Thus, direct integration of the characteristics as commonly done in 1-D applications is not required, they are (in principle) known for a specified metric. We give details for both flat and static spherically symmetric spacetimes. This work has direct application in 3-dimensional simulations of supernovae, gamma-ray bursts, and active galactic nuclei, as well as in modeling neutron star atmospheres.

 
astro-ph/0603258 [abs, ps, pdf, other] :
Title: A tale of two populations: Rotating Radio Transients and X-ray Dim Isolated Neutron Stars
Authors: S.B. Popov (1), R. Turolla (2), A. Possenti (3) (1-Sternberg Astronomical Institute; 2- University of Padova; 3- Osservatorio di Cagliari)
Comments: 5 pages, accepted to MNRAS Letters

We highlight similarities between recently discovered Rotating Radio Transients and X-ray Dim Isolated Neutron Stars. In particular, it is shown that X-ray Dim Isolated Neutron Stars have a birthrate comparable to that of Rotating Radio Transients. On the contrary, magnetars have too low a formation rate to account for the bulk of the radio transient population. The consequences of the recent detection of a thermal X-ray source associated with one of the Rotating Radio Transients on the proposed scenarios for these sources are also discussed.

 
astro-ph/0603267 [abs, ps, pdf, other] :
Title: The masses of PSR J1911-5958A and its white dwarf companion
Authors: C.G. Bassa (Utrecht), M.H. van Kerkwijk (Toronto), D. Koester (Kiel), F. Verbunt (Utrecht)
Comments: 15 pages, 7 figures, submitted to A&A

We present spectroscopic and photometric observations of the optical counterpart to PSR J1911-5958A, a millisecond pulsar located towards the globular cluster NGC 6752. We measure radial velocities from the spectra and determine the systemic radial velocity of the binary and the radial-velocity amplitude of the white-dwarf orbit. Combined with the pulsar orbit obtained from radio timing, we infer a mass ratio of Mpsr/Mwd=7.36+-0.25. The spectrum of the counterpart is that of a hydrogen atmosphere, showing Balmer absorption lines upto H12, and we identify the counterpart as a helium-core white dwarf of spectral type DA5. Comparison of the spectra with hydrogen atmosphere models yield a temperature Teff=10090+-150 K and a surface gravity log g=6.44+-0.20 cm s^-2. Using mass-radius relations appropriate for low-mass helium-core white dwarfs, we infer the white-dwarf mass Mwd=0.18+-0.02 Msun and radius Rwd=0.043+-0.009 Rsun. Combined with the mass ratio, this constrains the pulsar mass to Mpsr=1.40^+0.16_-0.10 Msun. If we instead use the white-dwarf spectrum and the distance of NGC 6752 to determine the white-dwarf radius, we find Rwd=0.058+-0.004 Rsun. For the observed temperature, the mass-radius relations predict a white-dwarf mass of Mwd=0.175+-0.010 Msun, constraining the pulsar mass to Mpsr=1.34+-0.08 Msun. We find that the white-dwarf radius determined from the spectrum and the systemic radial velocity of the binary are inconsistent at the 1 sigma and 2 sigma level with the values that are expected if PSR J1911-5958A is associated with NGC 6752. We discuss possible causes to explain this inconsistency, but conclude that our observations do not conclusively confirm nor disprove the assocation of the pulsar binary with the globular cluster.

 
astro-ph/0603269 [abs, ps, pdf, other] :
Title: The puzzling properties of the Helium White Dwarf orbiting the millisecond pulsar PSR J1911-5958A in NGC 6752
Authors: G. Cocozza (1,2), F. R. Ferraro (1), A. Possenti (3), N. D'Amico (4), ((1) Dipartimento di Astronomia Universita' di Bologna, (2) INAF-Osservatorio Astronomico di Bologna,(3) INAF-Osservatorio Astronomico di Cagliari,(4) Dipartimento di Fisica Universita' di Cagliari)
Comments: 12 pages, 3 figures, accepted for publication in APJletters

We have used phase-resolved high-resolution images and low resolution spectra taken at the ESO Very Large Telescope, to study the properties of the low-mass Helium White Dwarf companion to the millisecond pulsar \psr (hereafter COM J1911$-$5958A), in the halo of the Galactic Globular Cluster NGC 6752. The radial velocity curve confirms that \com is orbiting the pulsar and allows to derive a systemic velocity of the binary system nicely in agreement with that of NGC 6752. This strongly indicates that the system is a member of the cluster, despite its very offset position ($\sim 74$ core radii) with respect to the core. Constraints on the orbital inclination ($\gapp 70^\circ$) and pulsar mass ($1.2-1.5 {\rm M_\odot}$) are derived from the mass ratio $M_{PSR}/M_{COM}= 7.49\pm0.64$ and photometric properties of COM J1911$-$5958A. The light curve in B-band shows two phases of unequal brightening ($\Delta$mag$\sim 0.3$ and 0.2, respectively) located close to quadratures and superimposed on an almost steady baseline emission: this feature is quite surprising and needs to be further investigated.

 

Cross-listings


2 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0603030 [abs, ps, pdf, other] :
Title: Signals for Lorentz Violation in Post-Newtonian Gravity
Authors: Quentin G. Bailey, Alan Kostelecky
Comments: 112 pages

The pure-gravity sector of the minimal Standard-Model Extension is studied in the limit of Riemann spacetime. A method is developed to extract the modified Einstein field equations in the limit of small metric fluctuations about the Minkowski vacuum, while allowing for the dynamics of the coefficients for Lorentz violation. The linearized effective equations depend on 20 independent coefficients, and they are solved to obtain the post-newtonian metric. The corresponding post-newtonian behavior of a perfect fluid is studied and applied to the gravitating many-body system. Illustrative examples of the methodology are provided using bumblebee models. The implications of the general theoretical results are studied for a variety of existing and proposed gravitational experiments, including lunar and satellite laser ranging, laboratory experiments with gravimeters and torsion pendula, measurements of the spin precession of orbiting gyroscopes, timing studies of signals from binary pulsars, and the classic tests involving the perihelion precession and the time delay of light. Previously unexplored possibilities include certain high-sensitivity measurements based on the local anisotropy of gravity and observations of effects determined by coefficients coupling to the Weyl tensor. For each type of experiment considered, estimates of the attainable sensitivities are provided. Numerous effects of local Lorentz violation can be studied in existing or near-future experiments at sensitivities ranging from parts in 10^4 down to parts in 10^{15}.

 
nucl-th/0602052 [abs, ps, pdf, other] :
Title: Testing Deconfinement at High Isospin Density
Authors: M. Di Toro, A.Drago, T.Gaitanos, V.Greco, A.Lavagno
Comments: 32 pages, 14 figures, elsart latex

We study the transition from hadronic matter to a mixed phase of quarks and hadrons at high baryon and isospin densities reached in heavy ion collisions. We focus our attention on the role played by the nucleon symmetry energy at high density.In this respect the inclusion of a scalar isovector meson, the \delta-coupling, in the Hadron Lagrangian appears rather important. We study in detail the formation of a drop of quark matter in the mixed phase, and we discuss the effects on the quark drop nucleation probability of the finite size and finite time duration of the high density region. We find that, if the parameters of quark models are fixed so that the existence of quark stars is allowed, then the density at which a mixed phase starts forming drops dramatically in the range Z/A \sim 0.3--0.4. This opens the possibility to verify the Witten-Bodmer hypothesis on absolute stability of quark matter using ground-based experiments in which neutron-rich nuclei are employed. These experiments can also provide rather stringent constraints on the Equation of State (EoS) to be used for describing the pre-Supernova gravitational collapse. Consistent simulations of neutron rich heavy ion collisions are performed in order to show that even at relatively low energies, in the few AGeV range, the system can enter such unstable mixed phase. Some precursor observables are suggested, in particular a ``neutron trapping'' effect.

 

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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 14 Mar 06 01:00:09 GMT
0603276 -- 0603322 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603277 [abs, ps, pdf, other] :
Title: General Relativistic Binary Merger Simulations and Short Gamma Ray Bursts
Authors: Joshua A. Faber, Thomas W. Baumgarte, Stuart L. Shapiro, Keisuke Taniguchi
Comments: 5 Pages, 3 figures, accepted by ApJ Lett

The recent localization of some short-hard gamma ray bursts (GRBs) in galaxies with low star formation rates has lent support to the suggestion that these events result from compact object binary mergers. We discuss how new simulations in general relativity are helping to identify the central engine of short-hard GRBs. Motivated by our latest relativistic black hole-neutron star merger calculations, we discuss a scenario in which these events may trigger short-hard GRBs, and compare this model to competing relativistic models involving binary neutron star mergers and the delayed collapse of hypermassive neutron stars. Distinguishing features of these models may help guide future GRB and gravitational wave observations to identify the nature of the sources.

 
astro-ph/0603297 [abs, pdf] :
Title: A non-spherical core in the explosion of supernova SN 2004dj
Authors: Douglas C. Leonard, Alexei V. Filippenko, Mohan Ganeshalingam, Franklin J. D. Serduke, Weidong Li, Brandon J. Swift, Avishay Gal-Yam, Ryan J. Foley, Derek B. Fox, Sung Park, Jennifer L. Hoffman, Diane S. Wong
Comments: Accepted for publication by Nature (results embargoed until 23 March 2006); 14 pages, 2 figures

An important and perhaps critical clue to the mechanism driving the explosion of massive stars as supernovae is provided by the accumulating evidence for asymmetry in the explosion. Indirect evidence comes from high pulsar velocities, associations of supernovae with long-soft gamma-ray bursts, and asymmetries in late-time emission-line profiles. Spectropolarimetry provides a direct probe of young supernova geometry, with higher polarization generally indicating a greater departure from spherical symmetry. Large polarizations have been measured for 'stripped-envelope' (that is, type Ic) supernovae, which confirms their non-spherical morphology; but the explosions of massive stars with intact hydrogen envelopes (type II-P supernovae) have shown only weak polarizations at the early times observed. Here we report multi-epoch spectropolarimetry of a classic type II-P supernova that reveals the abrupt appearance of significant polarization when the inner core is first exposed in the thinning ejecta (~90 days after explosion). We infer a departure from spherical symmetry of at least 30 per cent for the inner ejecta. Combined with earlier results, this suggests that a strongly non-spherical explosion may be a generic feature of core-collapse supernovae of all types, where the asphericity in type II-P supernovae is cloaked at early times by the massive, opaque, hydrogen envelope.

 
astro-ph/0603301 [abs, ps, pdf, other] :
Title: Statistics of the individual-pulse polarization based on propagation effects in pulsar magnetosphere
Authors: S. A. Petrova
Comments: 15 pages, 6 figures. Accepted for publication in MNRAS

Pulsar radio emission is modelled as a sum of two completely polarized non-orthogonal modes with the randomly varying Stokes parameters and intensity ratio. The modes are the result of polarization evolution of the original natural waves in the hot magnetized weakly inhomogeneous plasma of pulsar magnetosphere. In the course of wave mode coupling, the linearly polarized natural waves acquire purely orthogonal elliptical polarizations. Further on, as the waves pass through the cyclotron resonance, they become non-orthogonal. The pulse-to-pulse fluctuations of the final polarization characteristics and the intensity ratio of the modes are attributed to the temporal fluctuations in the plasma flow.
The model suggested allows to reproduce the basic features of the one-dimensional distributions of the individual-pulse polarization characteristics. Besides that, propagation origin of pulsar polarization implies a certain correlation between the mode ellipticity and position angle. On a qualitative level, for different sets of parameters, the expected correlations appear compatible with the observed ones. Further theoretical studies are necessary to establish the quantitative correspondence of the model to the observational results and to develop a technique of diagnostics of pulsar plasma on this basis.

 
astro-ph/0603322 [abs, ps, pdf, other] :
Title: Beta decay radiation signature from neutron-rich gamma-ray bursts?
Authors: Soebur Razzaque, Peter Meszaros
Comments: 11 pages, 2 figures

Core collapse of massive stars and binary neutron stars or black hole-neutron star binary mergers are likely progenitors of long and short duration gamma-ray bursts respectively. Neutronized material in the former and neutron star material in the latter are ejected by the central engine implying a neutron-rich jet outflow. A free neutron, however, beta decays to a proton, an electron (beta) and an anti-neutrino in about fifteen minutes in its rest frame. Sudden creation of a relativistic electron is accompanied by radiation with unique temporal and spectral signature. We calculate here this radiation signature collectively emitted by all beta decay electrons from neutron-rich outflow. Detection of this signature may thus provide strong evidence for not only neutron but also for proton content in the relativistic gamma-ray burst jets.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0509447 [abs, ps, pdf, other] :
Title: Gravitational Waves from Phase-Transition Induced Collapse of Neutron Stars
Authors: L.-M. Lin, K. S. Cheng, M.-C. Chu, W.-M. Suen
Comments: Minor changes to match the published version in ApJ
Journal-ref: Astrophys.J. 639 (2006) 382
Note: replaced with revised version Mon, 13 Mar 2006 10:47:42 GMT (167kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 15 Mar 06 01:00:11 GMT
0603323 -- 0603371 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603324 [abs, ps, pdf, other] :
Title: The effect of mass-segregation on gravitational wave sources near massive black holes
Authors: Clovis Hopman, Tal Alexander (Weizmann)
Comments: Submitted to ApJL

Gravitational waves (GWs) from the inspiral of compact remnants (CRs) into massive black holes (MBHs) will be observable to cosmological distances. While a CR spirals in, 2-body scattering by field stars may cause it to fall into the MBH before reaching a short period orbit that would give an observable signal. As a result, only CRs very near (~0.01 pc) the MBH can spiral in successfully. In a multi-mass stellar population, the heaviest objects sink to the center, where they are more likely to slowly spiral into the MBH without being swallowed prematurely. We study how mass-segregation modifies the stellar distribution and the rate of GW events. We find that the inspiral rate per galaxy for white dwarfs is 30 per Gyr, for neutron stars 6 per Gyr, and for stellar black holes (SBHs) 250 per Gyr. The high rate for SBHs is due to their extremely steep density profile, n_{BH}(r)\propto r^{-2}. The GW detection rate will be dominated by SBHs.

 
astro-ph/0603328 [abs, ps, pdf, other] :
Title: Neutron-capture elements in the metal-poor globular cluster M15
Authors: Kaori Otsuki, Satoshi Honda, Wako Aoki, Toshitaka Kajino, Grant J. Mathews
Comments: Accepted to ApJL

We report on observations of six giants in the globular cluster M15 (NGC 7078) using the Subaru Telescope to measure neutron-capture elemental abundances. Our abundance analyses based on high-quality blue spectra confirm the star-to-star scatter in the abundances of heavy neutron-capture elements (e.g., Eu), and no significant s-process contribution to them, as was found in previous studies. We have found, for the first time, that there are anti-correlations between the abundance ratios of light to heavy neutron-capture elements ([Y/Eu] and [Zr/Eu]) and heavy ones (e.g., Eu). This indicates that light neutron-capture elements in these stars cannot be explained by only a single r-process. Another process that has significantly contributed to the light neutron-capture elements is required to have occurred in M15. Our results suggest a complicated enrichment history for M15 and its progenitor.

 
astro-ph/0603352 [abs, ps, pdf, other] :
Title: What can we learn from long term monitoring of X-ray bursters?
Authors: Andrew Cumming (McGill University)
Comments: 5 pages, 2 figures, to be published in: "The Transient Milky Way: a perspective for MIRAX", eds. F. D'Amico, J. Braga & R. Rothschild, AIP Conf. Proc

The last few years have seen the discovery of a number of new aspects of Type I X-ray bursts: the extremely energetic and long duration superbursts, intermediate duration bursts at low luminosities, mHz QPOs, and burst oscillations. These discoveries promise a new understanding of nuclear burning on accreting neutron stars, and offer a chance to use observations to probe neutron star properties. I discuss what we can learn from future long term monitoring with MIRAX.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 16 Mar 06 01:00:09 GMT
0603372 -- 0603405 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603375 [abs, ps, pdf, other] :
Title: Cyclic evolution of radio pulsars on the time scale of hundreds of years
Authors: G.Beskin, A.Biryukov, S.Karpov
Comments: 14 pages, 6 figures, submitted to ApJL

The recent massive measurements of pulsar frequency second derivatives have shown that they are 100-1000 times larger than expected for standard pulsar slowdown low. Moreover, the second derivatives as well as braking indices are even negative for about half of pulsars. We explain these paradoxical results on the basis of the statistical analysis of the rotational parameters $\nu$, $\dot \nu$ and $\ddot \nu$ of the subset of 295 pulsars taken mostly from the ATNF database. We have found strong correlation of $\ddot \nu$ and $\dot \nu$ either for $\ddot\nu > 0$ (correlation coefficient $r\approx0.9$) and $\ddot\nu < 0$ ($r\approx0.85$), and of $\nu$ and $\dot\nu$ ($r\approx0.7$). We interpret these dependencies as evolutionary ones due to $\dot\nu$ being nearly proportional to characteristic age $\tau_{ch}$. The derived statistical relations as well as "anomalous" values of $\ddot\nu$ are well explained in the framework of the simple model of cyclic evolution of the rotational frequency of the pulsars. It combines the secular change of $\nu_{tr}(t)$, $\dot\nu_{tr}(t)$ and $\ddot\nu_{tr}(t)$ according to the power law with $n\approx5$ and harmonic oscillations of 100--1000 years period with an amplitude from $10^{-3}$ Hz for young pulsars to $10^{-10}$ Hz for elder ones. The physical nature of these cyclic variations of the rotational frequency may be similar to the well-known red timing noise, however, with much larger characteristic time scale.

 
astro-ph/0603381 [abs, ps, pdf, other] :
Title: TEMPO2, a new pulsar timing package. I: Overview
Authors: G. Hobbs, R. Edwards, R. Manchester
Comments: Accepted by MNRAS

Contemporary pulsar timing experiments have reached a sensitivity level where systematic errors introduced by existing analysis procedures are limiting the achievable science. We have developed tempo2, a new pulsar timing package that contains propagation and other relevant effects implemented at the 1ns level of precision (a factor of ~100 more precise than previously obtainable). In contrast with earlier timing packages, tempo2 is compliant with the general relativistic framework of the IAU 1991 and 2000 resolutions and hence uses the International Celestial Reference System, Barycentric Coordinate Time and up-to-date precession, nutation and polar motion models. Tempo2 provides a generic and extensible set of tools to aid in the analysis and visualisation of pulsar timing data. We provide an overview of the timing model, its accuracy and differences relative to earlier work. We also present a new scheme for predictive use of the timing model that removes existing processing artifacts by properly modelling the frequency dependence of pulse phase.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0603048 [abs, ps, pdf, other] :
Title: Rotating star initial data for a constrained scheme in numerical relativity
Authors: Lap-Ming Lin, Jerome Novak
Comments: 17 pages, 7 figures

A new numerical code for computing stationary axisymmetric rapidly rotating stars in general relativity is presented. The formulation is based on a fully constrained-evolution scheme for 3+1 numerical relativity using the Dirac gauge and maximal slicing. We use both the polytropic and MIT bag model equations of state to demonstrate that the code can construct rapidly rotating neutron star and strange star models. We compare numerical models obtained by our code and a well-established code, which uses a different gauge condition, and show that the two codes agree to high accuracy.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0509915 [abs, ps, pdf, other] :
Title: Accretion of helium and metal-rich gas onto neutron stars and black holes at high luminosities
Authors: J. Dunkel, J. Chluba, R. A. Sunyaev
Comments: 10 pages
Journal-ref: Astron. Lett., 32(4), pp. 288-294 (2006)
Note: replaced with revised version Wed, 15 Mar 2006 14:20:48 GMT (12kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 17 Mar 06 01:00:11 GMT
0603406 -- 0603438 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603411 [abs, ps, pdf, other] :
Title: Relativistic Electrodynamics of Spinning Compact Objects
Authors: Hongsu Kim, Hyung Mok Lee, Chul H. Lee, Hyun Kyu Lee
Comments: 23 pages, Revtex4
Journal-ref: J. Korean Phys. Soc. 48, 352 (2006)

A theoretical study of some electrodynamic features of a region close to a {\it slowly-rotating} magnetized relativistic star is performed. To be a little more specific, based on the solution-generating method given by Wald, the magnetic fields around both uncharged and (slightly) charged relativistic stars have been obtained. Particularly for a charged relativistic star, again following the argument by Wald, the star was shown to gradually accrete charge until it reached an equilibrium value $\tilde{Q}=2B_{0}J$. This value of the equilibrium charge seems to be generic as a rotating black hole is known to accrete exactly the same amount. Although these results are equally relevant to all species of slowly-rotating relativistic stars, we particularly have the rotating neutron star in mind. As such, it would be of some interest to attempt to make contact with a real pulsar case. Thus, we discuss how many of the theoretical results obtained in the present work can be carried over to a realistic, general relativistic description of a pulsar's magnetosphere.

 
astro-ph/0603436 [abs, ps, pdf, other] :
Title: Signature of Temporary Burning Front Stalling from a Non-Photospheric Radius Expansion Double-peaked Burst
Authors: Sudip Bhattacharyya, Tod E. Strohmayer
Comments: 11 pages, 3 figures, accepted for publication in ApJ Letters

Non-photospheric-radius-expansion (non-PRE) double-peaked bursts may be explained in terms of spreading (and temporary stalling) of thermonuclear flames on the neutron star surface, as we argued in a previous study of a burst assuming polar ignition. Here we analyze Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data of such a burst (but with a considerably different intensity profile from the previous one) from the low mass X-ray binary (LMXB) system 4U 1636-536, and show that this model can qualitatively explain the observed burst profile and spectral evolution, if we assume an off-polar, but high-latitude ignition, and burning front stalling at a higher latitude compared to that for the previous burst. The off-polar ignition can account for the millisecond period brightness oscillations detected from this burst. This is the first time oscillations have been seen from such a burst. Our model can qualitatively explain the oscillation amplitude measured during the first (weaker) peak, and the absence of oscillations during the second peak. The higher latitude front stalling facilitates the first clear detection of a signature of this stalling, which is the primary result of this work, and may be useful for understanding thermonuclear flame spreading on neutron stars.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0506545 [abs, ps, pdf, other] :
Title: A Multi-wavelength study of the Pulsar PSR B1929+10 and its X-ray trail
Authors: Werner Becker, Michael Kramer, Axel Jessner, Ronald E. Taam, Jian J. Jia, Kwong S. Cheng, Roberto Mignani, Alberto Pellizzoni, Andrea de Luca, Agnieszka Slowikowska, Patrizia Caraveo
Comments: Accepted for publication in ApJ. A draft with higher resolution images can be found at this ftp URL
Note: replaced with revised version Thu, 16 Mar 2006 11:36:27 GMT (546kb)
 
astro-ph/0603145 [abs, ps, pdf, other] :
Title: Merger of binary neutron stars to a black hole: Disk mass, short gamma-ray bursts, and quasinormal mode ringing
Authors: Masaru Shibata, Keisuke Taniguchi
Comments: 29 pages, 21 figures, references added, typos corrected, Phys.Rev.D in press
Note: replaced with revised version Wed, 15 Mar 2006 23:12:01 GMT (587kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 20 Mar 06 01:00:10 GMT
0603439 -- 0603482 received


6 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603440 [abs, ps, pdf, other] :
Title: The redshift distribution of short gamma-ray bursts from dynamically formed neutron star binaries
Authors: Clovis Hopman, Dafne Guetta, Eli Waxman, Simon Portegies Zwart
Comments: Submitted to ApJL

Short-hard gamma-ray bursts (SHBs) may arise from gravitational wave (GW) driven mergers of double neutron star (DNS) systems. DNSs may be "primordial" or can form dynamically by binary exchange interactions in globular clusters during core-collapse. For primordial binaries, the time delay between formation and merger is expected to be short, tau~0.1 Gyr, implying that the redshift distribution of merger events should follow that of star-formation. We point out here that for dynamically formed DNSs, the time delay between star-formation and merger is dominated by the cluster core-collapse time, rather than by the GW inspiral time, yielding delays comparable to the Hubble time. We derive the redshift distribution of merger events of dynamically formed DNSs, and find it to differ significantly from that typically expected for primordial binaries. The observed redshift distribution of SHBs favors dynamical formation, although a primordial origin cannot be ruled out due to possible detection biases. Future red-shift observations of SHBs may allow to determine whether they are dominated by primordial or dynamically formed DNSs.

 
astro-ph/0603446 [abs, ps, pdf, other] :
Title: Orientation Angles of a Pulsar's Polarization Vector
Authors: Mark M. McKinnon
Comments: 14 pages, 4 figures, accepted for publication in ApJ

A statistical model of the polarization of pulsar radio emission is used to derive the general statistics of a polarization vector's orientation angles. The theoretical distributions are compared with orientation angle histograms computed from single-pulse, polarization observations of PSR B2020+28. The favorable agreement between the theoretical and measured distributions lends support to the underlying assumptions of the statistical model, and demonstrates, like recent work on other pulsars, that the handedness of circular polarization is associated with the radiation's orthogonally polarized modes. Comprehensive directional statistics of the vector's orientation angles are also derived, and are shown to follow the Watson bipolar and Fisher distributions in its limiting forms.

 
astro-ph/0603464 [abs, ps, pdf, other] :
Title: Constraining the MIT Bag Model of Quark Matter with Gravitational Wave Observations
Authors: Omar Benhar, Valeria Ferrari, Leonardo Gualtieri, Stefania Marassi
Comments: Four pages, four figures

Most theoretical studies of strange stars are based on the MIT bag model of quark matter, whose main parameter, the bag constant B, is only loosely constrained by phenomenology. We discuss the possibility that detection of gravitational waves emitted by a compact star may provide information on both the nature of the source and the value of B. Our results show that the combined knowledge of the frequency of the emitted gravitational wave and of the mass or the radiation radius of the source allows one to discriminate between strange stars and neutron stars and set stringent bounds on the bag constants.

 
astro-ph/0603467 [abs, ps, pdf, other] :
Title: Discovery of luminous pulsed hard X-ray emission from anomalous X-ray pulsars 1RXS J1708-4009, 4U 0142+61 and 1E 2259+586 by INTEGRAL and RXTE
Authors: L.Kuiper (1), W. Hermsen (1 and 2), P.R. den Hartog (1), W. Collmar (3) ((1) SRON-The Netherlands, (2) University of Amsterdam, (3) MPI Garching, Germany)
Comments: Accepted for publication in ApJ; 19 pages; 4 Tables; 15 Figures (6 color)

We report on the discovery of hard spectral tails for energies above 10 keV in the total and pulsed spectra of anomalous X-ray pulsars 1RXS J1708-4009, 4U 0142+61 and 1E 2259+586 using RXTE PCA (2-60 keV) and HEXTE (15-250 keV) data and INTEGRAL IBIS ISGRI (20-300 keV) data. Improved spectral information on 1E 1841-045 is presented. The pulsed and total spectra measured above 10 keV have power-law shapes and there is so far no significant evidence for spectral breaks or bends up to ~150 keV. The pulsed spectra are exceptionally hard with indices measured for 4 AXPs approximately in the range -1.0 -- 1.0. We also reanalyzed archival CGRO COMPTEL (0.75-30 MeV) data to search for signatures from our set of AXPs. No detections can be claimed, but the obtained upper-limits in the MeV band indicate that for 1RXS J1708-4009, 4U 0142+61 and 1E 1841-045 strong breaks must occur somewhere between 150 and 750 keV.

 
astro-ph/0603468 [abs, ps, pdf, other] :
Title: Is PSR B0943+10 a low-mass quark star?
Authors: Y. L. Yue, X. H. Cui, R. X. Xu
Comments: 4 pages, 2 figures

Recent X-ray observation has shown that the drifting pulsar B0943+10 has a much smaller polar cap area than the conventional one of pulsars with mass of $\sim\msun$ and radius of $\sim10$ km. This leads to conflict with the original vacuum gap model. The discrepancy would vanish if PSR B0943+10 is a low-mass quark star. It is found that vacuum gap potential drop could be two orders larger when considering the effects of inclination angle, and the vacuum gap model would therefore still work well.

 
astro-ph/0603481 [abs, ps, pdf, other] :
Title: Local Kelvin-Helmholtz instability and synchrotron modulation in Pulsar Wind Nebulae
Authors: N. Bucciantini (1), L. Del Zanna (2) ((1) Astronomy Dep., Univ. of California at Berkeley, (2) Dipartimento di Astronomia, Univ. di Firenze)
Comments: 10 pages, 7 figures, Accepted for publication in A&A

We present here a series of numerical simulations of the development of Kelvin-Helmholtz instability in a relativistically hot plasma. The physical parameters in the unperturbed state are chosen to be representative of local conditions encountered in Pulsar Wind Nebulae (PWNe), with a main magnetic field perpendicular to a mildly relativistic shear layers. By using a numerical code for Relativistic MHD, we investigate the effect of an additional magnetic field component aligned with the shear velocity, and we follow the evolution of the instability to the saturation and turbulent regimes. Based on the resulting flow structure, we then compute synchrotron maps in order to evaluate the signature of Kelvin-Helmholtz instability on the emission and we investigate how the time scale and the amplitude of the synchrotron modulations depend on shear velocity and magnetic field. Finally we compare our results to the observed variable features in the Crab Nebula. We show that the Kelvin-Helmholtz instability cannot account for the wisps variability, but it might be responsible for the time dependent filamentary structure observed in the main torus.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0511364 [abs, ps, pdf, other] :
Title: The pulsar wind nebula of the Geminga pulsar
Authors: G.G. Pavlov, D. Sanwal, V.E. Zavlin
Comments: Revised version: data analysis described in more detail, Figure 2 replaced; 6 pages, 2 color figures; accepted for publication in ApJ (v.643, 2006 June 1)
Note: replaced with revised version Fri, 17 Mar 2006 19:33:38 GMT (75kb)
 
astro-ph/0512653 [abs, ps, pdf, other] :
Title: Interrelation between radio and X-ray signatures of drifting subpulses in pulsars
Authors: Janusz Gil, George Melikidze, Bing Zhang
Note: replaced with revised version Fri, 17 Mar 2006 12:46:13 GMT (10kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 21 Mar 06 01:00:12 GMT
0603483 -- 0603540 received


6 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603490 [abs, ps, pdf, other] :
Title: Interstellar Scintillation of PSR J0437-4715
Authors: T.V. Smirnova, C.R. Gwinn, V.I. Shishov
Comments: 9 pages, 3 figures, 2 tables

We studied the turbulence spectrum of the local interstellar plasma in the direction of PSR J0437-4715, on the basis of our observations and those reported earlier by others. We combine these data to form a structure function for the variations of phase along the line of sight to the pulsar. For observations that did not report them, we infer modulation indices from a theoretical model. We find that all of the observations fit a power-law spectrum of turbulence with index n=3.46+/-0.20. We suggest that differences among reported values for scintillation bandwidth and timescale for this pulsar arise from differences in observing parameters. We suggest that refractive effects dominate for this line of sight, with refraction angle about twice the diffraction angle at 330 MHz observing frequency. We suggest that the scattering of this pulsar lies in a layer of enhanced turbulence, about 10 pc from the Sun. We propose that the flux variations of the extragalactic source PKS 0405-385 arise in the same scattering layer.

 
astro-ph/0603501 [abs, ps, pdf, other] :
Title: New Results from High Energy Gamma-Ray Astronomy
Authors: Heinrich J. Völk
Comments: 10 pages, 6 figures, Invited paper at IAU Symposium No.230, 2005, in Dublin (Ireland); E.J.A. Meurs, G. Fabbiano, eds.; in press (2006)

High energy gamma-ray astronomy has recently made significant progresss through ground-based instruments like the {\it H.E.S.S.} array of imaging atmospheric Cherenkov telescopes. The unprecedented angular resolution and the large field of view has allowed to spatially resolve for the first time the morphology of gamma-ray sources in the TeV energy range. The experimental technique is described and the types of sources detected and still expected are discussed. Selected results include objects as different as a Galactic binary Pulsar, the Galactic Center and Supernova Remnants but they also concern the diffuse extragalactic optical/infrared radiation field. Finally, a scan of the Galactic plane in TeV gamma rays is described which has led to a significant number of new TeV sources, many of which are still unidentified in other wavelengths. The field has a close connection with X-ray astronomy which allows the study of the synchrotron emission from these very high energy sources.

 
astro-ph/0603512 [abs, ps, pdf, other] :
Title: Magnetic fields in our Galaxy: How much do we know? III. Progress in the last decade
Authors: J.L. Han (NAOC)
Comments: 8 pages, 4 figures. Invited Talk at "2005 Hanas Pulsar Symposium". To be published in Chinese Journal of Astronomy and Astrophysics

A decade ago, there was very limited knowledge of magnetic fields of our Galaxy. The local fields in the Solar vicinity were known to be directed towards a Galactic longitude $l\sim~90^{\circ}$ with reversed directions at smaller Galacto-radii. The regular field strength was found to be about 2~$\mu$G. The filaments near the Galactic Center show the possible poloidal fields there. There was no information about the magnetic fields in the Galactic halo. In last decade, there has been significant progress on measurements of the Galactic magnetic fields. In the Galactic disk, from the RMs of a large number of newly observed pulsars, large-scale magnetic fields along the spiral arms have been delineated in a much larger region then ever before, with alternating directions in the arm and interarm regions. The toroidal fields in the Galactic halo were revealed to have opposite directions below and above the Galactic plane, which is an indication of A0 dynamo operating in the halo. The strength of large-scale fields also has been found from pulsar RM data to exponentially increase at smaller Galacto-radii. Compared to the steep Kolmogorov spectrum of magnetic energy at small scales, the large-scale magnetic fields show a shallow broken spatial magnetic energy spectrum.

 
astro-ph/0603519 [abs, ps, pdf, other] :
Title: The GRB060218/SN 2006aj link to Supernova-GRBs blazing and re-brightening by precessing showering Jets
Authors: D.Fargion, M.Grossi
Comments: 9 pages, 8 figures, Submitted for pubblication

A list of puzzles are unanswered by Fireball (even milli-steradiant beamed) explosive GRB and Magnetar spherical one-shoot SGR models. The early GRB 980425 and the last longest GRB060218 are the most emblematic GRBs out of the tune of any Fireball cone models. Too nearby, too soft, too underluminous and too long events. The huge flare of SGR 1806-20 and its radio rebrightening disagree with Magnetar model. Only a persistent, thin (even less than micro steradiant) precessing and spinning gamma jet evolution explains X-gamma time structure and afterglow bumps. The late relic neutron star, X-ray pulsar jet, its spinning and precessing lepton-gamma jet is the candidate blazing sources as anomalous X-ray Pulsars (AXRPs) and Soft Gamma-Ray Repeaters (SGRs). Precessing jet are like SS433 spiral jets. At SN power and in-axis they are GRBs. Late (weeks-months) GRB blazing jets are seldom orphan of their bright SN-OT. The last GRB060218 occurred within its SN2006aj smoothly and soft (because off-axis), ruled by outer jet component and slow by large impact angle. We foresaw OT and radio bumps and re-brightening, in analogy to the third nearest GRB030329-SN2003 event. Late decayed Jets are XRFs or brief GRBs and mostly in galaxy or Local Group distances as SGRs and AXRPs. Electron pairs beams are showering and feeding gamma-X jet by Synchrotron (or Inverse Compton Scattering) far from the dense SN star (or a Neutron Star magnetic fields): energetic and penetrating PeVs muon pairs bundle are the progenitors able to escape the Supernova shells matter and photon opacity decaying far away into PeV electron pairs (and gamma) and neutrinos. The mysterious GRBs (and SGRs) are not the most explosive event of the Universe, but just the most beamed ones.

 
astro-ph/0603525 [abs, ps, pdf, other] :
Title: Submillimeter corrections to gravity and the metastability of white dwarf and neutron stars
Authors: Mofazzal Azam, M. Sami
Comments: 5 pages, no figures

The string inspired higher dimensional theories suggest modification of Newton's law at submillimeter length scales. Inter-particle distances in white dwarf and neutron stars are $10^{-10} cms$ and $10^{-13} cms$ respectively, and therefore, the effects of of short distance corrections to gravity deserve investigation. We show, by carrying out explicit analytical many-body calculations that, in the presence of corrections, the normal state of these compact stars become metastable. The actual quantum mechanical ground state of the stars turns out to be unstable. However, the tunneling probability to the unstable ground state is so small that the stars may remain trapped in the metastable state practically for ever.

 
astro-ph/0603531 [abs, ps, pdf, other] :
Title: Magnetic Field Structure from Synchrotron Polarization
Authors: Rainer Beck (MPI fuer Radioastronomie, Bonn, Germany)
Comments: 18 pages, 9 figures. To be published in "Polarisation 2005" (Proc. of the conference held in Paris, 12-15 Sept. 2005), eds. F. Boulanger and M.A. Miville-Deschenes, EAS Publications Series

Total magnetic fields in spiral galaxies, as observed through their total synchrotron emission, are strongest (up to \simeq 30\mu G) in the spiral arms. The degree of radio polarization is low; the field in the arms must be mostly turbulent or tangled. Polarized synchrotron emission shows that the resolved regular fields are generally strongest in the interarm regions (up to \simeq 15\mu G), sometimes forming 'magnetic arms' parallel to the optical arms. The field structure is spiral in almost every galaxy, even in flocculent and bright irregular types which lack spiral arms. The observed large-scale patterns of Faraday rotation in several massive spiral galaxies reveal coherent regular fields, as predicted by dynamo models. However, in most galaxies observed so far no simple patterns of Faraday rotation could be found. Either many dynamo modes are superimposed and cannot be resolved by present-day telescopes, or most of the apparently regular field is in fact anisotropic random, with frequent reversals, due to shearing and compressing gas flows. In galaxies with massive bars, the polarization pattern follows the gas flow. However, around strong shocks in bars, the compression of the regular field is much lower than that of the gas; the regular field decouples from the cold gas and is strong enough to affect the flow of the diffuse warm gas. -- The average strength of the total magnetic field in the Milky Way is 6\mu G near the sun and increases to 20-40\mu G in the Galactic center region. The Galactic field is mostly parallel to the plane, except in the center region. Rotation measure data from pulsars indicate several field reversals, unlike external galaxies, but some reversals could be due to distortions of the nearby field.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0511143 [abs, ps, pdf, other] :
Title: Momentum constraint relaxation
Authors: Pedro Marronetti
Comments: 17 pages, 10 figures. New numerical tests and references added. More detailed description of the algorithms are provided. Final published version
Journal-ref: Class. Quantum Grav. 23 (2006) 2681-2695

Full relativistic simulations in three dimensions invariably develop runaway modes that grow exponentially and are accompanied by violations of the Hamiltonian and momentum constraints. Recently, we introduced a numerical method (Hamiltonian relaxation) that greatly reduces the Hamiltonian constraint violation and helps improve the quality of the numerical model. We present here a method that controls the violation of the momentum constraint. The method is based on the addition of a longitudinal component to the traceless extrinsic curvature generated by a vector potential w_i, as outlined by York. The components of w_i are relaxed to solve approximately the momentum constraint equations, pushing slowly the evolution toward the space of solutions of the constraint equations. We test this method with simulations of binary neutron stars in circular orbits and show that effectively controls the growth of the aforementioned violations. We also show that a full numerical enforcement of the constraints, as opposed to the gentle correction of the momentum relaxation scheme, results in the development of instabilities that stop the runs shortly.

 

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astro-ph new abstracts, Wed, 22 Mar 06 01:00:10 GMT
0603541 -- 0603588 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603567 [abs, ps, pdf, other] :
Title: A Neutron Star-driven XRF associated with SN 2006aj
Authors: Paolo A. Mazzali (1,3,4), Jinsong Deng (2,4), Ken'ichi Nomoto (5,4), Elena Pian (3,4), Nozomu Tominaga (5,4), Masaomi Tanaka (5), Keiichi Maeda (5,4) ((1) MPA, Germany, (2) Beijing Obs., China, (3) INAF-OATs, Italy, (4) KITP-UCSB, CA, (5) U. Tokyo, Japan)
Comments: Submitted to Nature on 20 March 2006

Observations and models of SN 2006aj, while bringing fresh evidence of the connection between long Gamma Ray Bursts (GRBs) and Supernovae (SNe), suggest that there is variety among these events. The previously well observed cases (GRB980425/SN 1998bw, GRB030329/SN 2003dh, GRB031203/SN 2003lw) could be explained as the prompt collapse to a black hole of the core of a massive star (M ~ 40 Msun) that had lost its outer hydrogen and helium envelopes. All these SNe exhibited strong oxygen lines, thus being classified as Type Ic, and their energies were much larger than those of typical SNe. The case of SN 2006aj/GRB060218 appears different: the GRB was weak and soft (an X-Ray Flash, XRF); the SN is dimmer and has very weak oxygen lines, suggesting a "Type Ic/d" classification. The explosion energy of SN 2006aj was smaller, as was the ejected mass. In our model, the progenitor star had a smaller mass than other GRB/SNe (M ~ 20 Msun), suggesting that a neutron star rather than a black hole was formed. If the nascent neutron star was strongly magnetized (a so-called magnetar) and rapidly spinning, it may launch a weak GRB or an XRF. At a later phase of its life, the neutron star may give rise to short GRBs.

 
astro-ph/0603569 [abs, ps, pdf, other] :
Title: On the nature of radio pulsars with long periods
Authors: D.Lomiashvili, G.Machabeli, I.Malov
Comments: 18 pages, 4 figures
Journal-ref: Astrophysical Journal, 2006, V. 637, P.1010-1015

It is shown that the drift waves near the light cylinder can cause the modulation of the emission with periods of the order several seconds. These periods explain the intervals between successive pulses observed in "magnetars" and radio pulsars with long periods. The model under consideration makes it possible to calculate the real rotation periods of the host neutron stars. They are less than 1 sec for the investigated objects. The magnetic fields at the surface of the neutron star of the order 10^(11)-10^(13) G and equal to the usual fields for known radio pulsars

 
astro-ph/0603571 [abs, ps, pdf, other] :
Title: The production of short-lived radionuclides by new non-rotating and rotating Wolf-Rayet model stars
Authors: M. Arnould, S. Goriely, G. Meynet
Comments: 8 pages, 8 figures

It has been speculated that WR winds may have contaminated the forming solar system, in particular with short-lived radionuclides (half-lives in the approximate 10^5 - 10^8 y range) that are responsible for a class of isotopic anomalies found in some meteoritic materials. We revisit the capability of the WR winds to eject these radionuclides using new models of single non-exploding WR stars with metallicity Z = 0.02. The earlier predictions for non-rotating WR stars are updated, and models for rotating such stars are used for the first time in this context. We find that (1) rotation has no significant influence on the short-lived radionuclide production by neutron capture during the core He-burning phase, and (2) 26Al, 36Cl, 41Ca, and 107Pd can be wind-ejected by a variety of WR stars at relative levels that are compatible with the meteoritic analyses for a period of free decay of around 10^5 y between production and incorporation into the forming solar system solid bodies. We confirm the previously published conclusions that the winds of WR stars have a radionuclide composition that can meet the necessary condition for them to be a possible contaminating agent of the forming solar system. Still, it remains to be demonstrated from detailed models that this is a sufficient condition for these winds to have provided a level of pollution that is compatible with the observations.

 

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astro-ph new abstracts, Thu, 23 Mar 06 01:00:15 GMT
0603589 -- 0603615 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603597 [abs, ps, pdf, other] :
Title: Circular Polarization in Pulsar Integrated Profiles: Updates
Authors: X. P. You, J. L. Han
Comments: 10 pages, 6 figures, accepted and will be published soon by Chinese Journal of Astronomy and Astrophysics (ChJAA)

We update the systematic studies of circular polarization in integrated pulse profiles by Han et al (1998). Data of circular polarization profiles are compiled. Sense reversals can occur in core or cone components, or near the intersection between components. The correlation between the sense of circular polarization and the sense of position angle variation for conal-double pulsars is confirmed with a much large database. Circular polarization of some pulsars has clear changes with frequency. Circular polarization of millisecond pulsars is marginally different from that of normal pulsars.

 

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astro-ph/0603567 [abs, ps, pdf, other] :
Title: A Neutron Star-driven XRF associated with SN 2006aj
Authors: Paolo A. Mazzali (1,3,4), Jinsong Deng (2,4), Ken'ichi Nomoto (5,4), Elena Pian (3,4), Nozomu Tominaga (5,4), Masaomi Tanaka (5), Keiichi Maeda (5,4) ((1) MPA, Germany, (2) NAOC, China, (3) INAF-OATs, Italy, (4) KITP-UCSB, CA, (5) U. Tokyo, Japan)
Comments: Submitted to Nature on 20 March 2006
Note: replaced with revised version Wed, 22 Mar 2006 14:39:32 GMT (100kb)
 

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astro-ph new abstracts, Fri, 24 Mar 06 01:00:22 GMT
0603616 -- 0603647 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603644 [abs, ps, pdf, other] :
Title: Effects of color superconductivity on the nucleation of quark matter in neutron stars
Authors: I. Bombaci, G. Lugones, I. Vidana
Comments: Submitted to A&A. 8 pages and 6 Figures. Structured abstract following A&A format

We study the nucleation of quark matter drops at the center of cold deleptonized neutron stars. This is relevant in the determination of the critical mass $M_{cr}$ of hadronic stars above which it is possible a transition to a quark star (strange or hybrid). We investigate the dependence of $M_{cr}$ upon the parameters of the quark model (the Bag constant $B$, the pairing gap $\Delta$, and the surface tension $\sigma$ of the quark-hadron interphase) and for different parametrization of the hadronic equations of state. The dependence of $M_{cr}$ on $B$, $\Delta$ and $\sigma$ is mild if the parameters of the quark model correspond to hybrid stars, and strong if they correspond to strange stars. For a large part of the parameter space corresponding to hybrid stars, the critical mass is very close (but smaller than) the maximum mass of hadronic stars, and therefore compatible with a "mixed" population of compact stars (pure hadronic up to the critical mass and hybrid above the critical mass). For very large $B$ the critical mass is never smaller than the maximum mass of hadronic stars, implying that quark stars cannot form through the here studied mechanism. The energy released in the conversion is $3 \times 10^{52}$ erg - $4 \times 10^{53}$ erg, i.e. sufficient to power a gamma ray burst.

 

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astro-ph new abstracts, Mon, 27 Mar 06 01:00:10 GMT
0603648 -- 0603686 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603649 [abs, ps, pdf, other] :
Title: A remark on ``On the Formation and Progenitor of PSR J0737-3039: New Constraints on the Supernova Explosion Forming Pulsar B" by Willems et al., astro-ph/0602024
Authors: Tsvi Piran, Nir J. Shaviv

Shortly after the discovery of the binary system PSR J0737-3039 we predicted that it has a small proper motion and suggested that this implies that the progenitor mass of the younger pulsar (B) must be around 1.45M_sun. This is in contradiction to standard evolutionary scenarios that suggest a He-star progenitor with M >2.1-2.3M_sun and in sharp contrast to a velocity of ~100 km/s predicted by these models. It requires a new previously unseen type of gravitational collapse. Our (generally ignored) prediction of a low peculiar motion was confirmed later by pulsar timing observations that found v_\bot < 30 km/s. Recently Willems et al. put forward an elaborate simulation suggesting that in spite of these observations, the most likely natal kick is large (50-170 km/s) and the corresponding most likely progenitor mass is large as well. We refute this claim and show that Willems et al. implicitly assume the result that they obtain.

 

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astro-ph new abstracts, Tue, 28 Mar 06 01:00:12 GMT
0603687 -- 0603740 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603724 [abs, ps, pdf, other] :
Title: Evidence for precession of the isolated neutron star RX J0720.4-3125
Authors: F. Haberl (MPE), R. Turolla (Univ. Padova), C.P. De Vries (SRON), S. Zane (MSSL), J. Vink (Univ. Utrecht), M. Mendez (SRON), F. Verbunt (Univ. Utrecht)
Comments: Accepted for publication in A&A Letters, 5 pages, 5 figures

The XMM-Newton spectra of the isolated neutron star RX J0720.4-3125 obtained over 4.5 years can be described by sinusoidal variations in the inferred blackbody temperature, the size of the emitting area and the depth of the absorption line with a period of 7.1 +/- 0.5 years, which we suggest to be the precession period of the neutron star. Precession of a neutron star with two hot spots of different temperature and size, probably not located exactly in antipodal positions, may account for the variations in the X-ray spectra, changes in the pulsed fraction, shape of the light curve and the phase-lag between soft and hard energy bands observed from RX J0720.4-3125. An independent sinusoidal fit to published and new pulse timing residuals from a coherent analysis covering ~12 years yields a consistent period of 7.7 +/- 0.6 years supporting the precession model.

 
astro-ph/0603731 [abs, ps, pdf, other] :
Title: Jet-dominated advective systems: radio and X-ray luminosity dependence on the accretion rate
Authors: Elmar Koerding (Southampton), Rob Fender (Southampton), Simone Migliari (UCSD)
Comments: Accepted for publication in MNRAS

We present a novel method to measure the accretion rate of radio emitting X-ray binaries (XRBs) and active galactic nuclei (AGN) independently of the X-ray luminosity. The radio emission of the jet is used as a tracer for the accretion rate and is normalised using sources of known accretion rates: island state neutron stars and efficiently radiating black holes close to a state transition. We show that the radio power in black holes and neutron stars is comparable for a given mass accretion rate and verify empirically the assumed analytic scaling of the radio luminosity with accretion rate. As our accretion measure is independent of the X-ray luminosities, we can search for radiatively inefficient accretion in black holes by comparing the X-ray luminosities with the accretion rate in XRBs and AGN. While the X-ray luminosity of efficiently radiating objects scales linearly with accretion rate, the scaling of hard state black holes is quadratical, in agreement with theoretical models. We show that the turnover from the inefficient quadratic scaling to the linear scaling has to occur at accretion rates of 1-10 % Eddington both in XRBs and AGN. The comparison of both accretion states supports the idea that in a black hole in the hard state some accretion power is advected into the black hole while the jet power exceeds the X-ray luminosity: these are therefore jet-dominated advective systems.

 

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astro-ph new abstracts, Wed, 29 Mar 06 01:00:09 GMT
0603741 -- 0603772 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603741 [abs, ps, pdf, other] :
Title: Magnetic Field Decay and Period Evolution of Anomalous X-Ray Pulsars in the Context of Quark Stars
Authors: Brian Niebergal, Rachid Ouyed, Denis Leahy
Comments: 4 pages, 4 figures

We discuss a model wherein soft gamma-ray repeaters (SGRs), anomalous X-ray pulsars (AXPs), and radio quiet isolated neutron stars (RQINSs) are all compact objects exhibiting superconductivity, namely quark stars. In particular we calculate the magnetic field decay due to the expulsion of spin-induced vortices from the star's superconducting-superfluid interior, and the resultant spin-down rate. We find that, for initial parameters characteristic of AXPs/SGRs ($10^{13}<B<10^{14} \rm{G}$; $3<P<12 \rm{s}$), the magnetic field strengths and periods remain unchanged within a factor of two for timescales of the order of $5\times 10^{5} - 5\times 10^{7} \rm{yrs}$ given a quark star of radius $10 \rm{km}$. Within these timescales, we show that the observed period clustering in RQINSs can be explained by compactness, as well as calculate how the magnetic field and period evolve in a manner concurrent with RQINS observations.

 
astro-ph/0603743 [abs, ps, pdf, other] :
Title: Quark deconfinement in neutron star cores: The effects of spin-down
Authors: Jan Staff, Rachid Ouyed, Prashanth Jaikumar
Comments: 4 pages, 4 figures, submitted to ApJL

We study the role of spin-down in driving quark deconfinement in the high density core of isolated neutron stars. Assuming spin-down to be solely due to magnetic braking, we obtain typical timescales to quark deconfinement for neutron stars that are born with Keplerian frequencies. Employing different equations of state (EOS), we determine the minimum and maximum neutron star masses that will allow for deconfinement via spin-down only. We find that the time to reach deconfinement is strongly dependent on the magnetic field and that this time is least for EOS that support the largest minimum mass at zero spin, unless rotational effects on stellar structure are large. For a fiducial critical density of $5\rho_0$ for the transition to the quark phase ($\rho_0=2.5\times10^{14}$g/cm$^3$ is the saturation density of nuclear matter), we find that neutron stars lighter than $1.5M_{\odot}$ cannot reach a deconfined phase. Depending on the EOS, neutron stars of more than $1.5M_{\odot}$ can enter a quark phase only if they are spinning faster than about 3 milliseconds as observed now, whereas larger spin periods imply that they are either already quark stars or will never become one.

 
astro-ph/0603752 [abs, ps, pdf, other] :
Title: A self-consistent model of isolated neutron stars: the case of the X-ray pulsar RX J0720.4-3125
Authors: J.F.Perez-Azorin, J.A.Pons, J.A.Miralles, G. Miniutti
Comments: 4 pages, 2 figures, submitted to ApJ lett. on Feb. 24 2006

We present a unified explanation for the observed properties of the isolated neutron star RX J0720.4-3125 by obtaining, for the first time, a self-consistent model that accounts simultaneously for the observed X-ray spectrum and optical excess, the pulsed fraction, the observed spectral feature around 0.3 keV, and the long--term spectral evolution. By fitting the parameters of our realistic self--consistent models to all archival XMM--Newton observations and available optical data, we show that all observed properties are consistent with a normal neutron star with a proper radius of about 12 km, a temperature at the magnetic pole of about 100 eV and a magnetic field strength of 2-3 x 10^{13} G, with no need to invoke additional emission and absorption components nor exotic internal composition. The observed variability of the blackbody temperature, strength of the spectral feature, and pulsed fraction is in good agreement with the predictions of our model in which the star is subject to free precession, producing changes in the angle between the magnetic field and the rotation axis of about 10--15 degrees in a few years.

 
astro-ph/0603772 [abs, ps, pdf, other] :
Title: A Unified Model of Active Galactic Nuclei, Black Hole X-Ray Sources and Gamma-Ray Bursts
Authors: J. I. Katz
Comments: 22 pages

I consider models of active galactic nuclei, stellar-mass accreting black holes and microquasars based on a previously developed (Katz 1997) model of gamma-ray bursts. When energy fluxes exceed a critical value ~ 10^{29} erg/cm^2s, as in GRB, a black body equilibrium pair plasma forms. At the lower fluxes found in AGN, BHXS and microquasars power electrodynamically accelerates a small number of very energetic particles, explaining their non-thermal spectra and the high energy gamma-ray emission of blazars. Ultra-high energy cosmic rays may be accelerated by massive black holes, otherwise undetectable, with very low thermal luminosities. New-born fast high-field pulsars may be in the black-body equilibrium regime, resembling SGR in permanent outburst. I also consider the question of whether collisionless plasmas interpenetrate rather than forming hydrodynamic shocks, and propose this as an alternative to internal shock models of gamma-ray bursts.

 

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astro-ph new abstracts, Thu, 30 Mar 06 01:00:12 GMT
0603773 -- 0603801 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603780 [abs, ps, pdf, other] :
Title: The Topology and Polarisation of Subbeams Associated with the `Drifting' Subpulse Emission of Pulsar B0943+10 -- IV. Q-to-B-Mode Recovery Dynamics
Authors: Joanna M. Rankin, Svetlana A. Suleymanova
Comments: 9 pages, 10 figures

Pulsar B0943+10 is well known for its `B' (burst) mode, characterized by accurately drifting subpulses, in contrast to its chaotic `Q' (quiet) mode. Six new Arecibo observations at 327 MHz with durations of 2+ hours each have shed considerable light on the modal dynamics of this pulsar. Of these, three were found to be exclusively `B' mode, and three were discovered to exhibit transitions from the `Q' to the `B' mode. One of these observations has permitted us to determine the circulation time of the subbeam carousel in the `Q' mode for the first time, at some 36.4$\pm$0.9 stellar rotation periods. The onset of the `B' mode is then observed to commence similarly in all three observations. The initial circulation time is about 36 periods and relaxes to nearly 38 periods in a roughly exponential fashion with a characteristic time of some 1.2 hours. This is the longest characteristic time ever found in a mode-switching pulsar. Moreover, just after the `B'-mode onset the pulsar exhibits a symmetrical resolved-double profile form with a somewhat stronger trailing component, but this second component slowly dies away leaving the usual single `B'-mode profile with the longitude of the magnetic axis falling at about its trailing half power point. Thus it would appear that Q-to-B- and B-to-Q-transitions have different characteristic times. Some speculations are given on the nature of this slow modal alternation.

 

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astro-ph new abstracts, Fri, 31 Mar 06 01:00:09 GMT
0603802 -- 0603833 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603810 [abs, ps, pdf, other] :
Title: Identifications of Four INTEGRAL Sources in the Galactic Plane via Chandra Localizations
Authors: John A. Tomsick (CASS/UCSD), Sylvain Chaty (AIM/CEA Saclay), Jerome Rodriguez (AIM/CEA Saclay), Luigi Foschini (INAF/IASF - Bologna), Roland Walter (ISDC), Philip Kaaret (Univ. of Iowa)
Comments: Submitted to the Astrophysical Journal on 2006 March 18

Hard X-ray imaging of the Galactic plane by the INTEGRAL satellite is uncovering many new 20-100 keV sources. A significant fraction of these sources are High-Mass X-Ray Binaries (HMXBs) containing neutron stars. In this work, we present results from INTEGRAL, Chandra, optical, and IR observations of 4 of the IGR sources: IGR J16195-4945, IGR J16207-5129, IGR J16167-4957, and IGR J17195-4100. In all four cases, one relatively bright Chandra source is seen in the INTEGRAL error circle, and these are all likely to be counterparts of the IGR sources. The sources have hard 0.3-10 keV spectra with power-law photon indices of 0.5-1.1. The Chandra positions along with optical and IR sky survey catalogs as well as our own photometry have allowed us to obtain optical and IR identifications for all 4 sources. The J-band magnitudes are in the range 14.9-10.4, and we have used the optical/IR spectral energy distributions to constrain the nature of the sources. Blackbody components with temperature lower limits of >9400 K for IGR J16195-4945 and >18,000 K for IGR J16207-5129 indicate that these are very likely HMXBs. However, for IGR J16167-4957, the spectral type of the putative companion is later than A0V, so this source is not a typical HMXB. For IGR J17195-4100, the extinction is very low, and we calculate distance and luminosity upper limits of d < 2.6 kpc and L < 2x10^34 ergs/s. The low X-ray luminosity allows for several possible source types.

 
astro-ph/0603828 [abs, ps, pdf, other] :
Title: The interaction of gravitational waves with strongly magnetized plasmas
Authors: H. Isliker, L. Vlahos
Comments: 5 pages, 7 figures

We study the interaction of a gravitational wave (GW) with a plasma that is strongly magnetized. The GW is considered a small disturbance, and the plasma is modeled by the general relativistic analogue of the induction equation of ideal MHD and the single fluid equations. The equations are derived without neglecting any of the non-linear interaction terms, and the non-linear equations are integrated numerically. We find that for strong magnetic fields of the order of $10^{15} $G the GW excites electromagnetic plasma waves very close to the magnetosonic mode. The magnetic and electric field oscillations have very high amplitude, and a large amount of energy is absorbed from the GW by the electromagnetic oscillations, of the order of $10^{23} $erg/cm$^3$ in the case presented here. The absorbed energy is proportional to $B_0^2$, with $B_0$ the background magnetic field. The energization of the plasma takes place on fast time scales of the order of milliseconds. The amount of absorbed energy is comparable to the energies emitted in the most energetic astrophysical events, such as giant flares on magnetars and possibly even short Gamma ray bursts (GRB), for which the mechanism analyzed here also has the fast time-scales required.

 

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astro-ph/0603512 [abs, ps, pdf, other] :
Title: Magnetic fields in our Galaxy: How much do we know? III. Progress in the last decade
Authors: J.L. Han (NAOC)
Comments: 8 pages, 4 figures. Invited Talk at "2005 Hanas Pulsar Symposium". To be published in Chinese Journal of Astronomy and Astrophysics
Note: replaced with revised version Thu, 30 Mar 2006 15:34:02 GMT (169kb)
 

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astro-ph new abstracts, Mon, 3 Apr 06 00:00:12 GMT
0603834 -- 0603860 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603845 [abs, ps, pdf, other] :
Title: Producing ultra-strong magnetic fields in neutron star mergers
Authors: Daniel Price (U. Exeter), Stephan Rosswog (Int. U. Bremen)
Comments: 14 pages, 4 figures, accepted to Science. Version with high resolution figures + animations can be found at this http URL or this http URL

We report an extremely rapid mechanism for magnetic field amplification during the merger of a binary neutron star system. This has implications for the production of the short class of Gamma-Ray Bursts, which recent observations suggest may originate in such mergers. In detailed magnetohydrodynamic simulations of the merger process, the fields are amplified via Kelvin-Helmholtz instabilities beyond magnetar field strength and may therefore represent the strongest magnetic fields in the Universe. The amplification occurs in the shear layer which forms between the neutron stars and on a time scale of only 1 millisecond, i.e. long before the remnant can collapse into a black hole.

 
astro-ph/0603847 [abs, ps, pdf, other] :
Title: A non-linear resonance model for the black hole and neutron star QPOs: theory supported by observations
Authors: Gabriel Torok, Marek A. Abramowicz, Wlodek Kluzniak, Zdenek Stuchlik
Comments: 8 pages, 8 figures, to appear in Proceedings of the Albert Einstein Century International Conference

Kilohertz Quasi-Periodic Oscillations (QPOs) have been detected in many accreting X-ray binaries. It has been suggested that the highest QPO frequencies observed in the modulation of the X-ray flux reflect a non-linear resonance between two modes of accreting disk oscillation. This hypothesis implies certain very general predictions, several of which have been borne out by observations. Some of these follow from properties of non-linear oscillators, while the others are specific to oscillations of fluid in strong gravity. A 3:2 resonant ratio of frequencies can be clearly recognized in the black-hole as well as in the neutron-star QPO data.

 
astro-ph/0603853 [abs, ps, pdf, other] :
Title: X-ray emission from the double neutron star binary B1534+12: Powered by the pulsar wind?
Authors: O. Kargaltsev, G. G. Pavlov, G. P. Garmire
Comments: 11 pages, 8 figures, accepted to ApJ

We report the detection of the double neutron star binary (DNSB) B1534+12 (= J1537+1155) with the Chandra X-ray Observatory. This DNSB (orbital period 10.1 hr) consists of the millisecond (recycled) pulsar J1537+1155A (P_A=37.9 ms) and a neutron star not detected in the radio. After the remarkable double pulsar binary J0737-3039, it is the only other DNSB detected in X-rays. We measured the flux of (2.2\pm 0.6)\times10^{-15} ergs s^{-1} cm^{-2} in the 0.3-6 keV band. The small number of collected counts allows only crude estimates of spectral parameters. The power-law fit yields the photon index of 3.2\pm 0.5 and the unabsorbed 0.2-10 keV luminosity L_X=6\times10^{29} ergs s^{-1} = 3\times 10^{-4}Edot_A, where Edot_A is the spin-down power of J1537+1155A. Alternatively, the spectrum can be fitted by a blackbody model with T = 2.2 MK and the projected emitting area of ~ 5\times 10^3 m^2. The distribution of photon arrival times over binary orbital phase shows a deficit of X-ray emission around apastron, which suggests that the emission is caused by interaction of the relativistic wind from J1537+1155A with its neutron star companion. We also reanalyzed the Chandra and XMM-Newton observations of J0737-3039 and found that its X-ray spectrum is similar to the spectrum of B1534+12, and its X-ray luminosity is about the same fraction of Edot_A, which suggests similar X-ray emission mechanisms. However, the X-ray emission from J0737-3039 does not show orbital phase dependence. This difference can be explained by the smaller eccentricity of J0737-3039 or a smaller misalignment between the equatorial plane of the millisecond pulsar and the orbital plane of the binary.

 

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astro-ph new abstracts, Tue, 4 Apr 06 00:00:12 GMT
0604001 -- 0604037 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0603073 [abs, ps, pdf, other] :
Title: High density behaviour of nuclear symmetry energy
Authors: D.N. Basu, Tapan Mukhopadhyay
Comments: 9 pages including 3 figures

Role of the isospin asymmetry in nuclei and neutron stars, with an emphasis on the density dependence of the nuclear symmetry energy, is discussed. The symmetry energy is obtained using the isoscalar as well as isovector components of the density dependent M3Y effective interaction. The constants of density dependence of the effective interaction are obtained by reproducing the saturation energy per nucleon and the saturation density of spin and isospin symmetric cold infinite nuclear matter. Implications for the density dependence of the symmetry energy in case of a neutron star are discussed, and also possible constraints on the density dependence obtained from finite nuclei are compared.

 

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astro-ph new abstracts, Wed, 5 Apr 06 00:00:11 GMT
0604038 -- 0604073 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604043 [abs, ps, pdf, other] :
Title: Spreading of thermonuclear flames on the neutron star in SAX J1808.4-3658: an observational tool
Authors: Sudip Bhattacharyya, Tod E. Strohmayer
Comments: 12 pages, 1 table, 2 figures, accepted for publication in ApJ Letters

We analyse archival Rossi X-Ray Timing Explorer (RXTE) proportional counter array (PCA) data of thermonuclear X-ray bursts from the 2002 outburst of the accreting millisecond pulsar SAX J1808.4-3658. We present evidence of nonmonotonic variations of oscillation frequency during burst rise, and correlations among the time evolution of the oscillation frequency, amplitude, and the inferred burning region area. We also discuss that the amplitude and burning region area evolutions are consistent with thermonuclear flame spreading on the neutron star surface. Based on this discussion, we infer that for the 2002 Oct. 15 thermonuclear burst, the ignition likely occured in the mid-latitudes, the burning region took ~ 0.2 s to nearly encircle the equatorial region of the neutron star, and after that the lower amplitude oscillation originated from the remaining asymmetry of the burning front in the same hemisphere where the burst ignited. Our observational findings and theoretical discussion indicate that studies of the evolution of burst oscillation properties during burst rise can provide a powerful tool to understand thermonuclear flame spreading on neutron star surfaces under extreme physical conditions.

 
astro-ph/0604064 [abs, ps, pdf, other] :
Title: Analysis of 26 Barium Stars II. Contributions of s-, r- and p-processes in the production of heavy elements
Authors: Dinah M. Allen, Beatriz Barbuy
Comments: 30 pages including 24 figures, accepted to A&A

Barium stars show enhanced abundances of the slow neutron capture (s-process) heavy elements, and for this reason they are suitable objects for the study of s-process elements. The aim of this work is to quantify the contributions of the s-, r- and p-processes for the total abundance of heavy elements from abundances derived for a sample of 26 barium stars. The abundance ratios between these processes and neutron exposures were studied. The abundances of the sample stars were compared to those of normal stars thus identifying the fraction relative to the s-process main component. The fittings of the sigmaN curves (neutron capture cross section times abundance, plotted against atomic mass number) for the sample stars suggest that the material from the companion asymptotic giant branch star had approximately the solar isotopic composition as concerns fractions of abundances relative to the s-process main component. The abundance ratios of heavy elements, hs, ls and s and the computed neutron exposure are similar to those of post-AGB stars. For some sample stars, an exponential neutron exposure fits well the observed data, whereas for others, a single neutron exposure provides a better fit. The comparison between barium and AGB stars supports the hypothesis of binarity for the barium star formation. Abundances of r-elements that are part of the s-process path in barium stars are usually higher than those in normal stars,and for this reason, barium stars seemed to be also enriched in r-elements, although in a lower degree than s-elements. No dependence on luminosity classes was found in the abundance ratios behaviour among the dwarfs and giants of the sample barium stars.

 
astro-ph/0604072 [abs, ps, pdf, other] :
Title: Pulsar twinkling and relativity
Authors: Isabelle A. Grenier, Alice K. Harding
Comments: 9 pages, 5 figures, to be published in proceedings of the Albert Einstein Century International Conference, Paris 2005

The number of pulsars with detected emission at X-ray and gamma-ray energies has been steadily growing, showing that beams of high-energy particles are commonly accelerated in pulsar magnetospheres, even though the location and number of acceleration sites remain unsettled. Acceleration near the magnetic poles, close to the polar cap surface or to higher altitudes in the slot gap along the last open field lines, involves an electric field component due to inertial-frame dragging. Acceleration can also take place in the outer magnetosphere where charge depletion due to global currents causes a large electric field along the magnetic field lines. All models require a detailed knowledge of the open magnetosphere geometry and its relativistic distortions. Observational trends with age, spin-down power and magnetic field as well as population synthesis studies in the Galactic disc and the nearby Gould Belt provide useful, however not yet conclusive, constraints on the competing models.

 

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astro-ph/0603012 [abs, ps, pdf, other] :
Title: Why the braking indices of young pulsars are less than 3?
Authors: W. C. Chen, X. D. Li
Comments: 4 pages, 3 figures, accepted for publication in A&A Letters
Journal-ref: Astron.Astrophys. 450 (2006) L1-L4
Note: replaced with revised version Tue, 4 Apr 2006 06:43:22 GMT (94kb)
 

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astro-ph new abstracts, Thu, 6 Apr 06 00:00:13 GMT
0604074 -- 0604112 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604076 [abs, ps, pdf, other] :
Title: A Debris Disk Around An Isolated Young Neutron Star
Authors: Zhongxiang Wang, Deepto Chakrabarty, David L. Kaplan (MIT)
Comments: 5 pages, 3 figures. To appear in Nature (6 Apr 2006)

Pulsars are rotating, magnetized neutron stars that are born in supernova explosions following the collapse of the cores of massive stars. If some of the explosion ejecta fails to escape, it may fall back onto the neutron star or it may possess sufficient angular momentum to form a disk. Such 'fallback' is both a general prediction of current supernova models and, if the material pushes the neutron star over its stability limit, a possible mode of black hole formation. Fallback disks could dramatically affect the early evolution of pulsars, yet there are few observational constraints on whether significant fallback occurs or even the actual existence of such disks. Here we report the discovery of mid-infrared emission from a cool disk around an isolated young X-ray pulsar. The disk does not power the pulsar's X-ray emission but is passively illuminated by these X-rays. The estimated mass of the disk is of order 10 Earth masses, and its lifetime (at least a million years) significantly exceeds the spin-down age of the pulsar, supporting a supernova fallback origin. The disk resembles protoplanetary disks seen around ordinary young stars, suggesting the possibility of planet formation around young neutron stars.

 
astro-ph/0604097 [abs, ps, pdf, other] :
Title: The XMM-Newton view of the Crab
Authors: M.G.F. Kirsch, G. Schoenherr, E. Kendziorra, M.J. Freyberg, M. Martin, J. Wilms, K. Mukerjee, M.G.Breitfellner, M.J.S. Smith, R. Staubert
Comments: 9 pages

We discuss the current X-ray view of the Crab Nebula and Pulsar, summarising our analysis of observations of the source with the EPIC-pn camera on board the XMM-Newton observatory. Different modes of EPIC-pn were combined in order to yield a complete scenario of the spectral properties of the Crab resolved in space and time (pulse phase). In addition we give a description of the special EPIC-pn Burst mode and guidance for data reduction in that mode.
We analysed spectra for the nebula and pulsar separately in the 0.6-12.0 keV energy band. All data were processed with the SAS 6.0.0 XMM-Newton Scientific Analysis System package; models were fitted to the data with XSPEC 11. The high time resolution of EPIC-pn in its Burst mode (7 micros) was used for a phase resolved analysis of the pulsar spectrum, after determination of the period with epoch folding techniques. Data from the Small Window mode were processed and corrected for pile-up allowing for spectroscopy simultaneously resolved in space and time.
The spatial variation of the spectrum over the entire region of the Crab shows a gradual spectral softening from the inner pulsar region to the outer nebula region with a variation in photon index, Gamma, from 2.0 to 2.4. Pulse phase resolved spectroscopy of the Crab Pulsar reveals a phase dependent modulation of the photon index in form of a significant hardening of the spectrum in the inter-peak phase from Gamma =1.7 during the pulse peak to Gamma =1.5.

 
astro-ph/0604099 [abs, ps, pdf, other] :
Title: Unexpected Dynamical Instabilities In Differentially Rotating Neutron Stars
Authors: Shangli Ou, Joel Tohline
Comments: 37 pages, to be submitted to ApJ, comments welcomed

A one-armed spiral instability has been found to develop in differentially rotating stellar models that have a relatively stiff, $n=1$ polytropic equation of state and a wide range of rotational energies. This suggests that such instabilities can arise in neutron stars that are differentially, although not necessarily rapidly, rotating. The instability seems to be directly triggered by the presence of a corotation resonance inside the star. Our analysis also suggests that a resonant cavity resulting from a local minimum in the radial vortensity profile of the star plays an important role in amplifying the unstable mode. Hence, it appears as through this instability is closely related to the so-called ``Rossby wave instability'' \citep{LLCN99} that has been found to arise in accretion disks. In addition to the one-armed ($m=1$) spiral mode, we have found that higher-order ($m = 2$ and $m=3$) nonaxisymmetric modes also can become unstable if corotation points that resonate with the eigenfrequencies of these higher-order modes also appear inside the star. The growth rate of each mode seems to depend on the location of its corotation radius with respect to the vortensity profile (or on the depth of its corotation radius inside the vortensity well). The existence of such instabilities makes the stability criterion for differentially rotating neutron stars non-unique. Also, the gravitational-waves emitted from such unstable systems generally will not have a monochromatic frequency spectrum.

 

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astro-ph new abstracts, Fri, 7 Apr 06 00:00:14 GMT
0604113 -- 0604145 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604115 [abs, ps, pdf, other] :
Title: Spitzer/MIPS Limits on Asteroidal Dust in the Pulsar Planetary System PSR B1257+1
Authors: G. Bryden, C. A. Beichman, G. H. Rieke, J. A. Stansberry, K. R. Stapelfeldt, D. E. Trilling, N. J. Turner, A. Wolszczan

With the MIPS camera on Spitzer, we have searched for far-infrared emission from dust in the planetary system orbiting pulsar PSR 1257+12. With accuracies of 0.05 mJy at 24 um and 1.5 mJy at 70 um, photometric measurements find no evidence for emission at these wavelengths. These observations place new upper limits on the luminosity of dust with temperatures between 20 and 1000 K. They are particularly sensitive to dust temperatures of 100-200 K, for which they limit the dust luminosity to below $3 \times 10^{-5}$ of the pulsar's spin-down luminosity, three orders of magnitude better than previous limits. Despite these improved constraints on dust emission, an asteroid belt similar to the Solar System's cannot be ruled out.

 

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astro-ph new abstracts, Mon, 10 Apr 06 00:00:09 GMT
0604146 -- 0604176 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604163 [abs, ps, pdf, other] :
Title: Resonant Tidal Excitations of Inertial Modes in Coalescing Neutron Star Binaries
Authors: Dong Lai (Cornell), Yanqin Wu (Toronto)
Comments: 6 pages. Phys. Rev. D. submitted 3/23/06

We study the effect of resonant tidal excitation of inertial modes in neutron stars during binary inspiral. For spin frequencies less than 100 Hz, the phase shift in the gravitational waveform associated with the resonance is small and does not affect the matched filtering scheme for gravitational wave detection. For higher spin frequencies, the phase shift can become significant. Most of the resonances take place at orbital frequencies comparable to the spin frequency, and thus significant phase shift may occur only in the high-frequency band (hundreds of Hertz) of gravitational wave. The exception is a single odd-paity $m=1$ mode, which can be resonantly excited for misaligned spin-orbit inclinations, and may occur in the low-frequency band (tens of Hertz) of gravitational wave and induce significant (>> 1 radian) phase shift.

 

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astro-ph/0601142 [abs, ps, pdf, other] :
Title: Collapse of Neutron Stars to Black Holes in Binary Systems: A Model for Short Gamma Ray Bursts
Authors: Charles D. Dermer (1), Armen Atoyan (2) ((1) NRL, (2) University of Montreal)
Comments: 4 pages, ApJ Letters, in press
Note: replaced with revised version Thu, 6 Apr 2006 22:42:12 GMT (11kb)
 

Astrophysics authors/titles "new"

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astro-ph new abstracts, Tue, 11 Apr 06 00:00:10 GMT
0604177 -- 0604214 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604180 [abs, ps, pdf, other] :
Title: Near-UV Observations of HD221170: New Insights into the Nature of r-Process-Rich Stars
Authors: Inese I. Ivans, Jennifer Simmerer, Christopher Sneden, James E. Lawler, John J. Cowan, Roberto Gallino, Sara Bisterzo
Comments: 22 pages, 12 figures (10 colour), 6 tables, accepted by ApJ

Employing high resolution spectra obtained with the near-UV sensitive detector on the Keck I HIRES, supplemented by data obtained with the McDonald Observatory 2-d coude, we have performed a comprehensive chemical composition analysis of the bright r-process-rich metal-poor red giant star HD221170. Analysis of 57 individual neutral and ionized species yielded abundances for a total of 46 elements and significant upper limits for an additional five. Model stellar atmosphere parameters were derived with the aid of ~200 Fe-peak transitions. From more than 350 transitions of 35 neutron-capture (Z > 30) species, abundances for 30 neutron-capture elements and upper limits for three others were derived. Utilizing 36 transitions of La, 16 of Eu, and seven of Th, we derive ratios of log epsilon(Th/La) = -0.73 (sigma = 0.06) and log epsilon(Th/Eu) = -0.60 (sigma = 0.05), values in excellent agreement with those previously derived for other r-process-rich metal-poor stars such as CS22892-052, BD+17 3248, and HD115444. Based upon the Th/Eu chronometer, the inferred age is 11.7 +/- 2.8 Gyr. The abundance distribution of the heavier neutron-capture elements (Z >= 56) is fit well by the predicted scaled solar system r-process abundances, as also seen in other r-process-rich stars. Unlike other r-process-rich stars, however, we find that the abundances of the lighter neutron-capture elements (37 < Z < 56) in HD221170 are also statistically in better agreement with the abundances predicted for the scaled solar r-process pattern.

 
astro-ph/0604187 [abs, ps, pdf, other] :
Title: Supernova remnant energetics and magnetars: no evidence in favour of millisecond proto-neutron stars
Authors: Jacco Vink (1), Lucien Kuiper (2) ((1) Utrecht University, The Netherlands, (2) SRON Netherlands Institute for Space Research, Utrecht, The Netherlands)
Comments: Accepted for publication in MNRAS Letters. 5 pages, one color figure

It is generally accepted that Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs) are magnetars, i.e. neutron stars with extremely high surface magnetic fields (B > 10^{14} G). The origin of these high magnetic fields is uncertain, but a popular hypothesis is that magnetars are born with an initial spin period close to the break-up limit (~1 ms), which results in a powerful dynamo action, amplifying the seed magnetic field to > 10^{15} G. A neutron star spinning at such a rate has a rotational energy in excess of 10^{52} erg, and part of that energy will power the supernova through rapid magnetic braking. It is therefore expected that if magnetars are born with periods < 3 ms their supernova remnants should be an order of magnitude more energetic than ordinary supernova remnants. However, we list here evidence that the explosion energies of these supernova remnants associated with AXPs and SGRs -- Kes 73 (AXP 1E 1841-045), CTB 109 (AXP 1E2259+586) and N49 (SGR 0526-66) -- are close to the canonical supernova explosion energy of 10^{51} erg.
We therefore do not find evidence that magnetars are formed from rapidly rotating proto-neutron stars, allowing for the possibility that they descend from stellar progenitor with high magnetic field cores, and discuss the merits of both formation scenarios.
In an appendix we describe the analysis of XMM-Newton observations of Kes 73 and N49 used to derive the explosion energies for these remnants.

 
astro-ph/0604190 [abs, ps, pdf, other] :
Title: Microlensing in phase space II: Correlations analysis
Authors: Artem V. Tuntsov, Geraint F. Lewis (Sydney Uni)
Comments: 17 pages, 8 figure. Accepted for publication in MNRAS. Part I is currently with the referee

Applications of the phase space approach to the calculation of the microlensing autocorrelation function are presented. The continuous propagation equation for a random star field with a Gaussian velocity distribution is solved in the leading non-trivial approximation using the perturbation technique. It is shown that microlensing modulations can be important in the interpretation of optical and shorter-wavelength light curves of pulsars, power spectra of active galactic nuclei and coherence estimates for quasi-periodic oscillations of dwarf novae and low-mass X-ray binaries. Extra scatter in the brightness of type Ia supernovae due to gravitational microlensing is shown to be of order up to 0.2 stellar magnitudes depending on the extent of the light curves.

 
astro-ph/0604193 [abs, ps, pdf, other] :
Title: XMM-Newton observation of the Be/neutron star system RX J0146.9+6121: a soft X-ray excess in a low luminosity accreting pulsar
Authors: Nicola La Palombara, Sandro Mereghetti (INAF/IASF Milano (I))
Comments: 8 pages, 7 figures, 4 tables. Accepted for publication by Astronomy & Astrophysics

We report on the XMM-Newton observation of the Be/neutron star X-ray binary system RX J0146.9+6121, a long period (~ 23 m) pulsar in the NGC 663 open cluster. The X-ray luminosity decreased by a factor two compared to the last observation carried out in 1998, reaching a level of ~ 10^34 erg/s, the lowest ever observed in this source. The spectral analysis reveals the presence of a significant excess at low energies over the main power-law spectral component. The soft excess can be described by a black-body spectrum with a temperature of about 1 keV and an emitting region with a radius of ~ 140 m. Although the current data do not permit to ascertain whether the soft excess is pulsed or not, its properties are consistent with emission from the neutron star polar cap. This is the third detection of a soft excess in a low luminosity (~ 10^34 erg/s) pulsar, the other being X Per and 3A 0535+262, suggesting that such spectral component, observed up to date in higher luminosity systems, is a rather common feature of accreting X-ray pulsars. The results on these three sources indicate that, in low luminosity systems, the soft excess tends to have a higher temperature and a smaller surface area than in the high luminosity ones.

 

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astro-ph/0508595 [abs, ps, pdf, other] :
Title: Supernova remnant S147 and its associated neutron star(s)
Authors: V.V.Gvaramadze
Comments: 9 pages, 5 figures, revised version accepted for publication in A&A
Note: replaced with revised version Sat, 8 Apr 2006 11:09:27 GMT (351kb)
 

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astro-ph new abstracts, Wed, 12 Apr 06 00:00:10 GMT
0604215 -- 0604248 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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astro-ph new abstracts, Thu, 13 Apr 06 00:00:08 GMT
0604249 -- 0604278 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604261 [abs, ps, pdf, other] :
Title: Envelope Expansion with Core Collapse. III. Similarity Isothermal Shocks in a Magnetofluid
Authors: Cong Yu, Yu-Qing Lou, Fu-Yan Bian, Yan Wu
Comments: 21 pages, 33 figures, accepted by MNRAS

We explore MHD solutions for envelope expansions with core collapse (EECC) with isothermal MHD shocks in a quasi-spherical symmetry and outline potential astrophysical applications of such magnetized shock flows. MHD shock solutions are classified into three classes according to the downstream characteristics near the core. Class I solutions are those characterized by free-fall collapses towards the core downstream of an MHD shock, while Class II solutions are those characterized by Larson-Penston (LP) type near the core downstream of an MHD shock. Class III solutions are novel, sharing both features of Class I and II solutions with the presence of a sufficiently strong magnetic field as a prerequisite. Various MHD processes may occur within the regime of these isothermal MHD shock similarity solutions, such as sub-magnetosonic oscillations, free-fall core collapses, radial contractions and expansions. We can also construct families of twin MHD shock solutions as well as an `isothermal MHD shock' separating two magnetofluid regions of two different yet constant temperatures. The versatile behaviours of such MHD shock solutions may be utilized to model a wide range of astrophysical problems, including star formation in magnetized molecular clouds, MHD link between the asymptotic giant branch phase to the proto-planetary nebula phase with a hot central magnetized white dwarf, relativistic MHD pulsar winds in supernova remnants, radio afterglows of soft gamma-ray repeaters and so forth.

 

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astro-ph new abstracts, Fri, 14 Apr 06 00:00:16 GMT
0604279 -- 0604317 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604288 [abs, ps, pdf, other] :
Title: The Parkes Pulsar Timing Array
Authors: R N Manchester
Comments: 10 pages, in press ChJAA

Given sufficient sensitivity, pulsar timing observations can make a direct detection of gravitational waves passing over the Earth. Pulsar timing is most sensitive to gravitational waves with frequencies in the nanoHertz region, with the most likely astronomical sources being binary super-massive black holes in galaxy cores. The Parkes Pulsar Timing Array project uses the Parkes 64-m radio telescope to make precision timing observations of a sample of about 20 millisecond pulsars with a principal goal of making a direct detection of gravitational waves. Observations commenced about one year ago and so far sub-microsecond timing residuals have been achieved for more than half of these pulsars. New receiver and software systems are being developed with the aim of reducing these residuals to the level believed necessary for a positive detection of gravitational waves.

 

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astro-ph new abstracts, Mon, 17 Apr 06 00:00:09 GMT
0604318 -- 0604335 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604318 [abs, ps, pdf, other] :
Title: Chandra X-Ray Observations of Nineteen Millisecond Pulsars in the Globular Cluster 47 Tucanae
Authors: Slavko Bogdanov, Jonathan E. Grindlay, Craig O. Heinke, Fernando Camilo, Paulo C. C. Freire, Werner Becker
Comments: 13 pages, 6 figures, accepted for publication in the Astrophysical Journal

We present spectral and long-timescale variability analyses of \textit{Chandra} ACIS-S observations of the 19 millisecond pulsars (MSPs) with precisely known positions in the globular cluster 47 Tucanae. The X-ray emission of the majority of these MSPs is well described by a thermal (blackbody or neutron star hydrogen atmosphere) spectrum with a temperature $T_{\rm eff}\sim(1-3)\times10^6$ K, emission radius $R_{\rm eff}\sim0.1-3$ km, and luminosity $L_{X}\sim10^{30-31}$ ergs s$^{-1}$. For several MSPs, there is indication that a second thermal component is required, similar to what is seen in some nearby field MSPs. The radio-eclipsing binary MSPs 47 Tuc J, O, and W show a significant non-thermal component, with photon index $\Gamma\sim 1-1.5$, which may originate in an shock formed due to interaction between the relativistic pulsar wind and matter from the stellar companion. We re-examine the X-ray--spindown luminosity relation ($L_{X}-\dot{E}$) and find that due to the large uncertainties in both parameters the result is consistent with both the linear $L_{X}-\dot{E}$ relation and the flatter $L_X\propto\dot{E}^{0.5}$ predicted by polar cap heating models. In terms of X-ray properties, we find no clear systematic differences between MSPs in globular clusters and in the field of the Galaxy.

 

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astro-ph new abstracts, Tue, 18 Apr 06 00:00:08 GMT
0604336 -- 0604357 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604345 [abs, ps, pdf, other] :
Title: Accretion-powered Millisecond Pulsar Outbursts
Authors: Duncan K. Galloway
Comments: 5 pages, 2 figures, to be published in: "The Transient Milky Way: a perspective for MIRAX", eds. F. D'Amico, J. Braga & R. Rothschild, AIP Conf. Proc

The population of accretion-powered millisecond pulsars has grown rapidly over the last four years, with the discovery of six new examples to bring the total sample to seven. While the first six discovered are transients active for a few weeks every two or more years, the most recently-discovered source HETE J1900.1-2455, has been active for more than 8 months. We summarise the transient behaviour of the population to estimate long-term time-averaged fluxes, and equate these fluxes to the expected mass transfer rate driven by gravitational radiation in order to constrain the distances. We also estimate an upper limit of 6 kpc to the distance of IGR J00291+5934 based on the non-detection of bursts from this source.

 

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astro-ph/0512176 [abs, ps, pdf, other] :
Title: Evidence of a Change in the Long Term Spin-down Rate of the X-ray Pulsar 4U 1907+09
Authors: A. Baykal (1), S.C. Inam (2), E. Beklen (1,3) ((1) Physics Department, Middle East Technical University, Ankara, Turkey (2) Department of Electrical and Electronics Engineering, Baskent University, Ankara, Turkey (3) Physics Department, Suleyman Demirel University, Isparta, Turkey)
Comments: Revised version. Accepted for publication in MNRAS
Note: replaced with revised version Mon, 17 Apr 2006 19:40:11 GMT (37kb)
 

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astro-ph new abstracts, Wed, 19 Apr 06 00:00:10 GMT
0604358 -- 0604387 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604364 [abs, ps, pdf, other] :
Title: Force-Free Electrodynamics of Pulsars
Authors: Andrei Gruzinov (CCPP, NYU)
Comments: 9 pages, 5 figures

We show that FFE (Force-Free Electrodynamics) describes pulsar magnetospheres -- even when radiation and particle wind power are comparable to the spin-down power. At the same time, we show that FFE is insufficient for calculating pulsar magnetospheres. This is because FFE admits a large family of stationary solutions with different currents flowing in the closed line region. To choose the actual solution one needs a model of current generation which goes beyond pure FFE.
We calculate several FFE magnetospheres for the aligned rotator. The Poynting power of these solutions fills the range $c^{-3}\mu ^2\Omega^4~< ~L~ <~ 0.67 c^{-3}\mu ^2\Omega^4(c/\Omega R_s)^2$, for angular velocity $\Omega$ and magnetic field which is a pure dipole $\mu$ on the surface of the star of radius $R_s$.
Anomalous braking indices of young pulsars might be explained by currents flowing in the closed-line region.

 
astro-ph/0604368 [abs, ps, pdf, other] :
Title: What is special about HBRPs
Authors: N. Vranesevic, D. B. Melrose, R. N. Manchester
Comments: 6 pages, 5 figures, in press ChJAA

The Parkes Multibeam Survey led to the identification ofa number of long-period radio pulsars with magnetic field well above the quantum critical field of 4.4 times 10 to 13 G (defined as high magnetic field radio pulsars - HBRPs). Traditional pulsar emission theories postulate that radio emission is suppressed above this critical field. The aim of thisproject is to understand emission properties of HBRPs.

 
astro-ph/0604379 [abs, ps, pdf, other] :
Title: Flux predictions of high-energy neutrinos from pulsars
Authors: Bennett Link (Montana State University, Bozeman, USA), Fiorella Burgio (INFN Sezione di Catania, Italy)
Comments: 6 pages, 3 figures

Young, rapidly rotating neutron stars could accelerate ions from their surface to energies of $\sim 1$ PeV. If protons reach such energies, they will produce pions (with low probability) through resonant scattering with x-rays from the stellar surface. The pions subsequently decay to produce muon neutrinos. Here we calculate the energy spectrum of muon neutrinos, and estimate the event rates at Earth. The spectrum consists of a sharp rise at $\sim 50$ TeV, corresponding to the onset of the resonance, above which the flux drops with neutrino energy as $\epsilon_\nu^{-2}$ up to an upper-energy cut-off that is determined by either kinematics or by the maximum energy to which protons are accelerated. We estimate event rates as high as 10-100 km^${-2}$ yr$^{-1}$ from some candidates, a flux that would be easily detected by IceCube. Lack of detection would allow constraints on the energetics of the poorly-understood pulsar magnetosphere.

 
astro-ph/0604386 [abs, ps, pdf, other] :
Title: Magnetars' Giant Flares: the case of SGR 1806-20
Authors: Nanda Rea (SRON - Netherlands Institute for Space Research), et al
Comments: 6 pages, 2 figures; accepted for publication in the Chinese Journal for Astronomy and Astrophysics (Vulcano conference - 2005)

We first review on the peculiar characteristics of the bursting and flaring activity of the Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars. We then report on the properties of the SGR 1806-20's Giant Flare occurred on 2004 December 27th, with particular interest on the pre and post flare intensity/hardness correlated variability. We show that these findings are consistent with the picture of a twisted internal magnetic field which stresses the star solid crust that finally cracks causing the giant flare (and the observed torsional oscillations). This crustal fracturing is accompanied by a simplification of the external magnetic field with a (partial) untwisting of the magnetosphere.

 

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astro-ph new abstracts, Thu, 20 Apr 06 00:00:09 GMT
0604388 -- 0604413 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604389 [abs, ps, pdf, other] :
Title: Relativistic ejecta from XRF 060218 and the complete census of cosmic explosions
Authors: A. M. Soderberg, S. R. Kulkarni, E. Nakar, E. Berger, D. B. Fox, D. A. Frail, A. Gal-Yam, R. Sari, S. B. Cenko, M. Kasliwal, P. B. Cameron, R. A. Chevalier, T. Piran, P. A. Price, B. P. Schmidt, G. Pooley, D.-S. Moon, B. E. Penprase, N. Gehrels, J. A. Nousek, D. N. Burrows, S. E. Perrson, P. J. McCarthy
Comments: Submitted to Nature (13 pages, 3 figures)

Over the last decade, long-duration gamma-ray bursts (GRBs) and X-ray flashes (XRFs) have been revealed to be a rare variety of Type Ibc supernova (SN). While all these events result from the death of massive stars, the electromagnetic luminosities of GRBs and XRFs exceed those of ordinary Type Ibc SNe by many orders of magnitude. The essential physical process that causes a dying star to produce a GRB or XRF, and not just an SN, remains the crucial open question. Here we present radio and X-ray observations of XRF 060218 (associated with SN 2006aj), the second nearest GRB identified to-date, which allow us to measure its total energy and place it in the larger context of cosmic explosions. We show that this event is 100 times less energetic but ten times more common than cosmological GRBs. Moreover, it is distinguished from ordinary Type Ibc SNe by the presence of 10^48 erg of mildly-relativistic ejecta, along with a central engine which produces X-rays for weeks after the explosion. This suggests that the presence of relativistic ejecta is the key physical distinction between GRBs/XRFs and ordinary SNe, while the nature of the central engine (black hole or magnetar) may distinguish cosmological GRBs from the low-luminosity and spherical events like XRF 060218.

 
astro-ph/0604392 [abs, ps, pdf, other] :
Title: Arecibo and the ALFA Pulsar Survey
Authors: J. van Leeuwen, J. M. Cordes, D. R. Lorimer, P. C. C. Freire, F. Camilo, I. H. Stairs, D. J. Nice, D. J. Champion, R. Ramachandran, A. J. Faulkner, A. G. Lyne, S. M. Ransom, Z. Arzoumanian, R. N. Manchester, M. A. McLaughlin, J. W. T. Hessels, W. Vlemmings, A. A. Deshpande, N. D. R. Bhat, S. Chatterjee, J. L. Han, B. M. Gaensler, L. Kasian, J. S. Deneva, B. Reid, T. J. W. Lazio, V. M. Kaspi, F. Crawford, A. N. Lommen, D. C. Backer, M. Kramer, B. W. Stappers, G. B. Hobbs, A. Possenti, N. D'Amico, C.-A. Faucher-Giguère, M. Burgay
Comments: 8 pages, invited review for the Hanas Pulsar Symposium, ChJAA in press

The recently started Arecibo L-band Feed Array (ALFA) pulsar survey aims to find ~1000 new pulsars. Due to its high time and frequency resolution the survey is especially sensitive to millisecond pulsars, which have the potential to test gravitational theories, detect gravitational waves and probe the neutron-star equation of state. Here we report the results of our preliminary analysis: in the first months we have discovered 21 new pulsars. One of these, PSR J1906+0746, is a young 144-ms pulsar in a highly relativistic 3.98-hr low-eccentricity orbit. The 2.61 +- 0.02 solar-mass system is expected to coalesce in ~300 Myr and contributes significantly to the computed cosmic inspiral rate of compact binary systems.

 
astro-ph/0604404 [abs, ps, pdf, other] :
Title: High frequency observations of southern pulsars
Authors: {Simon Johnston, Aris Karastergiou, Kyle Willett
Comments: Accepted by MNRAS. 13 pages. 6 figures

We present polarization data for 32 mainly southern pulsars at 8.4 GHz. The observations show that the polarization fraction is low in most pulsars at this frequency except for the young, energetic pulsars which continue to show polarization fractions in excess of 60 per cent. All the pulsars in the sample show evidence for conal emission with only one third also showing core emission. Many profiles are asymmetric, with either the leading or the trailing part of cone not detectable. Somewhat surprisingly, the asymmetric profiles tend to be more polarized than the symmetrical profiles. Little or no pulse narrowing is seen between 1 and 8.4 GHz. The spectral behaviour of the orthogonal polarization modes and radius to frequency mapping can likely account for much of the observational phenomenology. Highly polarized components may orginate from higher in the magnetosphere than unpolarized components.

 
astro-ph/0604411 [abs, ps, pdf, other] :
Title: Precision Measurement of Optical Pulsation using a Cherenkov Telescope
Authors: J. A. Hinton, G. Hermann, P. Kroetz, S. Funk
Comments: Accepted for publication in Astroparticle Physics, 14 pages, 7 figures

During 2003, a camera designed to measure the optical pulsations of pulsars was installed on a telescope of the H.E.S.S. array. The array is designed for gamma-ray astronomy in the ~100 GeV - 100 TeV energy regime. The aims of this exercise were two-fold: to prove the pulsar timing capabilities of H.E.S.S. on all relevant time-scales, and to explore the possibility of performing sensitive optical pulsar measurements using the ~100 m^2 mirror of a Cherenkov telescope. Measurements of the Crab pulsar with this instrument demonstrate an order of magnitude sensitivity improvement over previous attempts using Cherenkov telescopes. Here we describe the design and performance of the system and discuss design considerations for future instruments of this type.

 

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astro-ph new abstracts, Fri, 21 Apr 06 00:00:09 GMT
0604414 -- 0604440 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604421 [abs, ps, pdf, other] :
Title: Discovery of 14 radio pulsars in a survey of the Magellanic Clouds
Authors: R N Manchester, G Fan, A G Lyne, V M Kaspi
Comments: In press, ApJ

A systematic survey of the Large and Small Magellanic Clouds for radio pulsars using the Parkes radio telescope and the 20-cm multibeam receiver has resulted in the discovery of 14 pulsars and the redetection of five of the eight previously known spin-powered pulsars believed to lie in the Magellanic Clouds. Of the 14 new discoveries, 12 are believed to lie within Clouds, three in the Small Cloud and nine in the Large Cloud, bringing the total number of known spin-powered pulsars in the Clouds to 20. Averaged over all positions within the survey area, the survey had a limiting flux density of about 0.12 mJy. Observed dispersion measures suggest that the mean free electron density in the Magellanic Clouds is similar to that in the disk of our Galaxy. The observed radio luminosities have little or no dependence on pulsar period or characteristic age and the differential luminosity function is consistent with a power-law slope of -1 as is observed for Galactic pulsars.

 
astro-ph/0604422 [abs, ps, pdf, other] :
Title: Strangeness in Neutron Stars
Authors: Fridolin Weber, Alexander Ho, Rodrigo P. Negreiros, Philip Rosenfield (San Diego State University)
Comments: 16 pages, 5 figures, 3 tables; Accepted for publication in the Proceedings of the International Workshop on Astronomy and Relativistic Astrophysics (IWARA) 2005, Int. J. Mod. Phys. D

It is generally agreed on that the tremendous densities reached in the centers of neutron stars provide a high-pressure environment in which several intriguing particles processes may compete with each other. These range from the generation of hyperons to quark deconfinement to the formation of kaon condensates and H-matter. There are theoretical suggestions of even more exotic processes inside neutron stars, such as the formation of absolutely stable strange quark matter. In the latter event, neutron stars would be largely composed of strange quark matter possibly enveloped in a thin nuclear crust. This paper gives a brief overview of these striking physical possibilities with an emphasis on the role played by strangeness in neutron star matter, which constitutes compressed baryonic matter at ultra-high baryon number density but low temperature which is no accessible to relativistic heavy ion collision experiments.

 

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astro-ph new abstracts, Mon, 24 Apr 06 00:00:10 GMT
0604441 -- 0604476 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604458 [abs, ps, pdf, other] :
Title: The Constraints on the Relic Gravitational Waves By the Current and Future Observations
Authors: Wen Zhao, Yang Zhang
Comments: 13 pages, 4 figures

In this paper, by solving the inflationary flow equations, we study the constraints on the relic gravitational waves (RGW) from the observations at large scale, i.e. cosmic microwave background radiation (CMB) and large scale structure (LSS), and those at small scale, i.e. the pulsar timing, LIGO, and big bang nucleosynthesis (BBN). We find that the current constraints on the RGW from small scale are too loose to be ignored, but which from large scale is relatively tight. Under the current constraints, and considering the the damping effect of neutrino and accelerating expansion of the Universe, we also study the detection ability on RGW of the future observation projects at large scale. i.e. Planck, CMBPol, and those at small scale, i.e. advanced LIGO, LISA, ASTROD, BBO and DECIGO. We find the observations from CMB observations have larger probability to detect RGW ($>50%$). But the laser interferometers have relatively smaller probability for detection: the BBO and Ultimate DECIGO project are the possible ways to detect RGW at small scale ($\sim3.48%$ and $\sim26.49%$), but the Advanced LIGO, LISA and ASTROD have little change to detect them.

 
astro-ph/0604466 [abs, ps, pdf, other] :
Title: Discovery of a 3.6-hr Eclipsing Luminous X-Ray Binary in the Galaxy NGC 4214
Authors: Kajal K. Ghosh, Saul Rappaport, Allyn F. Tennant, Douglas A. Swartz, David Pooley, N. Madhusudhan
Comments: 7 pages, submitted to ApJ

We report the discovery of an eclipsing X-ray binary with a 3.62-hr period within 24'' of the center of the dwarf starburst galaxy NGC 4214. The orbital period places interesting constraints on the nature of the binary, and allows for a few very different interpretations. The most likely possibility is that the source lies within NGC 4214 and has an X-ray luminosity of up to 0.7e39 erg/s or just below the ultraluminous X-ray source range. In this case the binary may well be comprised of a naked He-burning donor star with a neutron-star accretor, though a stellar-mass black-hole accretor cannot be completely excluded. There is no obvious evidence for a strong stellar wind in the X-ray orbital light curve that would be expected from a massive He star; thus, the mass of the He star should be < 3-4 solar masses. If correct, this would represent a new class of very luminous X-ray binary -- perhaps related to Cyg X-3. Other less likely possibilities include a conventional low-mass X-ray binary that somehow manages to produce such a high X-ray luminosity and is apparently persistent over an interval of years; or a foreground AM Her binary of much lower luminosity that fortuitously lies in the direction of NGC 4214. Any model for this system must accommodate the lack of an optical counterpart down to a limiting magnitude of 22.6 in the visible.

 

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astro-ph/0601530 [abs, ps, pdf, other] :
Title: A Braking Index for the Young, High-Magnetic-Field, Rotation-Powered Pulsar in Kes 75
Authors: Margaret A. Livingstone, Victoria M. Kaspi, E. V. Gotthelf, Lucien Kuiper
Comments: Includes major changes to analysis. Updated postion used for the pulsar which significantly changed the result and conclusions of the paper. 21 pages, 6 Figures. ApJ submitted
Note: replaced with revised version Fri, 21 Apr 2006 19:38:51 GMT (42kb)
 

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astro-ph new abstracts, Tue, 25 Apr 06 00:00:09 GMT
0604477 -- 0604501 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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astro-ph/0603440 [abs, ps, pdf, other] :
Title: The redshift distribution of short gamma-ray bursts from dynamically formed neutron star binaries
Authors: Clovis Hopman, Dafne Guetta, Eli Waxman, Simon Portegies Zwart
Comments: Accepted to ApJL; Minor revisions
Note: replaced with revised version Mon, 24 Apr 2006 12:23:39 GMT (37kb)
 

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Astrophysics


astro-ph new abstracts, Wed, 26 Apr 06 00:00:09 GMT
0604502 -- 0604526 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604513 [abs, ps, pdf, other] :
Title: Polarised views of the drifting subpulse phenomenon
Authors: R. T. Edwards
Comments: 7 pages, 2 figures, to appear in Chin. J. Astron. Astrophys, proceedings of 2005 Lake Hanas International Pulsar Symposium

I review recent results concerning the shape of drifting subpulse patterns, and the relationship to model predictions. While a variety of theoretical models exist for drifting subpulses, observers typically think in terms of a spatio-temporal model of circulating beamlets. Assuming the model is correct, geometric parameters have been inferred and animated "maps" of the beam have been made. However, the model makes very specific predictions about the curvature of the drift bands that have remained largely untested. Work so far in this area indicates that drift bands tend not to follow the prediction, and in some cases discontinuities are seen that are suggestive of the superposition of out of phase drift patterns. Recent polarimetric observations also show that the drift patterns in the two orthogonal polarisation modes are offset in phase. In one case the pattern in one of the modes shows a discontinuity suggesting no less than three superposed, out-of-phase drift patterns! I advise caution in the interpretation of observational data in the context of overly simplistic models.

 

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astro-ph new abstracts, Thu, 27 Apr 06 00:00:08 GMT
0604527 -- 0604550 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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astro-ph new abstracts, Fri, 28 Apr 06 00:00:09 GMT
0604551 -- 0604580 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604559 [abs, ps, pdf, other] :
Title: Millisecond Pulsar Emission Altitude from Relativistic Phase Shift: PSR J0437-4715
Authors: R. T. Gangadhara, R. M. C. Thomas (Indian Institute of Astrophysics)
Comments: 12 pages, 2 figures

We have analyzed the profile of the millisecond pulsar PSR J0437-4715 at 1440 MHz by fitting the Gaussians to pulse components, and identified its 11 emission components. We propose that they form a emission beam with 5 nested cones centered on the core. Using the phase location of component peaks, we have estimated the aberration--retardation (A/R) phase shift. Due to A/R phase shift, the centroid of intensity profile and the inflection point of polarization angle swing are symmetrically shifted in the opposite directions with respect to the meridional plane, which is defined by the rotation and magnetic axes. By recognizing this fact, we have been able to locate the phase location of meridional plane and estimate the absolute altitude of emission of core and conal components relative to the neutron star center. Using the more exact expression for phase shift given recently by Gangadhara (2005), we find that the radio emission comes from a range of altitude starting from the core at 7% of light cylinder radius to outer most cone at 30%.

 
astro-ph/0604562 [abs, ps, pdf, other] :
Title: Short Gamma-Ray Bursts from Binary Neutron Star Mergers
Authors: Roland Oechslin, Thomas Janka
Comments: 6 pages, 2 figures, Proceedings of the Albert Einstein Century International Conference, Paris, France, 2005, edited by Jean-Michel Alimi and Andre Fuzfa

We present the results from new relativistic hydrodynamic simulations of binary neutron star mergers using realistic non-zero temperature equations of state. We vary several unknown parameters in the system such as the neutron star (NS) masses, their spins and the nuclear equation of state. The results are then investigated with special focus on the post-merger torus-remnant system. Observational implications on the Gamma-ray burst (GRB) energetics are discussed and compared with recent observations.

 

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astro-ph new abstracts, Mon, 1 May 06 00:00:12 GMT
0604581 -- 0604619 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604605 [abs, ps, pdf, other] :
Title: A periodically active pulsar giving insight into magnetospheric physics
Authors: M. Kramer, A.G. Lyne, J.T. O'Brien, C.A. Jordan, D.R. Lorimer (Jodrell Bank Observatory, University of Manchester, Macclesfield, SK11 9DL, UK)
Comments: 12 pages, 2 figures
Journal-ref: Published in Science, 2006, Vol. 312, 549-551

PSR B1931+24 (J1933+2421) behaves as an ordinary isolated radio pulsar during active phases that are 5-10 days long. However, the radio emission switches off in less than 10 seconds and remains undetectable for the next 25-35 days, then it switches on again. This pattern repeats quasi-periodically. The origin of this behaviour is unclear. Even more remarkably, the pulsar rotation slows down 50% faster when it is on than when it is off. This indicates a massive increase in magnetospheric currents when the pulsar switches on, proving that pulsar wind plays a substantial role in pulsar spin-down. This allows us, for the first time, to estimate the currents in a pulsar magnetospheric during the occurrence of radio emission.

 

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astro-ph new abstracts, Tue, 2 May 06 00:00:11 GMT
0605001 -- 0605035 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605001 [abs, ps, pdf, other] :
Title: A Two-Zone Model for Type I X-ray Bursts on Accreting Neutron Stars
Authors: Randall L. Cooper, Ramesh Narayan
Comments: 12 pages, 7 figures, expanded version resubmitted to ApJ

We construct a two-zone model to describe hydrogen and helium burning on the surface of an accreting neutron star and use it to study the triggering of type I X-ray bursts. Although highly simplified, the model reproduces all of the bursting regimes seen in the more complete global linear stability analysis of Narayan & Heyl (2003), including the regime of delayed mixed bursts. The results are also consistent with observations of type I X-ray bursts. At accretion rates <~ 10% of the Eddingtion limit, thermonuclear helium burning via the well-known thin-shell thermal instability triggers bursts. As the accretion rate increases, however, the trigger mechanism evolves from the fast thermal instability to a slowly growing overstability involving both hydrogen and helium burning. The competition between nuclear heating via the beta-limited CNO cycle as well as the triple-alpha process and radiative cooling via photon diffusion and emission drives oscillations with a period approximately equal to the hydrogen-burning timescale. If these oscillations grow, the gradually rising temperature at the base of the helium layer eventually provokes a thin-shell thermal instability and hence a delayed mixed burst. This overstability closely resembles the delayed mixed bursts of Narayan & Heyl. For accretion rates >~ 25% of the Eddington limit, there is no instability or overstability, and there are no bursts.

 
astro-ph/0605007 [abs, ps, pdf, other] :
Title: Predicting the Starquakes in PSR J0537-6910
Authors: John Middleditch, Francis E. Marshall, Q. Daniel Wang, Eric V. Gotthelf, William Zhang
Comments: 58 pages, 14 figures. Submitted to The Astrophysical Journal

We report the results of more than seven years of monitoring of PSR J0537-6910, the 16 ms pulsar in the Large Magellanic Cloud, using data acquired with the Rossi X-ray Timing Explorer. During this campaign the pulsar experienced 21 sudden increases in frequency (``glitches'' -- 20 with increases of at least 8 uHz) amounting to a total gain of over six parts per million of rotation frequency superposed on its gradual spindown of d(nu)/d(t) = -2e-10 Hz/s. The time interval from one glitch to the next obeys a strong linear correlation to the amplitude of the first glitch, with a mean slope of about 400 days per part per million (6.5 days per uHz), such that these intervals can be predicted to within a few days, an accuracy which has never before been seen in any other pulsar. There appears to be an upper limit of ~40 uHz for the size of glitches in_all_ pulsars, with the 1999 April glitch of J0537 as the largest so far. The change in the spindown of J0537 across the glitches, Delta(d(nu)/d(t)), appears to have the same hard lower limit of -1.5e-13 Hz/s, as, again, that observed in all other pulsars. The spindown continues to increase in the long term, d(d(nu)/d(t))/d(t) = -1e-21 Hz/s/s, and thus the timing age of J0537 (-0.5 nu d(nu)/d(t)) continues to decrease at a rate of nearly one year every year, consistent with movement of its magnetic moment away from its rotational axis by one radian every 10,000 years, or about one meter per year. J0537 was likely to have been born as a nearly-aligned rotator spinning at 75-80 Hz, with a |d(nu)/d(t)| considerably smaller than its current value of 2e-10 Hz/s. The pulse profile of J0537 consists of a single pulse which is found to be flat at its peak for at least 0.02 cycles.

 
astro-ph/0605024 [abs, ps, pdf, other] :
Title: Broad band X-ray spectrum of KS 1947+300 with BeppoSAX
Authors: S. Naik (1,2), P. J. Callanan (2), B. Paul (3), T. Dotani (1) ((1): The Institute of Space and Astronautical Science, Sagamihara, Japan, (2): University College Cork, Ireland, (3): Tata Institute of Fundamental Research, Homi Bhabha road, Mumbai, India)
Comments: 17 pages, 5 figures, Accepted for publication in The Astrophysical Journal

We present results obtained from three BeppoSAX observations of the accretion-powered transient X-ray pulsar KS 1947+300 carried out during the declining phase of its 2000 November -- 2001 June outburst. A detailed spectral study of KS 1947+300 across a wide X-ray band (0.1--100.0 keV) is attempted for the first time here. Timing analysis of the data clearly shows a 18.7 s pulsation in the X-ray light curves in the above energy band. The pulse profile of KS 1947+300 is characterized by a broad peak with sharp rise followed by a narrow dip. The dip in the pulse profile shows a very strong energy dependence. Broad-band pulse-phase-averaged spectroscopy obtained with three of the BeppoSAX instruments shows that the energy spectrum in the 0.1--100 keV energy band has three components, a Comptonized component, a ~0.6 keV blackbody component, and a narrow and weak iron emission line at 6.7 keV with a low column density of material in the line of sight. We place an upper limit on the equivalent width of the iron K_\alpha line at 6.4 keV of ~13 eV (for a width of 100 eV). Assuming a spherical blackbody emitting region and the distance of the source to be 10 kpc, the radius of the emitting region is found to be in the range of 14--22 km, which rules out the inner accretion disk as the soft X-ray emitting region.

 
astro-ph/0605028 [abs, ps, pdf, other] :
Title: Searching for sub-millisecond pulsars: A theoretical view
Authors: Renxin Xu (PKU)
Comments: 9 pages, in: ICGA7 Proceedings

Sub-millisecond pulsars should be triaxial (Jacobi ellipsoids), which may not spin down to super-millisecond periods via gravitation wave radiation during their lifetimes if they are extremely low mass bare strange quark stars. It is addressed that the spindown of sub-millisecond pulsars would be torqued dominantly by gravitational wave radiation (with braking index n ~ 5). The radio luminosity of sub-millisecond pulsars could be high enough to be detected in advanced radio telescopes. Sub-millisecond pulsars, if detected, should be very likely quark stars with low masses and/or small equatorial ellipticities.

 
astro-ph/0605034 [abs, ps, pdf, other] :
Title: Parameter estimation of binary compact objects with LISA: Effects of time-delay interferometry, Doppler modulation, and frequency evolution
Authors: Aaron Rogan, Sukanta Bose (Washington State University)
Comments: 21 pages, with 37 figures; uses revtex4

We study the limits on how accurately LISA will be able to estimate the parameters of low-mass compact binaries, comprising white dwarfs (WDs), neutron stars (NSs) or black holes (BHs), while battling the amplitude, frequency, and phase modulations of their signals. We show that Doppler-phase modulation aids sky-position resolution in every direction, improving it especially for sources near the poles of the ecliptic coordinate system. However, it increases the frequency estimation error by a factor of over 1.5 at any sky position, and at f=3 mHz. Since accounting for Doppler-phase modulation is absolutely essential at all LISA frequencies and for all chirp masses in order to avoid a fractional loss of signal-to-noise ratio (SNR) of more than 30%, LISA science will be simultaneously aided and limited by it. For a source with f > 2.5mHz, searching for its frequency evolution for 1 year worsens the error in the frequency estimation by a factor of over 3.5 relative to that of sources with f < 1mHz. Increasing the integration time to 2 years reduces this relative error factor to about 2, which still adversely affects the resolvability of the galactic binary confusion noise. Thus, unless the mission lifetime is increased several folds, the only other recourse available for reducing the errors is to exclude the chirp parameter from ones search templates. Doing so improves the SNR-normalized parameter estimates. This works for the lightest binaries since their SNR itself does not suffer from that exclusion. However, for binaries involving a neutron star, a black hole, or both, the SNR and, therefore, the parameter estimation, can take a significant hit, thus, severely affecting the ability to resolve such members in LISA's confusion noise.

 

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gr-qc/0604123 [abs, ps, pdf, other] :
Title: Gravitational radiation from nonaxisymmetric spherical Couette flow in a neutron star
Authors: C. Peralta (1,2), A. Melatos (1), M. Giacobello (3), A. Ooi (3)
Comments: (1) School of Physics, University of Melbourne, Parkville, VIC 3010, Australia. (2) Departamento de Fisica, Escuela de Ciencias,Universidad de Oriente, Cumana, Venezuela, (3) Department of Mechanical Engineering, University of Melbourne, Parkville, VIC 3010, Australia. Accepted for publication in The Astrophysical Journal Letters

The gravitational wave signal generated by global, nonaxisymmetric shear flows in a neutron star is calculated numerically by integrating the incompressible Navier--Stokes equation in a spherical, differentially rotating shell. At Reynolds numbers $\Rey \gsim 3 \times 10^{3}$, the laminar Stokes flow is unstable and helical, oscillating Taylor--G\"ortler vortices develop. The gravitational wave strain generated by the resulting kinetic-energy fluctuations is computed in both $+$ and $\times$ polarizations as a function of time. It is found that the signal-to-noise ratio for a coherent, $10^{8}$-{\rm s} integration with LIGO II scales as $ 6.5 (\Omega_*/10^{4} {\rm rad} {\rm s}^{-1})^{7/2}$ for a star at 1 {\rm kpc} with angular velocity $\Omega_*$. This should be regarded as a lower limit: it excludes pressure fluctuations, herringbone flows, Stuart vortices, and fully developed turbulence (for $\Rey \gsim 10^{6}$).

 

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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0510229 [abs, ps, pdf, other] :
Title: Multi-Dimensional Radiation/Hydrodynamic Simulations of Protoneutron Star Convection
Authors: L. Dessart, A. Burrows, E. Livne, C.D. Ott
Comments: 19 pages, 18 figures, in emulateapj format, revised version including referee's comments and a new high-resolution simulation, accepted to ApJ; Paper with high-resolution images and movies available at this http URL
Note: replaced with revised version Mon, 1 May 2006 14:36:53 GMT (1071kb)
 
astro-ph/0601603 [abs, ps, pdf, other] :
Title: Multi-Dimensional Simulations of the Accretion-Induced Collapse of White Dwarfs to Neutron Stars
Authors: Luc Dessart, Adam Burrows, Christian Ott, Eli Livne, Sung-Chul Yoon, Norbert Langer
Comments: 25 pages, 19 figures, accpeted to ApJ, high resolution of the paper and movies available at this http URL
Note: replaced with revised version Mon, 1 May 2006 18:10:08 GMT (3389kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 3 May 06 00:00:10 GMT
0605036 -- 0605071 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605051 [abs, ps, pdf, other] :
Title: Spitzer Reveals Infrared Optically-Thin Synchrotron Emission from the Compact Jet of the Neutron Star X-Ray Binary 4U 0614+091
Authors: S. Migliari (UCSD), J.A. Tomsick (UCSD), T.J. Maccarone (Southampton), E. Gallo (UCSB), R.P. Fender (Southampton), G. Nelemans (Nijmegen), D.M. Russell (Southampton)
Comments: Accepted for publication in ApJ Letters

Spitzer observations of the neutron star (ultra-compact) X-ray binary (XRB) 4U 0614+091 with the Infrared Array Camera reveal emission of non-thermal origin in the range 3.5-8 um. The mid-infrared spectrum is well fit by a power law with spectral index of alpha=-0.57+/-0.04 (where the flux density is F_nu \propto nu^(alpha)). Given the ultra-compact nature of the binary system, we exclude the possibility that either the companion star or the accretion disk can be the origin of the observed emission. These observations represent the first spectral evidence for a compact jet in a low-luminosity neutron star XRB and furthermore of the presence, already observed in two black hole (BH) XRBs, of a `break' in the synchrotron spectrum of such compact jets. We can derive a firm upper limit on the break frequency of the spectrum of nu_thin=3.7x10^(13) Hz, which is lower than that observed in BH XRBs by at least a factor of 10. Assuming a high-energy cooling cutoff at ~1 keV, we estimate a total (integrated up to X-rays) jet power to X-ray bolometric luminosity ratio of \~5%, much lower than that inferred in BHs.

 
astro-ph/0605055 [abs, ps, pdf, other] :
Title: Chandra Observation of the Persistent Emission from the Dipping Source XB 1916-053
Authors: R. Iaria, T. Di Salvo, G. Lavagetto, N. R. Robba, L. Burderi
Comments: 20 pages, 10 figures, submitted to ApJ on 2005-09-22, accepted by ApJ on 2006-05-02

We present the results of a 50 ks long Chandra observation of the dipping source XB 1916-053. During the observation two X-ray bursts occurred and the dips were not present at each orbital period. From the zero-order image we estimate the precise X-ray coordinates of the source with a 90% uncertainty of 0.6''. In this work we focus on the spectral study of discrete absorption features, during the persistent emission, using the High Energy Transmission Grating Spectrometer on board the Chandra satellite. We detect, for the first time in the 1st-order spectra of XB 1916-053, absorption lines associated to Ne X, Mg XII, Si XIV, and S XVI, and confirm the presence of the Fe XXV and Fe XXVI absorption lines with a larger accuracy with respect to the previous XMM EPIC pn observation. Assuming that the line widths are due to a bulk motion or a turbulence associated to the coronal activity, we estimate that the lines are produced in a photoionized absorber distant from the neutron star 4 x 10^{10} cm, near the disk edge.

 
astro-ph/0605059 [abs, ps, pdf, other] :
Title: The Abundances of Light Neutron-Capture Elements in Planetary Nebulae
Authors: N. C. Sterling, Harriet L. Dinerstein (University of Texas at Austin)
Comments: 4 pages, 1 figure, to appear in IAU Symp. 234, "Planetary Nebulae in our Galaxy and Beyond", eds. M. J. Barlow and R. H. Mendez

We present preliminary results from a large-scale survey of the neutron(n)-capture elements Se and Kr in Galactic planetary nebulae (PNe). These elements may be produced in PN progenitors by s-process nucleosynthesis, and brought to the stellar envelope by third dredge-up (TDU). We have searched for [Kr III] 2.199 and [Se IV] 2.287 $\mu$m in 120 PNe, and detected one or both lines in 79 objects, for a detection rate of 66%. In order to determine abundances of Se and Kr, we have added these elements to the atomic database of the photoionization code CLOUDY, and constructed a large grid of models to derive corrections for unobserved ionization stages. Se and Kr are enriched in 73% of the PNe in which they have been detected, and exhibit a wide range of abundances, from roughly solar to enriched by a factor of 10 or more. These enrichments are interpreted as evidence for the operation of the s-process and TDU in the progenitor stars. In line with theoretical expectations, Kr is more strongly enhanced than Se, and the abundances of both elements are correlated with the carbon abundance. Kr and Se are strongly enhanced in Type I PNe, which may be evidence for the operation of the $^{22}$Ne neutron source in intermediate-mass AGB stars. These results constitute the first broad characterization of s-process enrichments in PNe as a population, and reveal the impact of low- and intermediate-mass stars on the chemical evolution of trans-iron elements in the Galaxy.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605028 [abs, ps, pdf, other] :
Title: Searching for sub-millisecond pulsars: A theoretical view
Authors: Renxin Xu (PKU)
Comments: 9 pages, in: ICGA7 Proceedings. Also in: this http URL
Note: replaced with revised version Tue, 2 May 2006 03:57:00 GMT (24kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 4 May 06 00:00:09 GMT
0605072 -- 0605104 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605086 [abs, ps, pdf, other] :
Title: Giant Pulses in Pulsar PSR J1752+2359
Authors: A. A. Ershov, A. D. Kuzmin
Comments: 5 pages, 4 figures, to appear in Chin. J. Astron. Astrophys, proceedings of The 2005 Lake Hanas International Pulsar Symposium

We report the detection of Giant Pulses (GPs) in the pulsar PSR J1752+2359. The energy of the strongest GP exceeds the energy of the average pulse by a factor of 200, in which it stands out from all known pulsars with GPs. PSR J1752+2359 as well as the previously detected PSR B0031-07 and PSR B1112+50, belongs to the first group of pulsars found to have GPs without a high magnetic field at the light cylinder.

 
astro-ph/0605087 [abs, ps, pdf, other] :
Title: Probing the Pulsar Wind Nebula of PSR B0355+54
Authors: Katherine E. McGowan (1,2), W. Tom Vestrand (3), Jamie A. Kennea (4), Silvia Zane (2), Mark Cropper (2), France A. Cordova (5) ((1) University of Southampton, (2) MSSL, (3) LANL, (4) PSU, (5) UC Riverside)
Comments: 9 pages (uses emulateapj.cls), 8 figures, 2 tables, accepted for publication in ApJ

We present XMM-Newton and Chandra X-ray observations of the middle-aged radio pulsar PSR B0355+54. Our X-ray observations reveal emission not only from the pulsar itself, but also from a compact diffuse component extending ~50'' in the opposite direction to the pulsar's proper motion. There is also evidence for the presence of fainter diffuse emission extending ~5' from the point source. The compact diffuse feature is well-fitted with a power-law, the index of which is consistent with the values found for other pulsar wind nebulae. The morphology of the diffuse component is similar to the ram-pressure confined pulsar wind nebulae detected for other sources. The X-ray emission from the pulsar itself is described well by a thermal plus power-law fit, with the thermal emission most likely originating in a hot polar cap.

 

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astro-ph new abstracts, Fri, 5 May 06 00:00:11 GMT
0605105 -- 0605134 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605106 [abs, ps, pdf, other] :
Title: EXO 0748-676 Rules out Soft Equations of State for Neutron Star Matter
Authors: F. Ozel (University of Arizona)
Comments: To appear in Nature, press embargo until publication

The interiors of neutron stars contain matter at very high densities, in a state that differs greatly from those found in the early universe or achieved at terrestrial experiments. Matter in these conditions can only be probed through astrophysical observations that measure the mass and radius of neutron stars with sufficient precision. Here I report for the first time a unique determination of the mass and radius of the neutron star EXO 0748-676, which appears to rule out all the soft equations of state of neutron star matter. If this object is typical, then condensates and unconfined quarks do not exist in the centers of neutron stars.

 
astro-ph/0605115 [abs, ps, pdf, other] :
Title: Neutron stars in globular clusters: formation and observational manifestations
Authors: A.G.Kuranov, K.A.Postnov
Comments: LATEX, 21 pages, 8 gif figures, Astronomy Letters, in press

Population synthesis is used to model the number of neutron stars in globular clusters that are observed as LMXBs and millisecond PSRs. The dynamical interaction between binary and single stars in a GC are assumed to take place with a permanently replenished "background" of single stars whose density distribution keeps track with the cluster evolution as a whole and evolution of single stars. We use the hypothesis (Podsiadlowski et al) that NS forming in binary systems from components with initial masses \sim 8-12 M_\odot during the electron-capture collapse of the degenerate O-Ne-Mg core do not acquire a high space velocities (kicks). The remaining NSs (i.e. from single stars with M>8 M_\odot or binary comonents with M>12 M_\odot) are assumed to be born with high kicks, as found from obsrevations of single pulsars (Hobbs et al. 2005). Under this assumption, a sizeable fraction of NSs remain in GCs (about 1000 NSs in a GC with a mass of 5\times 10^5 M_\odot). The number of ms PSRs formed in the cluster via accretion spin-up in binaries is then about 10, which is consistent with observations. Our modelling reproduces the observed shape of the X-ray luminosity function for accreting NSs in binaries with normal and degenerate components and the distribution of spin periods of ms PSRs in GCs under the assumption of accretion-driven magnetic field decay of NSs up to a bottom value of 10^8 G. The number of LMXBs and ms PSRs dynamically expelling from GCs is also calculated.

 
astro-ph/0605117 [abs, pdf] :
Title: A Neutron Star in F-sharp
Authors: Jonathan E. Grindlay
Comments: Invited Perspective for Science; 3 pages, 3 figures
Journal-ref: Science, 311, 1876 (2006)

In this short introductory commentary on the paper (Hessels et al 2006, Science, 311, 1901) reporting the discovery of the shortest spin period millisecond pulsar (MSP) Ter5-ad in the globular cluster Terzan 5, I also point out a new explanation for possible minimum spin periods, P, of MSPs without requiring gravitational radiation (or other) slow-down torques. If the accretion of matter required to spinup a MSP also reduces (buries) the neutron star (NS) magnetic field, B, as commonly believed, an inverse correlation between neutron star mass, M, and B is expected together with a positive correlation between P and B. Both are suggested for the 4 MSPs with NS mass measures reported (Latimer and Prakash 2004, Science, 304, 536) to have <~10% uncertainties. The correlations imply the Ter5-ad NS has ~2.5 Msun, B ~5 x 10^7 G and thus Pdot ~3 x 10^-21 s/s -- which can be tested when a timing solution is found. If confirmed, the highest spin frequency NSs do not pulse simply because their B fields are too low.

 
astro-ph/0605133 [abs, ps, pdf, other] :
Title: Compact X-ray Binaries in and out of Core Collapsed Globulars
Authors: Jonathan E. Grindlay
Comments: 12 pages, 6 figures, invited talk at COSPAR Colloquium on "Spectra and Timing of Compact X-ray Binaries", Mumbai, India (Jan. 2005), to be published in journal: Advances in Space Research (Elsevier)

We review new Chandra and HST observations of the core collapsed cluster NGC 6397 as a guide to understanding the compact binary (CB) populations in core collapse globulars. New cataclysmic variables (CVs) and main sequence chromospherically active binaries (ABs) have been identified, enabling a larger sample for comparison of the Lx, Fx/Fv and X-ray vs. optical color distributions. Comparison of the numbers of CBs with Lx >10^31 erg/s in 4 core collapse vs. 12 King model clusters reveals that the specific frequency Sx (number of CBs per unit cluster mass) is enhanced in core collapse clusters, even when normalized for their stellar encounter rate. Although core collapse is halted by the dynamical heating due to stellar (and binary) interaction with CBs in the core, we conclude that production of the hardest CBs -- especially CVs -- is enhanced during core collapse. NGC 6397 has its most luminous CVs nearest the cluster center, with two newly discovered very low luminosity (old, quiescent) CVs far from the core. The active binaries as well as neutron star systems (MSP and qLMXB) surround the central core. The overall CB population appears to be asymmetric about the cluster center, as in several other core collapse clusters observed with Chandra, suggesting still poorly-understood scattering processes.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0605018 [abs, ps, pdf, other] :
Title: Hydro-without-Hydro Framework for Simulations of Black Hole-Neutron Star Binaries
Authors: Carlos F. Sopuerta (1), Ulrich Sperhake (1 and 2), Pablo Laguna (1) ((1) CGWP, Penn State, (2) TPI, Jena)
Comments: 16 pages, 7 figures. To appear in the Classical and Quantum Gravity special issue on Numerical Relativity

We introduce a computational framework which avoids solving explicitly hydrodynamic equations and is suitable to study the pre-merger evolution of black hole-neutron star binary systems. The essence of the method consists of constructing a neutron star model with a black hole companion and freezing the internal degrees of freedom of the neutron star during the course of the evolution of the space-time geometry. We present the main ingredients of the framework, from the formulation of the problem to the appropriate computational techniques to study these binary systems. In addition, we present numerical results of the construction of initial data sets and evolutions that demonstrate the feasibility of this approach.

 

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Astrophysics


astro-ph new abstracts, Mon, 8 May 06 00:00:09 GMT
0605135 -- 0605169 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605137 [abs, ps, pdf, other] :
Title: Nucleosynthesis: Stellar and Solar Abundances and Atomic Data
Authors: John J. Cowan, James E. Lawler, Christopher Sneden, E. A. Den Hartog, Jason Collier
Comments: 8 pages, 2 figures, 1 table. To appear in the Proceedings of the NASA Laboratory Astrophysics Workshop in Las Vegas, NV (February 2006)

Abundance observations indicate the presence of often surprisingly large amounts of neutron capture (i.e., s- and r-process) elements in old Galactic halo and globular cluster stars. These observations provide insight into the nature of the earliest generations of stars in the Galaxy -- the progenitors of the halo stars -- responsible for neutron-capture synthesis. Comparisons of abundance trends can be used to understand the chemical evolution of the Galaxy and the nature of heavy element nucleosynthesis. In addition age determinations, based upon long-lived radioactive nuclei abundances, can now be obtained. These stellar abundance determinations depend critically upon atomic data. Improved laboratory transition probabilities have been recently obtained for a number of elements. These new gf values have been used to greatly refine the abundances of neutron-capture elemental abundances in the solar photosphere and in very metal-poor Galactic halo stars. The newly determined stellar abundances are surprisingly consistent with a (relative) Solar System r-process pattern, and are also consistent with abundance predictions expected from such neutron-capture nucleosynthesis.

 
astro-ph/0605145 [abs, ps, pdf, other] :
Title: Rocking the Lighthouse: Circumpulsar Asteroids and Radio Intermittency
Authors: J. M. Cordes, R. M. Shannon
Comments: 20 pages, 6 figures, submitted to ApJ

We propose that neutral, circumpulsar debris entering the light cylinder can account for many time-dependent pulsar phenomena that are otherwise difficult to explain. Neutral material avoids propeller ejection and injects sufficient charges -- after heating, evaporation, and ionization -- to alter current flows and pair-production and thus trigger, detune, or extinguish coherent emission. Relevant phenomena, with time scales from seconds to months, include nulls, rotating radio transients (RRATs), rapid changes in pulse profile (``mode changes''), variable subpulse drift rates, quasi-periodic bursts from B1931+24, and torque variations. Over the 10 Myr lifetime of a canonical pulsar with trillion-gauss surface magnetic field, less than a millionth of an Earth mass of material is needed to modulate the Goldreich-Julian current by 100%. Circumpulsar material originates from metal-rich, supernova fallback gas that aggregates into asteroids. Debris disks can inject sufficient material on time scales of interest, yet be too tenuous to form large planets detectable in pulse timing data. Asteroid migration results from collisions and the radiation-driven Yarkovsky and Poynting-Robertson effects. For B1931+24, an asteroid in a $\sim 40$~day elliptical orbit pollutes the magnetosphere stochastically through collisions with other debris. Injection is less likely for hot, young and highly magnetized pulsars or millisecond pulsars that pre-ionize any debris material well outside their small magnetospheres. Injection effects will therefore be most prominent in long-period, cooler pulsars, consistent with the distribution of relevant objects in perid and period derivative. A pulsar's spin history and its radiation-beam orientation may influence whether it displays nulling, RRATs and other effects.

 
astro-ph/0605154 [abs, ps, pdf, other] :
Title: Nature of giant pulses in radio pulsars
Authors: S. A. Petrova
Comments: 8 pages, 2 figures. Invited review for the 2005 Hanas Lake International Pulsar Symposium, to appear in ChJAA

Formation of giant radio pulses is attributed to propagation effects in the plasma of pulsar magnetosphere. Induced scattering of radio waves by the plasma particles is found to lead to an efficient redistribution of the radio emission in frequency. With the steep spectrum of pulsar radiation, intensity transfer between the widely spaced frequencies may imply significant narrow-band amplification of the radiation. This may give rise to giant pulses. It is demonstrated that the statistics of giant pulse intensities observed can be reproduced if one take into account pulse-to-pulse fluctuations of the plasma number density and the original intensity. Polarization properties of the strongly amplified pulses, their location in the average pulse window and the origin of the nanostructure of giant pulses are discussed as well.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0605024 [abs, ps, pdf, other] :
Title: Relativistic mechanics of neutron superfluid in (magneto) elastic star crust
Authors: Brandon Carter, Lars Samuelsson
Comments: 28 pages, Latex

At densities below the neutron drip threshold, a purely elastic solid model (including, if necessary, a frozen-in magnetic field) can provide an adequate description of a neutron star crust, but at higher densities it will be necessary to allow for the penetration of the solid lattice by an independently moving current of superfluid neutrons. In order to do this, the previously available category of relativistic elasticity models is combined here with a separately developed category of relativistic superfluidity models in a unified treatment based on the use of an appropriate Lagrangian master function. As well as models of the purely variational kind, in which the vortices flow freely with the fluid, such a master function also provides a corresponding category of non-dissipative models in which the vortices are pinned to the solid structure.

 

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astro-ph new abstracts, Tue, 9 May 06 00:00:09 GMT
0605170 -- 0605201 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605201 [abs, ps, pdf, other] :
Title: Statistics of the drifting subpulse phenomenon
Authors: P. Weltevrede, R.T. Edwards, B.W. Stappers
Comments: 6 pages, 2 figures, to appear in Chin. J. Astron. Astrophys, proceedings of 2005 Lake Hanas International Pulsar Symposium

We present the statistical results of a systematic, unbiased search for subpulse modulation of 187 pulsars performed with the Westerbork Synthesis Radio Telescope (WSRT) in the Netherlands at an observing wavelength of 21 cm (Weltevrede et al. 2006). We have increased the list of pulsars that show the drifting subpulse phenomenon by 42, indicating that more than 55% of the pulsars show this phenomenon. The large number of new drifters we have found allows us, for the first time, to do meaningful statistics on the drifting phenomenon. We find that the drifting phenomenon is correlated with the pulsar age such that drifting is more likely to occur in older pulsars. Pulsars that drift more coherently seem to be older and have a lower modulation index. Contrary claims from older studies, both P3 (the repetition period of the drifting subpulse pattern) and the drift direction are found to be uncorrelated with other pulsar parameters.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0510668 [abs, ps, pdf, other] :
Title: Are neutron stars crushed? Gravitomagnetic tidal fields as a mechanism for binary-induced collapse
Authors: Marc Favata (Cornell)
Comments: 26 pages, 7 figures, published in Phys. Rev. D. V3: several minor changes made to match published version
Note: replaced with revised version Sat, 6 May 2006 17:34:47 GMT (142kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 10 May 06 00:00:10 GMT
0605202 -- 0605239 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0605044 [abs, ps, pdf, other] :
Title: The eigenmode frequency distribution of rapidly rotating neutron stars
Authors: Stratos Boutloukos, Hans-Peter Nollert
Comments: 10 pages, 6 figures, submitted to Physical Review D

We use perturbation theory and the relativistic Cowling approximation to numerically compute characteristic oscillation modes of rapidly rotating relativistic stars which consist of a perfect fluid obeying a polytropic equation of state. We find the expected infinite pressure mode spectrum extending towards higher frequencies, but also what appears to be an infinite number of inertial modes confined to a finite, well-defined frequency range, depending on the compactness and the rotation frequency of the star. We observe the shift of this range towards negative frequencies for non-axisymmetric modes with respect to the axisymmetric ones, making all m>2 modes unstable. We discuss whether our results indicate the existence of a continuous part of the star's spectrum, or whether they all are discrete solutions.

 

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Astrophysics


astro-ph new abstracts, Thu, 11 May 06 00:00:11 GMT
0605240 -- 0605270 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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Astrophysics


astro-ph new abstracts, Fri, 12 May 06 00:00:10 GMT
0605271 -- 0605301 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605273 [abs, ps, pdf, other] :
Title: X-rays from Radio Millisecond Pulsars: Comptonized Thermal Radiation
Authors: Slavko Bogdanov, Jonathan E. Grindlay, George B. Rybicki
Comments: 4 pages, 3 figures, submitted for publication in the Astrophysical Journal Letters

X-ray emission from many rotation-powered millisecond pulsars (MSPs) is observed to be of predominantly thermal nature. In PSR J0437--4715, the nearest MSP known, an additional faint power-law tail is observed above 2.5 keV, commonly attributed to non-thermal magnetospheric radiation. We propose that the hard emission in this and other similar MSPs is instead due to weak Comptonization of the thermal (blackbody or hydrogen atmosphere) polar cap emission by energetic electrons/positrons of small optical depth in the pulsar magnetosphere. This spectral model implies that all soft X-rays are of purely thermal origin, which has profound implications in the study of neutron star structure and fundamental pulsar physics.

 
astro-ph/0605281 [abs, ps, pdf, other] :
Title: Supernova Neutrinos: The Accretion Disk Scenario
Authors: G. C. McLaughlin, R. Surman

Neutrinos from core collapse supernovae can be emitted from a rapidly accreting disk surrounding a black hole, instead of the canonical proto-neutron star. For Galactic events, detector count rates are considerable and in fact can be in the thousands for Super-Kamiokande. The rate of occurrence of these accreting disks in the Galaxy is predicted to be on the order of 10^-5 yr^-1, yet there is little observational evidence to provide an upper limit on their formation rate. It would therefore be useful to discriminate between neutrinos which have been produced in a proto-neutron star and those which have been produced accretion disks. In order to distinguish between the two scenarios, either the time profile of the neutrino luminosity or the relative fluxes of different neutrino flavors may be considered. There are some signals that would clearly point to one scenario or the other.

 
astro-ph/0605287 [abs, ps, pdf, other] :
Title: Gamma-ray binaries: pulsars in disguise ?
Authors: Guillaume Dubus
Comments: 20 pages, 20 figures, accepted for publication in A&A

LS 5039 and LSI +61 303 are unique amongst high-mass X-ray binaries (HMXB) for their spatially-resolved radio emission and their counterpart at >GeV gamma-ray energies, canonically attributed to non-thermal particles in an accretion-powered relativistic jet. The only other HMXB known to emit very high energy (VHE) gamma-rays, PSR B1259-63, harbours a non-accreting millisecond pulsar. I investigate whether the interaction of the relativistic wind from a young pulsar with the wind from its stellar companion, as in PSR B1259-63, constitutes a viable scenario to explain the observations of LS 5039 and LSI +61 303. Emission would arise from the shocked pulsar wind material, which then flows away to large distances in a comet-shape tail, reproducing on a smaller scale what is observed in isolated, high motion pulsars interacting with the ISM. Simple expectations for the SED are derived and are shown to depend on few input parameters. Detailed modelling of the particle evolution is compared to the observations from radio to TeV energies. Acceleration at the shock provides high energy electrons that steadily emit synchrotron in X-rays and inverse Compton scatter stellar light to gamma-rays. Electrons streaming out of the system emit at IR frequencies and below. The overall aspect of the SEDs is adequately reproduced for standard values of the parameters. The morphology of the radio tail can mimic a microquasar jet. Good agreement is found with the published VLBI map of LS 5039 and predictions are made on the expected change in appearance with orbital phase. The pulsar wind scenario can provide a common, viable framework to interpret the emission from all three gamma-ray binaries.

 

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Astrophysics


astro-ph new abstracts, Mon, 15 May 06 00:00:09 GMT
0605302 -- 0605329 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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Astrophysics


astro-ph new abstracts, Tue, 16 May 06 00:00:13 GMT
0605330 -- 0605368 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605330 [abs, ps, pdf, other] :
Title: The infrared counterpart to the magnetar 1RXS J170849.0-400910
Authors: Martin Durant, Marten H. van Kerkwijk (University of Toronto)
Comments: 19 pages AASTEX, 4 figure. Accepted for publication in ApJ. Full resolution figures at: this http URL

We have analyzed both archival and new infrared imaging observations of the field of the Anomalous X-ray Pulsar 1RXS J170849.0-400910, in search of the infrared counterpart. This field has been previously investigated, and one of the sources consistent with the position of the AXP suggested as the counterpart. We, however, find that this object is more likely a background star, while another object within the positional error circle has non-stellar colors and shows evidence for variability. These two pieces of evidence, along with a consistency argument for the X-ray-to-infrared flux ratio, point to the second source being the more likely infrared counterpart to the AXP.

 
astro-ph/0605331 [abs, ps, pdf, other] :
Title: Evolution of magnetized, differentially rotating neutron stars: Simulations in full general relativity
Authors: Matthew D. Duez, Yuk Tung Liu, Stuart L. Shapiro, Masaru Shibata, Branson C. Stephens
Comments: 27 pages, 30 figures
Journal-ref: Phys. Rev. D73 (2006) 104015

We study the effects of magnetic fields on the evolution of differentially rotating neutron stars, which can form in stellar core collapse or binary neutron star coalescence. Magnetic braking and the magnetorotational instability (MRI) both redistribute angular momentum; the outcome of the evolution depends on the star's mass and spin. Simulations are carried out in axisymmetry using our recently developed codes which integrate the coupled Einstein-Maxwell-MHD equations. For initial data, we consider three categories of differentially rotating, equilibrium configurations, which we label normal, hypermassive and ultraspinning. Hypermassive stars have rest masses exceeding the mass limit for uniform rotation. Ultraspinning stars are not hypermassive, but have angular momentum exceeding the maximum for uniform rotation at the same rest mass. We show that a normal star will evolve to a uniformly rotating equilibrium configuration. An ultraspinning star evolves to an equilibrium state consisting of a nearly uniformly rotating central core, surrounded by a differentially rotating torus with constant angular velocity along magnetic field lines, so that differential rotation ceases to wind the magnetic field. In addition, the final state is stable against the MRI, although it has differential rotation. For a hypermassive neutron star, the MHD-driven angular momentum transport leads to catastrophic collapse of the core. The resulting rotating black hole is surrounded by a hot, massive, magnetized torus undergoing quasistationary accretion, and a magnetic field collimated along the spin axis--a promising candidate for the central engine of a short gamma-ray burst. (Abridged)

 
astro-ph/0605340 [abs, ps, pdf, other] :
Title: Neutron-capture elements in the s- and r-process-rich stars: Constraints on neutron-capture nucleosynthesis processes
Authors: Bo Zhang, Kun Ma, Guide Zhou (Department of Physics, Hebei Normal University, China)
Comments: 19 pages with aastex style, 4 PS figures and 1 table. Accepted for publication in ApJ

The chemical abundances of the very metal-poor double-enhanced stars are excellent information for setting new constraints on models of neutron-capture processes at low metallicity. These stars are known as s+r stars, since they show enhancements of both s-process and r-process elements. The observed abundance ratios for the double-enhanced stars can be explained by those of stars that were polluted by an AGB star and subsequently accreted very significant amounts of r-process material out of an AIC (accretion-induced collapse) or Type 1.5 supernova. In this paper we present for the first time an attempt to fit the elemental abundances observed in the s- and r-rich, very metal-poor stars using a parametric model and suggest a new concept of component coefficients to describe the contributions of the individual neutron-capture processes to double-enhanced stars. We find that the abundance ratios of these stars are best fitted by enrichments of s- and r-process material. The overlap factor in the AGB stars where the observed s-process elements were produced lies between 0.1 and 0.81. Taking into account the dependence of the initial-final mass relations on metallicity, this wide range of values could possibly be explained by a wide range of core-mass values of AGB stars at low metallicity. The component coefficient of the r-process is strongly correlated with the component coefficient of the s-process for the double-enhanced stars. This is significant evidence that the r-process material in double-enhanced stars comes from an AIC or Type 1.5 supernova.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0301161 [abs, ps, pdf, other] :
Title: Detailed atmosphere modelling for the neutron star 1E1207.4-5209: Evidence of Oxygen/Neon atmosphere
Authors: Kaya Mori (CITA), Charles J. Hailey (Columbia University)
Comments: 21 pages, 12 figures, resubmitted to ApJ
Note: replaced with revised version Fri, 12 May 2006 21:03:02 GMT (161kb)
 
astro-ph/0509538 [abs, ps, pdf, other] :
Title: Neutron Star Equation of State and the Possibility of Complex Self-Energy in Landau Theory of Fermi Liquid in Presence of Strong Quantizing Magnetic Field
Authors: Soma Manda, Roni Saha, Sutapa Ghosh, Somenath Chakrabarty
Comments: REVTEX 14 Pages, no figure
Note: replaced with revised version Mon, 15 May 2006 10:40:37 GMT (38kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 17 May 06 00:00:12 GMT
0605369 -- 0605395 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605375 [abs, ps, pdf, other] :
Title: Measurement of Orbital Decay in the Double Neutron Star Binary PSR B2127+11C
Authors: B. A. Jacoby, P. B. Cameron, F. A. Jenet, S. B. Anderson, R. N. Murty, S. R. Kulkarni
Comments: 12 pages, 4 figures, accepted for publication in ApJL

We report the direct measurement of orbital period decay in the double neutron star pulsar system PSR B2127+11C in the globular cluster M15 at the rate of $(-3.95 \pm 0.13) \times 10^{-12}$, consistent with the prediction of general relativity at the $\sim 3 %$ level. We find the pulsar mass to be $m_p = (1.358 \pm 0.010) M_\odot$ and the companion mass $m_c = (1.354 \pm 0.010) M_\odot$. We also report long-term pulse timing results for the pulsars PSR B2127+11A and PSR B2127+11B, including confirmation of the cluster proper motion.

 
astro-ph/0605380 [abs, ps, pdf, other] :
Title: A strong $\ddot{\nu} - \dot{\nu}$ correlation in radio pulsars with implications for torque variations
Authors: J. O. Urama, B. Link, J. M. Weisberg
Comments: MNRAS, in press. 5 pages, 2 figures

We present an analysis of the spin-down parameters for 131 radio pulsars for which $\ddot\nu$ has been well determined. These pulsars have characteristic ages ranging from $10^{3} - 10^{8}$ yr and spin periods in the range 0.4--30 s; nearly equal numbers of pulsars have $\ddot\nu>0$ as $\ddot\nu<0$. We find a strong correlation of $\ddot\nu$ with $\dot{\nu}$, {\em independent of the sign of} $\ddot\nu$. We suggest that this trend can be accounted for by small, stochastic deviations in the spin-down torque that are directly proportional (in magnitude) to the spin-down torque.

 
astro-ph/0605390 [abs, ps, pdf, other] :
Title: The magnetic nature of disk accretion onto black holes
Authors: J. M. Miller (1), J. Raymond (2), A. C. Fabian (3), D. Steeghs (2), J. Homan (4), C. S. Reynolds (5), M. van der Klis (6), Rudy Wijnands (6) ((1) University of Michigan, (2) Harvard-Smithsonian CfA, (3) University of Cambridge, (4) MIT, (5) University of Maryland, (6) University of Amsterdam)
Comments: 15 pages, 2 color figures, accepted for publication in Nature. Supplemental materials may be obtained by clicking this http URL

Although disk accretion onto compact objects - white dwarfs, neutron stars, and black holes - is central to much of high energy astrophysics, the mechanisms which enable this process have remained observationally elusive. Accretion disks must transfer angular momentum for matter to travel radially inward onto the compact object. Internal viscosity from magnetic processes and disk winds can in principle both transfer angular momentum, but hitherto we lacked evidence that either occurs. Here we report that an X-ray-absorbing wind discovered in an observation of the stellar-mass black hole binary GRO J1655-40 must be powered by a magnetic process that can also drive accretion through the disk. Detailed spectral analysis and modeling of the wind shows that it can only be powered by pressure generated by magnetic viscosity internal to the disk or magnetocentrifugal forces. This result demonstrates that disk accretion onto black holes is a fundamentally magnetic process.

 
astro-ph/0605395 [abs, ps, pdf, other] :
Title: Photometric Variability of Be/X-ray-Pulsar Binaries in the SMC
Authors: P. C. Schmidtke, A. P. Cowley
Comments: 20 pages and 7 figures

We have studied the photometric variability of ten SMC Be/X-ray pulsars using MACHO and OGLE-II data. For some of these systems we have found periodic behavior, including orbital outbursts and/or nonradial pulsations (NRP) of the Be star. For others we were unable to identify any clear photometric periodicity, although their longterm light curves show significant structure. We present periodograms, phase dispersion minimization (PDM) variances, and folded light curves for the systems which exhibit periodic photometric variability.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604187 [abs, ps, pdf, other] :
Title: Supernova remnant energetics and magnetars: no evidence in favour of millisecond proto-neutron stars
Authors: Jacco Vink (1), Lucien Kuiper (2) ((1) Utrecht University, The Netherlands, (2) SRON Netherlands Institute for Space Research, Utrecht, The Netherlands)
Comments: Accepted for publication in MNRAS Letters. 5 pages, one color figure. Revised version contains several small improvements, also present in the printed version
Note: replaced with revised version Mon, 15 May 2006 22:20:48 GMT (396kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 18 May 06 00:00:16 GMT
0605396 -- 0605428 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605397 [abs, ps, pdf, other] :
Title: An Investigation of Be/X-ray Pulsars with OGLE-III Data
Authors: P. C. Schmidtke, A. P. Cowley, A. Udalski

We have studied five seasons of OGLE-III data for eight SMC Be/X-ray pulsars for which no other survey data were available. We have determined orbital periods for four of these binary systems, one of which also shows nonradial pulsations. Optical identification of SMC X-2 is reconsidered, but no periods were found for either of the two possible candidates.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0510038 [abs, ps, pdf, other] :
Title: Accretion-powered millisecond pulsars
Authors: Juri Poutanen (University of Oulu, Finland)
Comments: 14 pages, 6 figures; invited review presented at COSPAR Colloquium "Spectra & Timing of Compact X-ray Binaries", January 17-20, 2005, Mumbai, India. Advances in Space Research, in press
Note: replaced with revised version Wed, 17 May 2006 18:15:48 GMT (72kb)
 
astro-ph/0601689 [abs, ps, pdf, other] :
Title: Spectra of the spreading layers on the neutron star surface and constraints on the neutron star equation of state
Authors: Valery Suleimanov, Juri Poutanen
Comments: 13 pages, 13 figures, MNRAS, in press
Note: replaced with revised version Wed, 17 May 2006 17:58:28 GMT (229kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 19 May 06 00:00:15 GMT
0605429 -- 0605469 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605429 [abs, ps, pdf, other] :
Title: Transient pulsed radio emission from a magnetar
Authors: Fernando Camilo (1), Scott Ransom (2), Jules Halpern (1), John Reynolds (3), David Helfand (1), Neil Zimmerman (1), John Sarkissian (3) ((1) Columbia, (2) NRAO, (3) ATNF)
Comments: 6 pages, 2 figures. Submitted to Nature

Anomalous X-ray pulsars (AXPs) are neutron stars whose properties are best explained by the magnetar model. Their very large X-ray luminosities exceed those available from braking of the stellar rotation by magnetic torque, and are generated instead by decay of ultra-strong magnetic fields. The ubiquitous radio pulsars, which are powered by rotational energy loss, display no magnetar-like X-ray activity and have enduring radio emission, while magnetars have lacked any radio emission. XTE J1810-197 was identified as a transient AXP in early 2003 when its X-ray luminosity increased by a factor of ~100 compared to the quiescent level, and X-ray pulsations were observed with period 5.54s. The detection from XTE J1810-197 of a point-like radio source of unknown origin one year after the X-ray outburst further distinguishes it from all other magnetars. Here we show that XTE J1810-197 emits remarkable radio pulsations. These are sharply modulated at the rotation period with peak flux density >1Jy and are highly linearly polarised, conclusively establishing the first detection of magnetospheric radio emission from a magnetar. In contrast to ordinary pulsars, there is no evidence of radio activity prior to the 2003 X-ray outburst, and the intrinsic flux varies on short timescales with an approximately flat spectrum such that, at >20GHz, XTE J1810-197 is currently the brightest neutron star known. This discovery provides a unique opportunity to probe in detail the dynamic magnetosphere of a neutron star with extreme properties.

 
astro-ph/0605445 [abs, ps, pdf, other] :
Title: The X-ray afterglow flat segment in short GRB 051221A: Energy injection from a millisecond magnetar?
Authors: Yizhong Fan, Dong Xu
Comments: 4 pages including 1 figure

In GRB 051221A, an X-ray afterglow flat segment lasting $\sim 10^4$ seconds represents the first clear case of strong energy injection in the external shock of a short GRB afterglow. In this work, we show that a millisecond pulsar with dipole magnetic field $\sim 10^{14}$ Gauss could well account for that energy injection. The good quality X-ray flat segment thus suggests that the central engine of this short burst may be a millisecond magnetar.

 
astro-ph/0605449 [abs, ps, pdf, other] :
Title: Magnetars as cooling neutron stars with internal heating
Authors: A.D. Kaminker (1), D.G. Yakovlev (1), A.Y. Potekhin (1), N. Shibazaki (2), P.S. Shternin (1), O.Y. Gnedin (3) ((1) Ioffe Inst., (2) Rikkyo Univ., (3) Ohio State Univ.)
Comments: 8 pages, 5 figures, submitted to MNRAS

We study thermal structure and evolution of magnetars as cooling neutron stars with a phenomenological heat source in a spherical internal layer. We explore the location of this layer as well as the heating rate that could explain high observable thermal luminosities of magnetars and would be consistent with the energy budget of neutron stars. We conclude that the heat source should be located in an outer magnetar's crust, at densities rho < 5e11 g/cm^3, and should have the heat intensity of the order of 1e20 erg/s/cm^3. Otherwise the heat energy is mainly emitted by neutrinos and cannot warm up the surface.

 
astro-ph/0605461 [abs, ps, pdf, other] :
Title: Elastic or magnetic? A toy model for global magnetar oscillations with implications for QPOs during flares
Authors: Kostas Glampedakis, Lars Samuelsson, Nils Andersson
Comments: 5 pages, 2 eps figures, submitted to MNRAS Letters

We use a simple toy-model to discuss global MHD modes of a neutron star, taking into account the magnetic coupling between the elastic crust and the fluid core. Our results suggest that the notion of pure torsional crust modes is not useful for the coupled system, all modes excite Alfven waves in the core. However, we also show that the modes that are most likely to be excited by a fractured crust, eg. during a magnetar flare, are such that the crust and the core oscillate in concert. For our simple model, the frequencies of these modes are similar to the ``pure crustal'' frequencies. In addition, our model provides a natural explanation for the presence of lower frequency ($< 30$~Hz) QPOs seen in the December 2004 giant flare of SGR 1806-20.

 

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Astrophysics


astro-ph new abstracts, Mon, 22 May 06 00:00:09 GMT
0605470 -- 0605511 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605486 [abs, ps, pdf, other] :
Title: The coherence of kHz quasi-periodic oscillations in the X-rays from accreting neutron stars
Authors: Didier Barret (CESR, Toulouse), Jean-Francois Olive (CESR, Toulouse), M. Coleman Miller (Univ. of Maryland)
Comments: Accepted for publication in MNRAS, 8 pages, 8 figures, figure 1 in color

We study in a systematic way the quality factor of the lower and upper kHz QPOs in a sample of low luminosity neutron star X-ray binaries, showing both QPOs varying over a wide frequency range. The sample includes 4U 1636-536, 4U 1608-522, 4U 1735-44, 4U 1728-34, 4U 1820-303 and 4U 0614+09. We find that all sources except 4U 0614+091 show evidence of a drop in the quality factor of their lower kHz QPOs at high frequency. For 4U 0614+091 only the rising part of the quality factor versus frequency curve has been sampled so far. At the same time, in all sources but 4U 1728-34, the quality factor of the upper kilo-Hz QPO increases all the way to the highest detectable frequencies. We show that the high-frequency behaviours of both the lower and upper kHz QPO quality factors are consistent with what is expected if the drop is produced by the approach of an active oscillating region to the innermost stable circular orbit: the existence of which is a key feature of General Relativity in the strong field regime. Within this interpretation, our results imply gravitational masses around 2 solar masses for the neutron stars in those systems.

 
astro-ph/0605490 [abs, ps, pdf, other] :
Title: Cooling of the quasi-persistent neutron star X-ray transients KS 1731-260 and MXB 1659-29
Authors: Edward M. Cackett (St Andrews), Rudy Wijnands, Manuel Linares (Amsterdam), Jon M. Miller (Michigan), Jeroen Homan, Walter Lewin (MIT)
Comments: 10 pages, 3 figures, 4 tables, submitted to MNRAS

We present Chandra and XMM-Newton X-ray observations that monitor the neutron star cooling of the quasi-persistent neutron star X-ray transients KS 1731-260 and MXB 1659-29 for approximately 4 years after these sources returned to quiescence from prolonged outbursts. In both sources the outbursts were long enough to significantly heat the neutron star crust out of thermal equilibrium with the core. The results of our analysis strengthen the preliminary findings of Wijnands et al. that in both sources the neutron star crust cools down very rapidly suggesting it has a high heat conductivity and that the neutron star core requires enhanced core cooling processes. Importantly, we now detect the flattening of the cooling in both sources as the crust returns to thermal equilibrium with the core. We measure the thermal equilbrium flux and temperature in both sources by fitting a curve that decays exponentially to a constant level. The cooling curves cannot be fit with just a simple exponential decay without the constant offset. We find the constant bolometric flux and effective temperature components to be (9.6 +/- 0.9)E-14 ergs cm^-2 s^-1 and 71.3 +/- 1.6 eV in KS 1731-260 and (1.8 +/- 0.3)E-14 ergs cm^-2 s^-1 and 52.1 +/- 1.6 eV in MXB 1659-29. In addition, we find that the crust of KS 1731-260 cools faster than that of MXB 1659-29 by a factor of ~2, likely due to different crustal properties. This is the first time that the cooling of a neutron star crust into thermal equilibrium with the core has been observed in such detail.

 
astro-ph/0605493 [abs, ps, pdf, other] :
Title: A New Mechanism for Gravitational Wave Emission in Core-Collapse Supernovae
Authors: Christian D. Ott (1), Adam Burrows (2), Luc Dessart (2), Eli Livne (3); ((1) Max-Planck-Institut fuer Gravitationsphysik, Albert-Einstein-Institut, Potsdam, Germany, (2) Department of Astronomy and Steward Observatory, The University of Arizona, Tucson, (3) Racah Institute of Physics, The Hebrew University, Jerusalem, Israel)
Comments: 4 pages, 4 figures, accepted for publication in Phys. Rev. Letters

We present a new theory for the gravitational wave signatures of core-collapse supernovae. Previous studies identified axisymmetric rotating core collapse, core bounce, postbounce convection, and anisotropic neutrino emission as the primary processes and phases for the radiation of gravitational waves. Our results, which are based on axisymmetric, Newtonian radiation-hydrodynamics supernova simulations (Burrows et al. 2006), indicate that the dominant emission process of gravitational waves in core-collapse supernovae may be the oscillations of the protoneutron star core. The oscillations are predominantly of g-mode character, are excited hundreds of milliseconds after bounce, and typically last for several hundred milliseconds. Our results suggest that even nonrotating core-collapse supernovae should be visible to current LIGO-class detectors throughout the Galaxy, and depending on progenitor structure, possibly out to Megaparsec distances.

 
astro-ph/0605497 [abs, ps, pdf, other] :
Title: Detection of the radial velocity curve of the B5-A0 supergiant companion star of Cir X-1?
Authors: P.G. Jonker, G. Nelemans, C.G. Bassa
Comments: 7 pages, 4 figures, submitted to MNRAS

In this Paper we report on phase resolved I-band optical spectroscopic and photometric observations of Cir X-1 obtained with the Very Large Telescope. The spectra are dominated by Paschen absorption lines at nearly all orbital phases except near phase zero (coinciding with the X-ray dip) when the absorption lines are filled-in by broad Paschen emission lines. The radial velocity curve of the absorption lines corresponds to an eccentric orbit (e=0.45) whose period and time of periastron passage are consistent with the period and phase predicted by the most recent X-ray dip ephemeris. We found that the I-band magnitude is consistent with being constant at I=17.6 in the binary phase interval 0.1-0.6. The source-brightness peaks at I=16.7-16.9 at phase 0.9-1.0. This I-band brightening coincides in phase with the X-ray dip. Even though it is likely that the absorption line spectrum is associated with the companion star of Cir X-1, we cannot exclude the possibility that the spectrum originates in the accretion disc. If the spectrum belongs to the companion star, it must be a supergiant of spectral type B5-A0. Under the assumption that the compact object is a 1.4 Msun neutron star and that it does not move through the companion star at periastron, the companion star mass is constrained to ~<2 Msun and the orbital inclination to i~< 27 degrees. In principle, a mass of ~2 Msun is too low for a supergiant, although it is conceivable that tidal effects have heated and enlarged a star of lower mass to resemble a supergiant. Furthermore, mass loss will have reduced the companion star mass. The stringent constraint on the companion star mass is alleviated if the mass of the compact object is higher than 1.4 Msun. For a 10 Msun compact object the companion star mass is more in line with that expected for a B5-A0 supergiant (abridged).

 
astro-ph/0605510 [abs, ps, pdf, other] :
Title: Timing properties of XB 1254-690
Authors: Sudip Bhattacharyya (NASA/GSFC, UMCP)
Comments: 8 pages, 1 table, 3 figures, submitted to MNRAS

We analyze archival Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data of the low mass X-ray binary (LMXB) system XB 1254-690. We calculate colour-colour diagram, hardness-intensity diagram and power spectra of this source and establish that XB 1254-690 is an atoll source. We also find moderate evidence of millisecond period brightness oscillations at the frequency ~ 95 Hz during a thermonuclear X-ray burst. This is the first such finding from this source, which suggests that the spin frequency of the neutron star in XB 1254-690 is ~ 95 Hz. We discuss that, if confirmed, such a low spin frequency will be useful for the detection of spectral lines from the surface of the neutron star.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603102 [abs, ps, pdf, other] :
Title: The radio SNR G65.1+0.6 and its associated pulsar J1957+2831
Authors: W.W. Tian, D.A. Leahy
Comments: 7pages, 5 pictures and tables, will appear in A&A
Note: replaced with revised version Fri, 19 May 2006 18:24:39 GMT (606kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 23 May 06 00:00:12 GMT
0605512 -- 0605570 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605512 [abs, ps, pdf, other] :
Title: Black Hole-Neutron Star Binary Merger Calculations: GRB Progenitors and the Stability of Mass Transfer
Authors: Joshua A. Faber, Thomas W. Baumgarte, Stuart L. Shapiro, Keisuke Taniguchi, Frederic A. Rasio
Comments: 8 pages, 5 figures, in Proceedings of the Albert Einstein Century International Conference, Paris, France, 2005, edited by Jean-Michel Alimi and Andre Fuzfa

We have calculated the first dynamical evolutions of merging black hole-neutron star binaries that treat the combined spacetime in a nonperturbative general relativistic framework. Using the conformal flatness approximation, we have studied how the location of the tidal disruption radius with respect to the the black hole horizon and innermost stable circular orbit (ISCO) affects the qualitative evolution of the system. Based on simple arguments, we show that for a binary mass ratio q>~0.24, tidal disruption occurs outside the ISCO, while the opposite is true for q<~0.24. When tidal disruption occurs sufficiently far outside the ISCO, mass is transferred unstably from the neutron star to the black hole, resulting in the complete disruption of the neutron star. When tidal disruption occurs slightly within the ISCO, we find that some of the mass forms an extremely hot disk around the black hole. The resulting configurations in this case are excellent candidates for the progenitors of short-hard gamma ray bursts.

 
astro-ph/0605514 [abs, ps, pdf, other] :
Title: Solutions of pulsar equation by finding the source term
Authors: Lukasz Bratek, Marcin Kolonko, Marek Kutschera
Comments: 13 pages, 4 figures

An algorithm of finding numerical solutions of pulsar equation is presented which is essentially different from the one used in the pioneering paper by Contopoulos, Kazanas and Fendt (CKF). The problem of finding the solutions was reduced to finding expansion coefficients of the source term in a base of orthogonal functions on the unit interval by minimizing a multi-variable mismatch function defined on the light cylinder. The whole infinite integration region was mapped onto a single rectangular lattice without the need of splitting it along the light cylinder. To compare the two methods on comparable size grids, the algorithm is applied to Scharlemann and Wagoner boundary conditions by which CKF solution is reconstructed that by construction passes successfully the Gruzinov test of the source function exponent.

 
astro-ph/0605567 [abs, ps, pdf, other] :
Title: Gravitational Waves from Light Cosmic Strings: Backgrounds and Bursts with Large Loops
Authors: Craig J. Hogan
Comments: 22 pages, Latex, 1 figure, submitted to Phys Rev D

The mean spectrum and burst statistics of gravitational waves produced by a cosmological population of cosmic string loops are estimated using analytic approximations, calibrated with earlier simulations. Formulas are derived showing the dependence of observables on the string tension, in the regime where newly-formed loops are relatively large, not very much smaller than the horizon. Large loops form earlier, are more abundant, and generate a more intense stochastic background and more frequent bursts than assumed in earlier background estimates, enabling experiments to probe lighter cosmic strings of interest to string theory. Predictions are compared with instrument noise from current and future experiments, and with confusion noise from known astrophysical gravitational wave sources such as stellar and massive black hole binaries. In these large-loop models, current data from millisecond pulsar timing already suggests that the tension is less than about $10^{-10}$, a typical value expected in strings from brane inflation. LISA will be sensitive to stochastic backgrounds created by strings as light as $G\mu\approx 10^{-15}$, at frequencies where it is limited by confusion noise of Galactic stellar populations; however, for those lightest detectable strings, bursts are rarely detectable.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-ex/0605024 [abs, ps, pdf, other] :
Title: Astrophysical factor for the neutron generator 13C(alpha,n)16O reaction in the AGB stars
Authors: E.D. Johnson, G.V. Rogachev, A.M. Mukhamedzhanov, L.T. Baby, S. Brown, W.T. Cluff, A.M. Crisp, E. Diffenderfer, V.Z. Goldberg, B.W. Green, T. Hinners, C.R. Hoffman, K.W. Kemper, O. Momotyuk, P. Peplowski, A. Pipidis, R. Reynolds, B.T. Roeder
Comments: 4 pages, 4 figures

The reaction 13C(alpha,n) is considered to be the main source of neutrons for the s-process in AGB stars. At low energies the cross section is dominated by the 1/2+ 6.356 MeV sub-threshold resonance in 17O whose contribution is determined with a very large uncertainty of ~1000% at stellar temperatures. In this work we performed the most precise determination of the low-energy astrophysical S factor using the indirect asymptotic normalization (ANC) technique. The alpha-particle ANC for the sub-threshold state has been measured using the sub-Coulomb alpha-transfer reaction (6Li,d). Using the determined ANC we calculated S(0), which turns out to be an order of magnitude smaller than in the NACRE compilation.

 

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Astrophysics


astro-ph new abstracts, Wed, 24 May 06 00:00:09 GMT
0605571 -- 0605599 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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Astrophysics


astro-ph new abstracts, Thu, 25 May 06 00:00:11 GMT
0605600 -- 0605634 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605634 [abs, ps, pdf, other] :
Title: Multiwavelength Observations of EXO 0748--676 -- II. Emission Line Behavior
Authors: K. J. Pearson, R. I. Hynes, D. Steeghs, P. G. Jonker, C. A. Haswell, A. R. King, K. O'Brien, G. Nelemans, M. Mendez
Comments: 15 pages, 10 figures, 3 tables, accepted for publication in ApJ

We present optical and ultraviolet spectra, lightcurves, and Doppler tomograms of the low-mass X-ray binary EXO 0748-676. Using an extensive set of 15 emission line tomograms, we show that, along with the usual emission from the stream and ``hot spot'', there is extended non-axisymmetric emission from the disk rim. Some of the emission and Halpha and beta absorption features lend weight to the hypothesis that part of the stream overflows the disk rim and forms a two phase medium. The data are consistent with a 1.35M_sun neutron star with a main sequence companion and hence a mass ratio q~0.34.

 

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Astrophysics


astro-ph new abstracts, Fri, 26 May 06 00:00:10 GMT
0605635 -- 0605651 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602354 [abs, ps, pdf, other] :
Title: A transient I band excess in the optical spectrum of the accreting millisecond pulsar SAX J1808.4-3658
Authors: J. G. Greenhill (1), A. B. Giles (1 and 2), C. Coutures (3) ((1) University of Tasmania (2) Spurion Technology (3) CEA / Saclay)
Comments: 7 pages, 5 figures, accepted by MNRAS, 10 May 2006. Ver. 2 - larger Table 2 + various modest text changes
Note: replaced with revised version Thu, 25 May 2006 02:34:59 GMT (74kb)
 

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astro-ph new abstracts, Mon, 29 May 06 00:00:08 GMT
0605652 -- 0605673 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605657 [abs, ps, pdf, other] :
Title: Orbital Parameters for the X-ray Pulsar IGR J16393-4643
Authors: T.W.J. Thompson (1), J.A. Tomsick (1), R.E. Rothschild (1), J.J.M. in't Zand (2), R. Walter (3) ((1) UCSD/CASS, (2) SRON, (3) Integral SDC)
Comments: Accepted for publication in ApJ; 8 pages, 8 figures

With recent and archival Rossi X-Ray Timing Explorer (RXTE) X-ray measurements of the heavily obscured X-ray pulsar IGR J16393-4643, we carried out a pulse timing analysis to determine the orbital parameters. Assuming a circular orbit, we phase-connected data spanning over 1.5 years. The most likely orbital solution has a projected semi-major axis of 43 +- 2 lt-s and an orbital period of 3.6875 +- 0.0006 days. This implies a mass function of 6.5 +- 1.1 M_sun and confirms that this INTEGRAL source is a High Mass X-ray Binary (HMXB) system. By including eccentricity in the orbital model, we find e < 0.25 at the 2 sigma level. The 3.7 day orbital period and the previously known ~910 s pulse period place the system in the region of the Corbet diagram populated by supergiant wind accretors, and the low eccentricity is also consistent with this type of system. Finally, it should be noted that although the 3.7 day solution is the most likely one, we cannot completely rule out two other solutions with orbital periods of 50.2 and 8.1 days.

 
astro-ph/0605663 [abs, ps, pdf, other] :
Title: On the origin of the TeV lightcurve of PSR B1259-63/SS2883
Authors: Dmitry Khangulyan, Slavomir Hnatic, Felix Aharonian, Sergey Bogovalov
Comments: 11 pages, 19 figures, submitted for MNRAS

The inverse Compton (IC) scattering of electrons accelerated at the pulsar wind termination shock is believed to be responsible for TeV gamma-ray signal recently reported from the binary system PSR B1259-63. While this process can explain the energy spectrum of the observed TeV emission, the gamma-ray fluxes detected by HESS do not agree with the published predictions of the TeV lightcurve. In this paper we study evolution of the energy spectra of relativistic electrons under different assumptions about the acceleration and energy-loss rates, and the impact of these processes on the lightcurve of IC gamma-rays. We demonstrate that the observed lightcurve can be explained (i) by adiabatic losses which dominate over the entire trajectory of the pulsar, or (ii) by the "early" cutoffs in the energy spectra of electrons due to the enhanced rate of Compton losses close to the periastron. The Compton cooling of the electron-positron pulsar wind contributes to the decrease of the nonthermal power released in the accelerated electrons after the wind termination, and thus to the reduction of the IC and synchrotron components of radiation close to the periastron. Although this effect alone cannot explain the observed TeV and X-ray lightcurves, the Comptonization of the cold ultrarelativistic wind leads to the formation of gamma-radiation with a specific line-type energy spectrum. While the HESS data already constrain the Lorentz factor of the wind, $\Gamma \le 10^6$, future observations of this object with GLAST should allow a deep probe of the wind Lorentz factor in the range between $10^4$ and $10^6$.

 

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astro-ph/0601304 [abs, ps, pdf, other] :
Title: The X-ray Structure of the Pulsar Bow Shock G189.22+2.90 in the Supernova Remnant IC 443
Authors: B. M. Gaensler, S. Chatterjee, P. O. Slane, E. van der Swaluw, F. Camilo, J. P. Hughes
Comments: 8 pages, including 3 color EPS figure. Expaneded to include new figures, plus discussion of the association between the pulsar and the supernova remnant. ApJ, in press
Note: replaced with revised version Thu, 25 May 2006 20:03:49 GMT (427kb)
 

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astro-ph new abstracts, Tue, 30 May 06 00:00:12 GMT
0605674 -- 0605704 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605689 [abs, ps, pdf, other] :
Title: The superburst recurrence time in luminous persistent LMXBs
Authors: L. Keek, J.J.M. in 't Zand, A. Cumming
Comments: 8 pages, 2 figures. Accepted for publication in A&A

Theory and observations favor stable helium burning as the most important means to produce fuel for superbursts on neutron star surfaces. However, all known superbursters exhibit unstable burning as well. This ambiguity prompted us to search for superbursts in data from the BeppoSAX Wide Field Cameras of ten luminous LMXBs, most of which do not exhibit normal type-I X-ray bursts. We found no superbursts and determine a lower limit on the recurrence time which varies between 30 and 76 days (90% confidence). All recurrence time limits except one are longer than the observed recurrence time for GX 17+2. This difference can be understood if the mass accretion rate in GX 17+2 is several tens of percent higher than in the other sources; alternatively, the accreted material in GX 17+2 might be hydrogen deficient, leading to larger carbon yields than in the other sources. We compare our results to the latest models of superbursts. As our search method is indiscriminate of the burst ignition scenario, the recurrence time limits may also be applied to other bursts of similar duration and brightness.

 

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astro-ph new abstracts, Wed, 31 May 06 00:00:10 GMT
0605705 -- 0605727 received


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gr-qc/0409037 [abs, ps, pdf, other] :
Title: Nonlinear r-modes in neutron stars: A hydrodynamical limitation on r-mode amplitudes
Authors: Lap-Ming Lin, Wai-Mo Suen
Comments: An extended version with the eigenfunctions of the coupled modes extracted. Version accepted for publication in MNRAS
Note: replaced with revised version Tue, 30 May 2006 15:37:18 GMT (58kb)
 

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astro-ph new abstracts, Thu, 1 Jun 06 00:00:17 GMT
0605728 -- 0605753 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605752 [abs, ps, pdf, other] :
Title: The Chandra View of the Supernova Remnant 0506-68.0 in the Large Magellanic Cloud
Authors: John P. Hughes (1), Marc Rafelski (2), Jessica S. Warren (1), Cara Rakowski (3), Patrick Slane (3), David Burrows (4), John Nousek (4) ((1) Rutgers University, (2) UCLA, (3) Harvard-Smithsonian CfA, (4) Penn State)
Comments: 5 pages, including 3 postscript figs, LaTeX, accepted to appear in ApJ Letters

A new Chandra observation of SNR 0506-68.0 (also called N23) reveals a complex, highly structured morphology in the low energy X-ray band and an isolated compact central object in the high energy band. Spectral analysis indicates that the X-ray emission overall is dominated by thermal gas whose composition is consistent with swept-up ambient material. There is a strong gradient in ambient density across the diameter of the remnant. Toward the southeast, near a prominent star cluster, the emitting density is 10 - 23 cm^{-3} while toward the northwest it has dropped to a value of only 1 cm^{-3}. The total extent of the X-ray remnant is 100" by 120" (24 pc x 29 pc for a distance of 50 kpc), somewhat larger than previously known. The remnant's age is estimated to be ~4600 yr. One part of the remnant shows evidence for enhanced O, Ne, and perhaps Mg abundances, which is interpreted as evidence for ejecta from a massive star core collapse supernova. The compact central object has a luminosity of a few times 10^{33} ergs/s and no obvious radio or optical counterpart. It does not show an extended nebula or pulsed emission as expected from a young energetic pulsar, but resembles the compact central objects seen in other core collapse SNe, such as Cas A.

 

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astro-ph new abstracts, Fri, 2 Jun 06 00:00:14 GMT
0606001 -- 0606034 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606012 [abs, ps, pdf, other] :
Title: Refining a relativistic, hydrodynamic solver: admitting ultra-relativistic flows
Authors: J. P. Bernstein (1), P. A. Hughes (1) ((1) University of Michigan, Ann Arbor)
Comments: 15 pages, 4 figures, submitted to SIAM Journal on Numerical Analysis (SINUM). Note that Figure 2 is a low-resolution version for Astro-ph. A pdf of the paper with the full-resolution version is available at this http URL

We have undertaken the simulation of hydrodynamic flows with bulk Lorentz factors in the range 10^2--10^6. We discuss the application of an existing relativistic, hydrodynamic primitive-variable recovery algorithm to a study of pulsar winds, and, in particular, the refinement necessary to admit such ultra-relativistic flows. We show that the use of an analytical quartic root finder is required for Lorentz factors above 10^2, but that an iterative quartic root finder, which is known to be robust for Lorentz factors up to at least 25, offers a 24% speed advantage. We demonstrate the existence of a simple diagnostic allowing for a hybrid primitives recovery algorithm that includes an automatic, real-time toggle between the iterative and analytical methods. We further determine the accuracy of the iterative and hybrid algorithms for a comprehensive selection of input parameters.

 
astro-ph/0606017 [abs, ps, pdf, other] :
Title: High-energy Emission from Pulsar Magnetospheres
Authors: Kouichi Hirotani
Comments: 16 pages, 9 figures, Mod. Phys. Lett. A in press (Brief Review)

A synthesis of the present knowledge on gamma-ray emission from the magnetosphere of a rapidly rotating neutron star is presented, focusing on the electrodynamics of particle accelerators. The combined curvature, synchrotron, and inverse-Compton emission from ultra-relativistic positrons and electrons, which are created by two-photon and/or one-photon pair creation processes, or emitted from the neutron-star surface, provide us with essential information on the properties of the accelerator -- electric potential drop along the magnetic field lines. A new accelerator model, which is a mixture of traditional inner-gap and outer gap models, is also proposed, by solving the Poisson equation for the electrostatic potential together with the Boltzmann equations for particles and gamma-rays in the two-dimensional configuration and two-dimensional momentum spaces.

 
astro-ph/0606025 [abs, ps, pdf, other] :
Title: Instantaneous Radio Spectra of Giant Pulses from the Crab Pulsar from Decimeter to Decameter Wavelengths
Authors: M.V. Popov (ASC Lpi), A.D. Kuzmin (PRAO Asc Lpi), O.M. Ul'yanov (IRA, Kharkov), A.A. Deshpande (RRI, Bangalore; Arecibo), A.A. Ershov (PRAO Asc Lpi), V.V. Zakharenko (IRA, Kharkov), V.I. Kondratiev (ASC Lpi), S.V. Kostyuk (ASC Lpi), B.Ya. Losovskii (PRAO Asc Lpi), V.A. Soglasnov (ASC Lpi)
Comments: 13 pages, 1 figure, 1 table (originally published in Russian in Astronomicheskii Zhurnal, 2006, vol. 83, No. 7, pp. 630-637), translated by Georgii Rudnitskii
Journal-ref: Astron. Rep. 2006, vol. 50, No. 7, pp. 562-568

The results of simultaneous multifrequency observations of giant radio pulses from the Crab pulsar, PSR B0531+21, at 23, 111, and 600 MHz are presented and analyzed. Giant pulses were detected at a frequency as low as 23 MHz for the first time. Of the 45 giant pulses detected at 23 MHz, 12 were identified with counterparts observed simultaneously at 600 MHz. Of the 128 giant pulses detected at 111 MHz, 21 were identified with counterparts observed simultaneously at 600 MHz. The spectral indices for the power-law frequency dependence of the giant-pulse energies are from -3.1 to -1.6. The mean spectral index is -2.7 +/- 0.1 and is the same for both frequency combinations (600-111 MHz and 600-23 MHz). The large scatter in the spectral indices of the individual pulses and the large number of unidentified giant pulses suggest that the spectra of the individual giant pulses do not actually follow a simple power law. The observed shapes of the giant pulses at all three frequencies are determined by scattering on interstellar plasma irregularities. The scatter broadening of the pulses and its frequency dependence were determined as tau_sc=20*(f/100)^(-3.5 +/- 0.1) ms, where the frequency f is in MHz.

 
astro-ph/0606027 [abs, ps, pdf, other] :
Title: Distances to Anomalous X-ray Pulsars using Red Clump Stars
Authors: Martin Durant, Marten H. van Kerkwijk (University of Toronto)
Comments: 38 pages aastex, 10 figures. Accepted for publication in ApJ

We identify `red clump stars' - core helium-burning giants - among 2MASS stars and use them to measure the run of reddening with distance in the direction of each of the Galactic Anomalous X-ray Pulsars (AXP). We combine this with extinction estimates from X-ray spectroscopy to infer distances and find that the locations of all AXP are consistent with being in Galactic spiral arms. We also find that the 2-10 keV luminosities implied by our distances are remarkably similar for all AXPs, being all around 1.3e35 erg s-1. Furthermore, using our distances to estimate effective black-body emitting radii, we find that the radii are tightly anti-correlated with pulsed fraction, and somewhat less tightly anti-correlated with black-body temperature. We find no obvious relationship of any property with the dipole magnetic field strength inferred from the spin-down rate.

 

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astro-ph new abstracts, Mon, 5 Jun 06 00:00:10 GMT
0606035 -- 0606062 received


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astro-ph new abstracts, Tue, 6 Jun 06 00:00:11 GMT
0606063 -- 0606091 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606070 [abs, ps, pdf, other] :
Title: INTEGRAL and XMM-Newton observations of micro-blazar LSI +61 303
Authors: M.Chernyakova, A.Neronov, R.Walter
Comments: 8 pages, submitted to MNRAS

LSI +61 303 is one of the few X-ray binaries with Be star companion from which both radio and high-energy gamma-ray emission have been observed. We present XMM-Newton and INTEGRAL observations which reveal variability of the X-ray spectral index of the system. The X-ray spectrum is hard (photon index ~ 1.5) during the orbital phases of both high and low X-ray flux. However, the spectrum softens at the moment of transition from high to low X-ray state. The spectrum of the system in the hard X-ray band does not reveal the presence of a cut-off (or, at least a spectral break) at 10-60 keV energies, expected if the compact object is an accreting neutron star. The observed spectrum and spectral variability can be explained if the compact object in the system is a rotation powered pulsar.

 
astro-ph/0606080 [abs, ps, pdf, other] :
Title: Multi-band study of NGC 7424 and its two newly-discovered ULXs
Authors: R. Soria (CfA & MSSL), Z. Kuncic (Sydney Uni), J. W. Broderick (Sydney Uni), S. D. Ryder (AAO)
Comments: 12 pages, 11 figures. Accepted by MNRAS. High-resolution colour images of NGC 7424 from the Gemini observations are available at this http URL

We have studied the face-on, barred spiral NGC 7424 (site of the rare Type IIb SN 2001ig) with Chandra, Gemini and the Australia Telescope Compact Array. After giving revised X-ray colours and luminosity of the supernova, here we focus on some other interesting sources in the galaxy: in particular, our serendipitous discovery of two ultraluminous X-ray sources (ULXs). The brighter one (~ 10^{40} erg/s) has a power-law-like spectrum with photon index Gamma ~ 1.8. The other ULX shows a spectral state transition or outburst between the two Chandra observations, 20 days apart. Optical data show that this ULX is located in a young (age ~ 7-10 Myr), bright complex rich with OB stars and clusters. An exceptionally bright, unresolved radio source (0.14 mJy at 4.79 GHz, implying a radio luminosity twice as high as Cas A) is found slightly offset from the ULX (~ 80 pc). Its radio spectral index alpha ~ -0.7 suggests optically-thin synchrotron emission, either from a young supernova remnant or from a radio lobe powered by a ULX jet. An even brighter, unresolved radio source (0.22 mJy at 4.79 GHz) is found in another young, massive stellar complex, not associated with any X-ray sources: based on its flatter radio spectral index (alpha ~ -0.3), we suggest that it is a young pulsar wind nebula, a factor of 10 more radio luminous than the Crab.

 
astro-ph/0606085 [abs, ps, pdf, other] :
Title: X-ray Timing beyond the Rossi X-ray Timing Explorer
Authors: Didier Barret (Centre d'Etude Spatiale des Rayonnements, Toulouse, France)
Comments: 12 pages, 6 figures, COSPAR Colloquium "Spectra & Timing of Compact X-ray Binaries", January 17-20, 2005, Mumbai, India. Advances in Space Research, 2006, in press

With its ability to look at bright galactic X-ray sources with sub-millisecond time resolution, the Rossi X-ray Timing Explorer (RXTE) discovered that the X-ray emission from accreting compact stars shows quasi-periodic oscillations on the dynamical timescales of the strong field region. RXTE showed also that waveform fitting of the oscillations resulting from hot spots at the surface of rapidly rotating neutron stars constrain their masses and radii. These two breakthroughs suddenly opened up a new window on fundamental physics, by providing new insights on strong gravity and dense matter. Building upon the RXTE legacy, in the Cosmic Vision exercise, testing General Relativity in the strong field limit and constraining the equation of state of dense matter were recognized recently as key goals to be pursued in the ESA science program for the years 2015-2025. This in turn identified the need for a large (10 m2 class) aperture X-ray observatory. In recognition of this need, the XEUS mission concept which has evolved into a single launch L2 formation flying mission will have a fast timing instrument in the focal plane. In this paper I will outline the unique science that will be addressed with fast X-ray timing on XEUS.

 
astro-ph/0606086 [abs, ps, pdf, other] :
Title: Light Curves of Swift Gamma Ray Bursts
Authors: Paolo Cea
Comments: 17 pages, 13 figures

Recent observations from the Swift gamma ray burst explorer indicate that a large fraction of gamma ray bursts are characterized by a canonical behaviour of the X-ray afterglows. We present an effective theory which allows us to account for X-ray light curves of both gamma ray bursts and X-ray rich flashes. We propose that gamma ray bursts originate from massive magnetic powered pulsars.

 

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astro-ph new abstracts, Wed, 7 Jun 06 00:00:11 GMT
0606092 -- 0606125 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606093 [abs, ps, pdf, other] :
Title: Ultra-Dense Neutron Star Matter, Strange Quark Stars, and the Nuclear Equation of State
Authors: Fridolin Weber (San Diego State University), Matthew Meixner (San Diego State University), Rodrigo P. Negreiros (San Diego State University), Manuel Malheiro (Instituto de Fisica, Universidade Federal Fluminense, Niteroi, RJ, Brazil)
Comments: 15 pages, 9 figures; paper presented at the International Symposium on Heavy Ion Physics 2006, April 3 to April 6, 2006, Frankfurt am Main, Germany

With central densities way above the density of atomic nuclei, neutron stars contain matter in one of the densest forms found in the universe. Depending of the density reached in the cores of neutron stars, they may contain stable phases of exotic matter found nowhere else in space. This article gives a brief overview of the phases of ultra-dense matter predicted to exist deep inside neutron stars and discusses the equation of state associated with such matter.

 
astro-ph/0606120 [abs, ps, pdf, other] :
Title: Magnetars versus Radio Pulsars: MHD Stability in Newborn Highly Magnetized Neutron Stars
Authors: U. Geppert, M. Rheinhardt
Comments: 14 pages, 5 figures; accepted by Astronomy & Astrophysics

We study the stability/establishment of dipolar magnetostatic equilibrium configurations in new--born neutron stars (NSs) in dependence on the rotational velocity $\Omega$ and on the initial angle $\alpha$ between rotation and magnetic axis. The NS is modeled as a sphere of a highly magnetized ($B \sim 10^{15}$G) incompressible fluid of uniform density which rotates rigidly. For the initial dipolar background magnetic field, which defines the magnetic axis, two different configurations are assumed. We solve the 3D non--linear MHD equations by use of a spectral code. The problem in dimensionless form is completely defined by the initial field strength (for a fixed field geometry), the magnetic Prandtl number $\Pm$, and the normalized rotation rate. The evolution of the magnetic and velocity fields is considered for initial magnetic field strengths characterized by the ratio of ohmic diffusion and initial \Alf{} travel times $\ttOhm/\ttAO \approx 1000$, for $\Pm = 0.1, 1, 10$, and the ratio of rotation period and initial \Alf{} travel time, $P/\ttAO = 0.012, 0.12, 1.2, 12$. We find hints for the existence of a unique stable dipolar magnetostatic configuration for any specific $\alpha$, independent of the initial field geometry. Comparing NSs possessing the same field structure at the end of their proto--NS phase, it turns out that sufficiently fast rotating NSs ($P\la6 $ms) with $\alpha \la 45^0$ retain their magnetar field, while the others lose almost all of their initial magnetic energy by transferring it into magnetic and kinetic energy of relatively small--scaled fields and continue their life as radio pulsars with a dipolar surface field of $10^{12...13}$G.

 

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astro-ph/0509880 [abs, ps, pdf, other] :
Title: Gravitational Wave Background from Magnetars
Authors: Tania Regimbau, José Antonio de Freitas Pacheco
Comments: accepted for publication in A&A; 17 pages, 7 figures; formula 21 has been corrected with respect to the published version
Journal-ref: A&A, 447,1 (2006)
Note: replaced with revised version Tue, 6 Jun 2006 08:17:14 GMT (665kb)
 

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astro-ph new abstracts, Thu, 8 Jun 06 00:00:08 GMT
0606126 -- 0606168 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606146 [abs, ps, pdf, other] :
Title: Absolute timing of the Crab Pulsar at optical wavelengths with STJs
Authors: T. Oosterbroek, J.H.J. de Bruijne, D. Martin, P. Verhoeve, M.A.C. Perryman, C. Erd, R. Schulz
Comments: 5 pages, 2 figures, accepted for publication in Astronomy & Astrophysics

We have observed the Crab Pulsar in the optical with S-Cam, an instrument based on Superconducting Tunneling Junctions (STJs) with $\mu$s time resolution. Our aim was to study the delay between the radio and optical pulse. The Crab Pulsar was observed three times over a time span of almost 7 years, on two different locations, using three different versions of the instrument, and using two different GPS units. We consistently find that the optical peak leads the radio peak by 49$\pm$90, 254$\pm$170, and 291$\pm$100 $\mu$s. On assumption of a constant optical lead, the weighted-average value is $\sim$170 $\mu$s, or when rejecting (based on a perhaps questionable radio ephemeris) the first measurement, 273$\pm$100 $\mu$s.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


hep-ph/0606066 [abs, ps, pdf, other] :
Title: The Crystallography of Strange Quark Matter
Authors: Krishna Rajagopal, Rishi Sharma
Comments: 6 pages, 3 figures. Contribution to the proceedings of Strangeness in Quark Matter 2006, UCLA. Talk given by Rishi Sharma
Subj-class: High Energy Physics - Phenomenology; Superconductivity

Cold three-flavor quark matter at large (but not asymptotically large) densities may exist as a crystalline color superconductor. We explore this possibility by calculating the gap parameter Delta and free energy Omega(Delta) for possible crystal structures within a Ginzburg-Landau approximation, evaluating Omega(Delta) to order Delta^6. We develop a qualitative understanding of what makes a crystal structure stable, and find two structures with particularly large values of Delta and the condensation energy, within a factor of two of those for the CFL phase known to characterize QCD at asymptotically large densities. The robustness of these phases results in their being favored over wide ranges of density and though it also implies that the Ginzburg-Landau approximation is not quantitatively reliable, previous work suggests that it can be trusted for qualitative comparisons between crystal structures. We close with a look ahead at the calculations that remain to be done in order to make contact with observed pulsar glitches and neutron star cooling.

 

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astro-ph new abstracts, Fri, 9 Jun 06 00:00:09 GMT
0606169 -- 0606207 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606187 [abs, ps, pdf, other] :
Title: Inelastic Neutrino-Helium Scatterings and Standing Accretion Shock Instability in Core-Collapse Supernovae
Authors: Naofumi Ohnishi, Kei Kotake, Shoichi Yamada
Comments: 19 pages, 6 figures, submitted to ApJ

We present the results of numerical experiments, in which we have investigated the influence of the inelastic neutrino-helium interactions on the standing accretion shock instability supposed to occur in the post-bounce supernova core. The axisymmetric hydrodynamical simulations of accretion flows through the standing accretion shock wave onto the protoneutron star show that the interactions are relatively minor and the linear growth of the shock instability is hardly affected. The extra heating given by the inelastic reactions becomes important for the shock revival after the instability enters the non-linear regime, but only when the neutrino luminosity is very close to the critical value, at which the shock would be revived without the interactions. We have also studied the dependence of the results on the initial amplitudes of perturbation and the temperatures of mu and tau neutrinos.

 
astro-ph/0606207 [abs, ps, pdf, other] :
Title: Low Mach number modeling of Type I X-ray burst deflagrations
Authors: David J. Lin, Alvin Bayliss, Ronald E. Taam
Comments: 33 pages, 12 figures, submitted to ApJ

The Low Mach Number Approximation (LMNA) is applied to 2D hydrodynamical modeling of Type I X-ray bursts on a rectangular patch on the surface of a non-rotating neutron star. Because such phenomena involve decidedly subsonic flows, the timestep increase offered by the LMNA makes routine simulations of these deflagrations feasible in an environment where strong gravity produces significant stratification, while allowing for potentially significant lateral differences in temperature and density. The model is employed to simulate the heating, peak, and initial cooling stages of a burst. During the deflagration, Benard-like cells naturally fill up a vertically expanding convective layer. The Mach number is always less than 0.10 throughout the simulation, thus justifying the low Mach number approximation. While the convective layer is superadiabatic on average, significant fluctuations in adiabaticity occur within it on subconvective timescales. Due to convective layer expansion, significant compositional mixing naturally occurs, but tracer particle penetration through the convective layer boundaries on convective timescales is temporary and spatially limited. Thus, mixing occurs on the relatively slow burst timescale through thermal expansion of the convective layer rather than from mass penetration of the convective layer boundary through particle convection. At the convective layer boundaries where mixing is less efficient, the actual temperature gradient more closely follows the Ledoux criteria.

 

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astro-ph new abstracts, Mon, 12 Jun 06 00:00:09 GMT
0606208 -- 0606241 received


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astro-ph/0604379 [abs, ps, pdf, other] :
Title: Flux predictions of high-energy neutrinos from pulsars
Authors: Bennett Link (Montana State University, Bozeman, USA), Fiorella Burgio (INFN Sezione di Catania, Italy)
Comments: version accepted for publication in MNRAS, with discussion of effects of gravitational light bending and minor changes
Note: replaced with revised version Fri, 9 Jun 2006 07:22:33 GMT (196kb)
 

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astro-ph new abstracts, Tue, 13 Jun 06 00:00:10 GMT
0606242 -- 0606275 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606254 [abs, ps, pdf, other] :
Title: Spinning-Down of Moving Magnetars in the Propeller Regime
Authors: O. D. Toropina, M. M. Romanova, R. V. Lovelace
Comments: 10 pages, 4 figures, accepted by MNRAS. See version with better resolution figures and animation at this http URL

We use axisymmetric magnetohydrodynamic simulations to investigate the spinning-down of magnetars rotating in the propeller regime and moving supersonically through the interstellar medium. The simulations indicate that magnetars spin-down rapidly due to this interaction, faster than for the case of a non-moving star. From many simulation runs we have derived an approximate scaling laws for the angular momentum loss rate, \dot{L} \propto \~\eta_m^{0.3}\mu^{0.6}\rho^{0.8}{\cal M}^{-0.4} \Omega_*^{1.5}, where \rho is the density of the interstellar medium, \cal M is Mach number, \mu is the star's magnetic moment, \Omega_* is its angular velocity, and \eta_m is magnetic diffusivity. A magnetar with a surface magnetic field of 10^{13} - 10^{15} G is found to spin-down to a period P > 10^5-10^6 s in \sim 10^4 - 10^5 years. There is however uncertainty about the value of the magnetic diffusivity so that the time-scale may be longer. We discuss this model in respect of Soft Gamma Repeaters (SGRs) and the isolated neutron star candidate RXJ1856.5-3754.

 
astro-ph/0606259 [abs, ps, pdf, other] :
Title: A Fallback Disk Around a Neutron Star Spinning Down While Accreting
Authors: U. Ertan, M. H. Erkut, K.Y. Eksi, M.A. Alpar
Comments: 18 pages, 3 figures, submitted to Apj

The recent detection of the anomalous X-ray pulsar (AXP) 4U 0142+61 in the far infrared with the Spitzer Observatory (Wang, Chakrabarty & Kaplan 2006) constitutes the first instance for a disk around an AXP. Analysis of earlier optical and near infrared data, together with the recent data, implies an active gaseous disk protruding the light cylinder, and not a passive dust disk beyond the light cylinder, as proposed on the basis of the far infrared data alone.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602538 [abs, ps, pdf, other] :
Title: Effect of hyperon-hyperon interaction on bulk viscosity and r-mode instability in neutron stars
Authors: Debarati Chatterjee, Debades Bandyopadhyay, (Saha Institute of Nuclear Physics, India)
Comments: 25 pages, 10 figures; two new figures added and results and discussion section revised; final version to appear in PRD
Note: replaced with revised version Mon, 12 Jun 2006 16:29:07 GMT (34kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 14 Jun 06 00:00:10 GMT
0606276 -- 0606327 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606308 [abs, ps, pdf, other] :
Title: Neutron star masses: dwarfs, giants and neighbors
Authors: S.B. Popov (1), D. Blaschke (2,3), H. Grigorian (2,4), M.E. Prokhorov (1) (1- Sternberg Astronomical Institute; 2- University of Rostock; 3 - JINR Dubna; 4 - Yerevan State University)
Comments: 4 pages, 1 figure, Ap&SS style, to be published in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface"

We discuss three topics related to the neutron star (NS) mass spectrum. At first we discuss the possibility to form low-mass ($ M \stackrel{<}{\sim} 1 M_{\odot}$) and suggest this is possible only due to fragmentation of rapidly rotating proto-NSs. Such low-mass NSs should have very high spatial velocities which could allow identification. A critical assessment of this scenario is given. Secondly, we discuss mass growth due to accretion for NSs in close binary systems. With the help of numerical population synthesis calculations we derive the mass spectrum of massive ($M > 1.8 M_{\odot}$) NSs. Finally, we discuss the role of the mass spectrum in population studies of young cooling NSs. We formulate a kind of {\it mass constraint} which can be helpful, in our opinion, in discussing different competive models of the thermal evolution of NSs.

 
astro-ph/0606310 [abs, ps, pdf, other] :
Title: Seismic signatures of strange stars with crust
Authors: A.I. Chugunov
Comments: 15 pages, 3 figures, Accepted for publication in MNRAS

We study acoustic oscillations (eigenfrequencies, velocity distributions, damping times) of normal crusts of strange stars. These oscillations are very specific because of huge density jump at the interface between the normal crust and the strange matter core. The oscillation problem is shown to be self-similar. For a low (but non-zero) multipolarity l the fundamental mode (without radial nodes) has a frequency ~300 Hz and mostly horizontal oscillation velocity; other pressure modes have frequencies >=20 kHz and almost radial oscillation velocities. The latter modes are similar to radial oscillations (have approximately the same frequencies and radial velocity profiles). The oscillation spectrum of strange stars with crust differs from the spectrum of neutron stars. If detected, acoustic oscillations would allow one to discriminate between strange stars with crust and neutron stars and constrain the mass and radius of the star.

 
astro-ph/0606311 [abs, ps, pdf, other] :
Title: Discovery of the two wings of the Kookaburra complex in VHE gamma -rays with H.E.S.S
Authors: The H.E.S.S. Collaboration: F.A. Aharonian, et al
Comments: 9 pages, 4 figures, accepted for publication in A&A

Aims. Search for Very High Energy gamma-ray emission in the Kookaburra complex through observations with the H.E.S.S. array. Methods. Stereoscopic imaging of Cherenkov light emission of the gamma-ray showers in the atmosphere is used for the reconstruction and selection of the events to search for gamma-ray signals. Their spectrum is derived by a forward-folding maximum likelihood fit. Results. Two extended gamma-ray sources with an angular (68%) radius of 3.3-3.4' are discovered at high (>13sigma) statistical significance: HESS J1420-607 and HESS J1418-609. They exhibit a flux above 1 TeV of (2.97+/-0.18stat +/-0.60sys)x10-12 and (2.17+/-0.17stat +/-0.43sys)x10-12 cm-2 s-1, respectively, and similar hard photon indices ~2.2. Multi-wavelength comparisons show spatial coincidence with the wings of the Kookaburra. Two pulsar wind nebulae candidates, K3/PSR J1420-6048 and the Rabbit, lie on the edge of the H.E.S.S. sources. Conclusions. The two new sources confirm the non-thermal nature of at least parts of the two radio wings which overlap with the gamma-ray emission and establish their connection with the two X-ray pulsar wind nebulae candidates. Given the large point spread function of EGRET, the unidentified source(s) 3EG J1420-6038/GeV J1417-6100 could possibly be related to either or both H.E.S.S. sources. The most likely explanation for the Very High Energy gamma-rays discovered by H.E.S.S. is inverse Compton emission of accelerated electrons on the Cosmic Microwave Background near the two candidate pulsar wind nebulae, K3/PSR J1420-6048 and the Rabbit. Two scenarios which could lead to the observed large (~10 pc) offset-nebula type morphologies are briefly discussed.

 
astro-ph/0606321 [abs, ps, pdf, other] :
Title: Spitzer Space Telescope Infrared Imaging and Spectroscopy of the Crab Nebula
Authors: Tea Temim (1), Robert D. Gehrz (1), Charles E. Woodward (1), Thomas L. Roellig (2), Nathan Smith (3 and 6), Lawrence R. Rudnick (1), Elisha F. Polomski (1), Kris Davidson (1), Lunming Yuen (4), Takashi Onaka (5) ((1) Department of Astronomy, University of Minnesota, (2) NASA Ames Research Center, Moffett Field, CA, (3) Center for Astrophysics and Space Astronomy, University of Colorado, (4) Technosciences Corp., Moffett Field, CA, (5) University of Tokyo, Tokyo, Japan, (6) Visiting Astronomer, Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory (NOAO))
Comments: 21 pages, 4 tables, 16 figures

We present 3.6, 4.5, 5.8, 8.0, 24, and 70 micron images of the Crab Nebula obtained with the Spitzer Space Telescope IRAC and MIPS cameras, Low- and High-resolution Spitzer IRS spectra of selected positions within the nebula, and a near-infrared ground-based image made in the light of [Fe II]1.644 micron. The 8.0 micron image, made with a bandpass that includes [Ar II]7.0 micron, resembles the general morphology of visible H-alpha and near-IR [Fe II] line emission, while the 3.6 and 4.5 micron images are dominated by continuum synchrotron emission. The 24 micron and 70 micron images show enhanced emission that may be due to line emission or the presence of a small amount of warm dust in the nebula on the order of less than 1% of a solar mass. The ratio of the 3.6 and 4.5 micron images reveals a spatial variation in the synchrotron power law index ranging from approximately 0.3 to 0.8 across the nebula. Combining this information with optical and X-ray synchrotron images, we derive a broadband spectrum that reflects the superposition of the flatter spectrum jet and torus with the steeper diffuse nebula, and suggestions of the expected pileup of relativistic electrons just before the exponential cutoff in the X-ray. The pulsar, and the associated equatorial toroid and polar jet structures seen in Chandra and HST images (Hester et al. 2002) can be identified in all of the IRAC images. We present the IR photometry of the pulsar. The forbidden lines identified in the high resolution IR spectra are all double due to Doppler shifts from the front and back of the expanding nebula and give an expansion velocity of approximately 1264 km/s.

 
astro-ph/0606322 [abs, ps, pdf, other] :
Title: Rotochemical Heating of Neutron Stars: Rigorous Formalism with Electrostatic Potential Perturbations
Authors: Andreas Reisenegger, Paula Jofre, Rodrigo Fernandez, Elena Kantor
Comments: 14 pages, including 4 eps figures. Accepted for publication in The Astrophysical Journal

The electrostatic potential that keeps approximate charge neutrality in neutron star matter is self-consistently introduced into the formalism for rotochemical heating presented in a previous paper by Fernandez and Reisenegger. Although the new formalism is more rigorous, we show that its observable consequences are indistinguishable from those of the previous one, leaving the conclusions of the previous paper unchanged.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603741 [abs, ps, pdf, other] :
Title: Magnetic Field Decay and Period Evolution of Anomalous X-Ray Pulsars in the Context of Quark Stars
Authors: Brian Niebergal, Rachid Ouyed, Denis Leahy
Comments: 4 pages, 4 figures, accepted to ApJ Letters
Note: replaced with revised version Tue, 13 Jun 2006 00:05:44 GMT (59kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 15 Jun 06 00:00:09 GMT
0606328 -- 0606357 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606345 [abs, ps, pdf, other] :
Title: Is pulsar B0656+14 a very nearby RRAT source?
Authors: P. Weltevrede, B.W. Stappers, J.M. Rankin, G.A.E. Wright
Comments: 4 pages, 4 figures, accepted by ApJL

The recently discovered RRAT sources are characterized by very bright radio bursts which, while being periodically related, occur infrequently. We find bursts with the same characteristics for the known pulsar B0656+14. These bursts represent pulses from the bright end of an extended smooth pulse-energy distribution and are shown to be unlike giant pulses, giant micropulses or the pulses of normal pulsars. The extreme peak-fluxes of the brightest of these pulses indicates that PSR B0656+14, were it not so near, could only have been discovered as an RRAT source. Longer observations of the RRATs may reveal that they, like PSR B0656+14, emit weaker emission in addition to the bursts.

 

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astro-ph new abstracts, Fri, 16 Jun 06 00:00:09 GMT
0606358 -- 0606387 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606374 [abs, ps, pdf, other] :
Title: Short-lived isotopes and 23Na production in low mass AGB Stars
Authors: S. Cristallo, R. Gallino, O. Straniero, L. Piersanti, I. Dominguez
Comments: 6 pages, 3 figures; in the proceedings of the VIII Torino Workshop on Nucleosynthesis in AGB stars; to be published in Mem.SAIt

We discuss the synthesis of some short-lived isotopes and of 23Na in thermally pulsing AGB stars with initial mass of 2 Msun and two different metallicities (Z=1.5e-2, corresponding to the metal amount in the Sun, and Z=1e-4), representative of disk and halo stars, respectively. The different nucleosynthesis channels are illustrated in some details. As previously found, the 13C formed after each third dredge up episode is usually completely consumed by alpha captures before the onset of the subsequent thermal pulse, releasing neutrons. This is the most efficient neutron source in low mass AGB stars and the resulting s-process nucleosynthesis is at the origin of the solar main component. However, in the solar metallicity model, we find that the temperature of the first formed 13C pocket remains too low during the interpulse and the 13C is not completely burnt, being partially engulfed in the convective zone generated by the following thermal pulse. Due to the rapid convective mixing in this zone, the 13C is exposed to a larger temperature and a nucleosynthesis characterized by a relatively high neutron density develops. The main effect is the strong enhancement of isotopes located beyond some critical branching in the neutron-capture path, like 60Fe, otherwise only marginally produced during a standard s-process nucleosynthesis.

 
astro-ph/0606375 [abs, ps, pdf, other] :
Title: Tearing instability in relativistic magnetically dominated plasmas
Authors: S.S. Komissarov, M. Barkov, M. Lyutikov
Comments: Submitted to MNRAS

Many astrophysical sources of high energy emission, such as black hole magnetospheres, superstrongly magnetized neutron stars (magnetars), and probably relativistic jets in Active Galactic Nuclei and Gamma Ray Bursts involve relativistically magnetically dominated plasma. In such plasma the energy density of magnetic field greatly exceeds the thermal and the rest mass energy density of particles. Therefore the magnetic field is the main reservoir of energy and its dissipation may power the bursting emission from these sources, in close analogy to Solar flares. One of the principal dissipative instabilities that may lead to release of magnetic energy is the tearing instability. In this paper we study, both analytically and numerically, the development of tearing instability in relativistically magnetically-dominated plasma using the framework of resistive magnetodynamics. We confirm and elucidate the previously obtained result on the growth rate of the tearing mode: the shortest growth time is the same as in the case of classical non-relativistic MHD, namely $\tau \sim 1/\sqrt{\tau_A \tau_r}$ where $\tau_A$ is the \Alfven crossing time and $\tau_r$ is the resistive time of a current layer.

 

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astro-ph new abstracts, Mon, 19 Jun 06 00:00:10 GMT
0606388 -- 0606412 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606393 [abs, pdf] :
Title: Very Energetic Gamma-Rays from Microquasars and Binary Pulsars
Authors: I.F. Mirabel
Comments: Perspective article to be published in Science vol. 312 (June 23, 2006)

Compact astrophysical objects produce some of the highest energy light in the universe. The challenge is to determine what mechanism produces these photons.

 
astro-ph/0606396 [abs, ps, pdf, other] :
Title: Chemical Abundance Study of One Red Giant Star in NGC 5694 : A Globular Cluster with Dwarf Spheroidals' Chemical Signature?
Authors: Jae-Woo Lee, Mercedes Lopez-Morales, Bruce W. Carney
Comments: ApJL accepted

We report the abundance analysis of one red giant branch star in the metal-poor outer halo globular cluster NGC 5694. We obtain [Fe/H] = -1.93, based on the ionized lines, and our metallicity measurement is in good agreement with previous estimates. We find that [Ca+Ti/2Fe] and [Cu/Fe] of NGC 5694 are about 0.3 -- 0.4 dex lower than other globular clusters with similar metallicities, but similar to some LMC clusters and stars in some dwarf spheroidal galaxies. Differences persist, however, in the abundances of neutron capture elements. The unique chemical abundance pattern and the large Galactocentric distance (30 kpc) and radial velocity (-138.6 +/- 1.0 km/sec) indicate that NGC 5694 had an extragalactic origin.

 
astro-ph/0606412 [abs, ps, pdf, other] :
Title: Non-Equilibrium Beta Processes in Neutron Stars: A Relationship between the Net Reaction Rate and the Total Emissivity of Neutrinos
Authors: Sergio Flores-Tulian, Andreas Reisenegger
Comments: 8 pages, non tables nor figures, uses aastex.cls

Several different processes could be changing the density in the core of a neutron star, leading to a departure from Beta-equilibrium, quantified by the chemical potential difference du=un-up-ue. The evolution of this quantity is coupled to that of the star's interior temperature T by two functions that quantify the rate at which neutrino-emitting reactions proceed: the net reaction rate (difference between decay and capture rates), Gamma_net(T,du), and the total emissivity (total energy emission rate in the form of neutrinos and antineutrinos), epsilon_tot(T,du). Here, we present a simple and general relationship between these variables, epsilon_tot/du=3 Gamma_net, and show that it holds even in the case of superfluid nucleons. This relation may simplify the numerical calculation of these quantities, including superfluid reduction factors.

 

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astro-ph new abstracts, Tue, 20 Jun 06 00:00:10 GMT
0606413 -- 0606458 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606427 [abs, ps, pdf, other] :
Title: Capture Rates of Compact Objects by Supermassive Black Holes
Authors: José Antonio de Freitas Pacheco, Charline Filloux, Tania Regimbau
Comments: 8 pages, 3 figures; accepted for publication in PRD

Capture rates of compact objects were calculated by using a recent solution of the Fokker-Planck equation in energy-space, including two-body resonant effects. The fraction of compact objects (white dwarfs, neutron stars and stellar black holes) was estimated as a function of the luminosity of the galaxy from a new grid of evolutionary models. Stellar mass densities at the influence radius of central supermassive black holes were derived from brightness profiles obtained by Hubble Space Telescope observations. The present study indicates that the capture rates scale as $\propto M_{bh}^{-1.048}$, consequence of the fact that dwarf galaxies have denser central regions than luminous objects. If the mass distribution of supermassive black holes has a lower cutoff at $\sim 1.4\times 10^6$ M$_{\odot}$ (corresponding to the lowest observed supermassive black hole mass, located in M32), then 9 inspiral events are expected to be seen by LISA (7-8 corresponding to white dwarf captures and 1-2 to neutron star and stellar black hole captures) after one year of operation. However, if the mass distribution extends down to $\sim 2\times 10^5$ M$_{\odot}$, then the total number of expected events increases up to 579 (corresponding to $\sim$ 274 stellar black hole captures, $\sim$ 194 neutron star captures and $\sim$ 111 white dwarf captures).

 

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astro-ph new abstracts, Wed, 21 Jun 06 00:00:13 GMT
0606459 -- 0606492 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606465 [abs, ps, pdf, other] :
Title: Discovery of two pulsars towards the Galactic Centre
Authors: Simon Johnston, M. Kramer, D. R. Lorimer, A. G. Lyne, M. McLaughlin, B. Klein, R. N. Manchester
Comments: Submitted to MNRAS Letters

We report the discovery of two highly dispersed pulsars in the direction of the Galactic Centre made during a survey at 3.1 GHz with the Parkes radio telescope. Both PSRs J1745-2912 and J1746-2856 have an angular separation from the Galactic Centre of less than 0.3 degrees and dispersion measures in excess of 1100 cm-3pc, placing them in the top 10 pulsars when ranked on this value. The frequency dependence of the scatter-broadening in PSR J1746-2856 is much shallower than expected from simple theory. We believe it likely that the pulsars are located between 150 and 500 pc from the Galactic Centre on the near side, and are part of an excess population of neutron stars associated with the Centre itself. A second survey made at 8.4 GHz did not detect any pulsars. This implies either that there are not many bright, long-period pulsars at the Galactic Centre or that the scattering is more severe at high frequencies than current models would suggest.

 
astro-ph/0606478 [abs, ps, pdf, other] :
Title: Statistical Analysis of Point-like Sources in Chandra Galactic Center Survey
Authors: J. F. Wu, S. N. Zhang, F. J. Lu, Y. K. Jin
Comments: 14 pages, 8 figures, accepted by Chinese Journal of Astronomy & Astrophysics

{\it Chandra} Galactic Center Survey detected $\sim 800$ X-ray point-like sources in the $2^{\circ} \times 0.8^{\circ}$ sky region around the Galactic Center. In this paper, we study the spatial and luminosity distributions of these sources according to their spectral properties. Fourteen bright sources detected are used to fit jointly an absorbed power-law model, from which the power-law photon index is determined to be $\sim$2.5. Assuming that all other sources have the same power-law form, the relation between hardness ratio and HI column density $N_H$ is used to estimate the $N_H$ values for all sources. Monte Carlo simulations show that these sources are more likely concentrated in the Galactic center region, rather than distributed throughout the Galactic disk. We also find that the luminosities of the sources are positively correlated with their HI column densities, i.e. a more luminous source has a higher HI column density. From this relation, we suggest that the X-ray luminosity comes from the interaction between an isolated old neutron star and interstellar medium (mainly dense molecular clouds). Using the standard Bondi accretion theory and the statistical information of molecular clouds in the Galactic center, we confirm this positive correlation and calculate the luminosity range in this scenario, which is consistent with the observation ($10^{32}\sim 10^{35}$ ergs s$^{-1}$).

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


hep-ph/0606199 [abs, ps, pdf, other] :
Title: A theory of Cosmic Rays
Authors: Arnon Dar, Alvaro De Rujula
Comments: 40 pages, 34 figures

We present a theory of non-solar cosmic rays (CRs) based on a single type of CR source at all energies. The total luminosity of the Galaxy, the broken power-law spectra with their observed slopes, the position of the `knee(s)' and `ankle', and the CR composition and its variation with energy are all predicted in terms of very simple and completely `standard' physics. The source of CRs is extremely `economical': it has only one parameter to be fitted to the ensemble of all of the mentioned data. All other inputs are `priors', that is, theoretical or observational items of information independent of the properties of the source of CRs, and chosen to lie in their pre-established ranges. The theory is part of a `unified view of high-energy astrophysics' --based on the `Cannonball' model of the relativistic ejecta of accreting black holes and neutron stars. If correct, this model is only lacking a satisfactory theoretical understanding of the `cannon' that emits the cannonballs in catastrophic processes of accretion.

 

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astro-ph new abstracts, Thu, 22 Jun 06 00:00:10 GMT
0606493 -- 0606532 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606504 [abs, ps, pdf, other] :
Title: Standing Accretion Shocks in the Supernova Core: Effects of Convection and Realistic EOS
Authors: Tatsuya Yamasaki, Shoichi Yamada
Comments: accepted by ApJ, 20 pages, 8 figures

We investigated the structure of the spherically symmetric accretion flows through the standing shock wave onto the proto-neutron star in the post-bounce phase of the collapse-driven supernova. We assume that the accretion flow is in a steady state controlled by the neutrino luminosity and mass accretion rate that are kept constant. We obtain solutions of the steady Euler equations for a wide range of neutrino luminosity and mass accretion rate. We employ a realistic EOS and neutrino-heating rates. More importantly, we take into account the effect of convection phenomenologically. For each mass accretion rate, we find the critical neutrino luminosity, above which there exists no steady solution. These critical points are supposed to mark the onset of the shock revival. As the neutrino luminosity increases for a given mass accretion rate, there appears a convectively unstable region at some point before the critical value is reached. We introduce a phenomenological energy flux by convection so that the negative entropy gradient should be canceled out. We find that the convection lowers the critical neutrino luminosity substantially. We also consider the effect of the self-gravity. It is found that the self-gravity is important only when the neutrino luminosity is high. The critical luminosity, however, is little affected if the energy transport by convection is taken into account.

 
astro-ph/0606508 [abs, ps, pdf, other] :
Title: On the Nature of Part Time Radio Pulsars
Authors: Xiang-Dong Li
Comments: 9 pages, accepted to ApJL

The recent discovery of rotating radio transients and the quasi-periodicity of pulsar activity in the radio pulsar PSR B1931$+$24 has challenged the conventional theory of radio pulsar emission. Here we suggest that these phenomena could be due to the interaction between the neutron star magnetosphere and the surrounding debris disk. The pattern of pulsar emission depends on whether the disk can penetrate the light cylinder and efficiently quench the processes of particle production and acceleration inside the magnetospheric gap. A precessing disk may naturally account for the switch-on/off behavior in PSR B1931$+$24.

 
astro-ph/0606523 [abs, ps, pdf, other] :
Title: The conversion of Neutron star to Strange star : A two step process
Authors: Abhijit Bhattacharyya, Sanjay K. Ghosh, Partha S. Joardar, Ritam Mallick, Sibaji Raha
Comments: 18 pages including 9 figures

The conversion of neutron matter to strange matter in a neutron star have been studied as a two step process. In the first step, the nuclear matter gets converted to two flavour quark matter. The conversion of two flavour to three flavour strange matter takes place in the second step. The first process is analysed with the help of equations of state and hydrodynamical equations, whereas, in the second process, non-leptonic weak interaction plays the main role. Velocities and the time of travel through the star of these two conversion fronts have been analysed and compared.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0507052 [abs, ps, pdf, other] :
Title: Brightness constraint for cooling models of young neutron stars
Authors: Hovik Grigorian
Comments: 13 pages 2 figures 1 table
Note: replaced with revised version Wed, 21 Jun 2006 00:59:32 GMT (50kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 23 Jun 06 00:00:11 GMT
0606533 -- 0606567 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606549 [abs, ps, pdf, other] :
Title: The Upper Limit of Magnetic Field Strength in Dense Stellar Hadronic Matter
Authors: Somenath Chakrabarty
Comments: 6 pages Revtex, 2 .eps figures, fig.(1) is not included

It is shown that in strongly magnetized neutron stars, there exist upper limits of magnetic field strength, beyond which the self energies for both neutron and proton components of neutron star matter become complex in nature. As a consequence they decay within the strong interaction time scale. However, in the ultra-strong magnetic field case, when the zeroth Landau level is only occupied by protons, the system again becomes stable against strong decay.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0601302 [abs, ps, pdf, other] :
Title: Multidimensional Supernova Simulations with Approximative Neutrino Transport I. Neutron Star Kicks and the Anisotropy of Neutrino-Driven Explosions in Two Spatial Dimensions
Authors: L. Scheck, K. Kifonidis, H.-Th. Janka, E. Mueller (MPI for Astrophysics, Garching)
Comments: 40 pages, 28 figures; significantly shortened and revised version according to referee's comments; accepted by Astronomy & Astrophysics
Note: replaced with revised version Thu, 22 Jun 2006 14:39:40 GMT (557kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 26 Jun 06 00:00:09 GMT
0606568 -- 0606599 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606581 [abs, ps, pdf, other] :
Title: Stability of the Accretion Flows with Stalled Shocks in Core-Collapse Supernovae
Authors: Tatsuya Yamasaki, Shoichi Yamada
Comments: 37 pages, 15 figures, submitted to ApJ

Bearing in mind the application to the theory of core-collapse supernovae, we performed a global linear analysis on the stability of spherically symmetric accretion flows through a standing shock wave onto a proto neutron star. As unperturbed flows, we adopted the spherically symmetric steady solutions to the Euler equations obtained with realistic equation of state and formulae for neutrino reaction rates taken into account. Then we solved the equations for linear perturbations numerically, and obtained the eigen frequencies and eigen functions. We found (1) the flows are stable for all modes if the neutrino luminosity is lower than $\sim 1\times 10^{52}$ ergs/s for $\dot{M}=1.0M_{\odot}/{\rm s}$. (2) For larger luminosities, the non-radial instabilities are induced, probably via the advection-acoustic cycles. Interestingly, the modes with $\ell=2$ and 3 become unstable at first for relatively low neutrino luminosities, e.g. $\gtrsim 2-3\times 10^{52}$ ergs/s for the same accretion rate, whereas the $\ell=1$ mode is the most unstable for higher luminosities, $\sim 3-7\times 10^{52}$ ergs/s. These are all oscillatory modes. (3) For still larger luminosities, $\sim 7\times 10^{52}$ ergs/s for $\dot{M}=1.0M_{\odot}/{\rm s}$, non-oscillatory modes, both radial and non-radial, become unstable. These non-radial modes were identified as convection. We confirmed the results obtained by numerical simulations that the instabilities induced by the advection-acoustic cycles are more important than the convection for lower neutrino luminosities.

 
astro-ph/0606596 [abs, ps, pdf, other] :
Title: A search for a counterpart of the unidentified gamma-ray source 3EG J2020+4017 (2CG078+2)
Authors: Martin C. Weisskopf, Douglas A. Swartz, Alberto Carraminana, Luis Carrasco, David L. Kaplan, Werner Becker, Ronald F. Elsner, Gottfried Kanbach, Stephen L. O'Dell, Allyn F. Tennant
Comments: 32 pages, 8 figures, submitted to ApJ

We report observations with the Chandra X-ray Observatory of a field in the gamma$-Cygni supernova remnant (SNR78.2+2.1) centered on the cataloged location of the unidentified, bright gamma-ray source 3EG J2020+4017. In this search for an X-ray counterpart to the gamma-ray source, we detected 30 X-ray sources. Of these, we found 17 strong-candidate counterparts in optical (visible through near-infrared) cataloged and an additional 3 through our optical observations. Based upon colors and (for several objects) optical spectra, nearly all the optically identified objects appear to be reddened main-sequence stars. None of the X-ray sources with an optical counterpart is a plausible X-ray counterpart to 3EG J2020+4017 --if that gamma-ray source is a spin-powered pulsar. Many of the 10 X-ray sources lacking optical counterparts are likely (extragalactic) active galactic nuclei, based upon the sky density of such sources. Although one of the 10 optically unidentified X-ray sources could be the gamma-ray source, there is no auxiliary evidence supporting such an identification.

 
astro-ph/0606598 [abs, ps, pdf, other] :
Title: Radio Spectrum and Distance of the SNR HB9
Authors: D.A. Leahy, W.W. Tian
Comments: 7 pages, 5 figures, 1 table, submitted to A&A

New images are presented of the supernova remnant HB9 based on 408 MHz and 1420 MHz continuum emission and HI-line emission data of the Canadian Galactic Plane Survey by the Dominion Radio Astrophysical Observatory. Two methods of spectral index analysis for HB9 are presented and compared: one removes compact sources at both frequencies but is limited to the resolution of the 408 MHz image; the other removes compact sources only in the 1420 MHz image so is effective at higher spatial resolution. The second allows more detailed spectral index variation studies than the first. The two T-T plot methods and new integrated flux densities give spectral index (S$_{\nu}$$\propto$$\nu$$^{-\alpha}$) for the whole of HB9 of 0.484$\pm$0.032; 0.485; and 0.47$\pm$0.06, respectively. These are lower than previous spectral index for HB9 ($\alpha$=0.61). Spatial variations of spectral index are derived using the second method and yield a lower spectral index for interior regions than for the rim. This can be explained by a standard curved interstellar electron energy spectrum combined with lower interior magnetic field compared to that near the outer shock, which results in a larger proportion of steep spectrum emission for lines-of-sight through the central body of the SNR. HI observations show structures probably associated with the SNR in the radial velocity range -22 to -25 km$/$s and suggest a distance of 1.1 kpc for the SNR. This is consistent with the distance to the radio pulsar 0458+46, offset from the center of HB9 by 23$^{\prime}$. However the pulsar spindown and kinematic ages are significantly greater than estimates of the SNR age: the Sedov age for HB9 is 9500 yr and the evaporative cloud model yields ages of 4000-10,000 yr.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0606088 [abs, ps, pdf, other] :
Title: Search for continuous gravitational waves: metric of the multi-detector F-statistic
Authors: Reinhard Prix
Comments: 20 pages, 15 figures, revtex4

We derive the parameter-space metric of the multi-detector F-statistic, which is the optimal detection statistic for continuous gravitational waves in stationary Gaussian noise. We find that there is a family of F-statistic metrics, parametrized by the (unknown) amplitude parameters. We explicitly derive the maximal mismatch-range of this metric family, and we introduce a corresponding "average" F-metric. We show that the multi-detector metric consists of noise-weighted averages of single-detector contributions, which implies that the number of templates required to cover the parameter space does not scale with the number of detectors. Contrary to using a longer observation time, combining more detectors (of similar sensitivity) is therefore the computationally cheapest way to improve the sensitivity of a coherent wide-parameter search for continuous gravitational waves. We explicitly compute the F-statistic metric (family) for signals from isolated spinning neutron stars, and we evaluate the quality of different metric approximations in a Monte-Carlo study. We also compare the metric predictions to the measured mismatches and identify two regimes in which the metric is not a good description of the parameter-space structure.

 

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astro-ph new abstracts, Tue, 27 Jun 06 00:00:13 GMT
0606600 -- 0606634 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606604 [abs, ps, pdf, other] :
Title: Extinction Columns and Intrinsic X-ray Spectra of the Anomalous X-ray Pulsars
Authors: Martin Durant, Marten H. van Kerkwijk (University of Toronto)
Comments: 24 pages, 4 figures. Accepted for publication in ApJ

The X-ray spectra of Anomalous X-ray Pulsars have long been fit by smooth, empirical models such as the sum of a black-body plus a power law. These reproduce the ~0.5 to 10 keV range well, but fail at lower and higher energies, grossly over-predicting the optical and under-predicting the hard X-ray emission. A poorly constrained source of uncertainty in determining the true, intrinsic spectra, in particular at lower energies, is the amount of interstellar extinction. In previous studies, extinction column densities with small statistical errors were derived as part of the fits of the spectra to simple continuum models. Different choices of model, however, each produced statistically acceptable fits, but a wide range of columns. Here, we attempt to measure the interstellar extinction in a model-independent way, using individual absorption edges of the elements O, Fe, Ne, Mg and Si in X-ray grating spectra taken with XMM-Newton. We find that our inferred equivalent hydrogen column density NH for 4U 0142+61 is a factor of 1.4 lower than the typically quoted value from black-body plus power-law fits, and is now consistent with estimates based on the dust scattering halo and visual extinction. For three other sources, we find column densities consistent with earlier estimates. We use our measurements to recover the intrinsic spectra of the AXPs empirically, without making assumptions on what the intrinsic spectral shapes ought to be. We find that the power-law components that dominate at higher energies do not extend below the thermal peak.

 
astro-ph/0606613 [abs, ps, pdf, other] :
Title: Structure of pair winds from compact objects with application to emission from bare strange stars
Authors: A.G. Aksenov, M. Milgrom, V.V. Usov
Comments: 4 pages, 6 figures, 1 table, to appear in the proceedings of the conference "Isolated Neutron Stars: from the Surface to the Interior", London, UK, 24-28 April 2006

We present the results of numerical simulations of stationary, spherically outflowing, electron-positron pair winds, with total luminosities in the range 10^{34}- 10^{42} ergs/s. In the concrete example described here, the wind injection source is a hot, bare, strange star, predicted to be a powerful source of electron-positron pairs created by the Coulomb barrier at the quark surface. We find that photons dominate in the emerging emission, and the emerging photon spectrum is rather hard and differs substantially from the thermal spectrum expected from a neutron star with the same luminosity. This might help distinguish the putative bare strange stars from neutron stars.

 
astro-ph/0606616 [abs, ps, pdf, other] :
Title: Simulation of Coherent Non-Linear Neutrino Flavor Transformation in the Supernova Environment I: Correlated Neutrino Trajectories
Authors: Huaiyu Duan (UCSD), George M. Fuller (UCSD), J Carlson (LANL), Yong-Zhong Qian (UMN)
Comments: 22 pages, 28 (sub)figures, revtex4 format

We present results of large-scale numerical simulations of the evolution of neutrino and antineutrino flavors in the region above the late-time post-supernova-explosion proto-neutron star. Our calculations are the first to allow explicit flavor evolution histories on different neutrino trajectories and to self-consistently couple flavor development on these trajectories through forward scattering-induced quantum entanglement. Employing the atmospheric-scale neutrino mass-squared difference and values of theta_13 allowed by current bounds, we find transformation of neutrino and antineutrino flavors over broad ranges of energy and luminosity in roughly the ``bi-polar'' collective mode. We find that this large-scale flavor conversion, largely driven by the flavor off-diagonal neutrino-neutrino forward scattering potential, sets in much closer to the proto-neutron star than simple estimates based on flavor-diagonal potentials and Mikeheyev-Smirnov-Wolfenstein evolution would indicate. In turn, this suggests that models of r-process nucleosynthesis sited in the neutrino-driven wind could be affected substantially by active-active neutrino flavor mixing, even with the small measured neutrino mass-squared differences.

 

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astro-ph/0412107 [abs, ps, pdf, other] :
Title: The Shapes of Atomic Lines from the Surfaces of Weakly Magnetic Rotating Neutron Stars and Their Implications
Authors: Sudip Bhattacharyya, M. Coleman Miller, Frederick K. Lamb
Comments: Revised version, 16 pages, 6 figures, published in ApJ
Journal-ref: The Astrophysical Journal, 644 (2006) 1085-1089
Note: replaced with revised version Mon, 26 Jun 2006 15:29:11 GMT (391kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 28 Jun 06 00:00:09 GMT
0606635 -- 0606663 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606651 [abs, ps, pdf, other] :
Title: Vector current conservation and neutrino emission from singlet-paired baryons in neutron stars
Authors: L.B. Leinson, A. Perez
Comments: 5 pages, 1 figure
Journal-ref: Physics Letters B 638 (2006) 114

Neutrino emission caused by singlet Cooper pairing of baryons in neutron stars is recalculated by accurately taking into account for conservation of the vector weak currents. The neutrino emissivity via the vector weak currents is found to be several orders of magnitude smaller than that obtained before by different authors. This makes unimportant the neutrino radiation from singlet pairing of protons or hyperons.

 
astro-ph/0606653 [abs, ps, pdf, other] :
Title: Neutrino emission due to Cooper pairing in neutron stars
Authors: L.B. Leinson, A. Perez
Comments: 17 pages, 2 figures

Neutrino emission caused by Cooper pairing of baryons in neutron stars is recalculated by accurately taking into account for conservation of the vector weak current. The vector current contribution to the neutrino emissivity is found to be several orders of magnitude smaller than that obtained before by different authors. Therefore, the neutrino energy losses due to singlet-state pairing of baryons can in practice be neglected in simulations of neutron star cooling. This makes negligible the neutrino radiation from pairing of protons or hyperons. The neutrino radiation from triplet pairing takes place through axial weak currents. For these states, when the total momentum projection is $m_{j}=0$, the vanishing of the vector weak current contribution results in the suppression of the neutrino energy losses by about 25%. The neutrino emissivity due to triplet pairing with $| m_{j}| =2$ is suppressed by about a factor of 3, caused by the collective contribution of spin-density fluctuations in the condensate.

 

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astro-ph new abstracts, Thu, 29 Jun 06 00:00:10 GMT
0606664 -- 0606693 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606674 [abs, ps, pdf, other] :
Title: Physics of Strongly Magnetized Neutron Stars
Authors: Alice K. Harding (GSFC), Dong Lai (Cornell)
Comments: 93 pages. Reports on Progress in Physics, in press (2006)

There has recently been growing evidence for the existence of neutron stars possessing magnetic fields with strengths that exceed the quantum critical field strength of $4.4 \times 10^{13}$ G, at which the cyclotron energy equals the electron rest mass. Such evidence has been provided by new discoveries of radio pulsars having very high spin-down rates and by observations of bursting gamma-ray sources termed magnetars. This article will discuss the exotic physics of this high-field regime, where a new array of processes becomes possible and even dominant, and where familiar processes acquire unusual properties. We review the physical processes that are important in neutron star interiors and magnetospheres, including the behavior of free particles, atoms, molecules, plasma and condensed matter in strong magnetic fields, photon propagation in magnetized plasmas, free-particle radiative processes, the physics of neutron star interiors, and field evolution and decay mechanisms. Application of such processes in astrophysical source models, including rotation-powered pulsars, soft gamma-ray repeaters, anomalous X-ray pulsars and accreting X-ray pulsars will also be discussed. Throughout this review, we will highlight the observational signatures of high magnetic field processes, as well as the theoretical issues that remain to be understood.

 
astro-ph/0606686 [abs, ps, pdf, other] :
Title: A Search for Fallback Disks in Four Young Supernova Remnants
Authors: Zhongxiang Wang, David L. Kaplan, Deepto Chakrabarty
Comments: 9 pages, 5 figures, submitted to ApJ

We report on our search for the optical/infrared counterparts to the central compact objects in four young supernova remnants: Puppis A, PKS 1209-52, RCW 103, and Cassiopeia A. The X-ray point sources in these supernova remnants, likely members of a new class (or classes) of young neutron stars, are attractive targets for probing the existence of supernova ``fallback'' disks. Such disks, which are a general prediction of many supernova models, can form from supernova ejecta that fails to reach escape velocity during the initial explosion. Irradiation of the disk by a central X-ray source may lead to detectable optical/infrared emission from such a disk. We used imaging observations from ground-based telescopes in the optical and near-infrared regimes and from the Spitzer Space Telescope at 4.5 and 8.0 micron, to search for optical/infrared counterparts at the X-ray point source positions measured in these supernova remnants by the Chandra X-Ray Observatory. We did not detect any counterparts, and hence find no evidence for fallback disks around any of these sources. In RCW 103, a blend of 3 faint stars at the X-ray source position prevent us from deriving useful limits. For the other targets, the upper limits on the infrared/X-ray flux ratios are as deep as (1.0--1.7)e-4. Comparing these limits to the ratio of 6e-5 measured for 4U 0142+61 (a young pulsar recently found with an X-ray irradiated dust disk), we conclude that the non-detection of any disks around the young neutron stars studied here are consistent with their relatively low X-ray luminosities, although we note that a similar dust disk around the neutron star in Puppis A should be detectable by deeper infrared observations.

 

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astro-ph new abstracts, Fri, 30 Jun 06 00:00:07 GMT
0606694 -- 0606737 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606708 [abs, ps, pdf, other] :
Title: Constraining a possible time-variation of the gravitational constant through "gravitochemical heating" of neutron stars
Authors: Paula Jofre, Andreas Reisenegger (Pontificia Universidad Catolica de Chile), Rodrigo Fernandez (University of Toronto)
Comments: 4 pages, including 2 figures. Submitted to Phys. Rev. Lett

A hypothetical time-variation of the gravitational constant $G$ would cause neutron star matter to depart from beta equilibrium, due to the changing hydrostatic equilibrium. This forces non-equilibrium beta processes to occur, which release energy that is invested partly in neutrino emission and partly in heating the stellar interior. Eventually, the star arrives at a stationary state in which the temperature remains nearly constant, as the forcing through the change of $G$ is balanced by the ongoing reactions. Comparing the surface temperature of the nearest millisecond pulsar, PSR J0437-4715, inferred from ultraviolet observations, with our predicted stationary temperature, we estimate two upper limits for this variation: (1) $|\dot G/G| < 2 \times 10^{-10}$ yr$^{-1}$, if we allow direct Urca reactions operating in the neutron star core, and (2) $|\dot G/G| < 4 \times 10^{-12}$ yr$^{-1}$, considering only modified Urca reactions. Both results are competitive with those obtained by other methods, with (2) being among the most restrictive.

 
astro-ph/0606721 [abs, ps, pdf, other] :
Title: Global optical/infrared - X-ray correlations in X-ray binaries: quantifying disc and jet contributions
Authors: D. M. Russell (1), R. P. Fender (1), R. I. Hynes (2), C. Brocksopp (3), J. Homan (4), P. G. Jonker (5,6,7), M. M. Buxton (8) ((1) Southampton, (2) Louisiana State Univ., (3) MSSL, (4) MIT, (5) SRON, (6) Harvard, (7) Utrecht, (8) Yale)
Comments: Accepted for publication in MNRAS; 19 pages, 7 figures

The optical/near-infrared (OIR) region of the spectra of low-mass X-ray binaries appears to lie at the intersection of a variety of different emission processes. In this paper we present quasi-simultaneous OIR - X-ray observations of 33 XBs in an attempt to estimate the contributions of various emission processes in these sources, as a function of X-ray state and luminosity. A global correlation is found between OIR and X-ray luminosity for low-mass black hole candidate XBs (BHXBs) in the hard X-ray state, of the form L_OIR is proportional to Lx^0.6. This correlation holds over 8 orders of magnitude in Lx and includes data from BHXBs in quiescence and at large distances (LMC and M31). A similar correlation is found in low-mass neutron star XBs (NSXBs) in the hard state. For BHXBs in the soft state, all the near-infrared (NIR) and some of the optical emission is suppressed below the correlation, a behaviour indicative of the jet switching off/on in transition to/from the soft state. We compare these relations to theoretical models of a number of emission processes. We find that X-ray reprocessing in the disc and emission from the jets both predict a slope close to 0.6 for BHXBs, and both contribute to the OIR in BHXBs in the hard state, the jets producing ~90 percent of the NIR emission at high luminosities. X-ray reprocessing dominates the OIR in NSXBs in the hard state, with possible contributions from the jets (only at high luminosity) and the viscously heated disc. We also show that the optically thick jet spectrum of BHXBs extends to near the K-band. (abridged)

 
astro-ph/0606732 [abs, ps, pdf, other] :
Title: Chandra X-Ray Observatory Observations of Neutron Stars: An Overview
Authors: M. C. Weisskopf, M. Karovska, G. G. Pavlov, , V. E. Zavlin, T. Clarke
Comments: 10 pages, 14 figures. Submitted to Astronomy and Space Science. Based on presentation at Isolated Neutron Stars, London, 2006

We present a brief review of Chandra X-ray Observatory observations of neutron stars. The outstanding spatial and spectral resolution of this great observatory have allowed for observations of unprecedented clarity and accuracy. Many of these observations have provided new insights into neutron star physics. We present an admittedly biased and overly brief overview of these observations, highlighting some new discoveries made possible by the Observatory's unique capabilities. We also include our analysis of recent multiwavelength observations of the putative pulsar and its pulsar-wind nebula in the IC 443 SNR.

 

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astro-ph new abstracts, Mon, 3 Jul 06 00:00:16 GMT
0606738 -- 0606763 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606752 [abs, ps, pdf, other] :
Title: Disc-Jet coupling in the LMXB 4U1636-53 from INTEGRAL
Authors: Mariateresa Fiocchi, Angela Bazzano, Pietro Ubertini, Pierre Jean
Comments: 6 pages, 4 figures, 2 tables. accepted ApJ

We report on the spectral analysis results of the neutron star, atoll type, low mass X-ray Binary 4U1636-53 observed by INTEGRAL and BeppoSAX satellites. Spectral behavior in three different epochs corresponding to three different spectral states has been deeply investigated. Two data set spectra show a continuum well described by one or two soft blackbody plus a Comptonized components with changes in the Comptonizing electrons and black body temperature and the accretion rates, which are typical of the spectral transitions from high to low state. In one occasion INTEGRAL spectrum shows, for first time in this source, a hard tail dominating the emission above 30 keV. The total spectrum is fitted as the sum of a Comptonized component similar to soft state and a power-law component (Gamma=2.76), indicating the presence of a non thermal electron distribution of velocities. In this case, a comparison with hard tails detected in soft states from neutron stars systems and some black hole binaries suggests that a similar mechanism could originate these components in both cases.

 
astro-ph/0606754 [abs, ps, pdf, other] :
Title: Type I and Two-Gap Superconductivity in Neutron Star Magnetism
Authors: P B Jones
Comments: 8 pages, 0 figures; to be published in MNRAS

Neutron-star inner cores with several charged baryonic components are likely to be analogues of the two-gap superconductor which is of current interest in condensed-matter physics. Consequently, type I superconductivity is less probable than type II but may nevertheless be present in some intervals of matter density. The intermediate state structure formed at finite magnetic flux densities after the superconducting transitions is subject to buoyancy, frictional and neutron-vortex interaction forces. These are estimated and it is shown that the most important frictional force is that produced by the stable stratification of neutron-star matter, the irreversible process being diffusion in the normal, finite magnetic-flux density, parts of the structure. The length-scale of the structure, in directions perpendicular to the local magnetic field is of crucial importance. For small scales, the flux comoves with the neutron vortices, as do the proton vortices of a type II superconductor. But for much larger length-scales, flux movement tends to that expected for normal charged Fermi systems.

 

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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602417 [abs, ps, pdf, other] :
Title: Corona of Magnetars
Authors: Andrei M. Beloborodov, Christopher Thompson
Comments: 69 pages, 14 figures, submitted to ApJ
Note: replaced with revised version Fri, 30 Jun 2006 00:51:10 GMT (119kb)
 
astro-ph/0603752 [abs, ps, pdf, other] :
Title: A self-consistent model of isolated neutron stars: the case of the X-ray pulsar RX J0720.4-3125
Authors: J.F.Perez-Azorin, J.A.Pons, J.A.Miralles, G. Miniutti
Comments: Replaced with extended version, 13 pages, 7 figures
Note: replaced with revised version Fri, 30 Jun 2006 09:00:40 GMT (85kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 4 Jul 06 00:00:11 GMT
0607001 -- 0607029 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607005 [abs, ps, pdf, other] :
Title: Exotic bulk viscosity and its influence on neutron star r-modes
Authors: Debarati Chatterjee, Debades Bandyopadhyay
Comments: 5 pages, 3 figure, presented in the Conference on Isolated Neutron Stars: From the Interior to The Surface, London, UK, 24-28 April, 2006

We investigate the effect of exotic matter in particular, hyperon matter on neutron star properties such as equation of state (EoS), mass-radius relationship and bulk viscosity. Here we construct equations of state within the framework of a relativistic field theoretical model. As large number of hyperons may be produced in dense matter, hyperon-hyperon interaction is important and included in this model. Hyperon-hyperon interaction makes the EoS softer resulting in a smaller maximum mass neutron star compared with the case without the interaction. Next we compute the coefficient of bulk viscosity and the corresponding damping time scale due to the non-leptonic weak process including $\Lambda$ hyperons. Further, we investigate the role of the bulk viscosity on gravitational radiation driven r-mode instability for a neutron star of given mass and temperature and find that the instability is effectively suppressed.

 
astro-ph/0607025 [abs, ps, pdf, other] :
Title: X-ray Spectral Study of the Photoionized Stellar Wind in Vela~X-1
Authors: Shin Watanabe (1), Masao Sako (2), Manabu Ishida (3), Yoshitaka Ishisaki (3), Steven M. Kahn (2), Takayoshi Kohmura (4), Fumiaki Nagase (1), Frederik Paerels (5), Tadayuki Takahashi (1) ((1) ISAS/JAXA, (2) KIPAC, Stanford University, (3) Department of Physics, Tokyo Metropolitan University, (4) Kogakuin University, (5) Columbia Astrophysics Laboratory)
Comments: 22 pages, 7 tables, 24 figures, accepted for publication in The Astrophysical Journal

We present results from quantitative modeling and spectral analysis of the high mass X-ray binary Vela X-1 obtained with the Chandra HETGS. The spectra exhibit emission lines from H-like and He-like ions driven by photoionization, as well as fluorescent emission lines from several elements in lower charge states. In order to interpret and make full use of the high-quality data, we have developed a simulator, which calculates the ionization and thermal structure of a stellar wind photoionized by an X-ray source, and performs Monte Carlo simulations of X-ray photons propagating through the wind. The emergent spectra are then computed as a function of the viewing angle accurately accounting for photon transport in three dimensions including dynamics. From comparisons of the observed spectra with the simulation results, we are able to find the ionization structure and the geometrical distribution of material in Vela X-1 that can reproduce the observed spectral line intensities and continuum shapes at different orbital phases remarkably well. It is found that a large fraction of X-ray emission lines from highly ionized ions are formed in the region between the neutron star and the companion star. We also find that the fluorescent X-ray lines must be produced in at least three distinct regions --(1)the extended stellar wind, (2)reflection off the stellar photosphere, and (3)in a distribution of dense material partially covering and possibly trailing the neutron star, which may be associated with an accretion wake. Finally, from detailed analysis of the emission lines, we demonstrate that the stellar wind is affected by X-ray photoionization.

 

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astro-ph new abstracts, Wed, 5 Jul 06 00:00:08 GMT
0607030 -- 0607060 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607035 [abs, ps, pdf, other] :
Title: The induced turbulence effect on propagation of radio emission in pulsar magnetospheres
Authors: Qinghuan Luo, D. B. Melrose
Comments: 11 pages, 3 figures, accepted for publication in MNRAS

The effect of photon-beam-induced turbulence on propagation of radio emission in a pulsar magnetosphere is discussed. Beamed radio emission with a high brightness temperature can generate low-frequency plasma waves in the pulsar magnetosphere and these waves scatter the radio beam. We consider this effect on propagation of radio emission both in the open field line region and in the closed field line region. The former is applicable to most cases of pulsar radio emission where the propagation is confined to the polar region; it is shown that the induced process is not effective for radio emission of moderately high brightness temperature but can have a severe effect on giant pulses. For giant pulses not to be affected by this process, they must be emitted very close to the light cylinder. We show that the induced process is efficient in the closed field line region, inhibiting propagation of the radio emission in this region.

 
astro-ph/0607051 [abs, ps, pdf, other] :
Title: Bulk viscosity of Mixed nucleon-hyperon-quark Matter in Neutron stars
Authors: Na-Na Pan, Xiao-Ping Zheng, Jia-Rong Li
Comments: This paper contains 17 pages,8 figures and 1 table and is accepted by Monthly Notices of the Royal Astronomical Society

We calculate the coefficient of bulk viscosity by considering the non-leptonic weak interactions in the cores of hybrid stars with both hyperons and quarks. We first determine the dependence of the production rate of neutrons on the reaction rate of quarks in the non-leptonic processes, that is $\Gamma_{n}=K_{s}\Gamma_{s}+\Gamma_{\Lambda}+2\Gamma_{\Sigma^{-}}$. The conversion rate, $K_{s}$ in our scenario is a complicated function of baryon number density. We also consider medium effect of quark matter on bulk viscosity. Using these results, we estimate the limiting rotation of the hybrid stars, which may suppress the r-mode instability more effectively. Hybrid stars should be the candidates for the extremely rapid rotators .

 

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astro-ph new abstracts, Thu, 6 Jul 06 00:00:08 GMT
0607061 -- 0607084 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607068 [abs, ps, pdf, other] :
Title: CXOU J121538.2+361921 in the galaxy NGC 4214: a double neutron star in the making?
Authors: J. Dewi
Comments: MNRAS Lett., accepted

CXOU J121538.2+361921 is the brightest X-ray source in the galaxy NGC 4214, with an X-ray luminosity of up to 0.7 x 10^39 erg/s. The observed periodicity of 3.62 hr is interpreted as the orbital period of the system. It has been suggested that the system is a low-mass helium star with a lower-mass compact companion. If this idea is correct, then CXOU J121538.2+361921 will evolve into a double neutron star, a binary consisting of a radio pulsar and another neutron star. In this study we investigate further this possibility. We find that the X-ray luminosity is consistent with super-Eddington accretion in a helium star-neutron star binary. The binary is in a state of mass transfer phase which is initiated when the helium-star donor is on the helium shell burning stage. A donor star with a current mass in the range of around 2.2 - 3.6 Msun is required to explain the observed orbital period. Helium stars in this mass range are massive enough to collapse in a supernova explosion, making CXOU J121538.2+361921 the immediate progenitor of a double neutron star.

 
astro-ph/0607081 [abs, ps, pdf, other] :
Title: Exploring the Central Compact Object in the RX J0852.0-4622 Supernova Remnant with XMM-Newton
Authors: W.Becker, C.Y.Hui, B.Aschenbach, A.Iyudin
Comments: submitted to Astronomy and Astrophysics

The properties of the presumably young galactic supernova remnant (SNR) RX J0852.0-4622, discovered by ROSAT, are still uncertain. The data concerning the distance to the SNR, its age, and the presence of a compact remnant remain controversial. We report the results of several XMM-Newton observations of CXOU J085201.4-461753, the central compact source in RX J0852.0-4622. The currently prefered interpretation of CXOU J085201.4-461753 being a neutron star is in line with our analysis. The Chandra candidate pulsation periods are not confirmed; actually no period was found down to a 3-sigma upper limit for any pulsed fraction. The spectrum of CXOU J085201.4-461753 is best described by either a two blackbody spectrum or a single blackbody spectrum with a high energy power law tail. The two blackbody temperatures of 4 MK and 6.6 MK along with the small size of the emitting regions with radii of 0.36 and 0.06 km invalidate the interpretation that the thermal radiation is cooling emission from the entire neutron star surface. The double blackbody model suggests emission from the neutron star's hot polar regions. No X-ray lines, including the emission feature previously claimed to be present in Chandra data, were found.

 

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astro-ph/0606613 [abs, ps, pdf, other] :
Title: Structure of pair winds from compact objects with application to emission from bare strange stars
Authors: A.G. Aksenov, M. Milgrom, V.V. Usov
Comments: 4 pages, 6 figures, 1 table, added references, to appear in the proceedings of the conference "Isolated Neutron Stars: from the Surface to the Interior", London, UK, 24-28 April 2006
Note: replaced with revised version Wed, 5 Jul 2006 12:46:47 GMT (103kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 7 Jul 06 00:00:09 GMT
0607085 -- 0607115 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607104 [abs, ps, pdf, other] :
Title: High Energy Neutrinos and Cosmic-Rays from Low-Luminosity Gamma-Ray Bursts?
Authors: Kohta Murase, Kunihito Ioka, Shigehiro Nagataki, Takashi Nakamura
Comments: 11 pages, 2 figures

The recently discovered gamma-ray burst (GRB) 060218/SN 2006aj is classified as an X-ray Flash with very long duration driven possibly by a neutron star. Since GRB 060218 is very near 140 Mpc and very dim, one-year observation by Swift suggests that the true rate of GRB 060218-like events might be very high so that such low luminosity GRBs (LL-GRBs) might form a different population of GRBs from the cosmological high luminosity GRBs (HL-GRBs). We found that the high energy neutrino background from such LL-GRBs could be comparable with or larger than that from HL-GRBs. If each neutrino event is detected by IceCube, later optical-infrared follow-up observations such as by Subaru could identify a Type Ibc supernova associated with LL-GRBs, even if gamma- and X-rays are not observed by Swift. This is in a sense a new window from neutrino astronomy, which might enable us to confirm the existence of LL-GRBs and to obtain information about their rate and origin. We also argue LL-GRBs as high energy gamma-ray and cosmic-ray sources.

 
astro-ph/0607105 [abs, ps, pdf, other] :
Title: Ekman layer damping of r-modes revisited
Authors: Kostas Glampedakis, Nils Andersson
Comments: 16 pages, 2 eps figures. Accepted for publication in MNRAS. Part of this paper's material has previously appeared in astro-ph/0411750

We investigate the damping of neutron star r-modes due to the presence of a viscous boundary (Ekman) layer at the interface between the crust and the core. Our study is motivated by the possibility that the gravitational-wave driven instability of the inertial r-modes may become active in rapidly spinning neutron stars, eg. in low-mass X-ray binaries, and the fact that a viscous Ekman layer at the core-crust interface provides an efficient damping mechanism for these oscillations. We review various approaches to the problem and carry out an analytic calculation of the effects due to the Ekman layer for a rigid crust. Our analytic estimates support previous numerical results, and provide further insight into the intricacies of the problem. We add to previous work by discussing the effect that compressibility and composition stratification have on the boundary layer damping. We show that, while stratification is unimportant for the r-mode problem, composition suppresses the damping rate by about a factor of two (depending on the detailed equation of state).

 
astro-ph/0607106 [abs, ps, pdf, other] :
Title: The superflares of soft Gamma-ray repeatres: giant quakes in solid quark stars?
Authors: R. X. Xu (PKU), D. J. Tao (PKU), Y. Yang (PKU)
Comments: 4 pages, 3 figures

Three times of supergiant flares from soft $\gamma$-ray repeatres are observed, with typical released energy of $\sim 10^{44-47}$ erg. A conventional model (i.e., the magnetar model) for such events is catastrophic magnetism-powered instability through magnetohydrodynamic process, in which a significant part of short-hard $\gamma$-ray bursts could also be the results of magnetars. Based on various observational features (e.g., precession, glitch, thermal photon emission) and the underlying theory of strong interaction (quantum chromodynamics, QCD), it could not be ruled out yet that pulsar-like stars might be actually solid quark stars. Strain energy develops during a solid star's life, and starquakes could occur when stellar stresses reach a critical value, with huge energy released. An alternative model for supergiant flares of soft $\gamma$-ray repeatres is presented, in which energy release during a star quake of solid quark stars is calculated. Numerical results for spherically asymmetric solid stars show that the released gravitational energy during a giant quake could be as high as $10^{48}$ erg if the tangential pressure is slightly higher than the radial one.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 10 Jul 06 00:00:09 GMT
0607116 -- 0607150 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607124 [abs, pdf] :
Title: Propeller driven spectral state transition in LMXB 4U 1608-52
Authors: Xie Chen, Shuang Nan Zhang, Guo Qiang Ding
Comments: 13 pages, 3 figures, accepted by Astrophysical Journal

Spectral state transitions in neutron star LMXB systems have been widely observed yet not well understood. Here we report an abrupt spectral change in 4U 1608-52, a typical atoll source, during its decay phase of the 2004 outburst. The source is found to undergo sudden changes in its spectral hardness and other properties. The transition occurred when its luminosity is between (3.3-5.3) E36 ergs/s, assuming a distance of 3.6 kpc. Interpreting this event in terms of the propeller effect, we infer the neutron star surface magnetic field as (1.4-1.8) E8 Gauss. We also briefly discuss similarities and differences between the spectral states of neutron star and black hole binary systems.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604163 [abs, ps, pdf, other] :
Title: Resonant Tidal Excitations of Inertial Modes in Coalescing Neutron Star Binaries
Authors: Dong Lai (Cornell), Yanqin Wu (Toronto)
Comments: Minor changes. 6 pages. Phys. Rev. D. in press (volume 74, issue 2)
Note: replaced with revised version Thu, 6 Jul 2006 21:33:30 GMT (11kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 11 Jul 06 00:00:12 GMT
0607151 -- 0607202 received


7 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607161 [abs, ps, pdf, other] :
Title: Transitions between turbulent and laminar superfluid vorticity states in the outer core of a neutron star
Authors: C. Peralta (1,2), A. Melatos (1), M. Giacobello (3), A. Ooi (3)
Comments: (1) School of Physics, University of Melbourne, Parkville, VIC 3010, Australia. (2) Departamento de Fisica, Escuela de Ciencias,Universidad de Oriente, Cumana, Venezuela, (3) Department of Mechanical and Manufacturing Engineering, University of Melbourne, Parkville, VIC 3010, Australia. Accepted for publication in The Astrophysical Journal. 30 pages, 9 figures (in jpg format)

We investigate the global transition from a turbulent state of superfluid vorticity to a laminar state, and vice versa, in the outer core of a neutron star. By solving numerically the hydrodynamic Hall-Vinen-Bekarevich-Khalatnikov equations for a rotating superfluid in a differentially rotating spherical shell, we find that the meridional counterflow driven by Ekman pumping exceeds the Donnelly-Glaberson threshold throughout most of the outer core, exciting unstable Kelvin waves which disrupt the rectilinear vortex array, creating a vortex tangle. In the turbulent state, the torque exerted on the crust oscillates, and the crust-core coupling is weaker than in the laminar state. This leads to a new scenario for the rotational glitches observed in radio pulsars: a vortex tangle is sustained in the differentially rotating outer core by the meridional counterflow, a sudden spin-up event brings the crust and core into corotation, the vortex tangle relaxes back to a rectilinear vortex array, then the crust spins down electromagnetically until enough meridional counterflow builds up to reform a vortex tangle. The turbulent-laminar transition can occur uniformly or in patches; the associated time-scales are estimated from vortex filament theory. We calculate numerically the global structure of the flow with and without an inviscid superfluid component, for Hall-Vinen and Gorter-Mellink forms of the mutual friction. We also calculate the post-glitch evolution of the angular velocity of the crust and its time derivative, and compare the results with radio pulse timing data, predicting a correlation between glitch activity and Reynolds number.

 
astro-ph/0607165 [abs, ps, pdf, other] :
Title: Force-free magnetosphere of an aligned rotator with differential rotation of open magnetic field lines
Authors: Andrey N. Timokhin (Sternberg Astronomical Institute, Moscow, Russia)
Comments: 5 pages, 4 figures. Presented at the conference "Isolated Neutron Stars: from the Interior to the Surface", London, April 24-28, 2006; to appear in Astrophysics and Space Science

Here we briefly report on results of self-consistent numerical modeling of a differentially rotating force-free magnetosphere of an aligned rotator. We show that differential rotation of the open field line zone is significant for adjusting of the global structure of the magnetosphere to the current density flowing through the polar cap cascades.

 
astro-ph/0607166 [abs, ps, pdf, other] :
Title: Density-Functional-Theory Calculations of Matter in Strong Magnetic Fields: I. Atoms and Molecules
Authors: Zach Medin, Dong Lai (Cornell)
Comments: 19 pages, 7 figures, submitted to Phys. Rev. A

We present new ab initio calculations of the electronic structure of various atoms and molecules in strong magnetic fields ranging from B=10^12 G to 2x10^15 G, appropriate for radio pulsars and magnetars. For these field strengths, the magnetic forces on the electrons dominate over the Coulomb forces, and to a good approximation the electrons are confined to the ground Landau level. Our calculations are based on the density functional theory, and use a local magnetic exchange-correlation function which is tested to be reliable in the strong field regime. Numerical results of the ground-state energies are given for H_N (up to N=10), He_N (up to N=8), C_N (up to N=5) and Fe_N (up to N=3), as well as for various ionized atoms. Fitting formulae for the B-dependence of the energies are also given. In general, as N increases, the binding energy per atom in a molecule, |E_N|/N, increases and approaches a constant value. For all the field strengths considered in this paper, hydrogen, helium, and carbon molecules are found to be bound relative to individual atoms (although for B less than a few x 10^12 G, the relative binding between C and C_2 is small). Iron molecules are not bound at B<10^13 G, but become energetically more favorable than individual atoms at larger field strengths.

 
astro-ph/0607168 [abs, ps, pdf, other] :
Title: Atmosphere Models of Magnetized Neutron Stars: QED Effects, Radiation Spectra, and Polarization Signals
Authors: Matthew van Adelsberg, Dong Lai (Cornell University)
Comments: 30 pages, 23 figures, MNRAS submitted

Theoretical modeling of surface emission from magnetized neutron stars (NSs) requires proper treatment of QED effects, in particular the effect of photon mode conversion due to the ``vacuum resonance'' between plasma and vacuum polarization. Previous NS atmosphere models incorporated this effect approximately, using transfer equations for the photon modes which are inadequate near the vacuum resonance, particularly for field strengths around $B_l\simeq 7\times 10^{13}$ G, where the vacuum resonance occurs near the photosphere. In this paper, we provide an accurate treatment of the QED-induced mode conversion effect in NS atmosphere models, employing both the modal radiative transfer equations, coupled with an accurate mode conversion probability at the resonance, and the full evolution equations for the photon Stokes parameters. In doing so, we are able to quantitatively calculate the effects of vacuum polarization on the atmosphere emission spectra, beam patterns, and polarizations for the entire range of field strengths, $B=10^{12}-10^{15}$ G. We find that for NSs with $B\ga 2 B_l$, vacuum polarization reduces the widths of spectral features, and softens the hard spectral tail typical of magnetized atmosphere models. For $B\la B_l/2$, vacuum polarization does not change the emission spectra, but can significantly affect the polarization signals. We show that vacuum polarization induces a unique energy-dependent linear polarization signature, and that circular polarization can be generated in the magnetospheres of rapidly rotating NSs. We discuss the implications of our results for recent observations of thermally emitting isolated NSs and magnetars, as well as the prospects for future spectral and polarization observations.

 
astro-ph/0607173 [abs, pdf] :
Title: A long-period, violently-variable X-ray source in a young SNR
Authors: A. De Luca, P.A. Caraveo, S. Mereghetti, A. Tiengo, G.F. Bignami
Comments: Accepted for publication in Science. Published online via Science Express on 2006, July 6. 17 pages, 7 figures

Observations with the Newton X-ray Multimirror Mission (XMM) show a strong periodic modulation at 6.67+/-0.03 hours of the X-ray source at the centre of the 2,000-year-old supernova remnant RCW 103. No fast pulsations are visible. If genetically tied to the supernova remnant, the source could either be an X-ray binary, comprising a compact object and a low-mass star in an eccentric orbit, or an isolated neutron star. In the latter case, its age-period combination would point to a peculiar magnetar, dramatically slowed-down, possibly by a supernova debris disc. Both scenarios require non-standard assumptions on the formation and evolution of compact objects in supernova explosions.

 
astro-ph/0607180 [abs, ps, pdf, other] :
Title: Neutrinos, Fisson Cycling, and the r-process
Authors: J. Beun, G. C. McLaughlin, R. Surman, W. R. Hix
Comments: Presented at NIC-IX, International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX, CERN, Geneva, Switzerland, 25-30 June, 2006

It has long been suggested that fission cycling may play an important role in the r-process. Fission cycling can only occur in a very neutron rich environment. In traditional calculations of the neutrino driven wind of the core-collapse supernova, the environment is not sufficiently neutron rich to produce the r-process elements. However, we show that with a reduction of the electron neutrino flux coming from the supernova, fission cycling does occur and furthermore it produces an abundance pattern which is consistent with observed r-process abundance pattern in halo stars. Such a reduction can be caused by active-sterile neutrino oscillations or other new physics.}

 
astro-ph/0607189 [abs, ps, pdf, other] :
Title: Accretion to a Magnetized Neutron Star in the "Propeller" Regime
Authors: O.D. Toropina, M.M. Romanova, R.V.E. Lovelace
Comments: Published in Proceedings of the 13th Young Scientists' Conference on Astronomy and Space Physics, held in Kyiv, Ukraine, April 25-29, 2006, Eds.: Golovin, A.; Ivashchenko, G.; Simon, A

We investigate spherical accretion to a rotating magnetized star in the "propeller" regime using axisymmetric resistive magnetohydrodynamic simulations. The regime is predicted to occur if the magnetospheric radius is larger than the corotation radius and smaller than the light cylinder radius. The simulations show that accreting matter is expelled from the equatorial region of the magnetosphere and that it moves away from the star in a supersonic, disk-shaped outflow. At larger radial distances the outflow slows down and becomes subsonic. The equatorial matter outflow is initially driven by the centrifugal force, but at larger distances the pressure gradient force becomes significant. We find the fraction of the Bondi accretion rate which accretes to the surface of the star.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 12 Jul 06 00:00:10 GMT
0607203 -- 0607233 received


7 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607213 [abs, ps, pdf, other] :
Title: Helium-rich thermonuclear bursts and the distance to the accretion-powered millisecond pulsar SAX J1808.4-3658
Authors: Duncan Galloway (1), Andrew Cumming (2) ((1) University of Melbourne, (2) McGill University)
Comments: 10 pages, 6 figures, accepted by ApJ

We analysed Rossi X-ray Timing Explorer observations of the accretion-powered 401 Hz pulsar SAX J1808.4-3658, in order to precisely determine the source distance. While the fluences for the five transient outbursts observed from 1996 were constant to within the uncertainties, the outburst interval varied signficantly, so that the time-averaged flux (and accretion rate) decreased by around 40%. By equating the time-averaged X-ray flux with the expected mass transfer rate from gravitational radiation, we derived a lower limit on the distance of 3.4 kpc. Combined with an upper limit from assuming that the four radius-expansion thermonuclear bursts observed during the 2002 October outburst reached at most the Eddington limit for a pure He atmosphere, we found that the probable distance range for the source is 3.4-3.6 kpc. The implied inclination, based on the optical/IR properties of the counterpart, is i<~30 degrees.
We compared the properties of the bursts with an ignition model. The time between bursts was long enough for hot CNO burning to significantly deplete the accreted hydrogen, so that ignition occurred in a pure helium layer underlying a stable hydrogen burning shell. This is the first time that this burning regime has been securely observationally identified. The observed energetics of the bursts give a mean hydrogen fraction at ignition of <X> approx. 0.1, and require that the accreted hydrogen fraction X_0 and the CNO metallicity Z_CNO are related by Z_CNO approx. 0.03(X_0/0.7)^2. We show that in this burning regime, a measurement of the burst recurrence time and energetics allows the local accretion rate onto the star to be determined independently of the accreted composition, giving a new method for estimating the source distance which is in good agreement with our other estimates.

 
astro-ph/0607214 [abs, ps, pdf, other] :
Title: Magnetic burial and the harmonic content of millisecond oscillations in thermonuclear X-ray bursts
Authors: D. J. B. Payne, A. Melatos
Comments: 8 pages, 3 figures, accepted for publication in The Astrophysical Journal

Matter accreting onto the magnetic poles of a neutron star spreads under gravity towards the magnetic equator, burying the polar magnetic field and compressing it into a narrow equatorial belt. Steady-state, Grad-Shafranov calculations with a self-consistent mass-flux distribution (and a semi-quantitative treatment of Ohmic diffusion) show that, for $\Ma \gtrsim 10^{-5}\Msun$, the maximum field strength and latitudinal half-width of the equatorial magnetic belt are $B_{\rm max} = 5.6\times 10^{15} (\Ma/10^{-4}\Msun)^{0.32}$ G and $\Delta\theta = \max[3^{\circ} (\Ma/10^{-4}\Msun)^{-1.5},3^{\circ} (\Ma/10^{-4}\Msun)^{0.5}(\dot{M}_{\rm a}/10^{-8}\Msun {\rm yr}^{-1})^{-0.5}]$ respectively, where $\Ma$ is the total accreted mass and $\dot{M}_{\rm a}$ is the accretion rate. It is shown that the belt prevents north-south heat transport by conduction, convection, radiation, and ageostrophic shear. This may explain why millisecond oscillations observed in the tails of thermonuclear (type I) X-ray bursts in low-mass X-ray binaries are highly sinusoidal: the thermonuclear flame is sequestered in the magnetic hemisphere which ignites first. The model is also consistent with the occasional occurrence of closely spaced pairs of bursts. Time-dependent, ideal-magnetohydrodynamic simulations confirm that the equatorial belt is not disrupted by Parker and interchange instabilities.

 
astro-ph/0607215 [abs, pdf] :
Title: The Origin Magnetars: the role of anisotropic neutron superfluid of neutron stars
Authors: Qiu-he Peng
Comments: 6 page, no figures

We estimate the strength of the induced magnetic field due to the total induced magnetic moment of the anisotropic ($^3PF^2$) neutron superfluid interior of neutron stars. The induced magnetic field of the neutron stars is found as follows. $B^{(in)} = \frac{\eta}{{T_7 - \eta}}B^{(0)} ,\begin{array}{*{20}c}{} & {\eta =} \ \end{array}\frac{{m(^3 P_2 )}}{{0.1m_{Sun}}}R_{NS,6}^{- 3} $ ($T_7$ denotes the interior temperature of the neutron star in unit of 10$^7$ K). The induced magnetic field will gradually increase with the temperature of the neutron star decreasing in their late evolutionary stage. A magnetar may appear in a condition when $T_7 \to \eta$. The upper limit of the induced magnetic field of $^3P^2$ superfluid is $3.35 \time 10^{14} \eta$.

 
astro-ph/0607217 [abs, ps, pdf, other] :
Title: Are peculiar Wolf-Rayet Stars of type WN8 Thorne-Zytkow Objects?
Authors: C. Foellmi, A.F.J. Moffat
Comments: Published in PASP in 2002, but was missing in astro-ph
Journal-ref: Stellar Collisions, Mergers and their Consequences, ASP Conference Proceedings, Vol. 263. Edited by Michael M. Shara. ISBN: 1-58381-103-6. San Francisco: Astronomical Society of the Pacific, 2002., p.123

Most population I Wolf-Rayet (WR) stars are the He-rich descendants of the most massive stars (M_i = 25 - 100 M_sun). Evidence has been accumulating over the years that among all pop I WR stars, those of the relatively cool, N-rich subtype "WN8" are among the most peculiar: 1. They tend to be runaways, with large space velocity and/or avoid clusters. 2. Unlike their equally luminous WN6,7 cousins, only a very small number of WN8 stars are known to belong to a close binary with an OB companion. 3. They are the systematically most highly stochastically variable among all (single) WR stars. Taken together, these suggest that many WN8 stars may originally have been in close binaries (like half of all stars), in which the original primary exploded as a supernova, leaving behind a very close binary containing a massive star with a neutron star/black hole companion (like Cyg X-3). When the massive remaining star evolved in turn, it engulfed and eventually swallowed the compact companion, leading to the presently puffed-up, variable WN8 star. Such stars could fall in the realm of the exotic Thorne-Zytkow objects.

 
astro-ph/0607224 [abs, ps, pdf, other] :
Title: Gravitational Radiation from Standing Accretion Shock Instability in Core-Collapse Supernovae
Authors: Kei Kotake, Naofumi Ohnishi, Shoichi Yamada
Comments: 21 pages, 9 figures, submitted to ApJ

We perform long-term two dimensional axisymmetric simulations in the postbounce phase of core-collapse supernovae to study how the asphericities induced by the growth of the standing accretion shock instability (SASI) produce the gravitational waveforms. To obtain the neutrino-driven explosions, we parameterize the neutrino fluxes emitted from the central protoneutron star and approximate the neutrino transfer by a light-bulb scheme. We find that the waveforms due to the anisotropic neutrino emissions show the monotonic increase with time, whose amplitudes are up to two order-of-magnitudes larger than the ones from the convective matter motions outside the protoneutron stars.
We point out that the amplitudes begin to become larger when the growth of the SASI enters the nonlinear phase, in which the deformation of the shocks and the neutrino anisotropy become large.
From the spectrum analysis of the waveforms, we find that the amplitudes from the neutrinos are dominant over the ones from the matter motions at the frequency below $\sim 100$ Hz, which are suggested to be within the detection limits of the detectors in the next generation such as LCGT and the advanced LIGO for a supernova at 10 kpc.
As a contribution to the gravitational wave background, we show that the amplitudes from this source could be larger at the frequency above $\sim$ 1 Hz than the primordial gravitational wave backgrounds, but unfortunately, invisible to the proposed space-based detectors.

 
astro-ph/0607229 [abs, ps, pdf, other] :
Title: Swift, RXTE, and INTEGRAL observation of Swift J1922.7-1716
Authors: M. Falanga (CEA-Saclay), T. Belloni (INAF-Oab), S. Campana (INAF-Oab)
Comments: 4 pages, 2 figures, accepted for publication on A&A Letters

We report the results of analyzing Swift, RossiXTE, and INTEGRAL data of Swift J1922.7-1716, a likely transient X-ray source discovered by Swift/BAT. Both the fast variability measured by the RXTE/PCA and the combined Swift/XRT, RXTE/PCA, and INTEGRAL/ISGRI (0.5-100 keV) energy spectrum suggest that the system is a neutron-star low-mass X-ray binary or a black-hole candidate at low accretion levels. The non-simultaneous spectra are consistent with the same spectral shape and flux, suggesting little variability over the period July to October 2005, but the analysis of archival INTEGRAL data shows that the source was not detected in 2003-2004, suggesting a transient or strongly variable behavior.

 
astro-ph/0607233 [abs, ps, pdf, other] :
Title: Limits on the high-energy gamma and neutrino fluxes from the SGR 1806-20 giant flare of December 27th, 2004 with the AMANDA-II detector
Authors: The IceCube Collaboration
Comments: 14 pages, 3 figures

On December 27th 2004, a giant gamma flare from the Soft Gamma-ray Repeater 1806-20 saturated many satellite gamma-ray detectors. This event was by more than two orders of magnitude the brightest cosmic transient ever observed. If the gamma emission extends up to TeV energies with a hard power law energy spectrum, photo-produced muons could be observed in surface and underground arrays. Moreover, high-energy neutrinos could have been produced during the SGR giant flare if there were substantial baryonic outflow from the magnetar. These high-energy neutrinos would have also produced muons in an underground array. AMANDA-II was used to search for downgoing muons indicative of high-energy gammas and/or neutrinos. The data revealed no significant signal. The upper limit on the gamma flux at 90% CL is dN/dE < 0.05 (0.5) TeV^-1 m^-2 s^-1 for gamma=-1.47 (-2). Similarly, we set limits on the normalization constant of the high-energy neutrino emission of 0.4 (6.1) TeV^-1 m^-2 s^-1 for gamma=-1.47 (-2).

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605380 [abs, ps, pdf, other] :
Title: A strong $\ddot{\nu} - \dot{\nu}$ correlation in radio pulsars with implications for torque variations
Authors: J. O. Urama, B. Link, J. M. Weisberg
Comments: MNRAS, 4 pages, 2 figures. Minor editorial changes and typos corrected
Note: replaced with revised version Mon, 10 Jul 2006 22:29:50 GMT (26kb)
 
astro-ph/0606674 [abs, ps, pdf, other] :
Title: Physics of Strongly Magnetized Neutron Stars
Authors: Alice K. Harding (GSFC), Dong Lai (Cornell)
Comments: Minor changes in references. 93 pages. Reports on Progress in Physics, in press (2006)
Note: replaced with revised version Tue, 11 Jul 2006 06:34:19 GMT (932kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 13 Jul 06 00:00:10 GMT
0607234 -- 0607266 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607248 [abs, ps, pdf, other] :
Title: Slow glitches in the pulsar B1822-09
Authors: Tatiana V. Shabanova (PRAO)
Comments: 3 pages, 2 figures. Accepted by Astrophysics and Space Science. Contribution to the proceedings of Isolated Neutron Stars, London, 2006

The pulsar B1822-09 (J1825-0935) experienced a series of five unusual slow glitches over the 1995-2004 interval. The results of further study of this unusual glitch phenomenon are presented. It is also reported the detection a new glitch of typical signature that occurred in the pulsar period in 2006 January.

 
astro-ph/0607251 [abs, ps, pdf, other] :
Title: XMM-Newton and ESO observations of the two unidentified gamma-ray sources 3EG J0616-3310 and 3EG J1249-8330
Authors: N. La Palombara (1), R. P. Mignani (2), E. Hatziminaoglou (3), M. Schirmer (4), G.F. Bignami (5,6), P. Caraveo (1) ((1) INAF/IASF-Milano (I); (2) MSSL, London (UK); (3) IAC, Tenerife (E); (4) ING, Santa Cruz de la Palma (E); (5) CESR, Toulouse (F); (6) Universita' di Pavia (I))
Comments: 18 pages, 10 figures, 8 tables. Accepted for publication by Astronomy & Astrophysics

The limited angular resolution of gamma-ray telescopes prevents a direct identification of the majority of sources detected so far. This is particularly true for the low latitude, probably galactic, ones only 10 % of which has been identified. Most counterparts of the identified low-latitude gamma-ray sources are Isolated Neutron Stars (INS), both radio-loud and radio-quiet (Geminga-like) objects, which are characterised by an extremely high value of the X-ray-to-optical flux ratio f_X/f_opt. Therefore, the systematic X-ray and optical coverage of low-latitude unidentified gamma-ray sources aiming at high f_X/f_opt sources seems one of the most promising ways to spot INS candidate counterparts. Since low latitude sources are heavily affected by the interstellar absorption at both X-ray and optical wavelengths, we have focussed on two middle-latitude, probably galactic, GRO/EGRET sources: 3EG J0616-3310 and 3EG J1249-8330. These two sources, which could belong to a local galactic population, have been selected owing to their relatively good positional accuracy, spectral shape and lack of candidate extragalactic radio counterparts. Here we report on X-ray observations of the two gamma-ray error boxes performed with XMM-Newton and on their optical follow-up carried on with the Wide Field Imager at the ESO/MPG 2.2m telescope. Less than half of the ~300 sources detected by the X-ray coverage have no optical counterparts. Among those, we have selected few interesting sources with f_X/f_opt > 100, which we consider promising INS candidates.

 
astro-ph/0607256 [abs, ps, pdf, other] :
Title: Electromagnetic Pulsar Spindown
Authors: Ioannis Contopoulos
Comments: 5 pages, no figures

We evaluate the result of the recent pioneering numerical simulations in Spitkovsky~2006 on the spindown of an oblique relativistic magnetic dipole rotator. Our discussion is based on our experience from two idealized cases, that of an aligned dipole rotator, and that of an oblique split-monopole rotator. We conclude that the issue of electromagnetic pulsar spindown may not have been resolved yet.

 
astro-ph/0607260 [abs, ps, pdf, other] :
Title: 30 Glitches in slow pulsars
Authors: G. H. Janssen (1), B. W. Stappers (2,1) ((1) University of Amsterdam, Netherlands, (2) ASTRON, Netherlands)
Comments: 9 pages, 6 figures, accepted by A&A

We have analyzed 5.5 years of timing observations of 7 'slowly' rotating radio pulsars, made with the Westerbork Synthesis Radio Telescope. We present improved timing solutions and 30, mostly small, new glitches. Particularly interesting are our results on PSR J1814-1744, which is one of the pulsars with similar rotation parameters and magnetic field strength to the Anomalous X-ray Pulsars (AXPs). Although the high-B radio pulsars do not show X-ray emission, and no radio emission is detected for AXPs, the roughly similar glitch parameters provide us with another tool to compare these classes of neutron stars. Furthermore, we were able to detect glitches one to two orders of magnitude smaller than before, for example in our well-sampled observations of PSR B0355+54. We double the total number of known glitches in PSR B1737-30, and improve statistics on glitch sizes for this pulsar individually and pulsars in general. We detect no significant variations in dispersion measure for PSRs B1951+32 and B2224+65, two pulsars located in high-density surroundings. We discuss the effect of small glitches on timing noise, and show it is possible to resolve timing-noise looking structures in the residuals of PSR B1951+32 by using a set of small glitches.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605445 [abs, ps, pdf, other] :
Title: The X-ray afterglow flat segment in short GRB 051221A: Energy injection from a millisecond magnetar?
Authors: Yizhong Fan, Dong Xu
Comments: 4 pages including 1 figure, accepted for publication in MNRAS Letters, minor revision
Note: replaced with revised version Wed, 12 Jul 2006 07:03:06 GMT (26kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 14 Jul 06 00:00:09 GMT
0607267 -- 0607304 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607277 [abs, ps, pdf, other] :
Title: Density-Functional-Theory Calculations of Matter in Strong Magnetic Fields: II. Infinite Chains and Condensed Matter
Authors: Zach Medin, Dong Lai (Cornell)
Comments: 35 pages, 24 figures, submitted to Phys. Rev. A

We present new, ab initio calculations of the electronic structure of one-dimensional infinite chains and three-dimensional condensed matter in strong magnetic fields ranging from B=10^12 G to 2x10^15 G, appropriate for observed magnetic neutron stars. At these field strengths, the magnetic forces on the electrons dominate over the Coulomb forces, and to a good approximation the electrons are confined to the ground Landau level. Our calculations are based on the density functional theory, and use a local magnetic exchange-correlation function appropriate in the strong field regime. The band structures of electrons in different Landau orbitals are computed self-consistently. Numerical results of the ground-state energies and electron work functions are given for one-dimensional chains of H, He, C, and Fe. Fitting formulae for the B-dependence of the energies are also provided. For all the field strengths considered in this paper, hydrogen, helium, and carbon chains are found to be bound relative to individual atoms (although for B less than a few x 10^12 G, the relative binding between C and C_infinity is small). Iron chains are significantly bound for B>10^14 G and are weakly bound if at all at B<10^13 G. We also study the cohesive property of three-dimensional condensed matter of H, He, C, and Fe at zero pressure, constructed from interacting chains in a body-centered tetragonal lattice. Such three-dimensional condensed matter is found to be bound relative to individual atoms, with the cohesive energy increasing rapidly with increasing B.

 
astro-ph/0607281 [abs, ps, pdf, other] :
Title: A Numerical Algorithm for Modeling Multigroup Neutrino-Radiation Hydrodynamics in Two Spatial Dimensions
Authors: F. Douglas Swesty, Eric S. Myra
Comments: 126 pages, 31 figures; submitted to Astrophysical Journal

It is now generally agreed that multidimensional, multigroup, radiation hydrodynamics is an indispensable element of any realistic model of stellar-core collapse, core-collapse supernovae, and protoneutron star instabilities. We have developed a new, two-dimensional, multigroup algorithm that can model neutrino-radiation-hydrodynamic flows in core-collapse supernovae. Our algorithm uses an approach that is similar to the ZEUS family of algorithms, originally developed by Stone and Norman. However, we extend that previous work in three significant ways: First, we incorporate multispecies, multigroup, radiation hydrodynamics in a flux-limited-diffusion approximation. Our approach is capable of modeling pair-coupled neutrino-radiation hydrodynamics, and includes effects of Pauli blocking in the collision integrals. Blocking gives rise to nonlinearities in the discretized radiation-transport equations, which we evolve implicitly in time. We employ parallelized Newton-Krylov methods to obtain a solution of these nonlinear, implicit equations. Our second major extension to the ZEUS algorithm is inclusion of an electron conservation equation, which describes evolution of electron-number density in the hydrodynamic flow. This permits following the effects of deleptonization in a stellar core. In our third extension, we have modified the hydrodynamics algorithm to accommodate realistic, complex equations of state, including those having non-convex behavior. In this paper, >... <abstract continues>

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604099 [abs, ps, pdf, other] :
Title: Unexpected Dynamical Instabilities In Differentially Rotating Neutron Stars
Authors: Shangli Ou, Joel E. Tohline
Comments: Accepted by ApJ, minor modifications added in
Note: replaced with revised version Thu, 13 Jul 2006 15:14:02 GMT (180kb)
 
astro-ph/0607256 [abs, ps, pdf, other] :
Title: Electromagnetic Pulsar Spindown
Authors: Ioannis Contopoulos
Comments: 5 pages, no figures
Note: replaced with revised version Thu, 13 Jul 2006 08:43:44 GMT (0kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 17 Jul 06 00:00:09 GMT
0607305 -- 0607340 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607320 [abs, ps, pdf, other] :
Title: Isolated neutron stars: Magnetic fields, distances, and spectra
Authors: M. H. van Kerkwijk (Toronto), D. L. Kaplan (MIT)
Comments: 10 pages, 7 figures, to appear Astrophysics and Space Science, in the proceedings of "Isolated Neutron Stars: from the Interior to the Surface", edited by D. Page, R. Turolla and S. Zane

We present timing measurements, astrometry, and high-resolution spectra of a number of nearby, thermally emitting, isolated neutron stars. We use these to infer magnetic field strengths and distances, but also encounter a number of puzzles. We discuss three specific ones in detail: (i) For RX J0720.4-3125 and RX J1308.6+2127, the characteristic ages are in excess of 1~Myr, while their temperatures and kinematic ages indicate that they are much younger; (ii) For RX J1856.5-3754, the brightness temperature for the optical emission is in excess of that measured at X-ray wavelengths for reasonable neutron-star radii; (iii) For RX J0720.4-3125, the spectrum changed from an initially featureless state to one with an absorption feature, yet there was only a relatively small change in effective temperature. Furthermore, we attempt to see whether the spectra of all seven sourced, in six of which absorption features have now been found, can be understood in the context of strongly magnetised hydrogen atmospheres. We find that the energies of the absorption features can be reproduced, but that the featureless spectra of some sources, especially the Wien-like high-energy tails, remain puzzling.

 
astro-ph/0607323 [abs, ps, pdf, other] :
Title: Detection of Giant Radio Pulses from the Pulsar PSR B0656+14
Authors: A. D. Kuzmin, A. A. Ershov
Comments: 10 pages, 3 figures, 1 table; originally published in Russian in Pis'ma Astron. Zh., 2006, v.32, 650; translated by George Rudnitskii; the English version will be appear in Astronomy Letters

Giant pulses (GPs) have been detected from the pulsar PSR B0656+14. A pulse that is more intense than the average pulse by a factor of 120 is encountered approximately once in 3000 observed periods of the pulsar. The peak flux density of the strongest pulse, 120 Jy, is a factor of 630 higher than that of the average pulse. The GP energy exceeds the energy of the average pulse by up to a factor of 110, which is comparable to that for other known pulsars with GPs, including the Crab pulsar and the millisecond pulsar PSR B1937+21. The giant pulses are a factor of 6 narrower than the average pulse and are clustered at the head of the average pulse. PSR B0656+14 along with PSR B0031-07, PSR B1112+50, and PSR J1752+2359 belong to a group of pulsars that differ from previously known ones in which GPs have been detected without any extremely strong magnetic field on the light cylinder.

 
astro-ph/0607329 [abs, ps, pdf, other] :
Title: Collapse of rotating stars in the Universe and the cosmic gamma ray bursts
Authors: A.I. Bogomazov, V.M. Lipunov, A.V. Tutukov
Comments: 18 pages, 3 figures

We analyze here late evolutionary stages of massive (with initial mass higher than 8 masses of the Sun) close binary stars. Our purposes are to study possible mechanisms of gamma ray bursts (GRBs) origin. We suppose in this paper that GRB phenomenon require formation of massive (approx. 1 M_sun) compact (approx. 10 km) accretion disks around Kerr black holes and neutron stars. Such Kerr black holes are products of collapse of Wolf-Rayet stars in extremely close binaries and merging of neutron stars with black holes and neutron stars with neutron stars in close binary systems. Required accretion disks also can be formed around neutron stars which were formed during collapse of accreting oxygen-neon white dwarfs. We have estimated frequencies of events which lead to a rotational collapse concerned with formation of rapidly rotating relativistic objects in the Galaxy. We made our calculations using the "Scenario Machine".

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0604379 [abs, ps, pdf, other] :
Title: Flux predictions of high-energy neutrinos from pulsars
Authors: Bennett Link (Montana State University, Bozeman, USA), Fiorella Burgio (INFN Sezione di Catania, Italy)
Comments: MNRAS, 6 pages, 3 figures, 1 table. Minor editorial changes and typos corrected
Note: replaced with revised version Fri, 14 Jul 2006 08:01:33 GMT (196kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 18 Jul 06 00:00:10 GMT
0607341 -- 0607393 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607354 [abs, ps, pdf, other] :
Title: Swift/XRT follow-up observations of TeV sources of the HESS Inner Galaxy survey
Authors: R. Landi, L. Bassani, A. Malizia, N. Masetti, J.B. Stephen, A. Bazzano, P. Ubertini, A.J. Bird, A.J. Dean
Comments: 22 pages, 6 figures, accepted for publication on The Astrophysical Journal

In order to provide a firm identification of the newly discovered Galactic TeV sources, a search for counterparts in a broad band from soft X-ray to soft gamma-rays is crucial as data in these wavebands allow us to distinguish between different types of suggested models (for example leptonic versus hadronic) and, in turn, to disentangle their nature. In this paper, we report the results of a set of follow-up observations performed by the Swift/X-Ray Telescope (XRT) on seven sources recently discovered by HESS, in the range from few hundred GeV to about 10 TeV, during the inner Galaxy survey (Aharonian et al. 2006). In all, but one case, we detect X-ray sources inside or close-by the extended TeV emitting region. All these putative X-ray counterparts have accurate arc-second location and are consistent with being point sources. The main result of our search is the discovery that three of them are located at the center of the diffuse radio emission of the supernova remnants, which have been spatially associated to these TeV objects. HESS J1640-465, HESS J1834-087 and HESS J1813-178 show this evidence, suggestive of a possible Pulsar Wind Nebula association.

 
astro-ph/0607364 [abs, ps, pdf, other] :
Title: Spin-down Rate of Pinned Superfluid
Authors: M Jahan-Miri
Comments: to appear in ApJ (vol. 649 ?)

The spinning down (up) of a superfluid is associated with a radial motion of its quantized vortices. In the presence of pinning barriers against the motion of the vortices, a spin-down may be still realized through ``random unpinning'' and ``vortex motion,'' as two physically separate processes, as suggested recently. The spin-down rate of a pinned superfluid is calculated, in this framework, by directly solving the equation of motion applicable to only the unpinned moving vortices, at any given time. The results indicate that the pinned superfluid in the crust of a neutron star may as well spin down at the same steady-state rate as the rest of the star, through random unpinning events, while pinning conditions prevail and the superfluid rotational lag is smaller than the critical lag value.

 
astro-ph/0607388 [abs, ps, pdf, other] :
Title: First broad band study of the mysterious source 1E 1743.1-2843
Authors: M. Del Santo, L. Sidoli, A. Bazzano, M. Cocchi, G. De Cesare, A. Paizis, P. Ubertini
Comments: 4 pages, 3 figures, accepted for publication in A&A

In the last years, the persistent source 1E 1743.1-2843 has been observed in the X-rays, but never above 20 keV. In previous works, it was stressed that a possible high energy emission could give further indications on the accreting object nature which remains still unknown. We present here more than two years of 1E 1743.1-2843 monitoring with INTEGRAL/IBIS as well as public XMM-Newton and Chandra X-ray observations. The temporal study in the 20-40 keV band shows a rather constant flux on few months time scale. Based on this result we have performed the broad-band spectral analysis using EPIC/IBIS non simultaneous data and ACIS-I/IBIS data collected during 2004. In ~2 Ms, we report a detection of 6 sigma in the energy range 35-70 keV. The first broad-band study (2-70 keV) shows a steep slope (~3) and a black body temperature of 1.7 keV. Combining spectral parameters and discussion about the luminosity evaluations for different possible distances, our conclusions are in favour of a LMXB system with a neutron star at distance higher than the Galactic Centre, even though a firm conclusion can not be stated.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 19 Jul 06 00:00:10 GMT
0607394 -- 0607423 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607410 [abs, ps, pdf, other] :
Title: The optical to gamma-ray emission of the Crab pulsar: a multicomponent model
Authors: E. Massaro (1), R. Campana (1), G. Cusumano (2), T. Mineo (2) ((1) Dipartimento di Fisica, Universita' La Sapienza, Roma, Italy; (2) INAF-IASF, Palermo, Italy)
Comments: 14 pages, 16 figures; accepted by Astronomy and Astrophysics

We present a multicomponent model to explain the features of the pulsed emission and spectrum of the Crab Pulsar, on the basis of X and gamma-ray observations obtained with BeppoSAX, INTEGRAL and CGRO. This model explains the evolution of the pulse shape and of the phase-resolved spectra, ranging from the optical/UV to the GeV energy band, on the assumption that the observed emission is due to more components. The first component, C_O, is assumed to have the pulsed double-peaked profile observed at the optical frequencies, while the second component, C_X, is dominant in the interpeak and second peak phase regions. The spectra of these components are modelled with log-parabolic laws and their spectral energy distributions have peak energies at 12.2 and 178 keV, respectively. To explain the properties of the pulsed emission in the MeV-GeV band, we introduce two more components, C_Ogamma and C_Xgamma, with phase distributions similar to those of C_O and C_X and log-parabolic spectra with the same curvature but peak energies at about 300 MeV and 2 GeV. This multicomponent model is able to reproduce both the broadband phase-resolved spectral behaviour and the changes of the pulse shape with energy. We also propose some possible physical interpretations in which C_O and C_X are emitted by secondary pairs via a synchrotron mechanism while C_Ogamma and C_Xgamma can originate either from Compton scattered or primary curvature photons.

 
astro-ph/0607420 [abs, ps, pdf, other] :
Title: The energy dependence of burst oscillations from the accreting millisecond pulsar XTE J1814-338
Authors: Anna L. Watts (MPA), Tod E. Strohmayer (NASA GSFC)
Comments: Submitted to MNRAS

The nature of the asymmetry that gives rise to Type I X-ray burst oscillations on accreting neutron stars remains a matter of debate. Of particular interest is whether the burst oscillation mechanism differs between the bursting millisecond pulsars and the non-pulsing systems. One means to diagnose this is to study the energy dependence of the burst oscillations: here we present an analysis of oscillations from 28 bursts observed during the 2003 outburst of the accreting millisecond pulsar XTE J1814-338. We find that the fractional amplitude of the burst oscillations falls with energy, in contrast to the behaviour found by Muno et al. (2003) in the burst oscillations from a set of non-pulsing systems. The drop with energy mirrors that seen in the accretion-powered pulsations; in this respect XTE J1814-338 behaves like the other accreting millisecond pulsars. The burst oscillations show no evidence for either hard or soft lags, in contrast to the persistent pulsations, which show soft lags of up to 50 $\mu$s. The fall in amplitude with energy is inconsistent with current surface mode and simple hot spot models of burst oscillations. We discuss improvements to the models and uncertainties in the physics that might resolve these issues.

 
astro-ph/0607422 [abs, ps, pdf, other] :
Title: From progenitor to afterlife
Authors: Roger A. Chevalier
Comments: 10 pages, Proceedings of 2006 STScI May Symposium on Massive Stars

The sequence of massive star supernova types IIP (plateau light curve), IIL (linear light curve), IIb, IIn (narrow line), Ib, and Ic roughly represents a sequence of increasing mass loss during the stellar evolution. The mass loss affects the velocity distribution of the ejecta composition; in particular, only the IIP's typically end up with H moving at low velocity. Radio and X-ray observations of extragalactic supernovae show varying mass loss properties that are in line with expectations for the progenitor stars. For young supernova remnants, pulsar wind nebulae and circumstellar interaction provide probes of the inner ejecta and higher velocity ejecta, respectively. Among the young remnants, there is evidence for supernovae over a range of types, including those that exploded with much of the H envelope present (Crab Nebula, 3C 58, 0540--69) and those that exploded after having lost most of their H envelope (Cas A, G292.0+1.8).

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0508626 [abs, ps, pdf, other] :
Title: Eccentricities of Double Neutron Star Binaries
Authors: Catherine Mia Ihm, Vassiliki Kalogera, Krzysztof Belczynski
Comments: 9 pages, 8 figures, accepted by ApJ. Figures reduced and some content changed, references added
Note: replaced with revised version Tue, 18 Jul 2006 01:52:38 GMT (33kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 20 Jul 06 00:00:11 GMT
0607424 -- 0607450 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607433 [abs, ps, pdf, other] :
Title: On the maximum amplitude and coherence of the kilohertz quasi-periodic oscillations in low-mass X-ray binaries
Authors: Mariano Mendez (SRON)
Comments: Accepted for publication in MNRAS. 16 pages + 10 figures. Uses mn2e.cls

I study the behaviour of the maximum rms fractional amplitude, $r_{\rm max}$ and the maximum coherence, $Q_{\rm max}$, of the kilohertz quasi-periodic oscillations (kHz QPOs) in a dozen low-mass X-ray binaries. I find that: (i) The maximum rms amplitudes of the lower and the upper kHz QPO, $r^{\ell}_{\rm max}$ and $r^{\rm u}_{\rm max}$, respectively, decrease more or less exponentially with increasing luminosity of the source; (ii) the maximum coherence of the lower kHz QPO, $Q^{\ell}_{\rm max}$, first increases and then decreases exponentially with luminosity, at a faster rate than both $r^{\ell}_{\rm max}$ and $r^{\rm u}_{\rm max}$; (iii) the maximum coherence of the upper kHz QPO, $Q^{\rm u}_{\rm max}$, is more or less independent of luminosity; and (iv) $r_{\rm max}$ and $Q_{\rm max}$ show the opposite behaviour with hardness of the source, consistent with the fact that there is a general anticorrelation between luminosity and spectral hardness in these sources. Both $r_{\rm max}$ and $Q_{\rm max}$ in the sample of sources, and the rms amplitude and coherence of the kHz QPOs in individual sources show a similar behaviour with hardness. This similarity argues against the interpretation that the drop of coherence and rms amplitude of the lower kHz QPO at high QPO frequencies in individual sources is a signature of the innermost stable circular orbit around a neutron star. I discuss possible interpretations of these results in terms of the modulation mechanisms that may be responsible for the observed variability.

 
astro-ph/0607442 [abs, ps, pdf, other] :
Title: Merger of Compact Objects
Authors: C.-H. Lee, G.E. Brown, E. Park
Comments: 11 pages

Bethe and Brown (1998) suggested that mergers resulting in short-hard gamma-ray bursts would be mainly those of low-mass black-hole(LMBH), neutron-star (NS) binaries, with those of NS-NS binaries down by an order of magnitude from these. The lower number of the latter resulted from the necessity that the two giant progenitors be within 4% of each other in ZAMS mass so that they burned He at the same time. Otherwise the first born pulsar would find itself in the red giant envelope of the companion giant as it evolved and accrete enough matter to go into a black hole (BH).
Using a flat distribution in mass (constant dn/dm), favored by Duquennoy and Mayer (1991), we calculated a ratio of LMBH-NS and NS-NS systems to be about 5, in agreement with Pinsonneault and Stanek (2006). These authors emphasize the importance of "twins", which we discuss. The two NS's in the twins would be close in mass and further increase the number of mergings.

 
astro-ph/0607447 [abs, ps, pdf, other] :
Title: The Discovery of a Neutron Star with a Spin Frequency of 530 Hz in A1744-361
Authors: Sudip Bhattacharyya (NASA/GSFC, UMCP), Tod E. Strohmayer (NASA/GSFC), Craig B. Markwardt (NASA/GSFC, UMCP), Jean H. Swank (NASA/GSFC)
Comments: 8 pages, 4 figures, published in ApJ Letters
Journal-ref: Astrophys.J. 639 (2006) L31-L34

We report the detection with the Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) of 530 Hz burst oscillations in a thermonuclear (type I) burst from the transient X-ray source A1744-361. This is only the second burst ever observed from this source, and the first to be seen in any detail. Our results confirm that A1744-361 is a low mass X-ray binary (LMXB) system harboring a rapidly rotating neutron star. The oscillations are first detected along the rising edge of the burst, and they show evidence for frequency evolution of a magnitude similar to that seen in other burst sources. The modulation amplitude and its increase with photon energy are also typical of burst oscillations. The lack of any strong indication of photospheric radius expansion during the burst suggests a 9 kpc upper limit of the source distance. We also find energy dependent dips, establishing A1744-361 as a high inclination, dipping LMXB. The timescale between the two episodes of observed dips suggests an orbital period of ~ 97 minutes. We have also detected a 2 - 4 Hz quasi-periodic-oscillation (QPO) for the first time from this source. This QPO appears consistent with ~ 1 Hz QPOs seen from other high-inclination systems. We searched for kilohertz QPOs, and found a suggestive 2.3 sigma feature at 800 Hz in one observation. The frequency, strength, and quality factor are consistent with that of a lower frequency kilohertz QPO, but the relatively low significance argues for caution, so we consider this a tentative detection requiring confirmation.

 

Cross-listings


2 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0607039 [abs, ps, pdf, other] :
Title: Neutron Rich Nuclei in Heaven and Earth: Proceedings of the International Conference on Current Problems in Nuclear Physics and Atomic Energy
Authors: J. Piekarewicz
Comments: 13 pages, 5 figures, proceedings of the "International Conference on Current Problems in Nuclear Physics and Atomic Energy" (May 29 - June 3, 2006) Kyiv, UKRAINE

The nucleus of 208Pb -- a system that is 18 order of magnitudes smaller and 55 orders of magnitude lighter than a neutron star -- may be used as a miniature surrogate to establish important correlations between its neutron skin and several neutron-star properties. Indeed, a nearly model-independent correlation develops between the neutron skin of 208Pb and the liquid-to-solid transition density in a neutron star. Further, we illustrate how a measurement of the neutron skin in 208Pb may be used to place important constraints on the cooling mechanism operating in neutron stars and may help elucidate the existence of quarks stars.

 
nucl-th/0607040 [abs, ps, pdf, other] :
Title: The High-Density Symmetry Energy and Direct Urca
Authors: Andrew W. Steiner
Comments: 6 pages, 3 figures, submitted to PRC

The symmetry energy of nucleonic matter is usually assumed to be quadratic in the isospin density. While this may be justified at sub-saturation densities, there is no need to enforce this restriction at super-saturation densities. The presence of a quartic term can strongly modify the critical density for the direct Urca process which leads to faster cooling of neutron stars. Neutron star cooling predictions which lie below the observational data can, for some equations of state, be repaired with a quartic term which effectively turns off the direct Urca process.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605001 [abs, ps, pdf, other] :
Title: A Two-Zone Model for Type I X-ray Bursts on Accreting Neutron Stars
Authors: Randall L. Cooper, Ramesh Narayan (Harvard/CfA)
Comments: 13 pages, 8 figures, accepted by ApJ
Note: replaced with revised version Tue, 18 Jul 2006 21:02:32 GMT (65kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 21 Jul 06 00:00:09 GMT
0607451 -- 0607479 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607453 [abs, ps, pdf, other] :
Title: Physics of accretion flows around compact objects
Authors: Jean-Pierre Lasota (IAP)
Comments: Submitted to Elsevier Science

Several physical and astrophysical problems related to accretion onto black holes and neutron stars are shortly reviewed. I discuss the observed differences between these two types of compact objects in quiescent Soft X-ray Transients. Then I review the status of various non-standard objects suggested as an alternative to black-holes. Finally I present new results and suggestions about the nature of the jet activity in Active Galactic Nuclei. {To cite this article: J.-P. Lasota, C. R. Physique 6 (2006).}

 
astro-ph/0607459 [abs, ps, pdf, other] :
Title: Proper Motion of Pulsar B1800-21
Authors: W. F. Brisken, M. Carrillo-Barragan, S. Kurtz, J. P. Finley
Comments: 13 pages, 1 color figure

We report high angular resolution, multi-epoch radio observations of the young pulsar PSR B1800-21. Using two pairs of data sets, each pair spanning approximately a ten year period, we calculate the proper motion of the pulsar. We obtain a proper motion of mu_alpha=11.6 +- 1.8 mas/yr, mu_delta=14.8 +- 2.3 mas/yr which clearly indicates a birth position at the extreme edge of the W30 supernova remnant. Although this does not definitively rule out an association of W30 and PSR B1800-21, it does not support an association.

 
astro-ph/0607461 [abs, ps, pdf, other] :
Title: Star Cluster Ecology: VII The evolution of young dense star clusters containing primordial binaries
Authors: Simon Portegies Zwart (UVA), Steve McMillan (Drexel), Jun Makino (Tokyo)
Comments: Submitted to MNRAS

We study the first 100Myr of the evolution of isolated star clusters initially containing 144179 stars, including 13107 (10%) primordial hard binaries. Our calculations include the effects of both stellar and binary evolution. Gravitational interactions among the stars are computed by direct N-body integration using high precision GRAPE-6 hardware. The evolution of the core radii and central concentrations of our simulated clusters are compared with the observed sample of young (about 100Myr) star clusters in the large Magellanic cloud. Even though our simulations start with a rich population of primordial binaries, core collapse during the early phase of the cluster evolution is not prevented. Throughout the simulations, the fraction of binaries remains roughly constant (about 10%). Due to the effects of mass segregation the mass function of intermediate-mass main-sequence stars becomes as flat as $\alpha=-1.8$ in the central part of the cluster (where the initial Salpeter mass function had $\alpha=-2.35$). About 6--12% of the neutron stars were retained in our simulations; the fraction of retained black holes is 40--70%. In each simulation about three neutron stars become members of close binaries with a main-sequence companion. Such a binary will eventually become an x-ray binary, when the main-sequence star starts to fill its Roche lobe. Black holes are found more frequently in binaries; in each simulated cluster we find about 11 potential x-ray binaries containing a black hole. Abstract abbreviated....

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 24 Jul 06 00:00:09 GMT
0607480 -- 0607510 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607509 [abs, ps, pdf, other] :
Title: Chromo-thermal instabilities and collapse of quark stars to black holes Astrophysical Implications
Authors: Manjari Bagchi, Rachid Ouyed, Jan Staff, Subharthi Ray, Jishnu Dey, Mira Dey
Comments: 4 pages, 3 figures

We have studied the effects of temperature on the properties of strange stars. We find that the maximum mass of the strange star decreases with the increase of temperature, because at high temperatures the equation of states become softer. Moreover, if the temperature of a strange star increases keeping its baryon number fixed, its gravitational mass increases and radius decreases which leads to a limiting temperature where it turns into a black hole. These features of strange stars is a combined effect of change of gluon mass and the quark distribution function with temperature. We have discovered a new kind of radial oscillations of strange stars driven by what we named chromo-thermal instability. This instability and the related radial oscillations of the star is inherent to strange quark matter making strange stars even more exotic than neutron stars within astrophysical context. In particular, we discuss the relevance of our findings in the astrophysics of core collapse supernovae and gamma ray bursts.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 25 Jul 06 00:00:10 GMT
0607511 -- 0607547 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607528 [abs, ps, pdf, other] :
Title: The Chandra X-ray Spectrum of the 10.6 s Pulsar in Westerlund 1: Testing the Magnetar Hypothesis
Authors: S.L. Skinner, R. Perna, S.A. Zhekov
Comments: 14 pages, 5 figures; to appear in ApJ

Two sensitive Chandra X-ray observations of the heavily-reddened galactic starburst cluster Westerlund 1 in May and June 2005 detected a previously unknown X-ray pulsar (CXO J164710.20-455217). Its slow 10.6 s pulsations, moderate X-ray temperature kT $\approx$ 0.5 keV, and apparent lack of a massive companion tentatively suggest that it is an Anomalous X-ray Pulsar (AXP). An isothermal blackbody model yields an acceptable spectral fit but the inferred source radius is much less than that of a neutron star, a result that has also been found for other AXPs. We analyze the X-ray spectra with more complex models including a model that assumes the pulsar is a strongly magnetized neutron star (``magnetar'') with a light element atmosphere. We conclude that the observed X-ray emission cannot be explained as global surface emission arising from the surface of a cooling neutron star or magnetar. The emission likely arises in one or more localized regions (``hot spots'') covering a small fraction of the surface. We discuss these new results in the context of both accretion and magnetar interpretations for the X-ray emission.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602024 [abs, ps, pdf, other] :
Title: On the Formation and Progenitor of PSR J0737-3039: New Constraints on the Supernova Explosion Forming Pulsar B
Authors: B. Willems, J. Kaplan, T. Fragos, V. Kalogera, K. Belczynski
Comments: Accepted by Physical Review D. Revised version incorporates a detailed rebuttal of the remarks made by Piran & Shaviv in astro-ph/0603649 (see Appendix A) and also minor clarifications requested by an anonymous referee
Note: replaced with revised version Mon, 24 Jul 2006 16:57:48 GMT (209kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 26 Jul 06 00:00:09 GMT
0607548 -- 0607571 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607548 [abs, ps, pdf, other] :
Title: Energy dependent gamma-ray morphology in the Pulsar wind nebula HESSJ1825-137
Authors: F.Aharonian (H.E.S.S. Collaboration)
Comments: Accepted for publication in A&A

Detailed morphological and spatially resolved spectral studies reveal the very high-energy (VHE) gamma-ray aspects of this object with unprecedented precision. We confirm previous results obtained in a survey of the Galactic Plane in 2004. The gamma-ray emission extends asymmetrically to the south and south-west of the energetic pulsar PSR J1826-1334, that is thought to power the pulsar wind nebula. The differential gamma-ray spectrum of the whole emission region is measured over more than two orders of magnitude, from 270 GeV to 35 TeV, and shows indications for a deviation from a pure power law. Spectra have also been determined for spatially separated regions of HESS J1825-137. The photon indices from a power-law fit in the different regions show a softening of the spectrum with increasing distance from the pulsar and therefore an energy dependent morphology. This is the first time that an energy dependent morphology has been detected in the VHE gamma-ray regime. The VHE gamma-ray emission of HESS J1825-137 is phenomenologically discussed in the scenario where the gamma-rays are produced by VHE electrons via Inverse Compton scattering. The high gamma-ray luminosity of the source cannot be explained on the basis of constant spin-down power of the pulsar and requires higher injection power in past.

 
astro-ph/0607551 [abs, ps, pdf, other] :
Title: A Multi-wavelength study of 1WGA J1346.5-6255: a new $\gamma$ Cas analog unrelated to the background supernova remnant G309.2-00.6
Authors: S. Safi-Harb, M. Ribo, Y. Butt, H. Matheson, I. Negueruela, F. Lu, S. Jia, Y. Chen
Comments: 28 pages using emulateapj.cls -- including 3 tables and 16 figures (figs 2, 3, 8, 10, 12, 14, 15 are in color). Submitted to ApJ on July 19. The resolution of figures 1 and 3 has been reduced for astro-ph submission only. The ApJ submitted paper with high-resolution images can be downloaded from this http URL

1WGA J1346.5-6255 is a ROSAT X-ray source found within the radio lobes of the supernova remnant (SNR) G309.2-00.6. This source also appears to coincide with the bright and early-type star HD 119682, which is in the middle of the galactic open cluster NGC 5281. The radio morphology of the remnant, consisting of two brightened and distorted arcs of emission on opposite sides of the 1WGA J1346.5-6255 source and of a jet-like feature and break in the shell, led to the suggestion that 1WGA J1346.5-6255/G309.2-00.6 is a young analog of the microquasar SS 433 powering the W50 nebula. This motivated us to study this source at X-ray and optical wavelengths. We here present new Chandra observations of 1WGA J1346.5-6255, archival XMM-Newton observations of G309.2-00.6, and optical spectroscopic observations of HD 119682, in order to search for X-ray jets from 1WGA J1346.5-6255, study its association with the SNR, and test for whether HD 119682 represents its optical counterpart. We do not find evidence for jets from 1WGA J1346.5-6255 down to an unabsorbed flux of 2.6E-13 ergs/cm2/s (0.5-7.5 keV), we rule out its association with G309.2-00.6, and we confirm that HD 119682 is its optical counterpart. We derive a distance of 1.2+/-0.3 kpc, which is consistent with the distance estimate to NGC 5281 (1.3+/-0.3 kpc), and much smaller than the distance derived to the SNR G309.2-00.6. We discuss the nature of the source, unveil that HD 119682 is a Be star and suggest it is a new member of the recently proposed group of $\gamma$-Cas analogs. The Chandra and XMM X-ray lightcurves show variability on timescales of hundreds of seconds, and the presence of a possible period of about 1500 s that could be the rotational period of an accreting neutron star or white dwarf in this $\gamma$-Cas analog.

 
astro-ph/0607557 [abs, ps, pdf, other] :
Title: Inverse Compton Scenarios for the TeV Gamma-Ray Emission of the Galactic Centre
Authors: J. A. Hinton, F. A. Aharonian
Comments: 9 pages, 6 figures, submitted to ApJ

The intense Compton cooling of ultra-relativistic electrons in the Klein-Nishina regime in radiation dominated environments, such as that found in the Galactic Centre, may result in radically different electron spectra than those produced by Synchrotron cooling. We explore these effects and their impact on the X-ray and gamma-ray spectra produced in electron accelerators in this region in comparison to elsewhere in our galaxy. We discuss the broad-band emission expected from the newly discovered pulsar wind nebula G 359.95-0.04 and the possible relationship of this X-ray source to the central TeV gamma-ray source HESS J1745-290. Finally we discuss the possible relationship of the Galactic Centre INTEGRAL source IGR J1745.6-2901 to the TeV emission.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606412 [abs, ps, pdf, other] :
Title: Non-Equilibrium Beta Processes in Neutron Stars: A Relationship between the Net Reaction Rate and the Total Emissivity of Neutrinos
Authors: Sergio Flores-Tulian, Andreas Reisenegger
Comments: Accepted for publication in MNRAS. 8 pages, non tables nor figures, uses aastex.cls
Note: replaced with revised version Tue, 25 Jul 2006 02:49:06 GMT (21kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 27 Jul 06 00:00:10 GMT
0607572 -- 0607601 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607583 [abs, ps, pdf, other] :
Title: Evidence for Heating of Neutron Stars by Magnetic Field Decay
Authors: J.A. Pons, B. Link, J.A. Miralles, U. Geppert
Comments: 5 pages, 2 figures

We show the existence of a strong trend between neutron star surface temperature and the dipolar component of the magnetic field extending through four orders of field magnitude, a range that includes magnetars, X-ray pulsars, and many ordinary radio pulsars. We show that this trend can be explained by the ohmic decay of currents in the crust over a time scale of $\sim 10^6$ yr. We predict the minimum temperature that a neutron star with a given magnetic field can reach.

 
astro-ph/0607592 [abs, ps, pdf, other] :
Title: Average hard X-ray emission from NS LMXBs: Observational evidence of different spectral states in NS LMXBs
Authors: A. Paizis, R. Farinelli, L. Titarchuk, T.J.-L. Courvoisier, A. Bazzano, V. Beckmann, F. Frontera, P. Goldoni, E. Kuulkers, S. Mereghetti, J. Rodriguez, O. Vilhu
Comments: 12 pages, 7 figures, Accepted for publication in A&A

We studied and compared the long term average hard X-ray (>20 keV) spectra of a sample of twelve bright low-mass X-ray binaries hosting a neutron star (NS). Our sample comprises the six well studied Galactic Z sources and six Atoll sources, four of which are bright ("GX") bulge sources while two are weaker ones in the 2-10 keV range (H 1750-440 and H 1608-55). For all the sources of our sample, we analysed available public data and extracted average spectra from the IBIS/ISGRI detector on board INTEGRAL. The two low-dim Atoll spectra are dominated by photons upscattered presumably due to dynamical and thermal Comptonization in an optically thin, hot plasma. For the first time, we extend the detection of H 1750-440 up to 150 keV. The Z and bright "GX" Atoll source spectra are very similar and are dominated by Comptonized blackbody radiation of seed photons presumably coming from the accretion disc and NS surface. The seed photons radiation is Comptonized in the optically thick cloud with plasma temperature in the range of 2.5-3 keV. Six sources show a hard tail in their average spectrum: Cyg X-2 (Z), GX 340+0 (Z), GX 17+2 (Z), GX 5-1 (Z), Sco X-1(Z) and GX 13+1 (Atoll). This is the first detection of a hard tail in the X-ray spectrum of the peculiar GX 13+1 that we discover to behave like a Z source not only in its variability and radio properties, but also from the spectral point of view. Using radio data from the literature we find, in all Z sources and bright "GX" Atolls, a systematic positive correlation between the X-ray hard tail (40-100 keV) and the radio luminosity. This suggests that hard tails and energetic electrons causing the radio emission may have the same origin, most likely the Compton cloud located inside the NS magnetosphere.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0607028 [abs, ps, pdf, other] :
Title: Nuclear Superconductivity in Compact Stars: BCS Theory and Beyond
Authors: Armen Sedrakian, John W. Clark
Comments: 41 pages, 16 figures. Chapter contributed to "Pairing in Fermionic Systems: Basic Concepts and Modern Applications", World Scientific
Subj-class: Nuclear Theory; Superconductivity

This chapter provides a review of microscopic theories of pairing in nuclear systems and neutron stars. Special attention is given to the mean-field BCS theory and its extensions to include effects of polarization of the medium and retardation of the interactions. Superfluidity in nuclear systems that exhibit isospin asymmetry is studied. We further address the crossover from the weak-coupling BCS description to the strong-coupling BEC limit in dilute nuclear systems. Finally, within the observational context of rotational anomalies of pulsars, we discuss models of the vortex state in superfluid neutron stars and of the mutual friction between superfluid and normal components, along with the possibility of type-I superconductivity of the proton subsystem.

 

Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0512128 [abs, ps, pdf, other] :
Title: The Duck Redux: An Improved Proper Motion Upper Limit for the Pulsar B1757-24 Near the Supernova Remnant G5.4-1.2
Authors: J. A. Blazek, B. M. Gaensler, S. Chatterjee, E. van der Swaluw, F. Camilo, B. W. Stappers
Comments: 9 pages, including 1 color and 1 B/W figure. Minor changes following referee's report. ApJ, in press
Note: replaced with revised version Wed, 26 Jul 2006 01:31:37 GMT (280kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 28 Jul 06 00:00:10 GMT
0607602 -- 0607628 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607612 [abs, ps, pdf, other] :
Title: The large-scale jet-powered radio nebula of Circinus X-1
Authors: V. Tudose (1,2), R. P. Fender (3,1), C. R. Kaiser (3), A. K. Tzioumis (4), M. van der Klis (1), R. Spencer (5) ((1) Amsterdam, (2) Bucharest, (3) Southampton, (4) ATNF, (5) Manchester)
Comments: Accepted to MNRAS

We present multi-epoch observations of the radio nebula around the neutron star X-ray binary Circinus X-1 made at 1.4 and 2.5 GHz with the Australia Telescope Compact Array between October 2000 and September 2004. The nebula can be seen as a result of the interaction between the jet from the system and the interstellar medium and it is likely that we are actually looking toward the central X-ray binary system through the jet-powered radio lobe. The study of the nebula thus offers a unique opportunity to estimate for the first time using calorimetry the energetics of a jet from an object clearly identified as a neutron star. An extensive discussion on the energetics of the complex is presented: a first approach is based on the minimum energy estimation, while a second one employs a self-similar model of the interaction between the jets and the surrounding medium. The results suggest an age for the nebula of \leq 10^5 years and a corresponding time-averaged jet power \geq 10^{35} erg s^{-1}. During periodic flaring episodes, the instantaneous jet power may reach values of similar magnitude to the X-ray luminosity.

 
astro-ph/0607613 [abs, ps, pdf, other] :
Title: VLT/UVES spectroscopy of Wray 977, the hypergiant companion to the X-ray pulsar GX301-2
Authors: L. Kaper (1), A. van der Meer (1), F. Najarro (2) ((1) Astr. Inst. Univ. of Amsterdam, (2) Inst. de Estructura de la Materia CSIC, Madrid)
Comments: 20 pages, including 14 figures, A&A in press

Model atmosphere fits to high-resolution optical spectra of Wray 977 confirm the B hypergiant classification of the massive companion to the X-ray pulsar GX301-2. The models give a radius of 62 Rsun, an effective temperature of 18,100 K and a luminosity of 5 x 10^^5 Lsun. The deduced mass-loss rate and terminal velocity of the stellar wind are 10^^-5 Msun/yr and 305 km/s, respectively. The interstellar Na I D absorption indicates that Wray 977 is located behind the first intersection with the Sagittarius-Carina spiral arm (1-2.5 kpc) and probably belongs to the stellar population of the Norma spiral arm at a distance of 3-4 kpc. The spectra obtained with UVES on the Very Large Telescope (VLT) cover a full orbit of the system, including periastron passage, from which we derive the radial-velocity curve of the B hypergiant. The measured radial-velocity amplitude is 10 +/-3 km/s yielding a mass ratio q = 0.046 +/- 0.014. The absence of an X-ray eclipse results in a lower limit to the mass of Wray 977 of 39 Msun. An upper limit of 53 Msun is derived for the mass of Wray 977 adopting a maximum neutron star mass of 2.5 Msun. The ``spectroscopic'' mass of Wray 977 is 43 +/- 10 Msun, consistent with the range in mass derived from the binarity constraints. The mass of the neutron star is 1.85 +/- 0.6 Msun. Time series of spectral lines formed in the dense stellar wind indicate the presence of a gas stream trailing the neutron star in its orbit. The long-term behaviour of the H alpha equivalent width exhibits strong variations in wind strength; the sampling of the data is insufficient to conclude whether a relation exists between wind mass-loss rate and pulsar spin period.

 
astro-ph/0607614 [abs, ps, pdf, other] :
Title: Search for radio pulsations in four Anomalous X-ray Pulsars and discovery of two new pulsars
Authors: M. Burgay, N. Rea, G.L. Israel, A. Possenti, L. Burderi, T. Di Salvo, N. D'Amico, L. Stella
Comments: 8 pages, 6 figures, accepted by MNRAS

We report on observations of four southern Anomalous X-ray Pulsars, (1RXS J170849.0-400910, 1E 1048.1-5937, 1E 1841-045 and AX J1845-0258), obtained at 1.4 GHz using the Parkes radio telescope. Radio pulsations from these sources have been searched (i) by directly folding the time series at a number of trial periods centered on the value of the spin rate obtained from the X-ray observations; (ii) by performing a blind search; (iii) using a code sensitive to single dedispersed pulses, in the aim to detect signals similar to those of the recently discovered Rotating RAdio Transients. No evidence for radio pulsations with an upper limit of ~0.1 mJy for any of the four targets has been found. The blind search led to the serendipitous discovery of two new pulsars, rotating with a spin period of about 0.7 s and of 92 ms respectively, and to the further detection of 18 known pulsars, two of which were also detected in the single-pulse search.

 
astro-ph/0607624 [abs, ps, pdf, other] :
Title: X-ray binaries
Authors: H. Schatz, K. E. Rehm
Comments: 23 pages, 1 figure, to appear in Nucl. Phys. A

We review the nuclear astrophysics aspects of accreting neutron stars in X-ray binaries. We summarize open astrophysical questions in light of recent observations and their relation to the underlying nuclear physics. Recent progress in the understanding of the nuclear physics, especially of X-ray bursts, is also discussed.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 31 Jul 06 00:00:09 GMT
0607629 -- 0607656 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607640 [abs, ps, pdf, other] :
Title: The Parkes multibeam pulsar survey: VI. Discovery and timing of 142 pulsars and a Galactic population analysis
Authors: D. R. Lorimer, A. J. Faulkner, A. G. Lyne, R. N. Manchester, M. Kramer, M. A. McLaughlin, G. Hobbs, A. Possenti, I. H. Stairs, F. Camilo, M. Burgay, N. D'Amico, A. Corongiu, F. Crawford
Comments: 30 pages, 8 figures, 9 tables, accepted for publication in MNRAS

[ABRIDGED] We present the discovery and follow-up observations of 142 pulsars found in the Parkes 20-cm multibeam pulsar survey of the Galactic plane. These new discoveries bring the total number of pulsars found by the survey to 742. In addition to tabulating spin and astrometric parameters, along with pulse width and flux density information, we present orbital characteristics for 13 binary pulsars which form part of the new sample. Combining these results from another recent Parkes multibeam survey at high Galactic latitudes, we have a sample of 1008 normal pulsars which we use to carry out a determination of their Galactic distribution and birth rate. We infer a total Galactic population of 30000 +/- 1100 potentially detectable pulsars (i.e. those beaming towards us) having 1.4-GHz luminosities above 0.1 mJy kpc squared. Using a pulsar current analysis, we derive the birth rate of this population to be 1.4 +/- 0.2 pulsars per century. An important conclusion from our work is that the inferred radial density function of pulsars depends strongly on the assumed distribution of free electrons in the Galaxy. As a result, any analyses using the most recent electron model of Cordes & Lazio predict a dearth of pulsars in the inner Galaxy. We show that this model can also bias the inferred pulsar scale height with respect to the Galactic plane. Combining our results with other Parkes multibeam surveys we find that the population is best described by an exponential distribution with a scale height of 330 pc.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 1 Aug 06 00:00:13 GMT
0607657 -- 0607674 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607659 [abs, ps, pdf, other] :
Title: Cyclotron resonance energies at a low X-ray luminosity: A0535+262 observed with Suzaku
Authors: Y. Terada (1), T. Mihara (1), M. Nakajima (1), M. Suzuki (1), N. Isobe (1), K. Makishima (1,2), H. Takahashi (2), T. Enoto (2), M. Kokubun (2), T. Kitaguchi (2), S. Naik (3), T. Dotani (3), F. Nagase (3), T. Tanaka (3), S. Watanabe (3), S. Kitamoto (4), K. Sudoh (4), A. Yoshida (5), Y. Nakagawa (5), S. Sugita (5), T. Kohmura (6), T. Kotani (7), D. Yonetoku (8), L. Angelini (9), J. Cottam (9), K. Mukai (9), R. Kelley (9), Y. Soong (9), M. Bautz (10), S. Kissel (10), J. Doty (11) ((1) RIKEN, Japan, (2) Univ of Tokyo, Japan, (3) ISAS/JAXA, Japan, (4) Rikkyo Univ Japan (5) Aoyama Gakuin Univ, Japan (6) Kogakuin Univ, Japan, (7) Tokyo Tech Univ, Japan (8) Kanazawa Univ, Japan (9) NASA/GSFC, USA (10) MIT, USA, (11) Noqsi Aerospace Ltd.)
Comments: 12 pages, 4 figures, accepted to ApJL, high resolution version is available from this http URL

The binary X-ray pulsar A0535+262 was observed with the Suzaku X-ray observatory, on 2005 September 14 for a net exposure of 22 ksec. The source was in a declining phase of a minor outburst, exhibiting 3--50 keV luminosity of about $3.7 \times 10^{35}$ ergs s$^{-1}$ at an assumed distance of 2 kpc. In spite of the very low source intensity (about 30 mCrab at 20 keV), its electron cyclotron resonance was detected clearly with the Suzaku Hard X-ray Detector, in absorption at about 45 keV. The resonance energy is found to be essentially the same as those measured when the source is almost two orders of magnitude more luminous. These results are compared with the luminosity-dependent changes in the cyclotron resonance energy, observed from 4U 0115+63 and X 0331+53.

 
astro-ph/0607664 [abs, ps, pdf, other] :
Title: Tempo2, a new pulsar timing package. II: The timing model and precision estimates
Authors: R. T. Edwards, G. B. Hobbs, R. N. Manchester
Comments: 30 pages, 3 figures, accepted for publication in MNRAS

Tempo2 is a new software package for the analysis of pulsar pulse times of arrival. In this paper we describe in detail the timing model used by tempo2, and discuss limitations on the attainable precision. In addition to the intrinsic slow-down behaviour of the pulsar, tempo2 accounts for the effects of a binary orbital motion, the secular motion of the pulsar or binary system, interstellar, Solar system and ionospheric dispersion, observatory motion (including Earth rotation, precession, nutation, polar motion and orbital motion), tropospheric propagation delay, and gravitational time dilation due to binary companions and Solar system bodies. We believe the timing model is accurate in its description of predictable systematic timing effects to better than one nanosecond, except in the case of relativistic binary systems where further theoretical development is needed. The largest remaining sources of potential error are measurement error, interstellar scattering, Solar system ephemeris errors, atomic clock instability and gravitational waves.

 
astro-ph/0607666 [abs, ps, pdf, other] :
Title: Spin-Kick Correlation in Neutron Stars: Alignment Conditions and Implications
Authors: Chen Wang; Dong Lai; JinLin Han
Comments: 17 pages, 8 figures. Submitted to ApJ on July 30, 2006

Recent observations of pulsar wind nebulae and radio polarization profiles revealed a tendency of the alignment between the spin and velocity directions in neutron stars. We study the condition for spin-kick alignment using a toy model, in which the kick consists of many off-centered, randomly-oriented thrusts. Both analytical considerations and numerical simulations indicate that spin-kick alignment cannot be easily achieved if the proto-neutron star does not possess some initial angular momentum. To obtain the observed spin-kick misalignment angle distribution, the initial spin period of the neutron star must be smaller than the kick timescale. Typically, an initial period of a hundred milliseconds or less is required.

 
astro-ph/0607671 [abs, ps, pdf, other] :
Title: Quasi-stationary Electromagnetic Effects in Conductors and Superconductors in Schwarzchild Space-time
Authors: B. J. Ahmedov, F. J. Fattoyev
Comments: 17 pages, 3 figures
Journal-ref: IJMPD, Vol.14, N 5, 2005, 817-835

The general principles needed to compute the effect of a stationary gravitational field on the quasistationary electromagnetic phenomena in normal conductors and superconductors are formulated from general relativistic point of view. Generalization of the skin effect, that is the general relativistic modification of the penetration depth (of the time-dependent magnetic field in the conductor) due to its relativistic coupling to the gravitational field is obtained. The effect of the gravitational field on the penetration and coherence depths in superconductors is also studied. As an illustration of the foregoing general results, we discuss their application to superconducting systems in the outer core of neutron stars. The relevance of these effects to electrodynamics of magnetized neutron stars has been shown.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0512653 [abs, ps, pdf, other] :
Title: Interrelation between radio and X-ray signatures of drifting subpulses in pulsars
Authors: Janusz Gil, George Melikidze, Bing Zhang
Comments: 4 pages
Note: replaced with revised version Sat, 29 Jul 2006 10:41:27 GMT (9kb)
 
astro-ph/0601613 [abs, ps, pdf, other] :
Title: Formation of a Partially-Screened Inner Acceleration Region in Radio Pulsars: Drifting Subpulses and Thermal X-Ray Emission from Polar Cap Surface
Authors: Janusz Gil, George Melikidze, Bing Zhang
Note: replaced with revised version Sat, 29 Jul 2006 11:03:22 GMT (276kb)
 
astro-ph/0605490 [abs, ps, pdf, other] :
Title: Cooling of the quasi-persistent neutron star X-ray transients KS 1731-260 and MXB 1659-29
Authors: Edward M. Cackett (St Andrews), Rudy Wijnands, Manuel Linares (Amsterdam), Jon M. Miller (Michigan), Jeroen Homan, Walter Lewin (MIT)
Comments: 11 pages, 3 figures, 4 tables, accepted for publication in MNRAS
Note: replaced with revised version Mon, 31 Jul 2006 13:23:10 GMT (55kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 2 Aug 06 00:00:14 GMT
0608001 -- 0608028 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608008 [abs, ps, pdf, other] :
Title: Hall Magnetohydrodynamics of weakly-ionized plasma
Authors: B. P. Pandey, Mark Wardle
Comments: 4 page, submitted to Physical Review Letters

We show that the Hall scale in a weakly ionized plasma depends on the fractional ionization of the medium and, Hall MHD description becomes important whenever the ion-neutral collision frequency is comparable to the ion-gyration frequency, or, the ion-neutral collisional mean free path is smaller than the ion gyro-radius. Wave properties of a weakly-ionized plasma also depends on the fractional ionization and plasma Hall parameters, and whistler mode is the most dominant mode in such a medium. Thus Hall MHD description will be important in astrophysical disks, dark molecular clouds, neutron star crusts, and, solar and planetary atmosphere.

 
astro-ph/0608013 [abs, ps, pdf, other] :
Title: The globular cluster mass/low mass X-ray binary correlation:implications for kick velocity distributions from supernovae
Authors: M. Smits (Amsterdam), T.J. Maccarone (Southampton & Amsterdam), A. Kundu, S.E. Zepf (Michigan State)
Comments: 9 pages, 5 figures, accepted to A&A

Optical and X-ray studies of six nearby galaxies show that the probability a globular cluster will be an X-ray source is consistent with being linearly proportional to its mass. We show that this result is consistent with some recent estimates of the velocity kick distributions for isolated radio pulsars -- those which are the sum of two Maxwellians, with the slower distribution at about 100 km/sec -- so long as a large fraction of the retained binaries are in binary systems with other massive stars. We confirm that over a large sample of galaxies, metallicity is clearly a factor in determining whether a globular cluster will contain an X-ray binary, and we estimate the transformations between color and metallicity for a large number of optical filter combinations. We also show that the core interaction rate is roughly linearly proportional to the stellar mass of a globular cluster for the Milky Way when one bins the clusters by mass.

 
astro-ph/0608021 [abs, ps, pdf, other] :
Title: Hybrid protoneutron stars with the MIT bag model
Authors: O. E. Nicotra, M. Baldo, G. F. Burgio, H.-J. Schulze
Comments: 12 pages, 9 figures submitted to Phys. Rev. D

We study the hadron-quark phase transition in the interior of protoneutron stars. For the hadronic sector, we use a microscopic equation of state involving nucleons and hyperons derived within the finite-temperature Brueckner-Bethe-Goldstone many-body theory, with realistic two-body and three-body forces. For the description of quark matter, we employ the MIT bag model both with a constant and a density-dependent bag parameter. We calculate the structure of protostars with the equation of state comprising both phases and find maximum masses below 1.6 solar masses. Metastable heavy hybrid protostars are not found.

 
astro-ph/0608023 [abs, ps, pdf, other] :
Title: The bright spiky emission of pulsar B0656+14
Authors: P. Weltevrede, G.A.E. Wright, B.W. Stappers, J.M. Rankin
Comments: 17 pages, 18 figures, accepted for publication in A&A

We present a detailed study of the single radio pulses of PSR B0656+14, a pulsar also known to be a strong pulsed source of high-energy emission. Despite the extensive studies at high-energy wavelengths, there is little or no published work on its single-pulse behaviour in the radio band. In this report we rectify this omission. We have found that the shape of the pulse profile of PSR B0656+14 requires an unusually long timescale to achieve stability (over 25,000 pulses at 327 MHz). This instability is caused by very bright and narrow pulses with widths and luminosities comparable to those observed for the RRATs. Many pulses are bright enough to qualify as "giant pulses", but are broader than those usually meant by this term. At 327 MHz the brightest pulse was about 116 times brighter than the average pulse. Although the most powerful pulses peak near the centre of the profile, occasional sudden strong pulses are also found on the extreme leading edge of the profile. One of them has a peak flux of about 2000 times the average flux at that pulse longitude. No "break" in the pulse-energy distributions is observed, but nevertheless there is evidence of two separate populations of pulses: bright pulses have a narrow "spiky" appearance consisting of short quasi-periodic bursts of emission with microstructure, in contrast to the underlying weaker broad pulses. Furthermore, the spiky pulses tend to appear in clusters which arise and dissipate over about 10 periods. We demonstrate that the spiky emission builds a narrow and peaked profile, whereas the weak emission produces a broad hump, which is largely responsible for the shoulders in the total emission profiles at both high and low frequencies.

 
astro-ph/0608025 [abs, ps, pdf, other] :
Title: Studies of Neutron Stars at Optical/IR Wavelengths
Authors: R. P. Mignani (MSSL), S. Bagnulo (ESO), A. De Luca, G. L. Israel (INAF), G. Lo Curto (ESO), C. Motch (OAS), R. Perna (UC), N. Rea (SRON), R. Turolla (UP), S. Zane (MSSL)
Comments: 8 pages, 6 Postscript figures

In the last years, optical studies of Isolated Neutron Stars (INSs) have expanded from the more classical rotation-powered ones to other categories, like the Anomalous X-ray Pulsars (AXPs) and the Soft Gamma-ray Repeaters (SGRs), which make up the class of the magnetars, the radio-quiet INSs with X-ray thermal emission and, more recently, the enigmatic Compact Central Objects (CCOs) in supernova remnants. Apart from 10 rotation-powered pulsars, so far optical/IR counterparts have been found for 5 magnetars and for 4 INSs. In this work we present some of the latest observational results obtained from optical/IR observations of different types of INSs.

 

Cross-listings


2 abstracts or titles contain neutron star, magnetar or pulsar


hep-ph/0607343 [abs, ps, pdf, other] :
Title: Neutron Star stability in the Nambu - Jona-Lasinio model and quark confinement
Authors: M. Baldo, G. F. Burgio, P. Castorina. S. Plumari, D. Zappala', (Dipartimento di Fisica, Universita' di Catania, and INFN Sezione di Catania, Italy)
Comments: 9 pages, 4 eps figures

The stability of neutron stars (NS) with a quark matter core has been studied within the Nambu - Jona-Lasinio (NJL) model with a momentum cut-off which depends on the density. This procedure, which improves the agreement between QCD and NJL model at large density, modifies the standard NJL equation of state, and then it is potentially relevant for the stability analysis. We show that also with the density dependent cut-off procedure, the NS instability still persists, and that the vacuum pressure, as a signal of quark confinement, has a fundamental role for the NS stability. In this respect, our conclusions point to a relationship between confinement and NS stability.

 
nucl-th/0607055 [abs, ps, pdf, other] :
Title: Structure of protoneutron stars within a static approach
Authors: O. E. Nicotra
Comments: 5 pages, 3 figures, 1 table

To investigate the stability of the protoneutron stars in its early evolution, the minimum gravitational mass plays a fundamental role. This quantity depends upon temperature profile assumed. We study within a static approach the stability of a protoneutron star. In particular we focus on a suitable temperature profile suggested by dynamical calculations. We indeed consider a protoneutron star as composed by an isothermal core and an isentropic outer part. To describe physical properties of the interior we employ a microscopically derived equation of state for nuclear matter. For the outer part we employ the Lattimer-Swesty equation of state. The global structure is studied. The assumed temperature profile turns out to give a range of stability which supports temperature values in line with those coming from dynamical calculations. The maximum mass instead depends only upon the equation of state employed.

 

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astro-ph new abstracts, Thu, 3 Aug 06 00:00:11 GMT
0608029 -- 0608066 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608043 [abs, ps, pdf, other] :
Title: New Self-Similar Solutions of Polytropic Gas Dynamics
Authors: Yu-Qing Lou (1,2,3), Wei-Gang Wang (1), ((1) Tsinghua Center For astrophysics, Tsinghua University, (2)The University of Chicago, (3) National Astronomical Observatories, Chinese Academy of Science.)
Comments: 17 pages, 11 figures, Accepted for publication in MNRAS

We explore semi-complete self-similar solutions for the polytropic gas dynamics involving self-gravity under spherical symmetry, examine behaviours of the sonic critical curve, and present new asymptotic collapse solutions that describe `quasi-static' asymptotic behaviours at small radii and large times. These new `quasi-static' solutions with divergent mass density approaching the core can have self-similar oscillations. Earlier known solutions are summarized. Various semi-complete self-similar solutions involving such novel asymptotic solutions are constructed, either with or without a shock. In contexts of stellar core collapse and supernova explosion, a hydrodynamic model of a rebound shock initiated around the stellar degenerate core of a massive progenitor star is presented. With this dynamic model framework, we attempt to relate progenitor stars and the corresponding remnant compact stars: neutron stars, black holes, and white dwarfs.

 
astro-ph/0608055 [abs, ps, pdf, other] :
Title: Pulsar Braking Indices, Glitches and Energy Dissipation In Neutron Stars
Authors: M.A.Alpar (Sabanci University, Turkey) A. Baykal (Middle East Technical University, Turkey)
Comments: Accepted for publication in MNRAS

Almost all pulsars with anomalous positive $\ddot \Omega $ measurements (corresponding to anomalous braking indices in the range 5$<n<$100), including all the pulsars with observed large glitches ($\Delta\Omega/\Omega$ $>$ 10$^{-7}$) as well as post glitch or interglitch $\ddot \Omega$ measurements obey the scaling between $\ddot \Omega$ and glitch parameters originally noted in the Vela pulsar. Negative second derivative values can be understood in terms of glitches that were missed or remained unresolved. We discuss the glitch rates and a priori probabilities of positive and negative braking indices according to the model developed for the Vela pulsar. This behavior supports the universal occurrence of a nonlinear dynamical coupling between the neutron star crust and an interior superfluid component. The implied lower limit to dynamical energy dissipation in a neutron star with spindown rate $\dot \Omega$ is $\dot E_{diss}> 1.7 \times 10 ^{-6} \dot E_{rot}$. Thermal luminosities and surface temperatures due to dynamical energy dissipation are estimated for old neutron stars which are spinning down as rotating magnetic dipoles beyond the pulsar death line.

 
astro-ph/0608058 [abs, ps, pdf, other] :
Title: Particle Accelerator in Pulsar Magnetospheres: Super Goldreich-Julian Current with Ion Emission from the Neutron Star Surface
Authors: Kouichi Hirotani
Comments: 36 pages, 14 figures, accepted to Astroph. J

We investigate the self-consistent electrodynamic structure of a particle accelerator in the Crab pulsar magnetosphere on the two-dimensional poloidal plane, solving the Poisson equation for the electrostatic potential together with the Boltzmann equations for electrons, positrons and gamma-rays. If the trans-field thickness of the gap is thin, the created current density becomes sub-Goldreich-Julian, giving the traditional outer-gap solution but with negligible gamma-ray luminosity. As the thickness increases, the created current increases to become super-Goldreich-Julian, giving a new gap solution with substantially screened acceleration electric field in the inner part. In this case, the gap extends towards the neutron star with a small-amplitude positive acceleration field, extracting ions from the stellar surface as a space-charge-limited flow. The acceleration field is highly unscreened in the outer magnetosphere, resulting in a gamma-ray spectral shape which is consistent with the observations.

 

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astro-ph new abstracts, Fri, 4 Aug 06 00:00:09 GMT
0608067 -- 0608090 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608068 [abs, ps, pdf, other] :
Title: On the Physics of Type I X-ray Bursts on Accreting Neutron Stars at High Accretion Rates
Authors: Randall L. Cooper, Ramesh Narayan (Harvard/CfA)
Comments: 4 pages, 1 figure, accepted by ApJL

We investigate the effect of the hot CNO cycle breakout reaction 15O(alpha,gamma)19Ne on the occurrence of type I X-ray bursts on accreting neutron stars. For f_rp <~ 0.1, where f_rp is a dimensionless factor by which we multiply the 15O(alpha,gamma)19Ne reaction rate of Caughlan & Fowler (1988), our model predicts that bursts should occur only for accretion rates below a critical value of approximately 0.3 times the Eddington limit. This agrees with observations. For larger values of f_rp, including the standard choice f_rp = 1, the model switches to a new regime in which bursts occur all the way up to roughly the Eddington limit. Since the latter regime disagrees with observations, we suggest that the true 15O(alpha,gamma)19Ne reaction rate is lower than usually assumed.

 
astro-ph/0608089 [abs, ps, pdf, other] :
Title: Discovery of twin kHz QPOs in the peculiar X-ray binary Circinus X-1
Authors: S. Boutloukos (1,2), M. van der Klis (1), D. Altamirano (1), M. Klein-Wolt (1), R. Wijnands (1), P.G. Jonker (3,4,5), R.P. Fender (1,6) ((1) Astronomical Insitute Amsterdam NL, (2) Theoretical Astrophysics Tuebingen D, (3) SRON Utrecht NL, (4) CfA Cambridge USA, (5) Astronomical Institute Utrecht NL, (6) School of Physics and Astronomy Southampton UK)
Comments: 24 pages, 12 figures, submitted to Astrophysical Journal

We report the discovery with the RXTE/PCA of twin kHz QPOs in Cir X-1. Eleven cases of simultaneous double QPOs occurred, with significances of up to 6.3 and 5.5 sigma and centroid frequencies ranging between approximately 56-225 and 230-500 Hz for the two QPO peaks, respectively, i.e., for the most part at frequencies well below those of other sources. The QPO properties clearly indicate that these double peaks are the kHz QPOs known from low magnetic field neutron stars, and not black-hole high-frequency QPOs, confirming that Cir X-1 is a neutron star. The kHz QPO peak separation varies over a wide range, ~175-340 Hz, and increases with QPO frequency. This is contrary to what is seen in other sources but agrees with predictions of the relativistic precession model and Alfven wave models; beat-frequency models require modification to accommodate this. In other observations single kHz QPOs can be seen down to frequencies as low as ~12 Hz, as well as a strong low-frequency (LF) QPO between 1 and 30 Hz. The relations between the frequencies of the kHz QPOs and the LF QPO are in good agreement with those found previously in Z sources, confirming that Cir X-1 may be a peculiar Z source. We suggest that the low frequencies of the kHz QPOs in Cir X-1 and to a lesser extent in (other) Z sources might be due to a relatively stronger radial inflow to the neutron star than in other kHz QPO sources.

 

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astro-ph new abstracts, Mon, 7 Aug 06 00:00:10 GMT
0608091 -- 0608121 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608096 [abs, ps, pdf, other] :
Title: Detecting sterile dark matter in space
Authors: Alexander Kusenko
Comments: 11 pages, 1 figure, to appear in proceedings "From Quantum to Cosmos: fundametal physics research in space", Washington, DC, May 22-24, 2006

Space-based instruments provide new and, in some cases, unique opportunities to search for dark matter. In particular, if dark matter comprises sterile neutrinos, the x ray detection of their decay line is by far the most promising strategy for discovery. Sterile neutrinos with masses in the keV range could solve several long-standing astrophysical puzzles, from supernova asymmetries and the pulsar kicks to star formation, reionization, and baryogenesis. The best current limits on sterile neutrinos come from Chandra and XMM-Newton. Future advances can be achieved with a high-resolution x-ray spectrometry in space.

 
astro-ph/0608112 [abs, ps, pdf, other] :
Title: First stars X. The nature of three unevolved Carbon-Enhanced Metal-Poor stars
Authors: T. Sivarani, T. C. Beers, P. Bonifacio, P. Molaro, R. Cayrel, F. Herwig, M. Spite, F. Spite, B. Plez, J. Andersen, B. Barbuy, E. Depagne, V. Hill, P. Francois, B. Nordstrom, F. Primas
Comments: A&A accepted 08/07/2006

From high-resolution VLT/UVES spectra (R~43,000), we determine abundances or upper limits for Li, C, N, O, and other important elements, as well as 12C/13C isotopic ratio for three Carbon enhanced metal poor stars. All three stars have -3.30 <= [Fe/H] <= -2.85 and moderate to high CNO abundances. CS 22958-042 is one of the most carbon-rich CEMP stars known ([C/Fe] = +3.2), while CS 29528-041 (one of the few N-enhanced metal-poor stars known) is one of the most nitrogen rich ([N/Fe] = +3.0). Oxygen is very high in CS 31080-095 ([O/Fe] = +2.35) and in CS 22958-042 ([O/Fe] = +1.35). All three stars exhibit [Sr/Fe] < 0; Ba is not detected in CS 22958-042 ([Ba/Fe] < -0.53), but it is moderately enhanced ([Ba/Fe] ~ 1) in the other two stars. CS 22958-042 displays one of the largest sodium overabundances yet found in CEMP stars ([Na/Fe] = +2.8). CS 22958-042 has 12C/13C = 9, similar to most other CEMP stars without enhanced neutron-capture elements, while 12C/13C <= 40 in CS 31080-095. CS 31080-095 and CS 29528-041 have A(Li) ~ 1.7, below the Spite Plateau, while Li is not detected in CS 22958-042. CS 22958-042 is a CEMP-no star, but the other two stars are in no known class of CEMP star and thus either constitute a new class or are a link between the CEMP-no and CEMP-s classes, adding complexity to the abundance patterns for CEMP stars. We interpret the abundance patterns in our stars to imply that current models for the presumed AGB binary progenitors lack an extra-mixing process, similar to those apparently operating in RGB stars.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0608017 [abs, ps, pdf, other] :
Title: Electromagnetic Effects in Superconductors in Gravitational Field
Authors: B. J. Ahmedov, V. G. Kagramanova
Comments: 11 pages 2 figures
Journal-ref: Int. J. Mod. Phys. D14, N 5, 2005, 837-847

The general relativistic modifications to the resistive state in superconductors of second type in the presence of a stationary gravitational field are studied. Some superconducting devices that can measure the gravitational field by its red-shift effect on the frequency of radiation are suggested. It has been shown that by varying the orientation of a superconductor with respect to the earth gravitational field, a corresponding varying contribution to AC Josephson frequency would be added by gravity. A magnetic flux (being proportional to angular velocity of rotation $\Omega$) through a rotating hollow superconducting cylinder with the radial gradient of temperature $\nabla_r T$ is theoretically predicted. The magnetic flux is assumed to be produced by the azimuthal current arising from Coriolis force effect on radial thermoelectric current. Finally the magnetic flux through the superconducting ring with radial heat flow located at the equatorial plane interior the rotating neutron star is calculated. In particular it has been shown that nonvanishing magnetic flux will be generated due to the general relativistic effect of dragging of inertial frames on the thermoelectric current.

 

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astro-ph new abstracts, Tue, 8 Aug 06 00:00:09 GMT
0608122 -- 0608154 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608128 [abs, ps, pdf, other] :
Title: Optical observations of Be/X-ray transient system KS 1947+300
Authors: U. Kiziloglu, A. Baykal, N. Kiziloglu (Middle East Technical University, Turkey)
Comments: to be publsihed on AN

ROTSE-IIId observations of the Be/X-ray transient system KS 1947+300 obtained between September 2004 and December 2005 make it possible to study the correlation between optical and X-ray activity. The optical outburst of 0.1 mag was accompanied by an increase in X-ray flux in 2004 observations. Strong correlation between the optical and X-ray light curves suggests that neutron star directly accretes from the outflowing material of Be star. The nearly zero time lag between X-ray and optical light curves suggests a heating of the disk of Be star by X-rays. No optical brightening and X-ray enhancement was seen in 2005 observations. There is no indication of the orbital modulation in the optical light curve.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607666 [abs, ps, pdf, other] :
Title: Spin-Kick Correlation in Neutron Stars: Alignment Conditions and Implications
Authors: Chen Wang, Dong Lai, JinLin Han
Comments: 17 pages, 8 figures. Submitted to ApJ on July 30, 2006. The forms of authors corrected to enable automate indexing and searching
Note: replaced with revised version Sat, 5 Aug 2006 03:39:02 GMT (68kb)
 
nucl-th/0607055 [abs, ps, pdf, other] :
Title: Structure of protoneutron stars within a static approach
Authors: O. E. Nicotra
Comments: 5 pages, 3 figures, 1 table
Note: replaced with revised version Mon, 7 Aug 2006 17:19:07 GMT (68kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 9 Aug 06 00:00:08 GMT
0608155 -- 0608181 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608155 [abs, ps, pdf, other] :
Title: A Study of Giant Pulses from PSR J1824-2452A
Authors: H. S. Knight, M. Bailes, R. N. Manchester, S. M. Ord
Comments: Accepted by ApJ

We have searched for microsecond bursts of emission from millisecond pulsars in the globular cluster M28 using the Parkes radio telescope. We detected a total of 27 giant pulses from the known emitter PSR J1824-2452A. At wavelengths around 20 cm the giant pulses are scatter-broadened to widths of around 2 microseconds and follow power-law statistics. The pulses occur in two narrow phase-windows which correlate in phase with X-ray emission and trail the peaks of the integrated radio pulse-components. Notably, the integrated radio emission at these phase windows has a steeper spectral index than other emission. The giant pulses exhibit a high degree of polarization, with many being 100% elliptically polarized. Their position angles appear random. Although the integrated emission of PSR J1824-2452A is relatively stable for the frequencies and bandwidths observed, the intensities of individual giant pulses vary considerably across our bands. Two pulses were detected at both 2700 and 3500 MHz. The narrower of the two pulses is 20 ns wide at 3500 MHz. At 2700 MHz this pulse has an inferred brightness temperature at maximum of 5 x 10^37 K. Our observations suggest the giant pulses of PSR J1824-2452A are generated in the same part of the magnetosphere as X-ray emission through a different emission process to that of ordinary pulses.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


hep-ph/0608041 [abs, ps, pdf, other] :
Title: Spin-one color superconductivity in compact stars?- an analysis within NJL-type models
Authors: D.N. Aguilera
Comments: 7 pages, 7 figures, contribution to the Conference Proceedings of "Isolated Neutron Stars: from the Interior to the Surface", London, 24-28. April 2006

We present results of a microscopic calculation using NJL-type model of possible spin-one pairings in two flavor quark matter for applications in compact star phenomenology. We focus on the color-spin locking phase (CSL) in which all quarks pair in a symmetric way, in which color and spin states are locked. The CSL condensate is particularly interesting for compact star applications since it is flavor symmetric and could easily satisfy charge neutrality. Moreover, the fact that in this phase all quarks are gapped might help to suppress the direct Urca process, consistent with cooling models. The order of magnitude of these small gaps (~1 MeV) will not influence the EoS, but their also small critical temperatures (T_c ~800 keV) could be relevant in the late stages neutron star evolution, when the temperature falls below this value and a CSL quark core could form.

 

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astro-ph new abstracts, Thu, 10 Aug 06 00:00:08 GMT
0608182 -- 0608207 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608187 [abs, ps, pdf, other] :
Title: Long-term evolution of accretion discs in Be/X-ray binaries
Authors: K. Hayasaki, Atsuo T. Okazaki
Comments: 10 pages, 7 figures, Accepted for publication in MNRAS

We numerically study the long-term evolution of the accretion disc around the neutron star in a coplanar Be/X-ray binary with a short period and a moderate eccentricity. From three dimensional Smoothed Particle Hydrodynamics simulations, we find that the disc evolves through three distinct phases, each characterized by different mass accretion patterns. In the first "developing phase", the disc is formed and develops towards a nearly Keplerian disc. It has a relatively large, double-peaked mass-accretion rate with the higher peak by the direct accretion at periastron, which is followed by the lower peak by the accretion induced by a one-armed spiral wave. In the second "transition phase", the disc is approximately Keplerian and grows with time. The mass-accretion rate increases as the disc grows. In the second phase, there is a transition in the mass accretion rate from a double peaked to a single peaked pattern. In the final quasi-steady state, the mass-accretion rate is on average balanced with the mass-transfer rate from the Be disc and exhibits a regular orbital modulation. In the quasi-steady state, the mass-accretion rate has a single peak by the wave-induced accretion as in a later stage of the transition phase. The orbital modulation of X-ray maxima could provide not only a circumstantial evidence for the persistent disc but also an observational diagnosis of the disc evolutionary state.

 
astro-ph/0608191 [abs, ps, pdf, other] :
Title: Discovery of a Compact X-ray Source in the LMC Supernova Remnant N23 with Chandra
Authors: Asami Hayato (1,2), Aya Bamba (1), Toru Tamagawa (1,2), Kiyoshi Kawabata (2) ((1) RIKEN, (2) Tokyo Univ. of Sci.)
Comments: 16 pages, 5 figures, 1 table, Accepted to ApJ

An X-ray compact source was discovered with Chandra in a supernova remnant (SNR) N23, located in the Large Magellanic Cloud. The compact source (CXOU J050552.3-680141) is seen in only the hard band (> 2 keV) image of N23, while the soft band image (< 2 keV) shows diffuse emission of the SNR, with an extent of ~60 arcsec times ~80 arcsec. The compact source is located at almost the center of N23, and there is no identifiable object for the source from previous observations at any other wavelength. The source spectrum is best explained by a power-law model with a photon index of 2.2 (1.9-2.7) and an absorption-corrected luminosity of 1.0 x 10^34 ergs s^-1 in the 0.5--10 keV band for a distance of 50 kpc. Neither pulsation nor time variability of the source was detected with this observation with a time resolution of 3.2 sec. These results correspond with those of Hughes et al. (2006) who carried out analysis independently around the same time as our work. Based on information from the best-fit power-law model, we suggest that the source emission is most likely from a rotation-powered pulsar and/or a pulsar wind nebula. It is generally inferred that the progenitor of N23 is a core-collapsed massive star.
Based on information from the best-fit power-law model, we suggest that the source emission is most likely from a rotation-powered pulsar and/or a pulsar wind nebula. It is generally inferred that the progenitor of N23 is a core-collapsed massive star.

 
astro-ph/0608194 [abs, ps, pdf, other] :
Title: Algorithm of Ensemble Pulsar Time
Authors: Alexander Rodin
Comments: 6 pages, 3 figures. Accepted to Chin. J. Astron. Astrophys. (ChJAA)

An algorithm of the ensemble pulsar time based on the Wiener filtration method has been constructed. This algorithm has allowed the separation of the contributions of an atomic clock and a pulsar itself to the post-fit pulsar timing residuals. The method has been applied to the timing data of the millisecond pulsars PSR B1855+09 and PSR B1937+21 and allowed the filtering out of the atomic scale component from the pulsar phase variations. Direct comparison of the terrestrial time TT(BIPM96) and the ensemble pulsar time PT$_{\rm ens}$ has displayed that the difference TT(BIPM96) -- PT$_{\rm ens}$ is within $\pm0.4 \mu$s range. A new limit of gravitational wave background based on the difference TT(BIPM96) -- PT$_{\rm ens}$ was established to be $\Omega_g {\rm h}^2\sim 10^{-10}$.

 
astro-ph/0608205 [abs, ps, pdf, other] :
Title: Direct Measurement of Neutron-Star Recoil in the Oxygen-Rich Supernova Remnant Puppis A
Authors: P. Frank Winkler, Robert Petre

A sequence of three Chandra X-ray Observatory High Resolution Camera images taken over a span of five years reveals arc-second-scale displacement of RX J0822-4300, the stellar remnant (presumably a neutron star) near the center of the Puppis A supernova remnant. We measure its proper motion to be 0.159+/-0.017 arcsec/yr toward the west-southwest. At a distance of 2 kpc, this corresponds to a transverse space velocity of 1500 km/s. This is the first case of a compact X-ray source with a directly measured proper motion. The space velocity is consistent with the explosion center inferred from proper motions of the oxygen-rich optical filaments, and confirms the idea that Puppis A resulted from an asymmetric explosion accompanied by a kick that imparted roughly 3*10^49 ergs of kinetic energy (some 3 percent of the supernova kinetic energy) to the stellar remnant.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0608039 [abs, ps, pdf, other] :
Title: Magnetic Fields of Spherical Compact Stars in Braneworld
Authors: B. J. Ahmedov, F. J. Fattoyev
Comments: 11 pages, 5 figures, 1 table

We study the dipolar magnetic field configuration in dependence on brane tension and present solutions of Maxwell equations in the internal and external background spacetime of a magnetized spherical star in a Randall-Sundrum II type braneworld. The star is modelled as sphere consisting of perfect highly magnetized fluid with infinite conductivity and frozen-in dipolar magnetic field. With respect to solutions for magnetic fields found in the Schwarzschild spacetime brane tension introduces enhancing corrections both to the interior and the exterior magnetic field. These corrections could be relevant for the magnetic fields of magnetized compact objects as pulsars and magnetars and may provide the observational evidence for the brane tension through the modification of formula for magneto-dipolar emission which gives amplification of electromagnetic energy loss up to few orders depending on the value of the brane tension.

 

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astro-ph new abstracts, Fri, 11 Aug 06 00:00:09 GMT
0608208 -- 0608227 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608210 [abs, ps, pdf, other] :
Title: Studying Millisecond Pulsars in X-rays
Authors: Vyacheslav E. Zavlin (NASA/MSFC)
Comments: To appear in Astrophysics and Space Science, Proceedings of "Isolated Neutron Stars: from the Interior to the Surface", eds. D. Page, R. Turolla and S. Zane; 10 pages, 12 figures (four of them are color)

Millisecond pulsars represent an evolutionarily distinct group among rotation-powered pulsars. Outside the radio band, the soft X-ray range ($\sim 0.1$--10 keV) is most suitable for studying radiative mechanisms operating in these fascinating objects. X-ray observations revealed diverse properties of emission from millisecond pulsars. For the most of them, the bulk of radiation is of a thermal origin, emitted from small spots (polar caps) on the neutron star surface heated by relativistic particles produced in pulsar acceleration zones. On the other hand, a few other very fast rotating pulsars exhibit almost pure nonthermal emission generated, most probably, in pulsar magnetospheres. There are also examples of nonthermal emission detected from X-ray nebulae powered by millisecond pulsars, as well as from pulsar winds shocked in binary systems with millisecond pulsars as companions. These and other most important results obtained from X-ray observations of millisecond pulsars are reviewed in this paper, as well as results from the search for millisecond pulsations in
X-ray flux of the radio-quite neutron star RX J1856.5-3754.

 
astro-ph/0608224 [abs, ps, pdf, other] :
Title: Quark Deconfinement inside Compact Stars and Gamma Ray Bursts Inner Engine
Authors: Alessandro Drago (Univ. Ferrara - Italy and INFN Sez. Ferrara - Italy), Giuseppe Pagliara (Univ. Ferrara - Italy and INFN Sez. Ferrara - Italy), Irene Parenti (Univ. Ferrara - Italy and INFN Sez. Ferrara - Italy)
Comments: 8 pages, 7 figures, Proceedings of "Fifth International Conference on Perspectives in Hadronic Physics", Trieste 2006

The temporal structure of Gamma Ray Bursts can be interpreted assuming as a inner engine a neutron star which undergoes a progressive compactification via production of strangeness (hyperons and kaons) and quarks. We will propose a tentative identification of various emission periods of the burst with specific structural changes of the star. Each of these modifications of the composition of the compact star takes place as a deflagration and not as a detonation, so the energy released in the transition goes mainly into heat and not into a mechanical wave. This is important in order to avoid an excessive baryonic contamination of the region surrounding the compact star. In this way a ultrarelativistic plasma of electron-positron pairs and of photons can be obtained, powering the Gamma Ray Burst.

 
astro-ph/0608225 [abs, ps, pdf, other] :
Title: A Survey of 56 Mid-latitude EGRET Error Boxes for Radio Pulsars
Authors: F. Crawford, M. S. E. Roberts, J. W. T. Hessels, S. M. Ransom, M. Livingstone, C. R. Tam, V. M. Kaspi
Comments: 24 pages, including 4 figures and 3 tables. Accepted for publication in ApJ

We have conducted a radio pulsar survey of 56 unidentified gamma-ray sources from the 3rd EGRET catalog which are at intermediate Galactic latitudes (5 deg. < |b| < 73 deg.). For each source, four interleaved 35-minute pointings were made with the 13-beam, 1400-MHz multibeam receiver on the Parkes 64-m radio telescope. This covered the 95% error box of each source at a limiting sensitivity of about 0.2 mJy to pulsed radio emission for periods P > 10 ms and dispersion measures < 50 pc cm-3. Roughly half of the unidentified gamma-ray sources at |b| > 5 deg. with no proposed active galactic nucleus counterpart were covered in this survey. We detected nine isolated pulsars and four recycled binary pulsars, with three from each class being new. Timing observations suggest that only one of the pulsars has a spin-down luminosity which is even marginally consistent with the inferred luminosity of its coincident EGRET source. Our results suggest that population models, which include the Gould belt as a component, overestimate the number of isolated pulsars among the mid-latitude Galactic gamma-ray sources and that it is unlikely that Gould belt pulsars make up the majority of these sources. However, the possibility of steep pulsar radio spectra and the confusion of terrestrial radio interference with long-period pulsars (P > 200 ms) having very low dispersion measures (< 10 pc cm-3, expected for sources at a distance of less than about 1 kpc) prevent us from strongly ruling out this hypothesis. Our results also do not support the hypothesis that millisecond pulsars make up the majority of these sources. Non-pulsar source classes should therefore be further investigated as possible counterparts to the unidentified EGRET sources at intermediate Galactic latitudes.

 
astro-ph/0608226 [abs, ps, pdf, other] :
Title: The X-ray binary 2S0114+650=LSI+65 010:A slow pulsar or tidally-induced pulsations?
Authors: G. Koenigsberger, L. Georgiev, E. Moreno, M. G. Richer, O. Toledano G. Canalizo, A. Arrieta
Comments: 12 pages, 14 figures

The X-ray source 2S0114+650=LSI+65 010 is a binary system containing a B-type primary and a low mass companion believed to be a neutron star. The system has three reported periodicities: the orbital period, P{orb}~11.6 d, X-ray flaring with P{flare}~2.7 hr, and a "superorbital" X-ray periodicity P{super}~30.7 d. The objective of this paper is to show that the puzzling periodicities in the system may be explained in the context of scenarios in which tidal interactions drive oscillations in the B-supergiant star. We calculate the solution of the equations of motion for one layer of small surface elements distributed along the equator of the star, as they respond to the forces due to gas pressure, centrifugal, coriolis, viscous forces, and the gravitational forces of both stars. This calculation provides variability timescales that can be compared with the observations. In addition, we use observational data obtained at the Observatorio Astron\'omico Nacional en San Pedro M\'artir (OAN/SPM) between 1993-2004 to determine which of the periodicities may be present in the optical region. We suggest that the tidal oscillations lead to a structured stellar wind which, when fed to the neutron star, produces the X-ray modulations. The connection between the stellar oscillations and the modulation of the mass ejection may lie in the shear energy dissipation generated by the tangential motions that are produced by the tidal interaction, particularly in the tidal bulge region. The tidal oscillation scenario weakens the case for 2S0114+650 containing a magnetar descendent.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0608024 [abs, ps, pdf, other] :
Title: Parity Violation, the Neutron Radius of Lead, and Neutron Stars
Authors: J. Piekarewicz
Comments: 5 pages, 5 figures, proceedings to the PAVI06 conference

The neutron radius of a heavy nucleus is a fundamental nuclear-structure observable that remains elusive. Progress in this arena has been limited by the exclusive use of hadronic probes that are hindered by large and controversial uncertainties in the reaction mechanism. The Parity Radius Experiment at the Jefferson Laboratory offers an attractive electro-weak alternative to the hadronic program and promises to measure the neutron radius of 208Pb accurately and model independently via parity-violating electron scattering. In this contribution we examine the far-reaching implications that such a determination will have in areas as diverse as nuclear structure, atomic parity violation, and astrophysics.

 

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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 14 Aug 06 00:00:10 GMT
0608228 -- 0608256 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608231 [abs, ps, pdf, other] :
Title: Aspects of Neutrino Production in Supernovae
Authors: Todd A. Thompson
Comments: 10 pages, 4 figures, proceedings for the International Workshop on the Energy Budget in the High Energy Universe, Kashiwa campus, Univ. of Tokyo, Chiba, Japan, Feb. 2006

I discuss neutrino production in supernovae (SNe) and the detection of both Galactic core collapse events and the diffuse extra-galactic MeV neutrino background expected from the integrated history of star formation. In particular, I consider what processes might affect our expectations for both. I focus on ``rapid'' rotation, defined as leading to millisecond initial neutron star spin periods. Rotation affects the neutrino luminosity, the average neutrino energy, the duration of the Kelvin-Helmholtz cooling epoch, and the ratios of luminosities and average energies between neutrino species; it can strongly suppresses the anti-electron as well as mu, anti-mu, tau, and anti-tau neutrino fluxes relative to those for the electron neutrinos. As a result, depending on the prevalence of rapid rotation in SN progenitors through cosmic time, this may affect predictions for the MeV neutrino background and the history of nucleosynthetic enrichment. I emphasize connections between the MeV neutrino background and tracers of the star formation rate density at high redshift in other neutrino and photon wavebands.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 15 Aug 06 00:00:09 GMT
0608257 -- 0608293 received


7 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608257 [abs, ps, pdf, other] :
Title: The gamma-ray burst GRB060614 requires a novel explosive process
Authors: A. Gal-Yam (CIT), D. Fox (PSU), P. Price (UH), M. Davis (SDSU), D. Leonard (SDSU), A. Soderberg (CIT), E. Nakar (CIT), E. Ofek (CIT), B. Schmidt (ANU), K. Lewis (ANU), B. Peterson (ANU), S. Kulkarni (CIT), E. Berger (OCIW), B. Cenko (CIT), R. Sari (CIT), K. Sharon (TAU), D. Frail (NRAO), N. Gehrels (NASA/Goddard), J. Nousek (PSU), D. Burrows (PSU), V. Mangano (INAF, Palermo), S. Holland (NASA/Goddard), P. Brown (PSU), D.-S. Moon (CIT), F. Harrison (CIT), T. Piran (HUJI), P. McCarthy (OCIW), B. Penprase (Pomona), R. Chevalier (UVir)

Over the past decade our physical understanding of gamma-ray bursts (GRBs) has progressed rapidly thanks to the discovery and observation of their long-lived afterglow emission. Long-duration (T < 2 s) GRBs are associated with the explosive deaths of massive stars (``collapsars''), which produce accompanying supernovae, while the short-duration (T > 2 s) GRBs arise from a different origin, which has been argued to be the merger of two compact objects, either neutron stars or black holes. Here we present observations of GRB060614, a 100-s long burst discovered by the Swift satellite, which require the invocation of a new explosive process: either a massive ``collapsar'' that powers a GRB without any associated supernova, or a new type of engine, as long-lived as the collapsar but without any such massive stellar host. We also discuss the properties of this burst's redshift z=0.125 host galaxy, which distinguish it from other long-duration GRBs and suggest that an entirely new type of GRB progenitor may be required.

 
astro-ph/0608258 [abs, ps, pdf, other] :
Title: MHD Models for Winds from Neutron Stars, and their Interaction with the Environment
Authors: N. Bucciantini (Astronomy Dep., Univ. of California at Berkeley)
Comments: 6 pages, 6 figures Proceedings of the 1st IGPP-Calspace Conference "Numerical Modeling of Space Plasma Flows", 26-30 March 2006, Palm Springs, CA

The recent development of numerical schemes for Relativistic MHD (RMHD) allows us to model the acceleration and outflow properties of winds from compact sources. Theoretical models suggest that acceleration and collimation of the flow are extremely inefficient when the speed is close to $c$, in contrast with many observations. Numerical results for an axisymmetric rotator, both in the case of monopolar and dipolar magnetic field will be presented, suggesting that in ideal RMHD acceleration is indeed inefficient. I will also mention numerical challenges and stability problems of present simulations. Finally I will discuss the interaction of a pulsar wind with the surrounding SNR. I will present emission maps based on numerical simulations of the flow inside the nebula and how they can be used in comparison with observations to derive informations about the properties of pulsar winds far away from the source.

 
astro-ph/0608259 [abs, ps, pdf, other] :
Title: Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
Authors: Duncan K. Galloway, Michael P. Muno, Jacob M. Hartman, Pavlin Savov, Dimitrios Psaltis, Deepto Chakrabarty
Comments: 62 pages, 25 figures, submitted to Astrophysical Journal Supplements. Full data tables will be made available online

We present a sample of 1035 thermonuclear (type-I) X-ray bursts from observations of 45 accreting neutron stars by the Rossi X-ray Timing Explorer (RXTE), spanning more than nine years. This sample contains for the first time confirmed examples of burst ignition in each of the three regimes identified theoretically: H-ignition of mixed H/He fuel, He-ignition in pure He, and He-ignition in mixed H/He fuel. We combined bursts from multiple sources to investigate the variation of the burst rate, energetics, and time scale as a function of accretion rate. We found a peak burst rate of 0.2-0.3/hr for a normalised peak flux of gamma approx. 0.02-0.06, corresponding to a source luminosity of (0.3-2)e37 ergs/cm^2/s.
For 35 sources with bursts exhibiting photospheric radius-expansion, we estimated the likely distance range arising from the possible range of the Eddington limit. We found that in general the peak flux of radius-expansion bursts from individual sources is not constant, varying with a fractional standard deviation of 14% in the mean. We also examined the bursts with very short (<~30 min) recurrence times. We found evidence for two distinct populations of such bursts, one of faint bursts following a much stronger burst by 6-18 min, and another with comparable intensity bursts separated by 7 min or more. We describe the properties of bursts observed from 5 new bursters discovered by RXTE, as well as two new transient outbursts of previously known sources. Finally, we searched for burst oscillations at the known oscillation frequencies in 14 sources. We describe the distribution of the oscillation amplitudes as well as the stages of each burst in which the oscillations are detected.

 
astro-ph/0608262 [abs, ps, pdf, other] :
Title: The gamma-ray binaries LS 5039, LS I +61 303 and PSR B1259-63
Authors: Guillaume Dubus
Comments: 10 pages, 3 figures, proceedings Vulcano workshop (22nd - 27th May, 2006), Frontier Objects in Astrophysics and Particle Physics, F. Giovannelli & G. Mannocchi (eds.), Italian Physical Society, Editrice Compositori, Bologna, Italy

Three binaries are now established sources of emission at very high energies (>1e11 eV). They are composed of a massive star and a compact object. The emission can be due to the interaction of the relativistic wind from a young ms pulsar with the stellar wind of the companion, by which rotation-power ends up as non-thermal flux. Variations at VHE energies are explained as due to gamma-gamma absorption and/or changes in shock location along the orbit. Resolved radio emission is due to cooling particles trailing the pulsar.

 
astro-ph/0608280 [abs, ps, pdf, other] :
Title: Effect of PSR J0737-3039 on the DNS Merger Rate and Implications for GW Detection
Authors: Chunglee Kim, Vicky Kalogera, Duncan R. Lorimer
Comments: 9 pages, 2 figures, To appear in proceedings of "A life with stars", a conference in honour of Ed van den Heuvel (Amsterdam, August 2005), New Ast. Rev

We present the current estimates of the Galactic merger rate of double-neutron-star (DNS) systems. Using a statistical analysis method, we calculate the probability distribution function (PDF) of the rate estimates, which allows us to assign confidence intervals to the rate estimates. We calculate the Galactic DNS merger rate based on the three known systems B1913+16, B1534+12, and J0737-3039. The discovery of J0737-3039 increases the estimated DNS merger rate by a factor ~6 than what is previously known. The most likely values of DNS merger rate lie in the range 3-190 per Myr depending on different pulsar models. Motivated by a strong correlation between the peak rate estimates and a pulsar luminosity function, we calculate a 'global' probability distribution as a single representation of the parameter space covered by different pulsar population models. We compare the global PDF with the observed supernova Ib/c rate, which sets an upper limit on the DNS merger rate. Finally, we remark on implications of new discoveries such as of J1756-2251, the 4th DNS in the Galactic disk, and J1906+0746, a possible DNS system.

 
astro-ph/0608281 [abs, ps, pdf, other] :
Title: Resonant Cyclotron Scattering in Three Dimensions and the Quiescent Non-thermal X-ray Emission of Magnetars
Authors: Rodrigo Fernandez (University of Toronto), Christopher Thompson (CITA)
Comments: 29 pages, 23 figures, submitted to the Astrophysical Journal

Although the surface of a magnetar is a source of bright thermal X-rays, its spectrum contains substantial non-thermal components. The X-ray emission is pulsed, with pulsed fractions that can be as high as ~ 70%. Several properties of magnetars indicate the presence of persistent, static currents flowing across the stellar surface and closing within the magnetosphere. The charges supporting these currents supply a significant optical depth to resonant cyclotron scattering in the 1-100 keV band. Here we describe a Monte Carlo approach to calculating the redistribution of thermal seed photons in frequency and angle by multiple resonant scattering in the magnetosphere. The calculation includes the full angular dependence of the cyclotron scattering cross section, the relativistic Doppler effect due to the motion of the charges, and allows for an arbitrary particle velocity distribution and magnetic field geometry. We construct synthetic spectra and pulse profiles for arbitrary orientations of the spin axis, magnetic axis, and line of sight, using a self-similar, twisted dipole field geometry, and assuming that the seed photons are supplied by single-temperature black body emission from the stellar surface. Pulse profiles and 1-10 keV spectra typical of AXPs are easily produced by this model, with pulsed fractions of ~ 50%. However, this model cannot reproduce the hard, rising energy spectra that are observed from SGRs during periods of activity, without overproducing the thermal emission peak. This suggests that the 1-100 keV emission of SGRs has a common origin with the hard X-ray emission detected from some AXPs above ~20 keV.

 
astro-ph/0608288 [abs, ps, pdf, other] :
Title: Optical and Infrared Emission from the AXPs and SGRs
Authors: Unal Ertan, Sirin Caliskan
Comments: 12 pages, accepted for publication in ApJ Letters

We show that the irradiated accretion disk model can account for all the optical and infrared observations of the anomalous X-ray pulsars in the persistent state. Model fits do not constrain the outer disk radii, while placing an upper limit to the inner disk radii, and thus to the strength of the dipole component of the stellar magnetic field. While magnetar fields (B_* > 10^{14} G) in higher multipoles are compatible with the irradiated disk model, magnetic dipole components of magnetar strength are not consistent with optical data.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


hep-ph/0608094 [abs, ps, pdf, other] :
Title: Limits on Neutron Lorentz Violation from Pulsar Timing
Authors: B. Altschul
Comments: 9 pages

Pulsars are the most accurate naturally occurring clocks, and data about them can be used to set bounds on neutron-sector Lorentz violations. If SO(3) rotation symmetry is completely broken for neutrons, then pulsars' rotation speeds will vary periodically. Pulsar timing data limits the relevant Lorentz-violating coefficients to be smaller than 1.7 x 10^(-8) at at least 90% confidence.

 

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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 16 Aug 06 00:00:09 GMT
0608294 -- 0608322 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608311 [abs, ps, pdf, other] :
Title: Chandra Smells a RRAT: X-ray Detection of a Rotating Radio Transient
Authors: B.M. Gaensler, M. McLaughlin, S. Reynolds, K. Borkowski, N. Rea, A. Possenti, G. Israel, M. Burgay, F. Camilo, S. Chatterjee, M. Kramer, A. Lyne, I. Stairs
Comments: 5 pages, 2 b/w figures, 1 color figure. To appear in the proceedings of "Isolated Neutron Stars", Astrophysics & Space Science, in press

"Rotating RAdio Transients" (RRATs) are a newly discovered astronomical phenomenon, characterised by occasional brief radio bursts, with average intervals between bursts ranging from minutes to hours. The burst spacings allow identification of periodicities, which fall in the range 0.4 to 7 seconds. The RRATs thus seem to be rotating neutron stars, albeit with properties very different from the rest of the population. We here present the serendipitous detection with the Chandra X-ray Observatory of a bright point-like X-ray source coincident with one of the RRATs. We discuss the temporal and spectral properties of this X-ray emission, consider counterparts in other wavebands, and interpret these results in the context of possible explanations for the RRAT population.

 
astro-ph/0608316 [abs, ps, pdf, other] :
Title: Neutron star binaries and long duration gamma-ray bursts
Authors: Andrew J. Levan, Melvyn B. Davies, Andrew R. King
Comments: 7 pages, accepted for publication in MNRAS

Cosmological long-duration gamma-ray bursts (LGRBs) are thought to originate from the core collapse to black holes of stripped massive stars. Those with sufficient rotation form a centrifugally-supported torus whose collapse powers the GRB. We investigate the role of tidal locking within a tight binary as a source of the necessary angular momentum. We find that the binary orbit must be no wider than a few solar radii for a torus to form upon core collapse. Comparing this criterion to the observed population of binaries containing two compact objects suggests that rotation may have been important in the formation of up to 50% of the observed systems. As these systems created a neutron star and not a black hole they presumably did not produce highly luminous GRBs. We suggest instead that they make the subset of GRBs in the relatively local universe which have much lower luminosity.

 
astro-ph/0608317 [abs, ps, pdf, other] :
Title: Strange Exotic States and Compact Stars
Authors: Irina Sagert, Mirjam Wietoska, Jurgen Schaffner-Bielich
Comments: 10 pages, invited talk given at the International Conference on Strangeness in Quark Matter 2006 (SQM2006), UCLA, USA, March 26-31, 2006, to be published in Journal of Physics G

We discuss the possible appearance of strange exotic multi-quark states in the interior of neutron stars and signals for the existence of strange quark matter in the core of compact stars. We show how the in-medium properties of possible pentaquark states are constrained by pulsar mass measurements. The possibility of generating the observed large pulsar kick velocities by asymmetric emission of neutrinos from strange quark matter in magnetic fields is outlined.

 
astro-ph/0608319 [abs, ps, pdf, other] :
Title: Incompatibility of long-period neutron star precession with creeping neutron vortices
Authors: Bennett Link
Comments: 4 pages

Aims: To determine whether ``vortex creep'' in neutron stars, the slow motion of neutron vortices with respect to pinning sites in the core or inner crust, is consistent with observations of long-period precession. Methods: Using the concept of vortex drag, I discuss the precession dynamics of a star with imperfectly-pinned (i.e., "creeping'') vortices. Results: The precession frequency is far too high to be consistent with observations, indicating that the standard picture of the inner core (superfluid neutrons in co-existence with type II, superconducting protons) should be reconsidered. There is a slow precession mode, but it is highly over-damped and cannot complete even a single cycle. Moreover, the vortices of the inner crust must be able to move with little dissipation with respect to the solid.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602417 [abs, ps, pdf, other] :
Title: Corona of Magnetars
Authors: Andrei M. Beloborodov, Christopher Thompson
Comments: 70 pages, 14 figures, accepted to ApJ
Note: replaced with revised version Tue, 15 Aug 2006 15:09:56 GMT (119kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 17 Aug 06 00:00:08 GMT
0608323 -- 0608349 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608341 [abs, ps, pdf, other] :
Title: Sensitivity of p-Process Nucleosynthesis to Nuclear Reaction Rates in a 25 Solar Mass Supernova Model
Authors: W. Rapp, J. Goerres, M. Wiescher, H. Schatz, F. Kaeppeler
Comments: 27 pages, 24 figures, accepted for publication in ApJS

The astrophysical p process, which is responsible for the origin of the proton rich stable nuclei heavier than iron, was investigated using a full nuclear reaction network for a type II supernova explosion when the shock front passes through the O/Ne layer. Calculations were performed with a multi-layer model adopting the seed of a pre-explosion evolution of a 25 solar mass star. The reaction flux was calculated to determine the main reaction path and branching points responsible for synthesizing the proton rich nuclei. In order to investigate the impact of nuclear reaction rates on the predicted p-process abundances, extensive simulations with different sets of collectively and individually modified neutron-, proton-, alpha-capture and photodisintegration rates have been performed. These results are not only relevant to explore the nuclear physics related uncertainties in p-process calculations but are also important for identifying the strategy and planning of future experiments.

 
astro-ph/0608345 [abs, ps, pdf, other] :
Title: Quark Matter in Neutron Stars: An apercu
Authors: Prashanth Jaikumar, Sanjay Reddy, Andrew W. Steiner
Comments: 15 pages, 1 figure. Invited review for Modern Physics Letters A

The existence of deconfined quark matter in the superdense interior of neutron stars is a key question that has drawn considerable attention over the past few decades. Quark matter can comprise an arbitrary fraction of the star, from 0 for a pure neutron star to 1 for a pure quark star, depending on the equation of state of matter at high density. From an astrophysical viewpoint, these two extreme cases are generally expected to manifest different observational signatures. An intermediate fraction implies a hybrid star, where the interior consists of mixed or homogeneous phases of quark and nuclear matter, depending on surface and Coulomb energy costs, as well as other finite size and screening effects. In this brief review article, we discuss what we can deduce about quark matter in neutron stars in light of recent exciting developments in neutron star observations. We state the theoretical ideas underlying the equation of state of dense quark matter, including color superconducting quark matter. We also highlight recent advances stemming from re-examination of an old paradigm for the surface structure of quark stars and discuss possible evolutionary scenarios from neutron stars to quark stars, with emphasis on astrophysical observations.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602522 [abs, ps, pdf, other] :
Title: Chandra Observations of the Transient 7-s X-ray Pulsar AX J1845.0-0258
Authors: C. R. Tam (1), V. M. Kaspi (1), B. M. Gaensler (2), E. V. Gotthelf (3) ((1) McGill University, (2) Harvard CfA, (3) Columbia University)
Comments: 8 pages, 2 figures, accepted for publication in ApJ. Added content, Figure 1 has been replaced, changed organization of text, other minor corrections
Note: replaced with revised version Tue, 15 Aug 2006 21:35:36 GMT (789kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 18 Aug 06 00:00:09 GMT
0608350 -- 0608377 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608354 [abs, ps, pdf, other] :
Title: Discovery of an eclipsing X-ray binary with a 32.69 hour period in M101: an analog of Her X-1 or LMC X-4?
Authors: Jifeng Liu, Rosanne di Stefano, Jeffrey McClintock (CfA), Albert Kong (MIT), Joel Bregman (UMich), Kip Kuntz (JHU/GSFC)
Comments: 24 pages, 9 figures, 2 tables, ApJ in press

We report the discovery of an eclipsing X-ray binary in M101, the first such system to be discovered outside the Local Group. Based on a sequence of 25 Chandra observations that sample a wide range of orbital phases, we find a period of 32.688 $\pm$ 0.002 hours, which we interpret as an orbital period. The folded light curve exhibits an eclipse lasting about 8 hours, suggesting a compact orbit in an nearly edge-on configuration. The X-ray binary has an average luminosity of $L_X(0.3-8 {\rm keV}) \approx 1.3\times10^{38}$ erg/sec, with only one out of the 25 observations significantly lower in flux than the average light curve.The presence of the eclipse and the $\sim$ 1.4-day orbital period suggests that this source is an analog of the well studied eclipsing X-ray binary pulsars Her X-1 or LMC X-4. Combining the Chandra data and the HST ACS/WFC images, we have identified several possible optical counterparts, including an O5-O3 star with V = 25.0. Follow-up optical monitoring observations should be able to identify the donor and further constrain the orbital properties.

 
astro-ph/0608364 [abs, ps, pdf, other] :
Title: XMM-Newton observations of Soft Gamma-ray Repeaters
Authors: S. Mereghetti (1), P. Esposito (1,2), A. Tiengo (1) ((1) INAF, IASF-Milano, Italy; (2) Univ. di Pavia, Italy)
Comments: 10 pages, 7 figures, 3 tables - Presented at the conference "Isolated Neutron Stars: from the Surface to the Interior", London, UK, 24-28 April 2006

All the confirmed Soft Gamma-ray Repeaters have been observed with the EPIC instrument on the XMM-Newton satellite. We review the results obtained in these observations, providing the most accurate spectra on the persistent X-ray emission in the 1-10 keV range for these objects, and discuss them in the context of the magnetar interpretation.

 
astro-ph/0608371 [abs, ps, pdf, other] :
Title: Electron thermal conductivity owing to collisions between degenerate electrons
Authors: P.S. Shternin, D.G. Yakovlev (Ioffe Physico-Technical Institute)
Comments: 8 pages, 3 figures
Journal-ref: Phys. Rev. D. 74 (2006) 043004

We calculate the thermal conductivity of electrons produced by electron-electron Coulomb scattering in a strongly degenerate electron gas taking into account the Landau damping of transverse plasmons. The Landau damping strongly reduces this conductivity in the domain of ultrarelativistic electrons at temperatures below the electron plasma temperature. In the inner crust of a neutron star at temperatures T < 1e7 K this thermal conductivity completely dominates over the electron conductivity due to electron-ion (electron-phonon) scattering and becomes competitive with the the electron conductivity due to scattering of electrons by impurity ions.

 
astro-ph/0608372 [abs, ps, pdf, other] :
Title: Magnetar Corona
Authors: A. M. Beloborodov, C. Thompson
Comments: 9 pages, 6 figures; talk at "Isolated Neutron Stars: from the Interior to the Surface," London, April 2006

Persistent high-energy emission of magnetars is produced by a plasma corona around the neutron star, with total energy output of ~10^{36}erg/s. The corona forms as a result of occasional starquakes that twist the external magnetic field of the star and induce electric currents in the closed magnetosphere. Once twisted, the magnetosphere cannot untwist immediately because of its self-induction. The self-induction electric field lifts particles from the stellar surface, accelerates them, and initiates avalanches of pair creation in the magnetosphere. The created plasma corona maintains the electric current demanded by curl(B) and regulates the self-induction e.m.f. by screening. This corona persists in dynamic equilibrium: it is continually lost to the stellar surface on the light-crossing time and replenished with new particles. In essence, the twisted magnetosphere acts as an accelerator that converts the toroidal field energy to particle kinetic energy. The voltage along the magnetic field lines is maintained near threshold for ignition of pair production, in the regime of self-organized criticality. The voltage is found to be about 1 GeV which is in agreement with the observed dissipation rate \~10^{36}erg/s. The coronal particles impact the solid crust, knock out protons, and regulate the column density of the hydrostatic atmosphere of the star. The transition layer between the atmosphere and the corona is the likely source of the observed 100-keV emission from magnetars. The corona also emits curvature radiation up to 10^{14}Hz and can supply the observed IR-optical luminosity.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607168 [abs, ps, pdf, other] :
Title: Atmosphere Models of Magnetized Neutron Stars: QED Effects, Radiation Spectra, and Polarization Signals
Authors: Matthew van Adelsberg, Dong Lai (Cornell University)
Comments: 30 pages, 23 figures, MNRAS submitted Corrected minor typo in Fig. 7 Improved fit function and corrected parameter values in Table 1
Note: replaced with revised version Thu, 17 Aug 2006 18:42:33 GMT (155kb)
 
astro-ph/0608210 [abs, ps, pdf, other] :
Title: Studying Millisecond Pulsars in X-rays
Authors: Vyacheslav E. Zavlin (NASA/MSFC)
Comments: To appear in Astrophysics and Space Science, Proceedings of "Isolated Neutron Stars: from the Interior to the Surface", eds. D. Page, R. Turolla and S. Zane; 10 pages, 12 figures (four of them are color); an aknowledgement has been added
Note: replaced with revised version Thu, 17 Aug 2006 19:53:00 GMT (227kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 21 Aug 06 00:00:08 GMT
0608378 -- 0608405 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608404 [abs, ps, pdf, other] :
Title: An unusual precursor burst with oscillations from SAX J1808.4-3658
Authors: Sudip Bhattacharyya (NASA/GSFC, UMCP), Tod E. Strohmayer (NASA/GSFC)
Comments: 8 pages, 3 figures, submitted to ApJ

We report the finding of an unusual, weak precursor to a thermonuclear X-ray burst from the accreting millisecond pulsar SAX J1808.4-3658. The burst in question was observed on Oct. 19, 2002 with the Rossi X-Ray Timing Explorer (RXTE) proportional counter array (PCA). The precursor began approximately 1 s prior to the onset of a strong radius expansion burst, lasted for about 0.4 s, and exhibited strong oscillations at the 401 Hz spin frequency. Oscillations are not detected in the approximately 0.5 s interval between the precursor and the main burst. The estimated peak photon flux and energy fluence of the precursor are about 1/25, and 1/500 that of the main burst, respectively. From joint spectral and temporal modeling, we find that an expanding burning region with a relatively low temperature on the spinning neutron star surface can explain the oscillations, as well as the faintness of the precursor with respect to the main part of the burst. We dicuss some of the implications of our findings for the ignition and spreading of thermonuclear flames on neutron stars.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606754 [abs, ps, pdf, other] :
Title: Type I and Two-Gap Superconductivity in Neutron Star Magnetism
Authors: P B Jones
Comments: 8 pages, 0 figures; to be published in MNRAS, with minor correction made in proof and added acknowledgments
Note: replaced with revised version Fri, 18 Aug 2006 11:14:54 GMT (18kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 22 Aug 06 00:00:12 GMT
0608406 -- 0608445 received


0 abstracts or titles contain neutron star, magnetar or pulsar



Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0207492 [abs, ps, pdf, other] :
Title: On The Problem with Only Zeroth Landau Level Occupancy of Electrons / Protons in Strongly Magnetized Neutron Star Matter in $\beta$-equilibrium Condition- The Role of Anomalous Magnetic Moments
Authors: Sutapa Ghosh, Soma Mandal, Somenath Chakrabarty
Comments: REVTEX File, Six Pages, Two .eps Figures (Included), Title and Text have been modified
Note: replaced with revised version Sun, 20 Aug 2006 11:36:14 GMT (15kb)
 
gr-qc/0605024 [abs, ps, pdf, other] :
Title: Relativistic mechanics of neutron superfluid in (magneto) elastic star crust
Authors: Brandon Carter, Lars Samuelsson
Comments: 29 pages, Latex. V. 2. Minor changes, matches published version
Journal-ref: Class. Quantum Grav. 23 (2006) 5367--5388
Note: replaced with revised version Sat, 19 Aug 2006 16:30:26 GMT (26kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 23 Aug 06 00:00:09 GMT
0608446 -- 0608470 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608463 [abs, ps, pdf, other] :
Title: The 2004 Hyperflare from SGR 1806-20: Further Evidence for Global Torsional Vibrations
Authors: Tod E. Strohmayer, Anna L. Watts
Comments: 27 pages, 10 figures, AASTeX. Accepted for Publication in the Astrophysical Journal

We report an analysis of the archival Rossi X-ray Timing Explorer (RXTE) data from the December 2004 hyperflare from SGR 1806-20. In addition to the 90 Hz QPO first discovered by Israel et al., we report the detection of higher frequency oscillations at 150, 625, and 1,840 Hz. In addition, we also find indications of oscillations at 720, and 2,384 Hz, but with lower significances. The 150 Hz QPO has a width (FWHM) of about 17 Hz, an average amplitude (rms) of 6.8 %, and is detected in average power spectra centered on the rotational phase of the strongest peak in the pulse profile. This is approximately half a cycle from the phase at which the 90 Hz QPO is detected. The 625 Hz oscillation was detected in an average power spectrum from nine successive cycles beginning approximately 180 s after the initial hard spike. It has a width (FWHM) of 2 Hz and an average amplitude (rms) during this interval of 8.5 %. We find a strong detection of the 625 Hz oscillation in a pair of successive rotation cycles begining about 230 s after the start of the flare. In these cycles we also detect the 1,840 Hz QPO. When the 625 Hz QPO is detected we also confirm the simultaneous presence of 30 and 92 Hz QPOs. The centroid frequency of the 625 Hz QPO detected with RXTE is within 1 Hz of the 626 Hz oscillation recently found in RHESSI data from this hyperflare by Watts & Strohmayer. We argue that these new findings provide further evidence for a connection of these oscillations with global oscillation modes of neutron stars, in particular, the high frequency signals may represent toroidal modes with at least one radial node in the crust. We discuss their implications in the context of this model, in particular for the depth of neutron star crusts

 
astro-ph/0608468 [abs, ps, pdf, other] :
Title: Chandra Monitoring of the Candidate Anomalous X-ray Pulsar AX J1845.0-0258
Authors: C. R. Tam (1), V. M. Kaspi (1), B. M. Gaensler (2), E. V. Gotthelf (3) ((1) McGill University, (2) Harvard, (3) Columbia)
Comments: 4 pages, 3 figures. To be published in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface" (April 24-28, 2006, London, UK), eds. D. Page, R. Turolla, & S. Zane

The population of clearly identified anomalous X-ray pulsars has recently grown to seven, however, one candidate anomalous X-ray pulsar (AXP) still eludes re-confirmation. Here, we present a set of seven Chandra ACIS-S observations of the transient pulsar AX J1845.0-0258, obtained during 2003. Our observations reveal a faint X-ray point source within the ASCA error circle of AX J1845.0-0258's discovery, which we designate CXOU J184454.6-025653 and tentatively identify as the quiescent AXP. Its spectrum is well described by an absorbed single-component blackbody (kT~2.0 keV) or power law (Gamma~1.0) that is steady in flux on timescales of at least months, but fainter than AX J1845.0-0258 was during its 1993 period of X-ray enhancement by at least a factor of 13. Compared to the outburst spectrum of AX J1845.0-0258, CXOU J184454.6-025653 is considerably harder: if truly the counterpart, then its spectral behaviour is contrary to that seen in the established transient AXP XTE J1810-197, which softened from kT~0.67 keV to ~0.18 keV in quiescence. This unexpected result prompts us to examine the possibility that we have observed an unrelated source, and we discuss the implications for AXPs, and magnetars in general.

 
astro-ph/0608470 [abs, ps, pdf, other] :
Title: A three stage model for the inner engine of Gamma Ray Burst: Prompt emission and early afterglow
Authors: Jan Staff, Rachid Ouyed, Manjari Bagchi
Comments: submitted to ApJ

We propose a new model within the ``Quark-nova'' scenario to interpret the recent observations of early afterglows of long Gamma-Ray Bursts (GRB) with the Swift satellite. This is a three-stage model within the context of a core-collapse supernova. Stage 1 is an accreting (proto-) neutron star leading to a possible delay between the core collapse and the GRB. Stage 2 is an accreting quark-star, generating the prompt GRB. Stage 3, which occurs only if the quark-star collapses to form a black-hole, consists of an accreting black-hole. The jet launched in this accretion process interacts with the ejecta from stage 2, and can generate the flaring activity frequently seen in X-ray afterglows. This model can account for both the energies and the timescales of GRBs, in addition to the newly discovered early X-ray afterglow features.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 24 Aug 06 00:00:10 GMT
0608471 -- 0608494 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608473 [abs, ps, pdf, other] :
Title: The Anatomy of a Magnetar: XMM Monitoring of the Transient Anomalous X-ray Pulsar XTE J1810-197
Authors: E. V. Gotthelf, J. P. Halpern (Columbia University)
Comments: 8 pages, 7 figures, 1 table, latex. To appear in the proceedings of "Isolated Neutron Stars", Astrophysics & Space Science, in press

We present the latest results from a multi-epoch timing and spectral study of the Transient Anomalous X-ray Pulsar XTE J1810-197. We have acquired seven observations of this pulsar with the Newton X-ray Multi-mirror Mission (XMM-Newton) over the course of two and a half years, to follow the spectral evolution as the source fades from outburst. The spectrum is arguably best characterized by a two-temperature blackbody whose luminosities are decreasing exponentially with tau_1 = 870 days and tau_2 = 280 days, respectively. The temperatures of these components are currently cooling at a rate of 22% per year from a nearly constant value recorded at earlier epochs of kT_1 = 0.25 keV and kT_2 = 0.67 keV, respectively. The new data show that the temperature T_1 and luminosity of that component have nearly returned to their historic quiescent levels and that its pulsed fraction, which has steadily decreased with time, is now consistent with the previous lack of detected pulsations in quiescence. We also summarize the detections of radio emission from XTE J1810-197, the first confirmed for any AXP. We consider possible models for the emission geometry and mechanisms of XTE J1810-197.

 
astro-ph/0608476 [abs, ps, pdf, other] :
Title: High frequency oscillations during magnetar flares
Authors: Anna L. Watts (MPA Garching), Tod E. Strohmayer (NASA GSFC)
Comments: 5 pages, 1 figure, to appear in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface" (April 2006, London), eds. D. Page, R. Turolla, & S. Zane, Astrophysics & Space Science in press

The recent discovery of high frequency oscillations during giant flares from the Soft Gamma Repeaters SGR 1806-20 and SGR 1900+14 may be the first direct detection of vibrations in a neutron star crust. If this interpretation is correct it offers a novel means of testing the neutron star equation of state, crustal breaking strain, and magnetic field configuration. We review the observational data on the magnetar oscillations, including new timing analysis of the SGR 1806-20 giant flare using data from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Rossi X-ray Timing Explorer (RXTE). We discuss the implications for the study of neutron star structure and crust thickness, and outline areas for future investigation.

 
astro-ph/0608483 [abs, ps, pdf, other] :
Title: Evidence for a Binary Companion to the Central Compact Object 1E 1207.4-5209
Authors: Peter M. Woods (Dynetics/USRA/NSSTC), Vyacheslav E. Zavlin (MSFC), George G. Pavlov (Penn State Univ)
Comments: 8 pages, 4 figures. To be published in the proceedings of "Isolated Neutron Stars: from the Interior to the Surface" (April 24-28, 2006) - eds. D. Page, R. Turolla & S. Zane

Unique among neutron stars, 1E 1207.4-5209 is an X-ray pulsar with a spin period of 424 ms that contains at least two strong absorption features in its energy spectrum. This neutron star has been identified as a member of the radio-quiet compact central objects in supernova remnants. It has been found that 1E 1207.4-5209 is not spinning down monotonically suggesting that this neutron star undergoes strong, frequent glitches, contains a fall-back disk, or possess a binary companion. Here, we report on a sequence of seven XMM-Newton observations of 1E 1207.4-5209 performed during a 40 day window in June/July 2005. Due to unanticipated variance in the phase measurements beyond the statistical uncertainties, we could not identify a unique phase-coherent timing solution. The three most probable timing solutions give frequency time derivatives of +0.9, -2.6, and +1.6 X 10^(-12) Hz/s (listed in descending order of significance). We conclude that the local frequency derivative during our XMM-Newton observing campaign differs from the long-term spin-down rate by more than an order of magnitude, effectively ruling out glitch models for 1E 1207.4-5209. If the long-term spin frequency variations are caused by timing noise, the strength of the timing noise in 1E 1207.4-5209 is much stronger than in other pulsars with similar period derivatives. Therefore, it is highly unlikely that the spin variations are caused by the same physical process that causes timing noise in other isolated pulsars. The most plausible scenario for the observed spin irregularities is the presence of a binary companion to 1E 1207.4-5209. We identified a family of orbital solutions that are consistent with our phase-connected timing solution, archival frequency measurements, and constraints on the companions mass imposed by deep IR and optical observations.

 
astro-ph/0608485 [abs, ps, pdf, other] :
Title: Faint X-ray Structure in the Crab Pulsar-Wind Nebula
Authors: F. D. Seward, W. H. Tucker, R. A. Fesen
Comments: accepted by ApJ, 26 pages including 12 figures

We report on a Chandra observation of the Crab Nebula that gives the first clear view of the faint boundary of the Crab's X-ray-emitting Pulsar Wind Nebula, or PWN.
There is structure in all directions. Fingers, loops, bays, and the South Pulsar Jet all indicate that either filamentary material or the magnetic field are controlling the relativistic electrons. In general, spectra soften as distance from the pulsar increases but do not change rapidly along linear features. This is particularly true for the Pulsar Jet. The termination of the Jet is abrupt; the E side is close to an [O {\small III}] optical filament which may be blocking propagation on this side. We argue that linear features have ordered magnetic fields and that the structure is determined by the synchrotron lifetime of particles diffusing perpendicular and parallel to the magnetic field. We find no significant evidence for thermal X-rays inside the filamentary envelope.

 
astro-ph/0608488 [abs, ps, pdf, other] :
Title: Fusion reactions in multicomponent dense matter
Authors: D.G. Yakovlev (1,2), L.R. Gasques (2), M. Beard (2), M. Wiescher (2), A.V. Afanasjev (3) ((1) Ioffe Institute, (2) JINA, (3) Missisipi State University)
Comments: 16 pages, 5 figures, to appear in Phys. Rev. C

We analyze thermonuclear and pycnonuclear fusion reactions in dense matter containing atomic nuclei of different types. We extend a phenomenological expression for the reaction rate, proposed recently by Gasques et al. (2005) for the one-component plasma of nuclei, to the multi-component plasma. The expression contains several fit parameters which we adjust to reproduce the best microscopic calculations available in the literature. Furthermore, we show that pycnonuclear burning is drastically affected by an (unknown) structure of the multi-component matter (a regular lattice, a uniform mix, etc.). We apply the results to study nuclear burning in a carbon_12-oxygen_16 mixture. In this context we present new calculations of the astrophysical S-factors for carbon-oxygen and oxygen-oxygen fusion reactions. We show that the presence of a CO lattice can strongly suppress carbon ignition in white dwarf cores and neutron star crusts at densities > 3e9 g cm^{-3} and temperatures T<1e8 K.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605429 [abs, ps, pdf, other] :
Title: Transient pulsed radio emission from a magnetar
Authors: Fernando Camilo (1), Scott Ransom (2), Jules Halpern (1), John Reynolds (3), David Helfand (1), Neil Zimmerman (1), John Sarkissian (3) ((1) Columbia, (2) NRAO, (3) ATNF)
Comments: accepted by Nature; some new data and significantly revised discussion
Journal-ref: Nature, 442, 892-895 (2006)
Note: replaced with revised version Tue, 22 Aug 2006 21:43:11 GMT (95kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 25 Aug 06 00:00:12 GMT
0608495 -- 0608530 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608518 [abs, ps, pdf, other] :
Title: A torque reversal of 4U 1907+09
Authors: S. Fritz, I. Kreykenbohm, J. Wilms, R. Staubert, F. Bayazit, K. Pottschmidt, J. Rodriguez, A. Santangelo
Comments: Accepted for publication in Astronomy & Astrophysics, 11 pages, 8 figures

We present an analysis of the accreting X-ray pulsar system 4U 1907+09 based on INTEGRAL data. The main focus of this analysis is a study of the timing behavior of this source. In addition we also show an analysis of the 5-90 keV spectrum. The data were extracted using the official INTEGRAL software OSA 5.1. Timing analysis was performed using epoch folding and pulsar pulse phasing. We have measured 12 individual pulse periods for the years 2003 to 2005. We confirm earlier RXTE results that during 2003 the spin down became slower and show furthermore that after this phase 4U 1907+09 started to spin up with dP/dt = -0.158 s/yr in 2004. The similarity of the pulse period histories of 4U 1907+09 and 4U 1626-26 suggests that accretion onto an oblique rotator, as recently proposed by Perna et al., is a possible explanation for this change.

 
astro-ph/0608527 [abs, ps, pdf, other] :
Title: Optical spectroscopy of the radio pulsar PSR B0656+14
Authors: S. Zharikov (1), R.E. Mennickent (2), Yu. Shibanov (3), V. Komarova (4) ((1) IA UNAM, Mexico, (2) Universidad de Concepcion, Concepcion, Chile, (3) Ioffe Physical Technical Inst. RAS, St. Petersburg, Russia, (4) Special Astrophysical Observatory, RAS, Russia)
Comments: 4 pages, 4 figures, To appear in Astrophysics and Space Science, Proceedings of "Isolated Neutron Stars: from the Interior to the Surface", eds. D. Page, R. Turolla and S. Zane

We have obtained the spectrum of a middle-aged PSR B0656+14 in the 4300-9000 AA range with the ESO/VLT/FORS2. Preliminary results show that at 4600-7000 AA the spectrum is almost featureless and flat with a spectral index $\alpha_nu ~ -0.2 that undergoes a change to a positive value at longer wavelengths. Combining with available multiwavelength data suggests two wide, red and blue, flux depressions whose frequency ratio is about 2 and which could be the 1st and 2nd harmonics of electron/positron cyclotron absorption formed at magnetic fields ~10^8G in upper magnetosphere of the pulsar.

 
astro-ph/0608529 [abs, ps, pdf, other] :
Title: Non-LTE modeling of supernova-fallback disks
Authors: K. Werner, T. Nagel, T. Rauch
Comments: ApSS, accepted, Proceedings of Isolated Neutron Stars: from the Interior to the Surface, April 24-28, 2006, London, UK

We present a first detailed spectrum synthesis calculation of a supernova-fallback disk composed of iron. We assume a geometrically thin disk with a radial structure described by the classical alpha-disk model. The disk is represented by concentric rings radiating as plane-parallel slabs. The vertical structure and emission spectrum of each ring is computed in a fully self-consistent manner by solving the structure equations simultaneously with the radiation transfer equations under non-LTE conditions. We describe the properties of a specific disk model and discuss various effects on the emergent UV/optical spectrum.
We find that strong iron-line blanketing causes broad absorption features over the whole spectral range. Limb darkening changes the spectral distribution up to a factor of four depending on the inclination angle. Consequently, such differences also occur between a blackbody spectrum and our model. The overall spectral shape is independent of the exact chemical composition as long as iron is the dominant species. A pure iron composition cannot be distinguished from silicon-burning ash. Non-LTE effects are small and restricted to few spectral features.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 28 Aug 06 00:00:10 GMT
0608531 -- 0608560 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608536 [abs, ps, pdf, other] :
Title: Fall-back crust around a quark-nova compact remnant I: The degenerate shell case with applications to SGRs, AXPs and XDINs
Authors: Rachid Ouyed, Denis Leahy, Brian Niebergal
Comments: submitted to ApJ

We explore the formation and evolution of debris ejected around quark stars in the Quark Nova scenario, and the application to Soft Gamma-ray Repeaters (SGRs) and Anomolous X-ray Pulsars (AXPs). If an isolated neutron star explodes as a Quark Nova, an Iron-rich shell of degenerate matter forms out of the fall-back (crust) material. Our model can account for many of the observed features of SGRs and AXPs such as: (i) the two types of bursts (giant and regular); (ii) the spin-up and spin-down episodes during and following the bursts with associated persistant increases in $\dot{P}$; (iii) the energetics of the boxing day burst, SGR1806$+$20; (iv) the presence of an Iron line as observed in SGR1900$+$14; (v) the correlation between the far-Infrared and the X-ray fluxes during the bursting episode and the quiescent phase; (vi) the hard X-ray component observed in SGRs during the giant bursts, and (vii) the discrepancy between the ages of SGRs/AXPs and their supernova remnants. We also find a natural evolutionary relationship between SGRs and AXPs in our model which predicts that only the youngest SGRs/AXPs are most likely to exhibit strong bursting. Many features of X-ray Dim Isolated Neutron stars (XDINs) are also accounted for in our model such as, (i) the two-component blackbody spectra; (ii) the absorption lines around 300 eV; and (iii) the excess optical emission.

 
astro-ph/0608539 [abs, ps, pdf, other] :
Title: The r-Process in the Proto-Neutron-Star Winds with Anisotropic Neutrino Emission
Authors: Shinya Wanajo
Comments: 8 pages, 3 figures, accepted for publication in ApJ Letters

The astrophysical origin of the r-process nuclei is still unknown. Even the most promising scenario, the neutrino-driven winds from a nascent neutron star, encounters severe difficulties in obtaining requisite entropy and short dynamic timescale for the r-process. In this study, the effect of anisotropy in neutrino emission from a proto-neutron star surface is examined with semi-analytic neutrino-driven wind models. The increase of neutrino number density in the wind owing to the anisotropy is modeled schematically by enhancing the effective neutrino luminosity. It is shown that the neutrino heating rate from neutrino-antineutrino pair annihilation into electron-positron pairs can significantly increase owing to the anisotropy and play a dominant role for the heating of wind material. A factor of five increase in the effective neutrino luminosity results in 50% higher entropy and a factor of ten shorter dynamic timescale owing to this enhanced neutrino heating. The nucleosynthesis calculations show that this change is enough for the robust r-process, producing the third abundance peak A = 195 and beyond. Future multi-dimensional studies with accurate neutrino transport will be needed if such anisotropy relevant for the current scenario (more than a factor of a few) is realized during the wind phase (~1-10 s).

 
astro-ph/0608540 [abs, ps, pdf, other] :
Title: Pushing the limit on neutron star spin rates
Authors: Duncan K Galloway (University of Melbourne)
Comments: 5 pages, 2 figures, to be published in the Proceedings of the 7th Pacific Rim Conference on Stellar Astrophysics, held 1-5 Nov 2005, Sejong University, Seoul, Korea (ASP Conference Series). Uses asp2004.sty and psfig.sty

Millisecond X-ray pulsars consist of a rapidly-spinning neutron star accreting from a low-mass stellar companion, and are the long-sought evolutionary progenitors of millisecond radio pulsars, as well as promising candidate sources for gravitational radiation. The population of these sources has grown significantly over the last three years, with the discovery of six new examples to bring the total sample to seven. Three sources are ultracompact binaries with H-depleted donors and orbital periods of approx. 40 min, like the 185 Hz pulsar XTE J0929-314. Three more have orbital periods of 2 hr or longer, similar to IGR J00291+5934, first detected in outburst by INTEGRAL in December 2004. The neutron star in this 2.46 hr binary has the most rapid spin of the accreting pulsars at 599 Hz. The most recently-discovered pulsar, HETE J1900.1-2455 (377 Hz), has an intermediate orbital period of 83.3 min, and has been active for more than 1 yr, much longer than the typical transient outburst. Pulsations were detected only in the first few months of the outburst; this source has since resembled a faint, persistent non-pulsing low-mass X-ray binary, typical of the broader low-mass X-ray binary population.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 29 Aug 06 00:00:10 GMT
0608561 -- 0608601 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608564 [abs, ps, pdf, other] :
Title: The Extreme Physics Explorer
Authors: Martin Elvis (Harvard-Smithsonian Center for Astrophysics)
Comments: Enhanced version of SPIE paper. 9 pages, 0 figures
Journal-ref: 2006SPIE.6266E..20E

Some tests of fundamental physics - the equation of state at supra-nuclear densities, the metric in strong gravity, the effect of magnetic fields above the quantum critical value - can only be measured using compact astrophysical objects: neutron stars and black holes. The Extreme Physics Explorer is a modest sized (~500 kg) mission that would carry a high resolution (R ~300) X-ray spectrometer and a sensitive X-ray polarimeter, both with high time resolution (~5 ?s) capability, at the focus of a large area (~5 sq.m), low resolution (HPD~1 arcmin) X-ray mirror. This instrumentation would enable new classes of tests of fundamental physics using neutron stars and black holes as cosmic laboratories.

 
astro-ph/0608565 [abs, ps, pdf, other] :
Title: QED can explain the non-thermal emission from SGRs and AXPs : Variability
Authors: Jeremy S. Heyl (UBC)
Comments: 7 pages, 5 figures, to appear in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface" (April 2006, London), eds. D. Page, R. Turolla, & S. Zane, Astrophysics & Space Science

Owing to effects arising from quantum electrodynamics (QED), magnetohydrodynamical fast modes of sufficient strength will break down to form electron-positron pairs while traversing the magnetospheres of strongly magnetised neutron stars. The bulk of the energy of the fast mode fuels the development of an electron-positron fireball. However, a small, but potentially observable, fraction of the energy ($\sim 10^{33}$ ergs) can generate a non-thermal distribution of electrons and positrons far from the star. This paper examines the cooling and radiative output of these particles. Small-scale waves may produce only the non-thermal emission. The properties of this non-thermal emission in the absence of a fireball match those of the quiescent, non-thermal radiation recently observed non-thermal emission from several anomalous X-ray pulsars and soft-gamma repeaters. Initial estimates of the emission as a function of angle indicate that the non-thermal emission should be beamed and therefore one would expect this emission to be pulsed as well. According to this model the pulsation of the non-thermal emission should be between 90 and 180 degrees out of phase from the thermal emission from the stellar surface.

 
astro-ph/0608589 [abs, ps, pdf, other] :
Title: Measuring proper motions of isolated neutron stars with Chandra
Authors: C. Motch, A. M. Pires, F. Haberl, A. Schwope
Comments: 8 pages, 3 figures, to appear in Astrophysics and Space Science, in the proceedings of "Isolated Neutron Stars: from the Interior to the Surface", edited by D. Page, R. Turolla and S. Zane

The excellent spatial resolution of the Chandra observatory offers the unprecedented possibility to measure proper motions at X-ray wavelength with relatively high accuracy using as reference the background of extragalactic or remote galactic X-ray sources. We took advantage of this capability to constrain the proper motion of RX J0806.4-4123 and RX J0420.0-5022, two X-ray bright and radio quiet isolated neutron stars (INSs) discovered by ROSAT and lacking an optical counterpart. In this paper, we present results from a preliminary analysis from which we derive 2 sigma upper limits of 76 mas/yr and 138 mas/yr on the proper motions of RX J0806.4-4123 and RX J0420.0-5022 respectively. We use these values together with those of other ROSAT discovered INSs to constrain the origin, distance and evolutionary status of this particular group of objects. We find that the tangential velocities of radio quiet ROSAT neutron stars are probably consistent with those of 'normal' pulsars. Their distribution on the sky and, for those having accurate proper motion vectors, their possible birth places, all point to a local population, probably created in the part of the Gould Belt nearest to the earth.

 
astro-ph/0608592 [abs, ps, pdf, other] :
Title: Establishing HZ43 A, Sirius B, and RX J185635-3754 as soft X-ray standards: a cross-calibration between the Chandra LETG+HRC-S, the EUVE spectrometer, and the ROSAT PSPC
Authors: K. Beuermann (1), V. Burwitz (2), T. Rauch (3) ((1) Institut fuer Astrophysik, Universitaet Goettingen, Germany, (2) Max-Planck-Institut fuer Extraterrestrische Physik, Germany, (3) Institut fuer Astronomie und Astrophysik, Universitaet Tuebingen, Germany)
Comments: 15 pages, 9 figures

The absolute calibration of space-borne instruments in the soft X-ray regime rests strongly on model spectra of hot white dwarfs.
We analyze the Chandra LETG+HRC-S observations of the white dwarfs HZ43 A and Sirius B and of the neutron star RX J185635-3754 in order to resolve current uncertainties in the soft X-ray spectral fluxes and photospheric parameters of the three stars. We have obtained improved parameters for which fit the observations from the optical to the soft X-ray regime. Our approach allows us to quote their absolute spectral fluxes at selected wavelengths which may aid the calibration of other space-borne instruments.

 
astro-ph/0608601 [abs, ps, pdf, other] :
Title: A Hard-to-Soft State Transition during A Luminosity Decline of Aquila X-1
Authors: Wenfei Yu, Joshua Dolence
Comments: 12 pages including 3 figures, AASTEX format, submitted to ApJ

Contrary to the idea that the X-ray spectral states of accreting black holes and neutron stars are determined by the mass accretion rate and that a transition from the low/hard (LH) state to the high/soft (HS) state is associated with an increase of luminosity, we have discovered a hard-to-soft state transition during a luminosity decay of Aquila X$-$1 in the observations made with the {\it Rossi X-ray Timing Explorer (RXTE)}. The 2--60 keV energy flux corresponding to the state transition is $9.3\times{10}^{-10} {\rm ergs cm^{-2} s^{-1}}$, an order of magnitude lower than the maximum observed in the past. The 2--60 keV peak flux of the following HS state is $1.5\times{10}^{-9} {\rm ergs cm^{-2} s^{-1}}$. This confirms the correlation between the luminosity of the hard-to-soft state transition and the peak luminosity of the following HS state previously found. The relation derived from the observations of four outbursts is consistent with a linear relation over a luminosity range of an order of magnitude. This implies that the luminosity of the hard-to-soft state transition is not determined solely by the mass accretion rate, but appears determined by the peak luminosities of the soft X-ray outbursts. The time lag of the peak of the HS state relative to the occurrence of the hard-to-soft state transition varied from about 5 days to 11 days, showing a weak trend of increasing time lag with increasing peak luminosity of the HS state. These results provide additional evidence that the mass in the accretion disk probably determines the luminosity of the hard-to-soft state transition.

 

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astro-ph/0603567 [abs, ps, pdf, other] :
Title: A neutron-star-driven X-ray flash associated with supernova SN 2006aj
Authors: Paolo A. Mazzali (1,3,4,5), Jinsong Deng (2,3,5), Ken'ichi Nomoto (3,5), Daniel N. Sauer (4,5), Elena Pian (4,5), Nozomu Tominaga (3,5), Masaomi Tanaka (3), Keiichi Maeda (3,5), Alexei V. Filippenko (6) ((1) MPA, Germany, (2) NAOC, China, (3) U. Tokyo, Japan, (4) INAF-OATs, Italy, (5) KITP-UCSB, CA, (6) UC Berkeley, CA)
Comments: 9 pages, 2 figures. To appear in Nature on August 31 2006
Note: replaced with revised version Mon, 28 Aug 2006 10:01:32 GMT (107kb)
 

Astrophysics authors/titles "new"

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astro-ph new abstracts, Wed, 30 Aug 06 00:00:10 GMT
0608602 -- 0608632 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608621 [abs, ps, pdf, other] :
Title: Exploration of the $\ps-\pb$ Relation for Wind-Fed X-Ray Pulsars
Authors: Hai-Lang Dai (NJU), Xi-Wei Liu (NJU), Xiang-Dong Li (NJU)
Comments: 18 pages,5 figures, accepted by ApJ

We have investigated the relation between the orbital periods ($\pb$) and the spin periods ($\ps$) of wind-fed X-ray pulsars in high-mass X-ray binaries (HMXBs), based on population synthesis calculations of the spin evolution of neutron stars during the pre-HMXB stage. We show that most of the neutron stars either have steady accretion or still reside in the radio pulsar phase when the donor star starts evolving off the main sequence. In the former case the values of $\ps$ can be decelerated to be $\sim 10^2-10^3$ s depending on $\pb$. We briefly discuss the possible origin of the $\ps-\pb$ correlation in Be/X-ray binaries, and the existence of HMXBs with main sequence donors. We have also investigated the evolution of the inclination angle between the magnetic and spin axes of neutron stars in a massive binary, suggesting secular alignment of the magnetic and spin axes during their evolution.

 
astro-ph/0608626 [abs, ps, pdf, other] :
Title: Torsional Oscillations of Relativistic Stars with Dipole Magnetic Fields
Authors: H. Sotani, K.D. Kokkotas, N. Stergioulas
Comments: 17 pages, 5 figures

We present the formalism and numerical results for torsional oscillations of relativistic stars endowed with a strong dipole magnetic field. We do a systematic search of parameter space by computing torsional mode frequencies for various values of the harmonic index $\ell$ and for various overtones, using an extended sample of models of compact stars, varying in mass, high-density equation of state and crust model. We show that torsional mode frequencies are sensitive to the crust model if the high-density equation of state is very stiff. In addition, torsional mode frequencies are drastically affected by a dipole magnetic field, if the latter has a strength exceeding roughly $10^{15}$G and we find that the magnetic field effects are sensitive to the adopted crust model. Using our extended numerical results we derive empirical relations for the effect of the magnetic field on torsional modes as well as for the crust thickness. We compare our numerical results to observed frequencies in SGRs and find that certain high-density EoS and mass values are favored over others in the non-magnetized limit. On the other hand, if the magnetic field is strong, then its effect has to be taken into account in attempts to formulate a theory of asteroseismology for magnetars.

 

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astro-ph new abstracts, Thu, 31 Aug 06 00:00:08 GMT
0608632 -- 0608678 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608650 [abs, ps, pdf, other] :
Title: Our distorted view of magnetars: application of the Resonant Cyclotron Scattering model
Authors: N. Rea (SRON), S. Zane (MSSL), M. Lyutikov (UBC), R. Turolla (Uni.Padua)
Comments: 5 pages, 5 color figures; Astrophysics & Space Science, in press ("Isolated Neutron Stars"; London, UK)

The X-ray spectra of the magnetar candidates are customarily fitted with an empirical, two component model: an absorbed blackbody and a power-law. However, the physical interpretation of these two spectral components is rarely discussed. It has been recently proposed that the presence of a hot plasma in the magnetosphere of highly magnetized neutron stars might distort, through efficient resonant cyclotron scattering, the thermal emission from the neutron star surface, resulting in the production of non-thermal spectra. Here we discuss the Resonant Cyclotron Scattering (RCS) model, and present its XSPEC implementation, as well as preliminary results of its application to Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters.

 
astro-ph/0608653 [abs, ps, pdf, other] :
Title: Recent Timing Studies on RXTE Observations of SAX J2103.5+4545
Authors: A. Baykal (1), S. C. Inam (2), M. J. Stark (3), C. M. Heffner (3), A. E. Erkoca (4), J. H. Swank (5) ((1) Physics Department, METU, (2) Department of Electrical and Electronics Engineering, Baskent University, (3) Lafayette College, (4) Department of Physics, University of Arizona, (5) NASA GSFC)
Comments: 24 pages, 8 figures, submitted to MNRAS

SAX J2103.5+4545 had been continously monitored for $\sim $ 900 days by Rossi X-ray Timing Explorer (RXTE) since its outburst at July 2002. Using these observations and previous archival RXTE observations of SAX J2103.5+4545, we refined the binary orbital parameters and find the new orbital period as P= (12.66536 $\pm $ 0.00088) days and the eccentricty as 0.4055$\pm$ 0.0032. With these new orbital parameters, we constructed the pulse frequency and pulse frequency derivative histories of the pulsar and confirmed the correlation between X-ray flux and pulse frequency derivative presented by Baykal, Stark and Swank (2002). We constructed the power spectra for the fluctuations of pulse frequency derivatives and found that the power law index of the noise spectra 2.13 $\pm$ 0.6. The power law index is consistent with random walk in pulse frequency derivative and is the steepest power law index seen among the HMXRBs.
X-ray spectra analysis confirmed the inverse correlation trend between power law index and X-ray flux found by Baykal, Stark and Swank (2002).

 
astro-ph/0608663 [abs, ps, pdf, other] :
Title: Pulse profiles of millisecond pulsars and their Fourier amplitudes
Authors: Juri Poutanen, Andrei M. Beloborodov
Comments: 9 pages, 6 figures, submitted to MNRAS

Approximate analytical formulae are derived for the pulse profile produced by small hot spots on a rapidly rotating neutron star. Its Fourier amplitudes and phases are calculated. The proposed formalism takes into account gravitational bending of light, Doppler effect, anisotropy of emission, and time delays. Its accuracy is checked with exact numerical calculations.

 

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astro-ph new abstracts, Fri, 1 Sep 06 00:00:10 GMT
0608679 -- 0608715 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608682 [abs, ps, pdf, other] :
Title: Proto-Neutron Star Winds with Magnetic Fields and Rotation
Authors: Brian D. Metzger, Todd A. Thompson, Eliot Quataert
Comments: 21 pages, 12 figures, submitted to ApJ

We solve the 1D neutrino-heated non-relativistic MHD wind problem for conditions that range from slowly rotating (spin period P > 10 ms) protoneutron stars (PNSs) with surface field strengths typical of radio pulsars (B < 10^13 G), to "proto-magnetars" with B ~ 10^14-10^15 G in their hypothesized rapidly rotating initial states (P ~ 1 ms). We use the simulations of Bucciantini et al. (2006) to map our monopole results onto a more physical dipole geometry and to estimate the spindown of PNSs when their winds are relativistic. We then quantify the effects of rotation and magnetic fields on the mass loss, energy loss, and r-process nucleosynthesis in PNS winds. We describe the evolution of PNS winds through the Kelvin-Helmholtz cooling epoch, emphasizing the transition between (1) thermal neutrino-driven, (2) non-relativistic magnetically-dominated, and (3) relativistic magnetically-dominated outflows. We find that proto-magnetars with P ~ 1 ms and B > 10^15 G drive relativistic winds with luminosities, energies, and Lorentz factors (magnetization sigma ~ 1-1000) consistent with those required to produce long duration gamma-ray bursts and hyper-energetic supernovae (SNe). A significant fraction of the rotational energy may be extracted in only a few seconds, sufficiently rapidly to alter the asymptotic energy of the SN remnant, its morphology, and, potentially, its nucleosynthetic yield. Winds from PNSs with more modest rotation periods (2 - 10 ms) and with magnetar-strength fields produce conditions significantly more favorable for the r-process than winds from slowly rotating PNSs. Lastly, we show that energy and momentum deposition by convectively-excited waves further increase the likelihood of successful r-process in PNS winds.

 
astro-ph/0608689 [abs, ps, pdf, other] :
Title: On the role of the current loss in radio pulsar evolution
Authors: V.S.Beskin, E.E.Nokhrina
Comments: 4 pages, to appear in Astrophysics and Space Science, Special Issue: Isolated Neutron Stars

The aim of this article is to draw attention to the importance of the electric current loss in the energy output of radio pulsars. We remind that even the losses attributed to the magneto-dipole radiation of a pulsar in vacuum can be written as a result of an Ampere force action of the electric currens flowing over the neutron star surface (Michel, 1991, Beskin et al., 1993). It is this force that is responsible for the transfer of angular momentum of a neutron star to an outgoing magneto-dipole wave. If a pulsar is surrounded by plasma, and there is no longitudinal current in its magnetosphere, there is no energy loss (Beskin et al., 1993, Mestel et al., 1999). It is the longitudinal current closing within the pulsar polar cap that exerts the retardation torque acting on the neutron star. This torque can be determined if the structure of longitudinal current is known. Here we remind of the solution by Beskin, Gurevitch & Istomin (1993) and discuss the validity of such an assumption. The behavior of the recently observed "part-time job" pulsar B1931+24 can be naturally explained within the model of current loss while the magneto-dipole model faces difficulties.

 

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astro-ph new abstracts, Mon, 4 Sep 06 00:00:09 GMT
0609001 -- 0609038 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609011 [abs, ps, pdf, other] :
Title: Implication of Existence of Hybrid stars and Theoretical Expectation of Submillisecond Pulsars
Authors: Zheng Xiaoping, Pan Nana, Yang Shuhua, Liu Xuewen, Kang Miao, Li Jiarong
Comments: 9 pages,3 figures, accepted by New Astronomy

We derive the bulk viscous damping timescale of hybrid stars, neutron stars with quark matter core. The r-mode instability windows of the stars show that the theoretical results are consistent with the rapid rotation pulsar data, which may give an indication for the existence of quark matter in the interior of neutron stars. Hybrid stars instead of neutron or strange stars may lead to submillisecond pulsars.

 
astro-ph/0609013 [abs, ps, pdf, other] :
Title: Upper bounds on the low-frequency stochastic gravitational wave background from pulsar timing observations: current limits and future prospects
Authors: F. A. Jenet, G. B. Hobbs, W. van Straten, R. N. Manchester, M. Bailes, J. P. W. Verbiest, R. T. Edwards, A. W. Hotan, J. M. Sarkissian, S. M. Ord
Comments: Accepted by ApJ

Using a statistically rigorous analysis method, we place limits on the existence of an isotropic stochastic gravitational wave background using pulsar timing observations. We consider backgrounds whose characteristic strain spectra may be described as a power-law dependence with frequency. Such backgrounds include an astrophysical background produced by coalescing supermassive black-hole binary systems and cosmological backgrounds due to relic gravitational waves and cosmic strings. Using the best available data, we obtain an upper limit on the energy density per unit logarithmic frequency interval of \Omega^{\rm SMBH}_g(1/8yr) h^2 <= 1.9 x 10^{-8} for an astrophysical background which is five times more stringent than the earlier Kaspi et al. (1994) limit of 1.1 x 10^{-7}. We also provide limits on a background due to relic gravitational waves and cosmic strings of \Omega^{\rm relic}_g(1/8yr) h^2 <= 2.0 x 10^{-8} and \Omega^{\rm cs}_g(1/8yr) h^2 <= 1.9 x 10^{-8} respectively. All of the quoted upper limits correspond to a 0.1% false alarm rate together with a 95% detection rate. We discuss the physical implications of these results and highlight the future possibilities of the Parkes Pulsar Timing Array project. We find that our current results can 1) constrain the merger rate of supermassive binary black hole systems at high red shift, 2) rule out some relationships between the black hole mass and the galactic halo mass, 3) constrain the rate of expansion in the inflationary era and 4) provide an upper bound on the dimensionless tension of a cosmic string background.

 
astro-ph/0609034 [abs, ps, pdf, other] :
Title: Heating and Non-thermal Particle Acceleration in Relativistic, Transverse Magnetosonic Shock Waves in Proton-Electron-Positron Plasmas
Authors: Elena Amato (1), Jonathan Arons (2) ((1) INAF - Osservatorio Astrofisico di Arcetri, (2) Astronomy Dep. U.C. Berkeley)
Comments: 32 pages, 13 figures, accepted for publication in ApJ

We report the results of 1D particle-in-cell simulations of ultrarelativistic shock waves in proton-electron-positron plasmas. We consider magnetized shock waves, in which the upstream medium carries a large scale magnetic field, directed transverse to the flow. Relativistic cyclotron instability of each species as the incoming particles encounter the increasing magnetic field within the shock front provides the basic plasma heating mechanism. The most significant new results come from simulations with mass ratio $m_p/m_\pm = 100$. We show that if the protons provide a sufficiently large fraction of the upstream flow energy density (including particle kinetic energy and Poynting flux), a substantial fraction of the shock heating goes into the formation of suprathermal power-law spectra of pairs. Cyclotron absorption by the pairs of the high harmonic ion cyclotron waves, emitted by the protons, provides the non-thermal acceleration mechanism. As the proton fraction increases, the non-thermal efficiency increases and the pairs' power-law spectra harden.
We suggest that the varying power law spectra observed in synchrotron sources powered by magnetized winds and jets might reflect the correlation of the proton to pair content enforced by the underlying electrodynamics of these sources' outflows, and that the observed correlation between the X-ray spectra of rotation powered pulsars with the X-ray spectra of their nebulae might reflect the same correlation.

 
astro-ph/0609035 [abs, ps, pdf, other] :
Title: Thermal and Bulk Comptonization in Accretion-Powered X-Ray Pulsars
Authors: Peter A. Becker, Michael T. Wolff
Comments: accepted for publication in ApJ

We develop a new theoretical model for the spectral formation process in accretion-powered X-ray pulsars based on a detailed treatment of the bulk and thermal Comptonization occurring in the accreting, shocked gas. A rigorous eigenfunction expansion method is employed to obtain the analytical solution for the Green's function describing the scattering of radiation injected into the column from a monochromatic source located at an arbitrary height above the stellar surface. The emergent spectrum is calculated by convolving the Green's function with source terms corresponding to bremsstrahlung, cyclotron, and blackbody emission. The energization of the photons in the shock, combined with cyclotron absorption, naturally produces an X-ray spectrum with a relatively flat continuum shape and a high-energy quasi-exponential cutoff. We demonstrate that the new theory successfully reproduces the phase-averaged spectra of the bright pulsars Her X-1, LMC X-4, and Cen X-3. In these luminous sources, it is shown that the emergent spectra are dominated by Comptonized bremsstrahlung emission.

 

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astro-ph new abstracts, Tue, 5 Sep 06 00:00:11 GMT
0609039 -- 0609088 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609047 [abs, ps, pdf, other] :
Title: Magnetar-Driven Magnetic Tower as a Model for Gamma-Ray Bursts and Asymmetric Supernovae
Authors: Dmitri A. Uzdensky (Princeton University and CMSO), Andrew I. MacFadyen (IAS)
Comments: 13 pages, 6 figures; submitted to ApJ

We consider a newly-born millisecond magnetar, focusing on its interaction with the dense stellar plasma in which it is initially embedded. We argue that the confining pressure and inertia of the surrounding plasma acts to collimate the magnetar's Poynting-flux-dominated outflow into tightly beamed jets and increases its magnetic luminosity. We propose this process as an essential ingredient in the magnetar model for gamma-ray burst and asymmetric supernova central engines. We introduce the ``pulsar-in-a-cavity'' as an important model problem representing a magnetized rotating neutron star inside a collapsing star. We describe its essential properties and derive simple estimates for the evolution of the magnetic field and the resulting spin-down power. We find that the infalling stellar mantle confines the magnetosphere, enabling a gradual build-up of the toroidal magnetic field due to continuous twisting. The growing magnetic pressure eventually becomes dominant, resulting in a magnetically-driven explosion. The initial phase of the explosion is quasi-isotropic, potentially exposing a sufficient amount of material to $^{56}$Ni-producing temperatures to result in a bright supernova. However, if significant expansion of the star occurs prior to the explosion, then very little $^{56}$Ni is produced and no supernova is expected. In either case, hoop stress subsequently collimates the magnetically-dominated outflow, leading to the formation of a magnetic tower. After the star explodes, the decrease in bounding pressure causes the magnetic outflow to become less beamed. However, episodes of late fallback can reform the beamed outflow, which may be responsible for late X-ray flares.

 
astro-ph/0609066 [abs, ps, pdf, other] :
Title: The Magnificent Seven: Magnetic fields and surface temperature distributions
Authors: F. Haberl
Comments: 10 pages, 8 figures, to appear in Astrophysics and Space Science, in the proceedings of "Isolated Neutron Stars: from the Interior to the Surface", edited by D. Page, R. Turolla and S. Zane

Presently seven nearby radio-quiet isolated neutron stars discovered in ROSAT data and characterized by thermal X-ray spectra are known. They exhibit very similar properties and despite intensive searches their number remained constant since 2001 which led to their name ``The Magnificent Seven''. Five of the stars exhibit pulsations in their X-ray flux with periods in the range of 3.4 s to 11.4 s. XMM-Newton observations revealed broad absorption lines in the X-ray spectra which are interpreted as cyclotron resonance absorption lines by protons or heavy ions and / or atomic transitions shifted to X-ray energies by strong magnetic fields of the order of 10^13 G. New XMM-Newton observations indicate more complex X-ray spectra with multiple absorption lines. Pulse-phase spectroscopy of the best studied pulsars RX J0720.4-3125 and RBS 1223 reveals variations in derived emission temperature and absorption line depth with pulse phase. Moreover, RX J0720.4-3125 shows long-term spectral changes which are interpreted as due to free precession of the neutron star. Modeling of the pulse profiles of RX J0720.4-3125 and RBS 1223 provides information about the surface temperature distribution of the neutron stars indicating hot polar caps which have different temperatures, different sizes and are probably not located in antipodal positions.

 
astro-ph/0609082 [abs, ps, pdf, other] :
Title: Further Evidence for Collimated Particle Beams from Pulsars, and Precession
Authors: Avinash A. Deshpande (1,2), V. Radhakrishnan (2) ((1) Arecibo Observatory, NAIC, Arecibo; (2) Raman Research Institute, Bangalore)
Comments: 11 (8+3) pages, 3 figures; Submitted to ApJ

We follow up on our (Radhakrishnan & Deshpande, 2001) radically different interpretation of the arcs in the nebular X-radiation from Vela observed by Pavlov et al. (2000) & Helfand et al. (2001) with the Chandra Observatory, and interpreted by the latter as an equatorial wind. The bright arcs, the jet-like feature and the diffuse components in the Vela X-ray nebula can be explained together in detail by our model in which the arcs are understood as traces of the particle beams from the two magnetic poles at the shock front. We consider this as important evidence for collimated particle beams from pulsars' magnetic poles. In this paper, we discuss the variability in the features in the Vela X-ray nebula observed by Pavlov et al. (2003), and assess the relevance and implication of our model to the observations on the Crab and other remnants. Our basic picture after incorporating the signatures of free precession of the central compact object can readily account for the variability and significant asymmetries, including the bent jet-like features, in the observed morphologies. The implications of these findings are discussed.

 

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astro-ph new abstracts, Wed, 6 Sep 06 00:00:11 GMT
0609089 -- 0609120 received


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astro-ph new abstracts, Thu, 7 Sep 06 00:00:09 GMT
0609121 -- 0609168 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609136 [abs, ps, pdf, other] :
Title: Constraints on the Geometry of the VHE Emission in LS 5039 from Photon-Photon Deabsorption
Authors: Markus Boettcher
Comments: Submitted to Astroparticle Physics. 16 pages, including 7 color eps figures and 2 tables

A detailed parameter study of the gamma-gamma absorption effects in LS 5039 is presented. For a range of plausible locations of the VHE gamma-ray emission region and the allowable range of viewing angles, the de-absorbed, intrinsic VHE gamma-ray spectra and total VHE photon fluxes and luminosities are calculated and compared to luminosity constraints based on wind accretion onto the compact object in LS 5039. It is found that (1) it is impossible to choose the viewing angle and location of the VHE emission region in a way that the intrinsic (deabsorbed) fluxes and spectra in superior and inferior conjunction are identical; consequently, the intrinsic VHE luminosities and spectral shapes must be fundamentally different in different orbital phases, (2) if the VHE luminosity is limited by wind accretion from the companion star and the system is viewed at an inclination angle of i > 40 deg., the emission is most likely beamed by a larger Doppler factor than inferred from the dynamics of the large-scale radio outflows, (3) the still poorly constrained viewing angle between the line of sight and the jet axis is most likely substantially smaller than the maximum of ~ 64 deg. inferred from the lack of eclipses.(4) Consequently, the compact object is more likely to be a black hole rather than a neutron star. (5) There is a limited range of allowed configurations for which the expected > 1 TeV neutrino flux would actually anti-correlate with the observed VHE gamma-ray emission.

 
astro-ph/0609138 [abs, ps, pdf, other] :
Title: Carbon-Enhanced Metal-Poor Stars. Osmium and Iridium Abundances in the Neutron-Capture-Enhanced Subgiants CS31062-050 and LP625-44
Authors: Wako Aoki, Sara Bisterzo, Roberto Gallino, Timothy C. Beers, John E. Norris, Sean G. Ryan, Stelios Tsangarides
Comments: 12 pages, 2 figures, 1 table, ApJ Letter, in press

We have investigated the abundances of heavy neutron-capture elements, including osmium (Os) and iridium (Ir), in the two Carbon-Enhanced Metal-Poor (CEMP) subgiants CS31062-050 and LP625-44. CS31062-050 is known to be a so-called CEMP-r/s star, which exhibits large excesses of s-process elements such as barium (Ba) and lead (Pb), as well as a significant enhancement of europium (Eu) that cannot be explained by conventional s-process production in Asymptotic Giant Branch star models. Our analysis of the high-resolution spectrum for this object has determined, for the first time, the abundances of Ir and Os, elements in the third peak of the r-process nucleosynthesis. They also exhibit significant excesses relative to the predictions of standard s-process calculations. These two elements are not detected in a similar-quality spectrum of LP625-44; the derived upper limits on their abundances are lower than the abundances in CS31062-050. We compare the observed abundance patterns of neutron-capture elements, including Os and Ir, in these two stars with recent model calculations of the s-process, and discuss possible interpretations.

 
astro-ph/0609154 [abs, ps, pdf, other] :
Title: Timing of millisecond pulsars in NGC 6752 - II. Proper motions of the pulsars in the cluster outskirts
Authors: A. Corongiu, A. Possenti, A.G. Lyne, R.N. Manchester, F. Camilo, N. D'Amico, J.M. Sarkissian
Comments: 8 pages, 3 figures, accepted for publication in ApJ

Exploiting a five-year span of data, we present improved timing solutions for the five millisecond pulsars known in the globular cluster NGC 6752. They include proper motion determinations for the two outermost pulsars in the cluster, PSR J1910-5959A and PSR J1910-5959C. The values of the proper motions are in agreement with each other within current uncertainties, but do not match (at 4 sigma and 2 sigma level respectively) with the value of the proper motion of the entire globular cluster derived in the optical band. Implications of these results for the cluster membership of the two pulsars are investigated. Prospects for the detection of the Shapiro delay in the binary system J1910-5959A are also discussed.

 

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astro-ph new abstracts, Fri, 8 Sep 06 00:00:11 GMT
0609169 -- 0609206 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609180 [abs, ps, pdf, other] :
Title: Dim Isolated Neutron Stars, Cooling and Energy Dissipation
Authors: M. Ali Alpar
Comments: To appear in Astrophysics and Space Science, in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface", London, April 2006; eds. D. Page, R. Turolla and S. Zane

The cooling and reheating histories of dim isolated neutron stars(DINs) are discussed. Energy dissipation due to dipole spindown with ordinary and magnetar fields, and due to torques from a fallback disk are considered as alternative sources of reheating which would set the temperature of the neutron star after the initial cooling era. Cooling or thermal ages are related to the numbers and formation rates of the DINs and therefore to their relations with other isolated neutron star populations. Interaction with a fallback disk, higher multipole fields and activity of the neutron star are briefly discussed.

 
astro-ph/0609183 [abs, ps, pdf, other] :
Title: Impact of neutron star oscillations on the accelerating electric field in the polar cap of pulsar: or could we see oscillations of the neutron star after the glitch in pulsar?
Authors: Andrey N. Timokhin (Sternberg Astronomical Institute, Moscow, Russia)
Comments: 7 pages, 8 figures. Presented at the conference "Isolated Neutron Stars: from the Interior to the Surface", London, April 24-28, 2006; to appear in Astrophysics and Space Science

Pulsar "standard model", that considers a pulsar as a rotating magnetized conducting sphere surrounded by plasma, is generalized to the case of oscillating star. We developed an algorithm for calculation of the Goldreich-Julian charge density for this case. We consider distortion of the accelerating zone in the polar cap of pulsar by neutron star oscillations. It is shown that for oscillation modes with high harmonic numbers (l,m) changes in the Goldreich-Julian charge density caused by pulsations of neutron star could lead to significant altering of an accelerating electric field in the polar cap of pulsar. In the moderately optimistic scenario, that assumes excitation of the neutron star oscillations by glitches, it could be possible to detect altering of the pulsar radioemission due to modulation of the accelerating field.

 
astro-ph/0609190 [abs, ps, pdf, other] :
Title: Electrodynamics for Nuclear Matter in Bulk
Authors: Remo Ruffini, Michael Rotondo, She-Sheng Xue
Comments: 10 pages, 5 figures

A general approach to analyze the electrodynamics of nuclear matter in bulk is presented using the relativistic Thomas-Fermi equation generalizing to the case of $N \simeq (m_{\rm Planck}/m_n)^3$ nucleons of mass $m_n$ the approach well tested in very heavy nuclei ($Z \simeq 10^6$). Particular attention is given to implement the condition of charge neutrality globally on the entire configuration, versus the one usually adopted on a microscopic scale. As the limit $N \simeq (m_{\rm Planck}/m_n)^3$ is approached the penetration of electrons inside the core increases and a relatively small tail of electrons persists leading to a significant electron density outside the core. Within a region of $10^2$ electron Compton wavelength near the core surface electric fields close to the critical value for pair creation by vacuum polarization effect develop. These results can have important consequences on the understanding of physical process in neutron stars structures as well as on the initial conditions leading to the process of gravitational collapse to a black hole.

 
astro-ph/0609194 [abs, ps, pdf, other] :
Title: Persistent and Transient Blank Field Sources
Authors: A. Treves, S. Campana, M. Chieregato, A. Moretti, T. Nelson, M. Orio
Comments: 3 pages, 0 figures. Paper presented at the Conference "Isolated Neutron Stars: from the interior to the surface", London, April 2006. Astrophysics and Space Science, in press

Blank field sources (BFS) are good candidates for hosting dim isolated neutron stars (DINS). The results of a search of BFS in the ROSAT HRI images are revised. We then focus on transient BFS, arguing that they belong to a rather large population. The perspectives of future research on DINS are then discussed.

 
astro-ph/0609200 [abs, ps, pdf, other] :
Title: Constraints on RRAT Emission Mechanisms from RXTE/PCA Observations of RRAT J1819-1458
Authors: Robert E. Rutledge (McGill)
Comments: 10 pages, ApJL, submitted

We derive the second and most stringent limit to date of the X-ray/radio flux ratio (F_x/F_R) for the radio bursts associated with the recently identified source class, the Rotating Radio Transients (RRATs). We analyze 20.1 hr of \rxte/PCA observations of RRAT J1819-1458 -- a period during which 350\ppm23 RRAT radio bursts occurred, based on the previously observed average radio burst rate. No X-ray bursts were detected, implying an upper-limit on the X-ray flux for RRAT-bursts of <1.5e-8 ergs cm-2 s-1 (2-10 keV) or a luminosity <2.3e37 (d/3.6\kpc)^2 ergs s-1. The time-average burst flux is <2e-13 ergs cm-2 s-1 (0.5-8 keV) -- a factor of 10 below that of the previously identified persistent X-ray counterpart. Thus, X-ray bursts from the RRAT are energetically unimportant compared with the persistent X-ray emission. From the previously observed burst radio flux, we derive an upper-limit F_x/F_R< 4.2e-12 erg cm-2 s-1 mJy-1 for the radio bursts from this RRAT, the most stringent to date, due to the high radio flux of bursts from this source. The F_x/F_R ratio is a factor approximately 80 larger than that of the millisecond pulsar PSR B1821-24; thus emission processes of X-ray/radio efficiency comparable to MSP pulses cannot be ruled out. However, if the RRAT burst emission mechanism is identical to the msec bursts of magnetars, then the msec bursts of magnetars should be easily detected with radio instrumentation; yet none have been reported to date.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605461 [abs, ps, pdf, other] :
Title: Elastic or magnetic? A toy model for global magnetar oscillations with implications for QPOs during flares
Authors: Kostas Glampedakis, Lars Samuelsson, Nils Andersson
Comments: 5 pages, 2 eps figures, minor corrections to match published version
Journal-ref: MNRAS Letters, Vol. 371, L74 (2006)
Note: replaced with revised version Thu, 7 Sep 2006 10:43:09 GMT (55kb)
 
astro-ph/0607165 [abs, ps, pdf, other] :
Title: Force-free magnetosphere of an aligned rotator with differential rotation of open magnetic field lines
Authors: Andrey N. Timokhin (Sternberg Astronomical Institute, Moscow, Russia)
Comments: 5 pages, 4 figures. Presented at the conference "Isolated Neutron Stars: from the Interior to the Surface", London, April 24-28, 2006; to appear in Astrophysics and Space Science. Significantly revised version, a mistake found by ourselfs in the numerical code was corrected, all presented results are obtained with the correct version of the code
Note: replaced with revised version Thu, 7 Sep 2006 09:44:58 GMT (406kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 11 Sep 06 00:10:54 GMT
0609207 -- 0609245 received


0 abstracts or titles contain neutron star, magnetar or pulsar



Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0609006 [abs, ps, pdf, other] :
Title: Nuclear Astrophysics: CIPANP 2006
Authors: W. C. Haxton
Comments: 11 pages; talk presented CIPANP 2006

I review progress that has been made in nuclear astrophysics over the past few years and summarize some of the questions that remain. Topics selected include solar neutrinos, supernovae (the explosion and associated nucleosynthesis), laboratory astrophysics, and neutron star structure.

 

Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 12 Sep 06 00:00:14 GMT
0609246 -- 0609295 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609261 [abs, ps, pdf, other] :
Title: Short time scale pulse stability of the Crab pulsar in the optical band
Authors: S. Karpov, G. Beskin, A. Biryukov, V. Debur, V. Plokhotnichenko, M. Redfern, A. Shearer
Comments: 4 pages, 6 figures. To appear in ApSS, in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface", London, April 2006; eds. D. Page, R. Turolla and S. Zane

The fine structure and the variations of the optical pulse shape and phase of the Crab pulsar are studied on various time scales. The observations have been carried out on 4-m William Hershel and 6-m BTA telescopes with APD photon counter, photomultiplier based 4-channel photometer and PSD based panoramic spectrophotopolarimeter with 1$\mu$s time resolution in 1994, 1999, 2003 and 2005-2006 years. The upper limit on the pulsar precession on Dec 2, 1999 is placed in the 10 s - 2 hours time range. The evidence of a varying from set to set fine structure of the main pulse is found in the 1999 and 2003 years data. No such fine structure is detected in the integral pulse shape of 1994, 1999 and 2003 years.
The drastic change of the pulse shape in the 2005-2006 years set is detected along with the pulse shape variability and quasi-periodic phase shifts.

 
astro-ph/0609265 [abs, ps, pdf, other] :
Title: Neutron Star Asteroseismology. Axial Crust Oscillations in the Cowling Approximation
Authors: Lars Samuelsson, Nils Andersson
Comments: 14 pages, 1 table, 4 figures

Recent observations of quasi-periodic oscillations in the aftermath of giant flares in soft gamma-ray repeaters suggest a close coupling between the seismic motion of the crust after a major quake and the modes of oscillations in a magnetar. In this paper we consider the purely elastic modes of oscillation in the crust of a neutron star in the relativistic Cowling approximation (disregarding any magnetic field). We determine the axial crust modes for a large set of stellar models, using a state-of-the-art crust equation of state and a wide range of core masses and radii. We also devise useful approximate formulae for the mode-frequencies. We show that the relative crust thickness is well described by a function of the compactness of the star and a parameter describing the compressibility of the crust only. Considering the observational data for SGR 1900+14 and SGR 1806-20, we demonstrate how our results can be used to constrain the mass and radius of an oscillating neutron star.

 
astro-ph/0609267 [abs, ps, pdf, other] :
Title: Hydrodynamic Thermonuclear Runaways in Superbursts
Authors: Nevin N. Weinberg (1, 2), Lars Bildsten (2, 3), Edward F. Brown (4) ((1) UC Berkeley, (2) KITP, (3) UCSB, (4) MSU/JINA)
Comments: 4 pages, 3 figures (emulateapj), accepted to ApJ Letters

We calculate the thermal and dynamical evolution of the surface layers of an accreting neutron star during the rise of a superburst. For the first few hours following unstable 12C ignition, the nuclear energy release is transported by convection. However, as the base temperature rises, the heating time becomes shorter than the eddy turnover time and convection becomes inefficient. This results in a hydrodynamic nuclear runaway, in which the heating time becomes shorter than the local dynamical time. Such hydrodynamic burning can drive shock waves into the surrounding layers and may be the trigger for the normal X-ray burst found to immediately precede the onset of the superburst in both cases where the Rossi X-Ray Timing Explorer was observing.

 
astro-ph/0609272 [abs, ps, pdf, other] :
Title: What do exotic equations of state have to offer?
Authors: J.E. Horvath
Comments: 8 pages, 2 figures. To be published in the Proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface" (April 24-28, 2006, London, UK), eds. D. Page, R. Turolla, & S. Zane

We present a short general overview of the main features of exotic models of neutron stars, focusing on the structural and dynamical predictions derived from them. In particular, we discuss the presence of ``normal'' quark matter and Color-Flavor Locked (CFL) states, including their possible self-bound versions, and mention some different proposals emerging from the study of QCD microphysics. A connection with actual observed data is the main goal to be addressed at this talk and along the meeting. It is demonstrated that exotic equations of state are {\it not} soft if the vacuum contributions are large enough, and argued that recent measurements of high pulsar masses ($M \geq 2 M_{\odot}$) create problems for {\it hadronic} models in which hyperons should be present.

 
astro-ph/0609275 [abs, ps, pdf, other] :
Title: The Magnificent Seven in the dusty prairie -- The role of interstellar absorption on the observed neutron star population
Authors: B. Posselt, S.B. Popov, F. Haberl, J. Truemper, R. Turolla, R. Neuhaeuser
Comments: 8 pages, 7 figures; to appear in Astrophysics and Space Science, in the proceedings of "Isolated Neutron Stars: from the Interior to the Surface", edited by D. Page, R. Turolla and S. Zane

The Magnificent Seven have all been discovered by their exceptional soft X-ray spectra and high ratios of X-ray to optical flux. They all are considered to be nearby sources. Searching for similar neutron stars with larger distances, one expects larger interstellar absorption resulting in harder X-ray counterparts. Current interstellar absorption treatment depends on chosen abundances and scattering cross-sections of the elements as well as on the 3D distribution of the interstellar medium. After a discussion of these factors we use the comprehensive 3D measurements of the Local Bubble by Lallement et al. 2003 to construct two simple models of the 3D distribution of the hydrogen column density. We test these models by using a set of soft X-ray sources with known distances. Finally, we discuss possible applications for distance estimations and population synthesis studies.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


hep-ph/0609081 [abs, ps, pdf, other] :
Title: Sterile neutrinos, dark matter, and the pulsar velocities in models with a Higgs singlet
Authors: Alexander Kusenko
Comments: 4 pages, one figure

We identify the range of parameters for which the sterile neutrinos can simultaneously explain the cosmological dark matter and the observed velocities of pulsars. To satisfy all cosmological bounds, the relic sterile neutrinos must be produced sufficiently cold. This is possible in a class of models with a gauge-singlet Higgs boson, coupled to the neutrinos as a singlet Majoron. Sterile dark matter can be detected by the x-ray telescopes. The presence of the singlet Majoron in the Higgs sector can be tested at the LHC.

 

Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606708 [abs, ps, pdf, other] :
Title: Constraining a possible time-variation of the gravitational constant through "gravitochemical heating" of neutron stars
Authors: Paula Jofre, Andreas Reisenegger (Pontificia Universidad Catolica de Chile), Rodrigo Fernandez (University of Toronto)
Comments: 4 pages, including 2 figures. Accepted for publication in Phys. Rev. Lett. Revised version includes minor changes in the wording, and more substantial changes in the last 2 paragraphs (Discussion and Conclusions). Equations, figures, and results are unchanged
Note: replaced with revised version Mon, 11 Sep 2006 13:30:53 GMT (16kb)
 
nucl-th/0511064 [abs, ps, pdf, other] :
Title: Constraining the Radii of Neutron Stars with Terrestrial Nuclear Laboratory Data
Authors: Bao-An Li, Andrew W. Steiner
Comments: 11 pages, 3 figures; version to be published in Phys. Lett. B
Note: replaced with revised version Mon, 11 Sep 2006 16:58:38 GMT (38kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 13 Sep 06 00:00:11 GMT
0609296 -- 0609331 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609309 [abs, ps, pdf, other] :
Title: A Shell of Thermal X-ray Emission Associated with the Young Crab-like Remnant 3C58
Authors: E. V. Gotthelf, D. J. Helfand, L. Newburgh (Columbia University)
Comments: 7 pages, 8 figures, 2 tables, Latex emulateapj style. To appear in the Astrophysical Journal

Deep X-ray imaging spectroscopy of the bright pulsar wind nebula 3C58 confirms the existence of an embedded thermal X-ray shell surrounding the pulsar PSR J0205+6449. Radially resolved spectra obtained with the XMM-Newton telescope are well-characterized by a power-law model with the addition of a soft thermal emission component in varying proportions. These fits reproduce the well-studied increase in the spectral index with radius attributed to synchrotron burn-off of high energy electrons. Most interestingly, a radially resolved thermal component is shown to map out a shell-like structure ~6' in diameter. The presence of a strong emission line corresponding to the Ne IX He-like transition requires an overabundance of ~3 x [Ne/Ne(sun)] in the Raymond-Smith plasma model. The best-fit temperature kT ~ 0.23 keV is essentially independent of radius for the derived column density of N_H = (4.2 +/- 0.1)E21 per cm squared. Our result suggests that thermal shells can be obscured in the early evolution of a supernova remnant by non-thermal pulsar wind nebulae emission; the luminosity of the 3C58 shell is more than an order of magnitude below the upper limit on a similar shell in the Crab Nebula. We find the shell centroid to be offset from the pulsar location. If this neutron star has a velocity similar to that of the Crab pulsar, we derive an age of 3700 yr and a velocity vector aligned with the long axis of the PWN. The shell parameters and pulsar offset add to the accumulating evidence that 3C58 is not the remnant of the supernova of CE 1181.

 
astro-ph/0609319 [abs, ps, pdf, other] :
Title: Long term spectral variability in the Soft Gamma-ray Repeater SGR 1900+14
Authors: A. Tiengo, P. Esposito, S. Mereghetti, L. Sidoli, D. Goetz, M. Feroci, R. Turolla, S. Zane, G.L. Israel, L. Stella, P. Woods
Comments: 4 pages, 3 figures. To be published in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface", London, April 2006; eds. D. Page, R. Turolla, & S. Zane

We present a systematic analysis of all the BeppoSAX data of SGR1900+14. The observations spanning five years show that the source was brighter than usual on two occasions: ~20 days after the August 1998 giant flare and during the 10^5 s long X-ray afterglow following the April 2001 intermediate flare. In the latter case, we explore the possibility of describing the observed short term spectral evolution only with a change of the temperature of the blackbody component. In the only BeppoSAX observation performed before the giant flare, the spectrum of the SGR1900+14 persistent emission was significantly harder and detected also above 10 keV with the PDS instrument. In the last BeppoSAX observation (April 2002) the flux was at least a factor 1.2 below the historical level, suggesting that the source was entering a quiescent period.

 
astro-ph/0609325 [abs, ps, pdf, other] :
Title: Light Curves for Rapidly-Rotating Neutron Stars
Authors: Coire Cadeau, Sharon M. Morsink, Denis Leahy, Sheldon S. Campbell
Comments: Accepted by the Astrophysical Journal. 13 pages & 7 figures

We present raytracing computations for light emitted from the surface of a rapidly-rotating neutron star in order to construct light curves for X-ray pulsars and bursters. These calculations are for realistic models of rapidly-rotating neutron stars which take into account both the correct exterior metric and the oblate shape of the star. We find that the most important effect arising from rotation comes from the oblate shape of the rotating star. We find that approximating a rotating neutron star as a sphere introduces serious errors in fitted values of the star's radius and mass if the rotation rate is very large. However, in most cases acceptable fits to the ratio M/R can be obtained with the spherical approximation.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609180 [abs, ps, pdf, other] :
Title: Dim Isolated Neutron Stars, Cooling and Energy Dissipation
Authors: M. Ali Alpar
Comments: To appear in Astrophysics and Space Science, in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface", London, April 2006; eds. D. Page, R. Turolla and S. Zane. Revised version: with minor change and typos corrected
Note: replaced with revised version Tue, 12 Sep 2006 06:46:44 GMT (25kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 14 Sep 06 00:00:09 GMT
0609332 -- 0609368 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609359 [abs, ps, pdf, other] :
Title: Source population synthesis and the Galactic diffuse gamma-ray emission
Authors: A. W. Strong
Comments: 6 pages, 9 figures. for Proceedings of Conference 'The multi-messenger approach to high-energy gamma-ray sources', Barcelona, July 2006

Population synthesis is used to study the contribution from undetected sources to the Galactic ridge emission measured by EGRET. Synthesized source counts are compared with the 3rd EGRET catalogue at low and high latitudes. For pulsar-like populations, 5-10% of the emission >100 MeV comes from sources below the EGRET threshold. A steeper luminosity function can increase this to 20% without violating EGRET source statistics. Less luminous populations can produce much higher values without being detected. Since the unresolved source spectrum is different from the interstellar spectrum, it could provide an explanation of the observed MeV and GeV excesses above the predictions, and we give an explicit example of how this could work.

 
astro-ph/0609364 [abs, ps, pdf, other] :
Title: Magnetar oscillations pose challenges for strange stars
Authors: Anna L. Watts (MPA), Sanjay Reddy (LANL)
Comments: 4 pages, 3 figures, to be submitted to PRL

High frequency oscillations have now been detected in giant flares from two magnetars (highly magnetized neutron stars). In the most promising model, a crustquake associated with the flare triggers global seismic vibrations. Attention has focused on toroidal shear modes of the neutron star crust, which are a good match to the observed frequencies. In this Letter we consider the possibility that magnetars are strange stars rather than neutron stars, and compute toroidal shear mode frequencies for strange star crust models. The frequencies differ significantly from those of neutron star crusts, and cannot be reconciled with the observations for reasonable magnetar parameters.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0603018 [abs, ps, pdf, other] :
Title: Entrainment parameters in cold superfluid neutron star core
Authors: Nicolas Chamel, Pawel Haensel
Comments: 10 pages, 7 figures. Revised version
Journal-ref: Phys.Rev. C73 (2006) 045802
Note: replaced with revised version Wed, 13 Sep 2006 07:57:51 GMT (51kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 15 Sep 06 00:00:11 GMT
0609369 -- 0609417 received


8 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609375 [abs, ps, pdf, other] :
Title: Sterile dark matter and reionization
Authors: Alexander Kusenko
Comments: 4 pages, 2 figures, to appear in proceedings of 7th UCLA Symposium on sources and detection of dark matter and dark energy in the universe, 22-24 Feb 2006, Marina de Rey, California

Sterile neutrinos with masses in the keV range can be the dark matter, and their emission from a supernova can explain the observed velocities of pulsars. The sterile neutrino decays could produce the x-ray radiation in the early universe, which could have an important effect on the formation of the first stars. X-rays could ionize gas and could catalyze the production of molecular hydrogen during the ``dark ages''. The increased fraction of molecular hydrogen could facilitate the cooling and collapse of the primordial gas clouds in which the first stars were formed.

 
astro-ph/0609377 [abs, ps, pdf, other] :
Title: The Effect of Orbital Eccentricity on Gravitational Wave Background Radiation from Cosmological Binaries
Authors: Motohiro Enoki, Masahiro Nagashima
Comments: 15 pages, 12 figures, submitted to Progress of Theoretical Physics

A compact binary on an eccentric orbit radiates gravitational waves (GWs) at all integer harmonics of its orbital frequency. Thus, the spectral energy distribution, the power and the timescale of GW radiation of a binary on an eccentric orbit are different from those of a binary on a circular orbit. Therefore, in order to predict spectra of gravitational wave background radiation (GWBR) from compact binaries, it is important to include the effect of orbital eccentricity of binaries. In this study, we investigate the effect of orbital eccentricity on expected GWBR from extragalactic compact binaries. For this purpose, we formulate the power spectrum of GWBR from cosmological evolving eccentric binaries. Then we apply this formulation to the case of the GWBR from supermassive black hole (SMBH) binaries in galaxy nuclei. The key to do this is correctly estimating the number density of coalescing SMBH binaries. In this study, we use a semi-analytic model of galaxy and SMBH formation. We find that the power spectrum of the GWBR from SMBH binaires on eccentric orbits is suppressed for frequencies $\lesssim 1 {\rm nHz}$ dependent on an assumed initial eccentricity. Our model predicts that while the overall shape and amplitude of the power spectrum depend largely on galaxy formation processes, eccentricity of binaries can affect the shape of the power spectrum for lower frequencies $\lesssim 1 {\rm nHz}$. Pulsar timing measurements, which can detect GW at this frequency range, would be able to constrain the effect of eccentricity on the power spectrum of the GWBR from SMBH binaries.

 
astro-ph/0609383 [abs, ps, pdf, other] :
Title: Parametric mechanism of the rotation energy pumping by a relativistic plasma
Authors: G.Z.Machabeli, Zaza Osmanov, Swadesh M. Mahajan
Comments: 6 pages 1 figure

An investigation of the kinematics of a plasma stream rotating in the pulsar magnetosphere is presented. On the basis of an exact set of equations describing the behavior of the plasma stream, the increment of the instability is obtained, and the possible relevance of this approach for the understanding of the pulsar rotation energy pumping mechanism is discussed.

 
astro-ph/0609386 [abs, ps, pdf, other] :
Title: Nucleonic gamma-ray production in Pulsar Wind Nebulae
Authors: D. Horns (1), F. Aharonian (2), A.I.D. Hoffmann (1), A. Santangelo (1) ((1) IAAT, Univ. Tuebingen (2) Max-Planck Institut f. Kernphysik, Heidelberg)
Comments: 6 pages, 3 figures, to appear in proceedings "The Multi-Messenger Approach to High-Energy Gamma-Ray Sources", Barcelona July 2006

Observations of the inner radian of the Galactic disk at very high energy (VHE) gamma-rays have revealed at least 16 new sources. Besides shell type super-nova remnants, pulsar wind nebulae (PWN) appear to be a dominant source population in the catalogue of VHE gamma-ray sources. Except for the Crab nebula, the newly discovered PWN are resolved at VHE gamma-rays to be spatially extended (5-20 pc). Currently, at least 3 middle aged ($t>10$ kyrs) PWN (Vela X, G18.0-0.7, and G313.3+0.6 in the ``Kookaburra'' region) and 1 young PWN MSH 15-5{\it2} ($t=1.55$ kyrs) have been identified to be VHE emitting PWN (sometimes called ``TeV Plerions''). Two more candidate ``TeV Plerions'' have been identifed and have been reported at this conference [1]. In this contribution, the gamma-ray emission from Vela X is explained by a nucleonic component in the pulsar wind. The measured broad band spectral energy distribution is compared with the expected X-ray emission from primary and secondary electrons. The observed X-ray emission and TeV emission from the three middle aged PWN are compared with each other.

 
astro-ph/0609402 [abs, pdf] :
Title: Close Pairs as Probes of the Galaxy's Chemical Evolution
Authors: Dany Vanbeveren, Erwin De Donder
Comments: 10 pages, 5 figures, Invited paper at IAUS240, IAUXXVI GA Prague

Understanding the galaxy in which we live is one of the great intellectual challenges facing modern science. With the advent of high quality observational data, the chemical evolution modeling of our galaxy has been the subject of numerous studies in the last years. However, all these studies have one missing element which is the evolution of close binaries. Reason: their evolution is very complex and single stars only perhaps can do the job. (Un)Fortunately at present we know that a significant fraction of the observed intermediate mass and massive stars are members of a binary or multiple system and that certain objects can only be formed through binary evolution. Therefore galactic studies that do not account for close binaries may be far from realistic. We implemented a detailed binary population in a galactic chemical evolutionary model. Notice that this is not something simple like replacing chemical yields. Here we discuss three topics: the effect of binaries on the evolution of 14N, the evolution of the type Ia supernova rate and the effects on the G-dwarf distribution, the link between the evolution of the r-process elements and double neutron star mergers (candidates of short gamma-ray burst objects).

 
astro-ph/0609404 [abs, ps, pdf, other] :
Title: Unveiling Soft Gamma-Ray Repeaters with INTEGRAL
Authors: D. Gotz, S. Mereghetti, K. Hurley
Comments: 8 pages, 7 figures, Presented at the conference "Isolated Neutron Stars: from the Surface to the Interior", London, UK, 24-28 April 2006

Thanks to INTEGRAL's long exposures of the Galactic Plane, the two brightest Soft Gamma-Ray Repeaters, SGR 1806-20 and SGR 1900+14, have been monitored and studied in detail for the first time at hard-X/soft gamma rays.
This has produced a wealth of new scientific results, which we will review here. Since SGR 1806-20 was particularly active during the last two years, more than 300 short bursts have been observed with INTEGRAL. and their characteristics have been studied with unprecedented sensitivity in the 15-200 keV range. A hardness-intensity anticorrelation within the bursts has been discovered and the overall Number-Intensity distribution of the bursts has been determined. In addition, a particularly active state, during which ~100 bursts were emitted in ~10 minutes, has been observed on October 5 2004, indicating that the source activity was rapidly increasing. This eventually led to the Giant Flare of December 27th 2004, for which a possible soft gamma-ray (>80 keV) early afterglow has been detected.
The deep observations allowed us to discover the persistent emission in hard X-rays (20-150 keV) from 1806-20 and 1900+14, the latter being in a quiescent state, and to directly compare the spectral characteristics of all Magnetars (two SGRs and three Anomalous X-ray Pulsars) detected with INTEGRAL.

 
astro-ph/0609416 [abs, ps, pdf, other] :
Title: The Formation of the Double Pulsar PSR J0737-3039A/B}
Authors: I. H. Stairs, S. E. Thorsett, R. J. Dewey, M. Kramer, C. A. McPhee
Comments: To appear in MNRAS Letters

Recent timing observations of the double pulsar J0737-3039A/B have shown that its transverse velocity is extremely low, only 10 km/s, and nearly in the Plane of the Galaxy. With this new information, we rigorously re-examine the history and formation of this system, determining estimates of the pre-supernova companion mass, supernova kick and misalignment angle between the pre- and post-supernova orbital planes. We find that the progenitor to the recently formed `B' pulsar was probably less than 2 MSun, lending credence to suggestions that this object may not have formed in a normal supernova involving the collapse of an iron core. At the same time, the supernova kick was likely non-zero. A comparison to the history of the double-neutron-star binary B1534+12 suggests a range of possible parameters for the progenitors of these systems, which should be taken into account in future binary population syntheses and in predictions of the rate and spatial distribution of short gamma-ray burst events.

 
astro-ph/0609417 [abs, ps, pdf, other] :
Title: Tests of general relativity from timing the double pulsar
Authors: M. Kramer, I.H. Stairs, R.N. Manchester, M.A. McLaughlin, A.G. Lyne, R.D. Ferdman, M. Burgay, D.R. Lorimer, A. Possenti, N. D'Amico, J.M. Sarkissian, G.B. Hobbs, J.E. Reynolds, P.C.C. Freire, F. Camilo
Comments: Appeared in Science Express, Sept. 14, 2006. Includes supporting material

The double pulsar system, PSR J0737-3039A/B, is unique in that both neutron stars are detectable as radio pulsars. This, combined with significantly higher mean orbital velocities and accelerations when compared to other binary pulsars, suggested that the system would become the best available testbed for general relativity and alternative theories of gravity in the strong-field regime. Here we report on precision timing observations taken over the 2.5 years since its discovery and present four independent strong-field tests of general relativity. Use of the theory-independent mass ratio of the two stars makes these tests uniquely different from earlier studies. By measuring relativistic corrections to the Keplerian description of the orbital motion, we find that the ``post-Keplerian'' parameter s agrees with the value predicted by Einstein's theory of general relativity within an uncertainty of 0.05%, the most precise test yet obtained. We also show that the transverse velocity of the system's center of mass is extremely small. Combined with the system's location near the Sun, this result suggests that future tests of gravitational theories with the double pulsar will supersede the best current Solar-system tests. It also implies that the second-born pulsar may have formed differently to the usually assumed core-collapse of a helium star.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0411750 [abs, ps, pdf, other] :
Title: Crust-core coupling in rotating neutron stars
Authors: K. Glampedakis, N. Andersson
Comments: 19 pages, 5 figures, RevTex, a significantly shorter version of the original paper to match the published version
Journal-ref: Phys. Rev. D 74, 044040 (2006)
Note: replaced with revised version Thu, 14 Sep 2006 16:43:39 GMT (106kb)
 
astro-ph/0512646 [abs, ps, pdf, other] :
Title: Short-living supermassive magnetar model for the early X-ray flares following short GRBs
Authors: W. H. Gao, Y. Z. Fan
Comments: The final version. Possible mechanisms giving rise to multiple flares in the magnetar wind model have been discussed
Journal-ref: Chin. J. Astron. Astrophys. 6 (2006) 513-516
Note: replaced with revised version Thu, 14 Sep 2006 08:48:01 GMT (24kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 18 Sep 06 00:00:09 GMT
0609418 -- 0609448 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609423 [abs, ps, pdf, other] :
Title: INTEGRAL observations of TeV plerions
Authors: A. I. D. Hoffmann, D. Horns, A. Santangelo
Comments: 4 pages, 6 figures, proceedings of conference "The Multi-Messenger Approach to High-Energy Gamma-ray Sources" Barcelona/Spain (2006)

Amongst the sources seen in very high gamma-rays several are associated with Pulsar Wind Nebulae (``TeV plerions''). The study of hard X-ray/soft gamma-ray emission is providing an important insight into the energetic particle population present in these objects. The unpulsed emission from pulsar/pulsar wind nebula systems in the energy range accessible to the INTEGRAL satellite is mainly synchrotron emission from energetic and fast cooling electrons close to their acceleration site. Our analyses of public INTEGRAL data of known TeV plerions detected by ground based Cherenkov telescopes indicate a deeper link between these TeV plerions and INTEGRAL detected pulsar wind nebulae. The newly discovered TeV plerion in the northern wing of the Kookaburra region (G313.3+0.6 powered by the middle aged PSR J1420-6048) is found to have a previously unknown INTEGRAL counterpart which is besides the Vela pulsar the only middle aged pulsar detected with INTEGRAL. We do not find an INTEGRAL counterpart of the TeV plerion associated with the X-ray PWN ``Rabbit'' G313.3+0.1 which is possibly powered by a young pulsar.

 
astro-ph/0609424 [abs, ps, pdf, other] :
Title: The Orbit of the Eclipsing X-ray Pulsar EXO 1722-363
Authors: Thomas W. J. Thompson (1), John A. Tomsick (1), J. J. M. in 't Zand (2), Richard E. Rothschild (1), Roland Walter (3) ((1) CASS/UCSD, (2) SRON, (3) Integral SDC)
Comments: Submitted to ApJ, 11 pages, 11 figures

With recent and archival Rossi X-Ray Timing Explorer (RXTE) X-ray measurements of the heavily obscured X-ray pulsar EXO 1722-363 (IGR J17252-3616), we carried out a pulse timing analysis to determine the orbital solution for the first time. The binary system is characterized by a_x sin(i) = 101 +/- 3 lt-s and P_orb = 9.7403 +/- 0.0004 days (90% confidence), with the precision of the orbital period being obtained by connecting datasets separated by more than 7 years (272 orbital cycles). The orbit is consistent with circular, and e < 0.19 at the 90% confidence level. The mass function is 11.7 +/- 1.2 M_sun and confirms that this source is a High Mass X-ray Binary (HMXB) system. The orbital period, along with the previously known ~414 s pulse period, places this system in the part of the Corbet diagram populated by supergiant wind accretors. Using previous eclipse time measurements by Corbet et al. and our orbital solution, combined with the assumption that the primary underfills its Roche lobe, we find i > 61 degrees at the 99% confidence level, the radius of the primary is between 21 R_sun and 37 R_sun, and its mass is less than about 22 M_sun. The acceptable range of radius and mass shows that the primary is probably a supergiant of spectral type B0I-B5I. Photometric measurements of its likely counterpart are consistent with the spectral type and luminosity if the distance to the system is between 5.3 kpc and 8.7 kpc. Spectral analysis of the pulsar as a function of orbital phase reveals an evolution of the hydrogen column density suggestive of dense filaments of gas in the downstream wake of the pulsar, with higher levels of absorption seen at orbital phases 0.5-1.0, as well as a variable Fe K_alpha line.

 
astro-ph/0609425 [abs, ps, pdf, other] :
Title: Dark matter sterile neutrinos in stellar collapse: alteration of energy/lepton number transport and a mechanism for supernova explosion enhancement
Authors: Jun Hidaka, George M. Fuller
Comments: 13 pages, 9 figures

We investigate matter-enhanced Mikheyev-Smirnov-Wolfenstein (MSW) active-sterile neutrino conversion in the $\nu_e \rightleftharpoons \nu_s$ channel in the collapse of the iron core of a pre-supernova star. For values of sterile neutrino rest mass $m_s$ and vacuum mixing angle $\theta$ (specifically, $0.5 {\rm keV}< m_s<10 {\rm keV}$ and $\sin^22\theta> 5\times{10}^{-12}$) which include those required for viable sterile neutrino dark matter, our one-zone in-fall phase collapse calculations show a significant reduction in core lepton fraction. This would result in a smaller homologous core and therefore a smaller initial shock energy, disfavoring successful shock re-heating and the prospects for an explosion. However, these calculations also suggest that the MSW resonance energy can exhibit a minimum located between the center and surface of the core. In turn, this suggests a post-core-bounce mechanism to enhance neutrino transport and neutrino luminosities at the core surface and thereby augment shock re-heating: (1) scattering-induced or coherent MSW $\nu_e\to\nu_s$ conversion occurs deep in the core, at the first MSW resonance, where $\nu_e$ energies are large ($\sim 150$ MeV); (2) the high energy $\nu_s$ stream outward at near light speed; (3) they deposit their energy when they encounter the second MSW resonance $\nu_s\to\nu_e$ just below the proto-neutron star surface.

 
astro-ph/0609438 [abs, ps, pdf, other] :
Title: Mountains on Neutron Stars: Accreted vs. Non-Accreted crusts
Authors: B. Haskell, D.I. Jones, N. Andersson
Comments: Accepted by MNRAS

The aim of this paper is to compare the two cases of an isolated neutron star, with a non-accreted crust, and that of an accreting neutron star, with an accreted crust, and try to estimate which one of the two would make a better source of gravitational waves. In order to do this we must evaluate the maximum ``mountain'' that the crust can sustain in these two cases. We first do this using the formalism of Ushomirsky, Cutler and Bildsten (2000) and find that the maximum quadrupole is very similar in the two cases, with the non-accreted crust sustaining a slightly larger mountain. We then develop a perturbation formalism for the problem, that allows us to drop the Cowling approximation and have more control over the boundaries. The use of this formalism confirms that there is not much difference between the two cases, but leads to results approximately one order of magnitude larger than those we obtain with the formalism of Ushomirsky, Cutler and Bildsten (2000).

 
astro-ph/0609448 [abs, ps, pdf, other] :
Title: Discovery of Five Recycled Pulsars in a High Galactic Latitude Survey
Authors: B. A. Jacoby, M. Bailes, S. M. Ord, H. S. Knight, A. W. Hotan
Comments: 15 pages, 3 figures, accepted for publication in ApJ

We present five recycled pulsars discovered during a 21-cm survey of approximately 4,150 deg^2 between 15 deg and 30 deg from the galactic plane using the Parkes radio telescope. One new pulsar, PSR J1528-3146, has a 61 ms spin period and a massive white dwarf companion. Like many recycled pulsars with heavy companions, the orbital eccentricity is relatively high (~0.0002), consistent with evolutionary models that predict less time for circularization. The four remaining pulsars have short spin periods (3 ms < P < 6 ms); three of these have probable white dwarf binary companions and one (PSR J2010-1323) is isolated. PSR J1600-3053 is relatively bright for its dispersion measure of 52.3 pc cm^-3 and promises good timing precision thanks to an intrinsically narrow feature in its pulse profile, resolvable through coherent dedispersion. In this survey, the recycled pulsar discovery rate was one per four days of telescope time or one per 600 deg^2 of sky. The variability of these sources implies that there are more millisecond pulsars that might be found by repeating this survey.

 

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astro-ph/0607420 [abs, ps, pdf, other] :
Title: The energy dependence of burst oscillations from the accreting millisecond pulsar XTE J1814-338
Authors: Anna L. Watts (MPA), Tod E. Strohmayer (NASA GSFC)
Comments: Some amendments to the discussion section, accepted for publication in MNRAS
Note: replaced with revised version Thu, 14 Sep 2006 20:23:43 GMT (70kb)
 
astro-ph/0609416 [abs, ps, pdf, other] :
Title: The Formation of the Double Pulsar PSR J0737-3039A/B
Authors: I. H. Stairs, S. E. Thorsett, R. J. Dewey, M. Kramer, C. A. McPhee
Comments: To appear in MNRAS Letters. Title typo fix only; no change to paper
Note: replaced with revised version Fri, 15 Sep 2006 19:21:54 GMT (20kb)
 

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astro-ph new abstracts, Tue, 19 Sep 06 00:00:10 GMT
0609449 -- 0609503 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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2 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0609044 [abs, ps, pdf, other] :
Title: Accurate and realistic initial data for black hole-neutron star binaries
Authors: Philippe Grandclement (LUTH)
Comments: 5 pages, 6 figures

This paper is devoted to the computation of compact binaries composed of one black hole and one neutron star. The objects are assumed to be on exact circular orbits. Standard 3+1 decomposition of Einstein equations is performed and the conformal flatness approximation is used. The obtained system of elliptic equations is solved by means of multi-domain spectral methods. Results are compared with previous work both in the high mass ratio limit and for one neutron star with very low compactness parameter. The accuracy of the present code is shown to be greater than with previous codes. Moreover, for the first time, some sequences containing one neutron star of realistic compactness are presented and discussed.

 
gr-qc/0609053 [abs, ps, pdf, other] :
Title: Quasiequilibrium sequences of black-hole--neutron-star binaries in general relativity
Authors: Keisuke Taniguchi, Thomas W. Baumgarte, Joshua A. Faber, Stuart L. Shapiro
Comments: 5 pages, 1 figure, revtex4, published in Phys.Rev.D
Journal-ref: Phys.Rev. D74 (2006) 041502

We construct quasiequilibrium sequences of black hole-neutron star binaries for arbitrary mass ratios by solving the constraint equations of general relativity in the conformal thin-sandwich decomposition. We model the neutron star as a stationary polytrope satisfying the relativistic equations of hydrodynamics, and account for the black hole by imposing equilibrium boundary conditions on the surface of an excised sphere (the apparent horizon). In this paper we focus on irrotational configurations, meaning that both the neutron star and the black hole are approximately nonspinning in an inertial frame. We present results for a binary with polytropic index n=1, mass ratio M_{irr}^{BH}/M_{B}^{NS}=5 and neutron star compaction M_{ADM,0}^{NS}/R_0=0.0879, where M_{irr}^{BH} is the irreducible mass of the black hole, M_{B}^{NS} the neutron star baryon rest-mass, and M_{ADM,0}^{NS} and R_0 the neutron star Arnowitt-Deser-Misner mass and areal radius in isolation, respectively. Our models represent valid solutions to Einstein's constraint equations and may therefore be employed as initial data for dynamical simulations of black hole-neutron star binaries.

 

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astro-ph new abstracts, Wed, 20 Sep 06 00:00:09 GMT
0609504 -- 0609544 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609509 [abs, pdf] :
Title: The Sun is a plasma diffuser that sorts atoms by mass
Authors: O. Manuel, S. A. Kamat, M. Mozina
Comments: 20 pages, 92 references, 8 figures show that the Sun is an iron rich magnetic plasma diffuser that selectively moves lightweight elements and isotopes of each element to its surface. Solar luminosity, neutrinos, mass fractionation, and the outpouring of H ions in the solar wind arise from neutron emission and decay at the solar core

The Sun is a magnetic plasma diffuser that selectively moves light elements like H and He and the lighter isotopes of each element to its surface. The Sun formed on the collapsed core of a supernova. It consists mostly of iron, oxygen, nickel, silicon and sulfur made near the SN core, like the rocky planets and ordinary meteorites. H ions, generated by emission and decay of neutrons at the core, are accelerated upward by deep magnetic fields, thus acting as a carrier gas that maintains mass separation in the Sun. Neutron emission from the central neutron star triggers a series of reactions that generate solar luminosity, solar neutrinos, solar mass-fractionation, and an outpouring of the neutron decay product, H, in the solar wind. Mass fractionation appears to have operated in the parent star as well, and likely occurs in other stars.

 
astro-ph/0609524 [abs, ps, pdf, other] :
Title: Astronomy meets QCD: cooling constraints for the theories of internal structure of compact objects
Authors: S.B. Popov (1), D. Blaschke (2), H. Grigorian (3), B. Posselt (4) (1-Sternberg Astronomical Institute; 2- Univ. Rostock and Bogoliubov Laboratory for Theoretical Physics, JINR; 3- Yerevan Univ. and Univ. Rostock; 4- MPE Garching)
Comments: 12 pages with 7 figures included, Proc. of QUARKS-2006

We discuss a set of tests which confront observations of cooling compact objects and theories of their thermal evolution. As an example we apply the recently developed $\mathrm{Log N}$-$\mathrm{Log S}$ test of compact star cooling theories to hybrid stars with a color superconducting quark matter core, we also apply and discuss other existing tests. While there is not yet a microscopically founded superconducting quark matter phase which would fulfill constraints from cooling phenomenology, we explore the hypothetical 2SC+X phase and show that the magnitude and density-dependence of the X-gap can be chosen to satisfy a set of tests: the temperature -- age ($\mathrm{T}$-$\mathrm{t}$) test, the $\mathrm{Log N}$-$\mathrm{Log S}$ test, the brightness constraint, and the mass spectrum constraint. Some recent modifications of the population synthesis model used to obtain the $\mathrm{Log N}$-$\mathrm{Log S}$ distribution are briefly discussed. In addition, we propose to use the age-distance diagram as a new tool to study the local population of young isolated neutron stars.

 

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astro-ph new abstracts, Thu, 21 Sep 06 00:00:12 GMT
0609545 -- 0609586 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609561 [abs, ps, pdf, other] :
Title: Production of high-energy \mu neutrinos from young neutron stars
Authors: G. F. Burgio (INFN Sezione di Catania, Italy), B. Link (Montana State University, Bozeman, USA)
Comments: 6 pages, 2 figures, to be published in the proceedings of the CRIS 2006 conference, Catania, Italy, May 29 - June 2, 2006

Young, rapidly rotating neutron stars could accelerate protons to energies of $\sim 1$ PeV close to the stellar surface, which scatter with x-rays from the stellar surface through the $\Delta$ resonance and produce pions. The pions subsequently decay to produce muon neutrinos. We find that the energy spectrum of muon neutrinos consists of a sharp rise at $\sim 50$ TeV, corresponding to the onset of the resonance, above which the flux drops as $\epsilon_\nu^{-2}$ up to an upper-energy cut-off that is determined by either kinematics or by the maximum energy to which protons are accelerated. We predict event rates as high as 10-50 km$^{-2}$ yr$^{-1}$ from relatively young, close neutron stars. Such fluxes would be detectable by IceCube.

 
astro-ph/0609580 [abs, ps, pdf, other] :
Title: A search for evidence of irradiation in Centaurus X-4 during quiescence
Authors: P. D'Avanzo, T. Munoz-Darias, J. Casares, I. G. Martinez-Pais, S. Campana
Comments: 4 pages, 5 figures, accepted for publication in A&A as a RN

We present a study of the neutron star X-Ray Transient Cen X-4. Our aim is to look for any evidence of irradiation of the companion with a detailed analysis of its radial velocity curve, relative contribution of the donor star and Doppler tomography of the main emission lines. To improve our study all our data are compared with a set of simulations that consider different physical parameters of the system, like the disc aperture angle and the mass ratio. We conclude that neither the radial velocity curve nor the orbital variation of the relative donor's contribution to the total flux are affected by irradiation. On the other hand, we do see emission from the donor star at H${\alpha}$ and HeI 5876 which we tentatively attribute to irradiation effects. In particular, the H${\alpha}$ emission from the companion is clearly asymmetric and we suggest is produced by irradiation from the hot-spot. Finally, from the velocity of the HeI 5876 spot we constrain the disc opening angle to alpha=7-14 deg.

 
astro-ph/0609583 [abs, ps, pdf, other] :
Title: Sedimentation and Type I X-ray Bursts at Low Accretion Rates
Authors: Fang Peng, Edward F. Brown, James W. Truran
Comments: 15 pages, 14 figures, submitted to ApJ, revised version

Neutron stars, with their strong surface gravity, have interestingly short timescales for the sedimentation of heavy elements. Motivated by observations of Type I X-ray bursts from sources with extremely low persistent accretion luminosities, $L_X < 10^{36}\usp\ergspersecond (\simeq 0.01\ensuremath{L_{\mathrm{Edd}}}$), we study how sedimentation affects the distribution of isotopes and the ignition of H and He in the envelope of an accreting neutron star. For local mass accretion rates $\mdot \lesssim 10^{-2}\medd$ (for which the ignition of H is unstable), where $\medd = 8.8\times 10^{4}\nsp\gpscps$, the helium and CNO elements sediment out of the accreted fuel before reaching a temperature where H would ignite. Using one-zone calculations of the thermonuclear burning, we find a range of accretion rates for which the unstable H ignition does not trigger unstable He burning. This range depends on the emergent flux from reactions in the deep neutron star crust; for $F = 0.1\nsp\MeV(\dot{m}/\mb)$, the range is $3\times 10^{-3}\medd\lesssim\mdot\lesssim 10^{-2}\medd$. We speculate that sources accreting in this range will build up a massive He layer that later produces an energetic and long X-ray burst. At mass accretion rates lower than this range, we find that the H flash leads to a strong mixed H/He flash. Surprisingly, even at accretion rates $\mdot \gtrsim 0.1\medd$, although the H and He do not completely segregate, the H abundance at the base of the accumulated layer is still reduced. While following the evolution of the X-ray burst is beyond the scope of this introductory paper, we note that the reduced proton-to-seed ratio favors the production of \iso{12}{C}--an important ingredient for subsequent superbursts.

 
astro-ph/0609586 [abs, ps, pdf, other] :
Title: Status of Identification of VHE gamma-ray sources
Authors: Stefan Funk (for the H.E.S.S. Collaboration)
Comments: To appear in Astrophysics and Space Science (Proceedings of "The multimessenger approach to unidentified gamma-ray sources"

With the recent advances made by Cherenkov telescopes such as H.E.S.S., the field of very high-energy (VHE) gamma-ray astronomy has recently entered a new era in which for the first time populations of Galactic sources such as e.g. Pulsar wind nebulae (PWNe) or Supernova remnants (SNRs) can be studied. However, while some of the new sources can be associated by positional coincidence as well as by consistent multi-wavelength data to a known counterpart at other wavelengths, most of the sources remain not finally identified. In the following, the population of Galactic H.E.S.S. sources will be used to demonstrate the status of the identifications, to classify them into categories according to this status and to point out outstanding problems.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0609052 [abs, ps, pdf, other] :
Title: Nuclear symmetry energy effects on neutron stars properties
Authors: V.P. Psonis, Ch.C. Moustakidis, S.E. Massen
Comments: 15 pages, 23 figures

We construct a class of nuclear equations of state based on a schematic potential model, that originates from the work of Prakash et. al. \cite{Prakash-88}, which reproduce the results of most microscopic calculations. The equations of state are used as input for solving the Tolman-Oppenheimer-Volkov equations for corresponding neutron stars. The potential part contribution of the symmetry energy to the total energy is parameterized in a generalized form both for low and high values of the baryon density. Special attention is devoted to the construction of the symmetry energy in order to reproduce the results of most microscopic calculations of dense nuclear matter. The obtained nuclear equations of state are applied for the systematic study of the global properties of a neutron star (masses, radii and composition). The calculated masses and radii of the neutron stars are plotted as a function of the potential part parameters of the symmetry energy. A linear relation between these parameters, the radius and the maximum mass of the neutron star is obtained. In addition, a linear relation between the radius and the derivative of the symmetry energy near the saturation density is found. We also address on the problem of the existence of correlation between the pressure near the saturation density and the radius.

 

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Astrophysics


astro-ph new abstracts, Fri, 22 Sep 06 00:00:10 GMT
0609587 -- 0609617 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609595 [abs, ps, pdf, other] :
Title: The Giant Flare from SGR 1806-20 and its Radio Afterglow
Authors: G.B. Taylor (1 and 2), J. Granot (3) ((1) University of New Mexico, (2) National Radio Astronomy Observatory, (3) Kavli Institute of Particle Astrophysics and Cosmology)
Comments: 25 pages, 7 figures, accepted for publication in Modern Physics Letters A

The multi-wavelength observations of the 2004 December~27 Giant Flare (GF) from SGR 1806-20 and its long-lived radio afterglow are briefly reviewed. The GF appears to have been produced by a dramatic reconfiguration of the magnetic field near the surface of the neutron star, possibly accompanied by fractures in the crust. The explosive release of over 10^46 ergs (isotropic equivalent) powered a one-sided mildly relativistic outflow. The outflow produced a new expanding radio nebula, that is still visible over a year after the GF. Also considered are the constraints on the total energy in the GF, the energy and mass in the outflow, and on the external density, as well as possible implications for short gamma-ray bursts and potential signatures in high energy neutrinos, photons, or cosmic rays. Some possible future observations of this and other GFs are briefly discussed.

 
astro-ph/0609596 [abs, ps, pdf, other] :
Title: Torsional Magnetic Oscillations in Type I X-Ray Bursts
Authors: Richard V.E. Lovelace, Akshay K. Kulkarni, Marina M. Romanova
Comments: 7 pages, 6 figures, accepted for publication in the ApJ

Thermonuclear burning on the surface of a neutron star causes the expansion of a thin outer layer of the star, $\Delta R(t)$. The layer rotates slower than the star due to angular momentum conservation. The shear between the star and the layer acts to twist the star's dipole magnetic field giving at first a trailing spiral field. The twist of the field acts in turn to `torque up' the layer increasing its specific angular momentum. As the layer cools and contracts, its excess specific angular momentum causes it to {\it rotate faster} than the star which gives a leading spiral magnetic field. The process repeats, giving rise to torsional oscillations. We derive equations for the angular velocity and magnetic field of the layer taking into account the diffusivity and viscosity which are probably due to turbulence. The magnetic field causes a nonuniformity of the star's photosphere (at the top of the heated layer), and this gives rise to the observed X-ray oscillations. The fact that the layer periodically rotates faster than the star means that the X-ray oscillation frequency may ``overshoot'' the star's rotation frequency. Comparison of the theory is made with observations of Chakrabarty et al. (2003) of an X-ray burst of SAX J1808.4-3658.

 

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astro-ph new abstracts, Mon, 25 Sep 06 00:00:11 GMT
0609618 -- 0609632 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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Astrophysics


astro-ph new abstracts, Tue, 26 Sep 06 00:00:15 GMT
0609633 -- 0609688 received


7 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609634 [abs, ps, pdf, other] :
Title: General Relativistic Simulations of Slowly and Differentially Rotating Magnetized Neutron Stars
Authors: Zachariah B. Etienne, Yuk Tung Liu, Stuart L. Shapiro (UIUC)
Comments: 21 pages, 11 figures, published in Phys.Rev.D
Journal-ref: Phys.Rev. D74 (2006) 044030

We present long-term (~10^4 M) axisymmetric simulations of differentially rotating, magnetized neutron stars in the slow-rotation, weak magnetic field limit using a perturbative metric evolution technique. Although this approach yields results comparable to those obtained via nonperturbative (BSSN) evolution techniques, simulations performed with the perturbative metric solver require about 1/4 the computational resources at a given resolution. This computational efficiency enables us to observe and analyze the effects of magnetic braking and the magnetorotational instability (MRI) at very high resolution. Our simulations demonstrate that (1) MRI is not observed unless the fastest-growing mode wavelength is resolved by more than about 10 gridpoints; (2) as resolution is improved, the MRI growth rate converges, but due to the small-scale turbulent nature of MRI, the maximum growth amplitude increases, but does not exhibit convergence, even at the highest resolution; and (3) independent of resolution, magnetic braking drives the star toward uniform rotation as energy is sapped from differential rotation by winding magnetic fields.

 
astro-ph/0609641 [abs, ps, pdf, other] :
Title: Thermal evolution of rotating hybrid stars
Authors: kang Miao, Zheng Xiaoping
Comments: 12 pages, 7 figures

As a neutron star spins down, the nuclear matter continuously is converted into quark matter due to the core density increase and then latent heat is released. We have investigated the thermal evolution of neutron stars undergoing such deconfinement phase transition. We have taken into account the conversion in the frame of the general theory of relativity. The released energy has been estimated as a function of change rate of deconfinement baryon number. Numerical solutions to cooling equation are obtained to be very different from the without heating effect. The results show that neutron stars may be heated to higher temperature which is well-matched with pulsar's data despite onset of fast cooling in neutron stars with quark matter core. It is also found that heating effect has magnetic field strength dependence. This feature could be particularly interesting for high temperature of low-field millisecond pulsar at late stage. The inferred temperature from observation for PSR J0437-4715 is just an illustration in quality.

 
astro-ph/0609644 [abs, ps, pdf, other] :
Title: Observational constraints on quarks in neutron stars
Authors: Pan Nana, Zheng Xiaoping
Comments: 16 pages,6 figures

We estimate the constraints of observational mass and redshift on the properties of equations of state for quarks in the compact stars. We discuss two scenarios: strange stars and hybrid stars. We construct the equations of state utilizing MIT bag model taking medium effect into account for quark matter and relativistic mean field theory for hadron matter. We find that quark may exist in strange stars and the interior of neutron stars, and only these quark matters with stiff equations of state could be consistent with both constraints. The bag constant is main one parameter that affects the mass strongly for strange stars and only the intermediate coupling constant may be the best choice for compatibility with observational constraints in hybrid stars.

 
astro-ph/0609651 [abs, ps, pdf, other] :
Title: Efficient approximations of neutrino physics for three-dimensional simulations of stellar core collapse
Authors: M. Liebendoerfer, U.-L. Pen, C. Thompson
Comments: 5 pages, 4 figures, in Proceedings of "Nuclei in the Cosmos IX, Geneva, Jun 25-30", associated movies are displayed at this http URL
Journal-ref: PoS(NIC-IX)132, 2006

Neutrino transport in spherically symmetric models of stellar core collapse and bounce has achieved a technically complete level, rewarded by the agreement among independent groups that a multi-dimensional treatment of the fluid-instabilities in the post-bounce phase is indispensable to model supernova explosions. While much effort is required to develop a reliable neutrino transport technique in axisymmetry, we explore neutrino physics approximations and parameterizations for an efficient three-dimensional simulation of the fluid-instabilities in the shock-heated matter that accumulates between the accretion shock and the protoneutron star. We demonstrate the reliability of a simple parameterization scheme in the collapse phase and extend our 3D magneto-hydrodynamical collapse simulations to a preliminary postbounce evolution. The growth of magnetic fields is investigated.

 
astro-ph/0609656 [abs, ps, pdf, other] :
Title: UV emission from young and middle-aged pulsars: Connecting X-rays with the optical
Authors: O. Kargaltsev, G. G. Pavlov
Comments: To appear in Astrophysics and Space Science, Proceedings of "Isolated Neutron Stars: from the Interior to the Surface", eds. D. Page, R. Turolla and S. Zane; 10 pages, 4 figures, 3 tables

We present the UV spectroscopy and timing of three nearby pulsars (Vela, B0656+14 and Geminga) recently observed with the Space Telescope Imaging Spectrograph. We also review the optical and X-ray properties of these pulsars and establish their connection with the UV properties. We show that the multiwavelengths properties of neutron stars (NSs) vary significantly within the sample of middle-aged pulsars. Even larger differences are found between the thermal components of Ge-minga and B0656+14 as compared to those of radio-quiet isolated NSs. These differences could be attributed to different properties of the NS surface layers.

 
astro-ph/0609663 [abs, ps, pdf, other] :
Title: High-energy particles in the wind nebula of pulsar B1509-58 as seen by INTEGRAL
Authors: M. Forot, W. Hermsen, M. Renaud, P. Laurent, I. Grenier, P. Goret, B. Khelifi, L. Kuiper
Comments: 4 pages, 6 figures, accepted for publication in Apj

We present observations with the INTEGRAL/IBIS telescope of the wind nebula powered by the young pulsar B1509-58 and we discuss the spatial and spectral properties of the unpulsed emission in the 20-200 keV energy band. The source extension and orientation along the northwest-southeast axis corresponds to the jet emission seen at keV and TeV energies. The hard X-ray spectrum is consistent with the earlier Beppo-SAX measurements. It follows a power law with a photon index alpha = -2.12 pm 0.05 up to 160 keV. A possible break at this energy is found at the 2.9 sigma confidence level. The 0.1-100 keV data are consistent with synchrotron aging of pairs in the jet and yield a magnetic field strength of 22-33 muG for a bulk velocity of 0.3-0.5c. The synchrotron cut-off energy thus corresponds to a maximum electron energy of 400-730 TeV.

 
astro-ph/0609685 [abs, ps, pdf, other] :
Title: An accreting millisecond pulsar with black hole-like X-ray variability: IGR J00291+5934
Authors: Manuel Linares, Michiel van der Klis, Rudy Wijnands (Amsterdam)
Comments: Submitted to ApJ. 15 pages, 8 figures, uses '\emulateapj'

IGR J00291+5934 is one of the seven accreting millisecond pulsars (AMPs) discovered so far. We report on the aperiodic timing and color analysis of its X-ray flux, using all the RXTE observations of the 2004 outburst. Flat-top noise and two harmonically related quasi-periodic oscillations, all of them at very low frequencies (0.01-0.1 Hz), were present in the power spectra during most of the outburst as well as a very high fractional variability (~50%). These properties are atypical not only for AMPs but also for neutron star low-mass X-ray binaries (LMXBs) in general. There are instead some remarkable similarities with the variability observed in black hole systems, reinforcing the connections between these two types of LMXB, as well as some interesting differences. We note finally that the results of this paper are difficult to reconcile with interpretations where any break frequency of power density spectra scales inversely with the mass of the central object at an accuracy sufficient to distinguish between the masses of neutron stars and black holes in LMXBs.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607168 [abs, ps, pdf, other] :
Title: Atmosphere Models of Magnetized Neutron Stars: QED Effects, Radiation Spectra, and Polarization Signals
Authors: Matthew van Adelsberg, Dong Lai (Cornell University)
Comments: 31 pages, 23 figures, 1 table; MNRAS accepted; Minor corrections
Note: replaced with revised version Fri, 22 Sep 2006 22:37:43 GMT (154kb)
 
astro-ph/0608319 [abs, ps, pdf, other] :
Title: Incompatibility of long-period neutron star precession with creeping neutron vortices
Authors: Bennett Link
Comments: 4 pages, v2. Typo corrected and references updated
Note: replaced with revised version Mon, 25 Sep 2006 17:57:50 GMT (30kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 27 Sep 06 00:00:09 GMT
0609689 -- 0609722 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609693 [abs, ps, pdf, other] :
Title: Intermittent pulsations in an accretion-powered millisecond pulsar
Authors: Duncan K. Galloway (1), Edward H. Morgan (2), Miriam I. Krauss (2,3), Philip Kaaret (4), Deepto Chakrabarty (2,3) ((1) University of Melbourne, (2) MIT Kavli Institute, (3) Department of Physics, MIT, (4) University of Iowa)
Comments: 4 pages, 3 figures, submitted to ApJL

We describe observations of the seventh accretion-powered millisecond pulsar, HETE J1900.1-2455 made with the Rossi X-ray Timing Explorer during the year of activity that followed its discovery in 2005 June. We detected intermittent pulsations at a peak fractional amplitude of 3%, but only in the first two months of the outburst. On three occasions during this time we observed an abrupt increase in the pulse amplitude, approximately coincident with the time of a thermonuclear burst, followed by a steady decrease on a timescale of approx. 10 d. HETE J1900.1-2455 has shown the longest active period by far for any transient accretion-powered millisecond pulsar, comparable instead to the outburst cycles for other transient X-ray binaries. Since the last detection of pulsations, HETE J1900.1-2455 has been indistinguishable from a low-accretion rate, non-pulsing LMXB; we hypothesize that other, presently active LMXBs may have also been detectable initially as millisecond X-ray pulsars.

 
astro-ph/0609705 [abs, ps, pdf, other] :
Title: The complex X-ray spectrum of the isolated neutron star RBS1223
Authors: Axel D. Schwope, Valeri Hambaryan, Frank Haberl, Christian Motch
Comments: 4 pages, 1 figure, to appear in Astrophysics and Space Science, in the proceedings of "Isolated Neutron Stars: from the Interior to the Surface", edited by D. Page, R. Turolla and S. Zane

We present a first analysis of a deep X-ray spectrum of the isolated neutron star RBS1223 obtained with XMM-Newton. Spectral data from four new monitoring observations in 2005/2006 were combined with archival observations obtained in 2003 and 2004 to form a spin-phase averaged spectrum containing 290000 EPIC-pn photons. This spectrum shows higher complexity than its predecessors, and can be parameterised with two Gaussian absorption lines superimposed on a blackbody. The line centers, E_2 ~ 2E_1, could be regarded as supporting the cyclotron interpretation of the absorption features in a field B ~ 4 x 10**13 G. The flux ratio of those lines does not support this interpretation. Hence, either feature might be of truly atomic origin.

 
astro-ph/0609712 [abs, ps, pdf, other] :
Title: Gravitational Faraday Rotation in Binary Pulsar Systems
Authors: Matteo Luca Ruggiero, Angelo Tartaglia
Comments: 6 pages, 3 figures

We study the gravitational Faraday rotation, on linearly polarized light rays emitted by a pulsar, orbiting another compact object. We relate the rotation angle to the orbital phase of the emitting pulsar, as well as to other parameters describing its orbit and the orientation of the angular momentum of the binary companion. We give numerical estimates of the effect for the double-pulsar system PSR J0737-3039, and we note that the expected magnitude is exceedingly small, making the effect unlikely to be observed with present technology. It is however interesting per se, since in this phenomenon, gravito-magnetism plays a leading role, unlike what happens, for instance, when studying light bending or gravitational time delay, where it appears as a correction to the gravito-electric contribution. Also, we envisage the possibility that this effect could be relevant, at least in principle, for a pulsar orbiting a non charged black-hole.

 
astro-ph/0609717 [abs, ps, pdf, other] :
Title: De-leptonization and Non-Axisymmetric Instabilities in Core Collapse Supernovae
Authors: J. Craig Wheeler, Shizuka Akiyama
Comments: 15 pages, 1 figure, accepted for publication in the Astrophysical Journal

The timescale of de-leptonization by neutrino loss and associated contraction of a proto-neutron star is short compared to the time to progagate a shock through the helium core of a massive star, and so the de-leptonization phase does not occur in the vacuum of space, but within the supernova ambiance whether or not there has been a successful explosion. Dynamical non-axisymmetric instabilities (NAXI) are predicted for sufficiently strongly differentially rotating proto-neutron stars. Some modes are unstable for small values of the ratio of rotational kinetic energy to binding energy, T/|W| > 0.01. The NAXI are likely to drive magnetoacoustic waves into the surrounding time-dependent density structure. These waves represent a mechanism of the dissipation of the free energy of differential rotation of the proto-neutron star, and the outward deposition of this energy may play a role in the supernova explosion process. We estimate the power produced by this process and the associated timescale and discuss the possible systematics of the de-leptonization phase in this context. A likely possibility is that the proto-neutron star will spin down through these effects before de-leptonization and produce substantial but not excessive energy input.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608319 [abs, ps, pdf, other] :
Title: Incompatibility of long-period neutron star precession with creeping neutron vortices
Authors: Bennett Link
Comments: 4 pages, v3. Missing reference added
Note: replaced with revised version Tue, 26 Sep 2006 13:08:35 GMT (30kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 28 Sep 06 00:00:12 GMT
0609723 -- 0609761 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609732 [abs, ps, pdf, other] :
Title: Simulation of the Magnetothermal Instability
Authors: Ian J. Parrish, James M. Stone
Comments: Accepted for publication in Astrophysics and Space Science as proceedings of the 6th High Energy Density Laboratory Astrophysics (HEDLA) Conference

In many magnetized, dilute astrophysical plasmas, thermal conduction occurs almost exclusively parallel to magnetic field lines. In this case, the usual stability criterion for convective stability, the Schwarzschild criterion, which depends on entropy gradients, is modified. In the magnetized long mean free path regime, instability occurs for small wavenumbers when (dP/dz)(dln T/dz) > 0, which we refer to as the Balbus criterion. We refer to the convective-type instability that results as the magnetothermal instability (MTI). We use the equations of MHD with anisotropic electron heat conduction to numerically simulate the linear growth and nonlinear saturation of the MTI in plane-parallel atmospheres that are unstable according to the Balbus criterion. The linear growth rates measured from the simulations are in excellent agreement with the weak field dispersion relation. The addition of isotropic conduction, e.g. radiation, or strong magnetic fields can damp the growth of the MTI and affect the nonlinear regime. The instability saturates when the atmosphere becomes isothermal as the source of free energy is exhausted. By maintaining a fixed temperature difference between the top and bottom boundaries of the simulation domain, sustained convective turbulence can be driven. MTI-stable layers introduced by isotropic conduction are used to prevent the formation of unresolved, thermal boundary layers. We find that the largest component of the time-averaged heat flux is due to advective motions as opposed to the actual thermal conduction itself. Finally, we explore the implications of this instability for a variety of astrophysical systems, such as neutron stars, the hot intracluster medium of galaxy clusters, and the structure of radiatively inefficient accretion flows.

 
astro-ph/0609742 [abs, ps, pdf, other] :
Title: The hot subdwarf B + white dwarf binary KPD 1930+2752 - a Supernova Type Ia progenitor candidate
Authors: S. Geier, S. Nesslinger, U. Heber, N. Przybilla, R. Napiwotzki, R.-P. Kudritzki
Comments: 10 pager, 11 figures, Astronomy & Astrophysics accepted

The nature of the progenitors of type Ia supernovae is still under controversial debate. KPD 1930+2752 is one of the best SN Ia progenitor candidates known today. The object is a double degenerate system consisting of a subluminous B star (sdB) and a massive white dwarf (WD). Maxted et al. (2000) conclude that the system mass exceeds the Chandrasekhar mass. This conclusion, however, rests on the assumption that the sdB mass is 0.5 Mo. However, recent binary population synthesis calculations suggest that the mass of an sdB star may range from 0.3 Mo to more than 0.7 Mo. It is therefore important to measure the mass of the sdB star simultaneously with that of the white dwarf. Since the rotation of the sdB star is tidally locked to the orbit the inclination of the system can be constrained if the sdB radius and the projected rotational velocity can be measured with high precision. An analysis of the ellipsoidal variations in the light curve allows to tighten the constraints derived from spectroscopy. We derive the mass-radius relation for the sdB star from a quantitative spectral analysis of 150 low-resolution spectra. The projected rotational velocity is determined for the first time from 200 high-resolution spectra. In addition a reanalysis of the published light curve is performed. The atmospheric and orbital parameters are measured with unprecedented accuracy. In particular the projected rotational velocity is determined. A neutron star companion can be ruled out and the mass of the sdB is limited between 0.45 Mo and 0.52 Mo. The total mass of the system ranges from 1.36 Mo to 1.48 Mo and hence is likely to exceed the Chandrasekhar mass. So KPD 1930+2752 qualifies as an excellent double degenerate supernova Ia progenitor candidate.

 

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Astrophysics


astro-ph new abstracts, Fri, 29 Sep 06 00:00:11 GMT
0609762 -- 0609791 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609775 [abs, ps, pdf, other] :
Title: Probing Axions with Radiation from Magnetic Stars
Authors: Dong Lai (Cornell), Jeremy Heyl (UBC)
Comments: 11 pages, 11 figures. PRD submitted

Recent experiments suggest that polarized photons may couple significantly to pseudoscalar particles such as axions. We study the possible observational signatures of axion-photon coupling for radiation from magnetic stars, with particular focus on neutron stars. We present general methods for calculating the axion-photon conversion probability during propagation through a varying magnetized vacuum as well as across an inhomogeneous atmosphere. Partial axion-photon conversion may take place in the vacuum region outside the star. Strong axion-photon mixing occurs due to a resonance in the atmosphere, and depending on the axion coupling strength and other parameters, significant axion-photon conversion can take place at the resonance. Such conversions may produce observable effects on the radiation spectra and polarization signals from the star. We also apply our results to axion-photon propagation in the Sun and in magnetic white dwarfs.

 
astro-ph/0609776 [abs, ps, pdf, other] :
Title: Simultaneous INTEGRAL and RXTE observations of the accreting millisecond pulsar HETE J1900.1-2455
Authors: M. Falanga, J. Poutanen, E. W. Bonning, L. Kuiper, J. M. Bonnet-Bidaud, A. Goldwurm, W. Hermsen, L. Stella
Comments: 7 pages, 4 figures, submitted to A&A

Aims: Hete J1900.1-2455 is the seventh known X-ray transient accreting millisecond pulsar and has been in outburst for more than one year. We compared the data on Hete J1900.1-2455 with other similar objects and made an attempt at deriving constraints on the physical processes responsible for a spectral formation. Methods: The broad-band spectrum of the persistent emission in the 2-300 keV energy band and the timing properties were studied using simultaneous INTEGRAL and the publicly available RXTE data obtained in October 2005. The properties of the X-ray bursts observed from Hete J1900.1-2455 were also investigated. Results: The spectrum is well described by a two-component model consisting of a blackbody-like soft X-ray emission at 0.8 keV temperature and a thermal Comptonized spectrum with the electron temperature of 30 keV and Thomson optical depth tau_T ~ 2 for the slab geometry. The source is detected by INTEGRAL up to 200 keV at the luminosity of 5E36 erg/s (assuming a distance of 5 kpc) in the 0.1-200 keV energy band. We have also detected one type I X-ray burst which shows the photospheric radius expansion. The burst occurred at an inferred persistent emission level of ~ 3-4% of the Eddington luminosity. Using the data for all X-ray bursts observed to date from Hete J1900.1-2455, the burst recurrence time is estimated to be about 2 days. No pulsations have been detected either in the RXTE or in the INTEGRAL data which puts interesting constraints on theories of the magnetic field evolution in neutron star low-mass X-ray binaries.

 
astro-ph/0609788 [abs, ps, pdf, other] :
Title: s-Process Nucleosynthesis in Advanced Burning Phases of Massive Stars
Authors: Lih-Sin The, Mounib F. El Eid, Bradley S. Meyer
Comments: 52 pages, 16 figures, accepted for publication in ApJ

We present a detailed study of s-process nucleosynthesis in massive stars of solar-like initial composition and masses 15, 20,25, and 30 Msun. We update our previous results of s-process nucleosynthesis during the core He-burning of these stars and then focus on an analysis of the s-process under the physical conditions encountered during the shell-carbon burning. We show that the recent compilation of the Ne22(alpha,n)Mg25 rate leads to a remarkable reduction of the efficiency of the s-process during core He-burning. In particular, this rate leads to the lowest overproduction factor of Kr80 found to date during core He-burning in massive stars. The s-process yields resulting from shell carbon burning turn out to be very sensitive to the structural evolution of the carbon shell. This structure is influenced by the mass fraction of C12 attained at the end of core helium burning, which in turn is mainly determined by the C12(alpha,gamma)O16 reaction. The still present uncertainty in the rate for this reaction implies that the s-process in massive stars is also subject to this uncertainty. We identify some isotopes like Zn70 and Rb87 as the signatures of the s-process during shell carbon burning in massive stars. In determining the relative contribution of our s-only stellar yields to the solar abundances, we find it is important to take into account the neutron exposure of shell carbon burning. When we analyze our yields with a Salpeter Initial Mass Function, we find that massive stars contribute at least 40% to s-only nuclei with mass A <= 87. For s-only nuclei with mass A >90, massive stars contribute on average ~7%, except for Gd152, Os187, and Hg198 which are ~14%, \~13%, and ~11%, respectively.

 

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Astrophysics


astro-ph new abstracts, Mon, 2 Oct 06 00:00:14 GMT
0609792 -- 0609832 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609803 [abs, ps, pdf, other] :
Title: A Spectroscopic Study of Nuclear Processing and Production of Anomalously Strong Lines in the Crab Nebula
Authors: G. M. MacAlpine (1), T. C. Ecklund (1), W. R. Lester (1), S. J. Vanderveer (1), L. G. Strolger (2) ((1) Trinity University, (2) Western Kentucky University)
Comments: 14 pages, 12 figures, to be published in the Astronomical Journal

We present and discuss correlations for optical and near-infrared (5500-10030 angstroms) line intensity measurements at many positions in the Crab Nebula. These correlations suggest the existence of gas produced by a range of nuclear processing, from material in which synthesis ended with the CNO-cycle, to some helium-burning and nitrogen depletion, to regions containing enriched products of oxygen-burning. The latter exhibit a gradual, linear rise of [Ni II] emission with increasing argon enrichment, whereas gas with less nuclear processing shows markedly different [Ni II] emission characteristics, including the highest derived abundances. This suggests two origins for stable, neutron-rich nickel in the nebula: a type of "alpha-rich freezeout" in the more highly processed material, and possibly removal of ions from the neutron star in other regions. In addition, the data indicate that anomalously strong observed [C I] emission comes from broad, low-ionization zones. Although the strongest He I emission could also be enhanced in similar low-ionization gas, correlations between relevant line ratios argue against that interpretation, strengthening the case for an exceptionally high helium mass fraction in some locations.

 
astro-ph/0609811 [abs, ps, pdf, other] :
Title: Gamma--ray Burst Models
Authors: Andrew King
Comments: Proceedings of the Royal Society Discussion meeting on Gamma-ray Bursts, September 18-20, 2006. To appear in Phil. Trans. Roy. Soc. A

I consider various possibilities for making gamma--ray bursts, particularly from close binaries. In addition to the much--studied neutron star + neutron star and black hole + neutron star cases usually considered good candidates for short--duration bursts, there are other possibilities. In particular neutron star + massive white dwarf has several desirable features. These systems are likely to produce long--duration GRBs, in some cases definitely without an accompanying supernova, as observed recently. This class of burst would have a strong correlation with star formation, and occur close to the host galaxy. However rare members of the class need not be near star--forming regions, and could have any type of host galaxy. Thus a long--duration burst far from any star--forming region would also be a signature of this class. Estimates based on the existence of a known progenitor suggest that this type of GRB may be quite common, in agreement with the fact that the absence of a supernova can only be established in nearby bursts.

 
astro-ph/0609821 [abs, ps, pdf, other] :
Title: An explanation of the Z-track sources
Authors: M. J. Church (1,2), G. S. Halai (1), M. Balucinska-Church (1,2) ((1) University of Birmingham, UK; (2) Jagiellonian University, Cracow, Poland)
Comments: 14 pages, 8 figures, accepted for publication in Astronomy and Astrophysics

We present an explanation of the Z-track phenomenon based on spectral fitting of RXTE observations of GX340+0 using the emission model previously shown to describe the dipping LMXB. In our Z-track model, the soft apex is a quiescent state of the source with lowest luminosity. Moving away from this point by ascending the normal branch the strongly increasing luminosity of the Accretion Disc Corona (ADC) Comptonized emission L_ADC provides substantial evidence for a large increase of mass accretion rate Mdot. There are major changes in the neutron star blackbody emission, kT increasing to high values, the blackbody radius R_BB decreasing, these changes continuing monotonically on both normal and horizontal branches. The blackbody flux increases by a factor of ten to three times the Eddington flux so that the physics of the horizontal branch is dominated by the high radiation pressure of the neutron star, which we propose disrupts the inner disc, and an increase of column density is detected. We further propose that the very strong radiation pressure is responsible for the launching of the jets detected in radio on the horizontal branch. On the flaring branch, we find that L_ADC is constant, suggesting no change in Mdot so that flaring must consist of unstable nuclear burning. At the soft apex, the mass accretion rate per unit area on the neutron star m_dot is minimum for the horizontal and normal branches and about equal to the theoretical upper limit for unstable burning. Thus it is possible that unstable burning begins as soon as the source arrives at this position, the onset being consistent with theory. The large increase in R_BB in flaring is reminiscent of radius expansion in X-ray bursts. Finally, in our model, Mdot does not increase monotonically along the Z-track as often previously thought.

 
astro-ph/0609828 [abs, ps, pdf, other] :
Title: Heating in the Accreted Neutron Star Ocean: Implications for Superburst Ignition
Authors: Sanjib Gupta, Edward F. Brown, Hendrik Schatz, Peter Moeller, Karl-Ludwig Kratz
Comments: 10 pages, 9 figures, submitted to the Astrophysical Journal

We perform a self-consistent calculation of the thermal structure in the crust of a superbursting neutron star. In particular, we follow the nucleosynthetic evolution of an accreted element from deposition into the atmosphere down to neutron drip density. We include temperature-dependent continuum electron capture rates and realistic sources of heat loss by thermal neutrino emission from the crust and core. We show that, in contrast to previous calculations, electron captures to excited states and subsequent gamma-emission significantly reduces the local heat loss due to weak-interaction neutrinos. Furthermore, temperature-sensitive (gamma,n) rates trigger further energy deposition as the distribution of nuclei evolves toward a lower neutron separation energy. Depending on the initial composition these reactions release up to a factor of ten times more heat at densities <10^{11} g/cc than obtained previously. This heating reduces the ignition depth of superbursts. In particular, it reduces the discrepancy noted by Cumming et al. between the temperatures needed for unstable 12C ignition on timescales consistent with observations and the reduction in crust temperature from Cooper pair neutrino emission.

 

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Astrophysics


astro-ph new abstracts, Tue, 3 Oct 06 00:00:17 GMT
0610001 -- 0610051 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610004 [abs, ps, pdf, other] :
Title: Discovery of a Central Compact Object in the Galactic Nonthermal SNR G330.2+1.0
Authors: Sangwook Park (Penn State), Koji Mori (Miyazaki), Oleg Kargaltsev (Penn State), Patrick O. Slane (CfA), John P. Hughes (Rutgers), David N. Burrows, Gordon P. Garmire, George G. Pavlov (Penn State)
Comments: 9 pages (AASTex preprint style) including 1 Table and 4 Figures. Submitted to ApJ Letters

We report on the discovery of a pointlike source (CXOU J160103.1$-$513353) at the center of a Galactic supernova remnant (SNR) G330.2+1.0 with {\it Chandra X-Ray Observatory}. The X-ray spectrum fits a black-body (BB) model with $kT$ $\sim$ 0.49 keV, implying a small emission region of $R$ $\sim$ 0.4 km at the distance of 5 kpc. The estimated X-ray luminosity is $L_X$ $\sim$ 1 $\times$ 10$^{33}$ ergs s$^{-1}$ in the 1 $-$ 10 keV band. A power law model may also fit the observed spectrum, but the fit results in a very large photon index ($\Gamma$ $\sim$ 5). We find no counterparts at other wavelengths. The X-ray emission was steady over the $\sim$13 hr observation period, showing no variability. While we find marginal evidence for X-ray pulsations with $P$ $\approx$ 7.5 s, the presence of a pulsar at the position of this object is not conclusive with the current data, requiring an independent confirmation. These results are generally consistent with an interpretation of this object as a Central Compact Object associated with SNR G330.2+1.0.

 
astro-ph/0610010 [abs, ps, pdf, other] :
Title: The flat X-ray segment of GRB051221A: two component jet in short gamma-ray bursts
Authors: Zhi-Ping Jin, Ting Yan, Yi-Zhong Fan, Da-Ming Wei
Comments: 11 pages, 1 figure

Recent observation to the afterglow of GRB051221A found a flat segment in the X-ray light curve around 0.1 day after the burst. This flat segment caused the flux increasing by a factor of 5 over the extension of a single power law decrease. It may be caused either by a strong energy injection or by contribution of a second outflow component. Such a two component jet could be formed if the initial ejecta launched in the double neutron stars merger or neutron star-black hole merger is neutron rich and magnetized. In this work we show that the multi-band afterglows of GRB051221A could be well fitted by a two component model, provided that the shock physics parameters in different components are much different. This result suggests that GRB051221A might be the first detection of two component jet in short gamma-ray burst outflow.

 
astro-ph/0610023 [abs, ps, pdf, other] :
Title: The Effect of Neutrino Radiation on Magnetorotational Instability in Proto-Neutron Stars
Authors: Youhei Masada, Takayoshi Sano, Kazunari Shibata
Comments: Accepted for publication in ApJ, 24 pages,6 figures

Neutrino radiation takes a major role in the momentum, heat, and lepton transports in proto-neutron stars (PNSs). These diffusive processes affect the growth of magnetorotational instability (MRI) in PNSs. We perform a local linear analysis for the axisymmetric and nonaxisymmetric MRI including the effects of neutrino transports and ohmic dissipation. We find that the MRI can grow even in the multi-diffusive situations that are realized in neutrino loaded PNSs. When the toroidal magnetic component dominates over the poloidal one, nonaxisymmetric MRI modes grow much faster than axisymmetric modes. These results suggest the importance of the nonaxisymmetric MRI in PNSs. Thus the understandings of three-dimensional nonlinear evolutions of the MRI are necessary to reveal the explosion mechanism of core-collapse supernovae.

 

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Astrophysics


astro-ph new abstracts, Wed, 4 Oct 06 00:00:11 GMT
0610052 -- 0610089 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610071 [abs, ps, pdf, other] :
Title: Soft Gamma Repeaters and Short Gamma Ray Bursts: making magnetars from WD-WD mergers
Authors: R. Chapman, A. J. Levan, G. A. Wynn, M. B. Davies, A. R. King, R. S. Priddey, N. R. Tanvir
Comments: 4 pages, 3 figures. Included in Proceedings of EuroWD06 to be published in Conference Series of the Astronomical Society of the Pacific

Recent progress on the nature of short duration Gamma Ray Bursts (GRBs) has shown that a fraction of them originate in the local universe. These systems may well be the result of giant flares from Soft Gamma Repeaters (SGRs) believed to be magnetars (neutron stars with extremely large magnetic fields >= 10^14 G). If these magnetars are formed via the core collapse of massive stars, then it would be expected that the bursts should originate from predominantly young stellar populations. However, correlating the positions of BATSE short bursts with structure in the local universe reveals a correlation with all galaxy types, including those with little or no ongoing star formation. This is a natural outcome if, in addition to magnetars forming via the core collapse of massive stars, they also form via Accretion Induced Collapse following the merger of two white dwarfs, one of which is magnetic. We investigate this possibility and find that the rate of magnetar production via WD-WD mergers in the Milky Way is comparable to the rate of production via core collapse. However, while the rate of magnetar production by core collapse is proportional to the star formation rate, the rate of production via WD-WD mergers (which have long lifetimes) is proportional to the stellar mass density, which is concentrated in early-type systems. Therefore magnetars produced via WD-WD mergers may produce SGR giant flares which can be identified with early type galaxies. We also comment on the possibility that this mechanism could produce a fraction of the observed short duration GRB population at low redshift.

 
astro-ph/0610076 [abs, ps, pdf, other] :
Title: Constraining population synthesis models via observations of compact-object binaries and supernovae
Authors: R. O'Shaughnessy (1), V. Kalogera (1), K. Belczynski (2) ((1) Northwestern University, (2) New Mexico State University)
Comments: 10 pages, 7 figures. Submitted to ApJ

The observed samples of supernovae (SN) and double compact objects (DCOs) provide several critical constraints on population-synthesis models: the parameters of these models must be carefully chosen to reproduce, among other factors, (i) the formation rates of double neutron star (NS-NS) binaries and of white dwarf-neutron star (WD-NS) binaries and (ii) the type II and Ib/c supernova rates. Even allowing for extremely conservative accounting of the uncertainties in observational and theoretical predictions, we find only a few plausible population synthesis models
(roughly 9%) are consistent with DCO and SN rates empirically determined from observations. As a proof of concept, we describe the information that can be extracted about population synthesis models given such stringent observational tests, including surprisingly good agreement with the observed pulsar proper motion distribution. In the present study, we find that the current observational constraints favor: kicks described by a single Maxwellian with a typical velocity of about 300km/s; mass-loss fractions during non-conservative, but stable, mass transfer episodes of about 90%; and common envelope parameters of about 0.2-0.5. Finally, we use the subset of astrophysically consistent models to predict the rates at which double black hole (BH-BH), black hole-neutron star (BH-NS), and NS-NS binaries merge in the Milky Way through the emission of gravitational waves.

 
astro-ph/0610087 [abs, ps, pdf, other] :
Title: Jets and Disk-Winds from Pulsar Magnetospheres
Authors: Richard V.E. Lovelace, Leaf Turner, Marina M. Romanova
Comments: 6 figures, accepted for publication in the ApJ

We discuss axisymmetric force-free pulsar magnetospheres with magnetically collimated jets and a disk-wind obtained by numerical solution of the pulsar equation.
This solution represents an alternative to the quasi-spherical wind solutions where a major part of the current flow is in a current sheet which is unstable to magnetic field annihilation.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0609040 [abs, ps, pdf, other] :
Title: The symmetry energy at subnuclear densities and nuclei in neutron star crusts
Authors: Kazuhiro Oyamatsu, Kei Iida
Comments: 13 pages, 9 figures; Fig. 6 corrected, typos corrected

We examine how the properties of inhomogeneous nuclear matter at subnuclear densities depend on the density dependence of the symmetry energy. Using a macroscopic nuclear model we calculate the size and shape of nuclei in neutron star matter at zero temperature in a way dependent on the density dependence of the symmetry energy. We find that for smaller symmetry energy at subnuclear densities, corresponding to larger density symmetry coefficient L, the charge number of nuclei is smaller, and the critical density at which matter with nuclei or bubbles becomes uniform is lower. The decrease in the charge number is associated with the dependence of the surface tension on the nuclear density and the density of a sea of neutrons, while the decrease in the critical density can be generally understood in terms of proton clustering instability in uniform matter.

 

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Astrophysics


astro-ph new abstracts, Thu, 5 Oct 06 00:00:12 GMT
0610090 -- 0610125 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610108 [abs, ps, pdf, other] :
Title: Mass transfer during low mass X-ray transient decays
Authors: Craig R. Powell, Carole A. Haswell, Maurizio Falanga
Comments: 11 pages, 15 figures, 3 tables. Accepted MNRAS Oct 2006

The outbursts of low mass X-ray binaries are prolonged relative to those of dwarf nova cataclysmic variables as a consequence of X-ray irradiation of the disc. We show that the time-scale of the decay light curve and its luminosity at a characteristic time are linked to the radius of the accretion disc. Hence a good X-ray light curve permits two independent estimates of the disc radius. In the case of the milli-second pulsars SAX J1808.4-3658 and XTE J0929-314 the agreement between these estimates is very strong. Our analysis allows new determinations of distances and accretion disc radii. Our analysis will allow determination of accretion disc radii for sources in external galaxies, and hence constrain system parameters where other observational techniques are not possible. We also use the X-ray light curves to estimate the mass transfer rate. The broken exponential decay observed in the 2002 outburst of SAX J1808.4-3658 may be caused by the changing self-shadowing of the disc.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603644 [abs, ps, pdf, other] :
Title: Effects of color superconductivity on the nucleation of quark matter in neutron stars
Authors: I. Bombaci, G. Lugones, I. Vidana
Comments: Version to appear in Astronomy & Astrophysics
Note: replaced with revised version Wed, 4 Oct 2006 16:55:53 GMT (115kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 6 Oct 06 00:00:12 GMT
0610126 -- 0610171 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610139 [abs, ps, pdf, other] :
Title: Hadronic model for radio-to-TeV gamma-ray emission from PSR B1259-63
Authors: A.Neronov, M.Chernyakova
Comments: Proceeding of "The multi messenger approach to high energy gamma ray sources", Barcelona, June 2006

We discuss the implications of the recent X-ray and TeV gamma-ray observations of the PSR B1259-63 system (a young rotation powered pulsar orbiting a Be star) for the theoretical models of interaction of pulsar and stellar winds. We show that previously considered models in which the pulsar wind is purely electron loaded have problems to account for the observed behaviour of the system in the TeV and X-ray bands. We develop a model in which the broad band (radio, X-ray and high energy gamma-ray) emission from the binary system is produced in result of collisions of GeV-TeV energy protons accelerated by the pulsar wind and interacting with the stellar disk. In this model the high energy gamma-rays are produced in the decays of secondary neutral pions, while radio and X-ray emission are synchrotron and inverse Compton emission produced by low-energy (< 100 MeV) electrons from the decays of secondary charged pi mesons. This model can explain not only the observed energy spectra, but also the correlations between TeV, X-ray and radio emission components.

 
astro-ph/0610156 [abs, ps, pdf, other] :
Title: The role of reconnection in the pulsar magnetosphere
Authors: Ioannis Contopoulos

The present work is our first attempt to understand the role of reconnection in the pulsar magnetosphere. Our discussion is based on the observationaly infered fact that, as the pulsar spins down, the region of closed corotating dipolar field lines grows with time. This implies that reconnection must take place in the magnetosphere. We argue that non-dissipative reconnection along the equatorial current sheet allows for the continuous channeling of pulsar spindown energy into particle energy, all the way from the light cylinder to the pulsar wind termination shock, and we propose that this effect may account for the low \sigma values inferred by observations. We present a simple model that allows us to relate the magnetic diffusivity in the equatorial current sheet to an observable pulsar parameter, the braking index n. When n~1, the global structure of the magnetosphere approaches that of a relativistic split monopole where the pulsar spindown energy is carried by the electromagnetic field. However, for values of n>1.5, almost all field lines close inside the pulsar wind termination shock, and thus most of the electromagnetic pulsar spindown energy flux is effectively transformed into particle energy in the equatorial current sheet.

 
astro-ph/0610158 [abs, ps, pdf, other] :
Title: A new symbiotic low mass X-ray binary system: 4U 1954+319
Authors: F. Mattana, D. Gotz, M. Falanga, F. Senziani, A. De Luca, P. Esposito, P.A. Caraveo
Comments: 5 pages, 3 figures, accepted for publication in A&A Letters

4U 1954+319 was discovered 25 years ago, but only recently has a clear picture of its nature begun to emerge. We present for the first time a broad-band spectrum of the source and a detailed timing study using more than one year of monitoring data. The timing and spectral analysis was done using publicly available Swift, INTEGRAL, BeppoSAX, and RXTE/ASM data in the 0.7-150 keV energy band. The source spectrum is described well by a highly absorbed (N_H~10^23 cm^-2) power law with a high-energy exponential cutoff around 15 keV. An additional black body component is needed below 3 keV to account for a soft excess. The derived ~5 hr periodicity, with a spin-up timescale of ~25 years, could be identified as the neutron star spin period. The spectral and timing characteristics indicate that we are dealing both with the slowest established wind-accreting X-ray pulsar and with the second confirmed member of the emerging class dubbed "symbiotic low mass X-ray binaries" to host a neutron star.

 
astro-ph/0610167 [abs, ps, pdf, other] :
Title: INTEGRAL observation of the accreting pulsar GX 1+4
Authors: Carlo Ferrigno, Alberto Segreto, Andrea Santangelo, Joern Wilms, Ingo Kreykenbohm, Miroslav Denis, Ruediger Staubert
Comments: 15 pages, 13 figures. Accepted for publication on Astronomy and Astrophysics

We present the results of the INTEGRAL monitoring campaign on the accreting low mass X-ray binary pulsar GX 1+4 performed during the Galactic plane scan of the INTEGRAL Core Programme. The source has been observed in different luminosity states ranging from L(20-40 keV)= 1.7x10^{-10} erg/cm^2/s, to L(20-40 keV)=10.5x10^{-10} erg/cm^2/s for about 779 ks from 2003 March until 2004 October. Our observations confirm the secular spin down of GX 1+4 with spin period varying from 139.63 s to 141.56 s. In the highest luminosity state a spin-up phase is observed. The phase averaged spectrum of the source has been modelled either with an absorbed cut-off power law or with a Comptonization model with parameters significantly different in the two brightest luminosity states. No evidence for any absorption-like feature is observed in the phase averaged spectrum up to 110 keV. At highest luminosity, the source is found to pulsate up to 130 keV. Phase resolved spectroscopy reveals a phase dependent continuum and marginal evidence for an absorption feature at 34 keV in the descending part of the pulse. If interpreted as due to electron resonant cyclotron scattering, the magnetic field in the emitting region would be 2.9x10^{12}(1+z) G where z is the gravitational red-shift of the emitting region. We also observed a very low luminosity state, typical of this source, which lasted for about two days during which the source spectrum was modelled by a simple power-law and a pulsed signal was still detectable in the 15-100 keV energy range.

 
astro-ph/0610169 [abs, ps, pdf, other] :
Title: The evolutionary status of the white dwarf companion of the binary pulsar PSR J1713+0747
Authors: O. G. Benvenuto, R. D. Rohrmann, M. A. De Vito
Comments: 11 pages, 9 figures. Published in MNRAS
Journal-ref: 2006 MNRAS 366, 1520B

Splaver and coworkers have measured the masses of the white dwarf and the neutron star components of the PSR J1713+0747 binary system pair by Shapiro Delay. We attempt to find the original configuration of this system performing a set of binary evolution calculations to simultaneously account for the masses of both stars and the orbital period. We considered initial masses of 1.5 and 1.4 \msun for the normal (donor) and the neutron star, respectively. We assumed two metallicity values (Z = 0.010 and 0.020), and an initial orbital period near 3 days. We assume that the neutron star is only able to retain \lesssim 0.10 of the matter transferred by the donor star.
Calculations were performed employing our binary hydro code that handles the mass transfer rate in a fully implicit way together with state-of-the-art physical ingredients, diffusion and a non-grey atmospheres.
We compare the structure of the resulting white dwarfs with the characteristic age of PSR J1713+0747 finding a nice agreement with observations by Lundgren et al. especially for the case of a donor star with Z= 0.010. This result indicates that the evolution of this kind of binary system is well understood.
The models predict that, due to diffusion, the atmosphere of the white dwarf is an almost hydrogen-pure one. We find that such structures are unable to account for the colours measured by Lundgren et al. within their error bars. Thus, some discrepances in the white dwarf emergent radiation remain to be explained.

 

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astro-ph new abstracts, Mon, 9 Oct 06 00:00:10 GMT
0610172 -- 0610210 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610175 [abs, ps, pdf, other] :
Title: Features of the Acoustic Mechanism of Core-Collapse Supernova Explosions
Authors: A. Burrows, E. Livne, L. Dessart, C.D. Ott, J. Murphy
Comments: Accepted to the Astrophysical Journal, 23 pages in emulateapj format, including 12 figures

In the context of 2D, axisymmetric, multi-group, radiation/hydrodynamic simulations of core-collapse supernovae over the full 180$^{\circ}$ domain, we present an exploration of the progenitor dependence of the acoustic mechanism of explosion. All progenitor models we have tested with our Newtonian code explode. We investigate the roles of the Standing-Accretion-Shock-Instability (SASI), the excitation of core g-modes, the generation of core acoustic power, the ejection of matter with r-process potential, the wind-like character of the explosion, and the fundamental anisotropy of the blasts. We find that the breaking of spherical symmetry is central to the supernova phenomenon and the blasts, when top-bottom asymmetric, are self-collimating. We see indications that the initial explosion energies are larger for the more massive progenitors, and smaller for the less massive progenitors, and that the neutrino contribution to the explosion energy may be an increasing function of progenitor mass. The degree of explosion asymmetry we obtain is completely consistent with that inferred from the polarization measurements of Type Ic supernovae. Furthermore, we calculate for the first time the magnitude and sign of the net impulse on the core due to anisotropic neutrino emission and suggest that hydrodynamic and neutrino recoils in the context of our asymmetric explosions afford a natural mechanism for observed pulsar proper motions. [abridged]

 
astro-ph/0610182 [abs, ps, pdf, other] :
Title: Axisymmetric oscillations of magnetic neutron stars
Authors: Umin Lee
Comments: submitted to monthly notices

We calculate axisymmetric oscillations of rotating neutron stars composed of the surface fluid ocean, solid crust, and fluid core, taking account of a dipole magnetic field as strong as $B_S\sim 10^{15}$G at the surface. The adiabatic oscillation equations for the solid crust threaded by a dipole magnetic field are derived in Newtonian dynamics, on the assumption that the axis of rotation is aligned with the magnetic axis so that perturbations on the equilibrium can be represented by series expansions in terms of spherical harmonic functions $Y_l^m(\theta,\phi)$ with different degrees $l$ for a given azimuthal wave number $m$ around the the magnetic axis. Although the three component models can support a rich variety of oscillation modes, axisymmetric ($m=0$) toroidal $_{l}t_n$ and spheroidal $_ls_n$ shear waves propagating in the solid crust are our main concerns, where $l$ and $n$ denote the harmonic degree and the radial order of the modes, respectively. In the absence of rotation, axisymmetric spheroidal and toroidal modes are completely decoupled, and we consider the effects of rotation on the oscillation modes only in the limit of slow rotation. We find that the oscillation frequencies of the fundamental toroidal torsional modes $_{l}t_n$ in the crust are hardly affected by the magnetic field as strong as $B_S\sim 10^{15}$G at the surface. As the radial order $n$ of the shear modes in the crust becomes higher, however, both spheroidal and toroidal modes become susceptible to the magnetic field and their frequencies in general get higher with increasing $B_S$. We also find that the surface $g$ modes and the crust/ocean interfacial modes are suppressed by a strong magnetic field, and that there appear magnetic modes in the presence of a strong magnetic field.

 
astro-ph/0610183 [abs, ps, pdf, other] :
Title: Asymmetry Function of Interstellar Scintillations of Pulsars
Authors: V.I. Shishov, T.V. Smirnova
Journal-ref: Astronomy Reports, v. 49, No.11, p. 905, 2005

A new method for separating intensity variations of a source's radio emission having various physical natures is proposed. The method is based on a joint analysis of the structure function of the intensity variations and the asymmetry function, which is a generalization of the asymmetry coefficient and characterizes the asymmetry of the distribution function of the intensity fluctuations on various scales for the inhomogeneities in the diffractive scintillation pattern. Relationships for the asymmetry function in the cases of a logarithmic normal distribution of the intensity fluctuations and a normal distribution of the field fluctuations are derived. Theoretical relationships and observational data on interstellar scintillations of pulsars (refractive, diffractive, and weak scintillations) are compared. Pulsar scintillations match the behavior expected for a normal distribution of the field fluctuations (diffractive scintillation) or logarithmic normal distribution of the intensity fluctuations (refractive and weak scintillation). Analysis of the asymmetry function is a good test for distinguishing scintillations against the background of variations that have different origins.

 
astro-ph/0610188 [abs, ps, pdf, other] :
Title: Energy release associated with a first-order phase transition in a rotating neutron star core
Authors: J. L. Zdunik, M. Bejger, P. Haensel, E. Gourgoulhon
Comments: 8 pages, 8 figures, submitted to A&A

We calculate energy release associated with a first order phase transition at the center of a rotating neutron star. The results are based on precise numerical 2-D calculations, in which both the polytropic equations of state (EOS) as well as realistic EOS of the normal phase are used. Presented results are obtained for a broad range of metastability of initial configuration and size of the new superdense phase core in the final configuration. For small radii of the superdense phase core analytical expressions for the energy release are obtained. For a fixed "overpressure" dP (the relative excess of central pressure of collapsing metastable star over the pressure of equilibrium first-order phase transition) the energy release remarkably does not depend on the stellar angular momentum and coincides with that for nonrotating stars with the same dP. The energy release is proportional to dP^2.5 for small dPs, when sufficiently precise brute force 2-D numerical calculations are out of question. For higher dPs, results of 1-D calculations of energy release for non-rotating stars are shown to reproduce, with very high precision, the exact 2-D results for rotating stars.

 
astro-ph/0610192 [abs, ps, pdf, other] :
Title: Modelling the dynamics of superfluid neutron stars
Authors: N. Andersson
Comments: 8 pages, to appear in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface" (April 2006, London), eds. D. Page, R. Turolla, & S. Zane, Astrophysics & Space Science in press

In this brief summary I describe our recent work on superfluid neutron star dynamics. I review results on shear viscosity, hyperon bulk viscosity, vortex mediated mutual friction and the modelling of multifluid systems in general. For each problem I provide a set of questions that need to be addressed by future work.

 

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Astrophysics


astro-ph new abstracts, Tue, 10 Oct 06 00:00:13 GMT
0610211 -- 0610256 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610237 [abs, ps, pdf, other] :
Title: Strangelets accelerated by pulsars in galactic cosmic rays
Authors: K.S. Cheng, V.V. Usov
Comments: 3 pages, submitted to Phys. Rev. D

It is shown that nuggets of strange quark matter may be extracted from the surface of pulsars and accelerated by strong electric fields to high energies if pulsars are strange stars with the crusts, comprised of nuggets embedded in a uniform electron background. Such high energy nuggets called usually strangelets give an observable contribution into galactic cosmic rays and may be detected by the upcoming cosmic ray experiment Alpha Magnetic Spectrometer AMS-02 on the International Space Station.

 
astro-ph/0610238 [abs, ps, pdf, other] :
Title: Mimicking neutron star precession by polar cap current-pattern drifting
Authors: M. Ruderman, J. Gil

We propose a model for rotating current patterns within radiopulsar polar cap accelerators which has observational consequences that mimic those which have been attributed to neutron star free precession. The model is a simple extension of a canonical one for the origin of the "drifting subpulses" often observed within the pulse envelope of radiopulsars.
The new model's current pattern rotation period (with respect to the neutron star) is estimated to be of order a year. Associated with that rotation are small oscillations in spin-down torque, pulse arrival time, and radiobeam direction with this same period. These have estimated magnitudes which support a reinterpretation of free precession "observations" which could resolve the severe problem of obtaining anywhere near the otherwise required precession parameters with canonical neutron star models.

 
astro-ph/0610253 [abs, ps, pdf, other] :
Title: Ionization and dissociation equilibrium in strongly-magnetized helium atmosphere
Authors: Kaya Mori (1, 2), Jeremy S. Heyl (3) ((1) University of Toronto, (2) CITA, (3) UBC)
Comments: 27 pages, 12 figures, submitted to MNRAS

Recent observations and theoretical investigations of neutron stars indicate that their atmospheres consist not of hydrogen or iron but possibly heavier elements such as helium. We calculate the ionization and dissociation equilibrium of helium in the conditions found in the atmospheres of magnetized neutron stars. For the first time this investigation includes the internal degrees of freedom of the helium molecule. We found that at the temperatures and densities of neutron star atmospheres the rotovibrational excitations of helium molecules are populated. Including these excitations increases the expected abundance of molecules by up to two orders of magnitude relative to calculations that ignore the internal states of the molecule; therefore, if the atmospheres of neutron stars indeed consist of helium, helium molecules and possibly polymers will make the bulk of the atmosphere and leave signatures on the observed spectra from neutron stars.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0610013 [abs, ps, pdf, other] :
Title: Nucleosynthesis in decompressing neutron star matter
Authors: Prashanth Jaikumar (Ohio U., Argonne (PHY)), Bradley S. Meyer (Clemson U.), Kaori Otsuki (U. Chicago), Rachid Ouyed (U. Calgary)
Comments: 12 pages, 9 figures

We explore heavy-element nucleosynthesis by rapid neutron capture (r-process) in the decompressing ejecta from the surface of a neutron star. The decompression is triggered by a violent phase transition to strange quark matter (quark-nova scenario). The presence of neutron-rich large Z nuclei (40,95)<(Z,A)<(70,177), the large neutron-to-seed ratio, and the low electron fraction Ye ~ 0.03 in the decompressing ejecta present favorable conditions for the r-process. We perform network calculations that are adapted to the quark-nova conditions, and which mimic usual (n-\gamma) equilibrium r-process calculations during the initially cold decompression phase. They match to dynamical r-process calculations at densities below neutron drip (4x10^11 g/cc). We present results for the final element abundance distribution with and without heating from nuclear reactions, and compare to the solar abundance pattern of r-process elements. We highlight the distinguishing features of quark-novae by contrasting it with conventional nucleosynthesis sites such as type II supernovae and neutron star mergers, especially in the context of heavy-element compositions of extremely metal-deficient stars.

 

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Astrophysics


astro-ph new abstracts, Wed, 11 Oct 06 00:00:12 GMT
0610257 -- 0610294 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610267 [abs, ps, pdf, other] :
Title: Using long-term transit timing to detect terrestrial planets
Authors: Jeremy S. Heyl, Brett J. Gladman
Comments: 10 pages, 5 figures, submitted to Monthly Notices

We propose that the presence of additional planets in extrasolar planetary systems can be detected by long-term transit timing studies. If a transiting planet is on an eccentric orbit then the presence of another planet causes a secular advance of the transiting planet's pericenter over and above the effect of general relativity. Although this secular effect is impractical to detect over a small number of orbits, it causes long-term differences in when future transits occur, much like the long-term decay observed in pulsars. Measuring this transit-timing delay would thus allow the detection of either one or more additional planets in the system or the first measurements of non-zero oblateness ($J_2$) of the central stars.

 
astro-ph/0610290 [abs, ps, pdf, other] :
Title: Frequency Evolution of the Gravitational Waves for Compact Binaries
Authors: Balázs Mikóczi
Comments: 4 pages, in Proceedings of Astrophysics of Variable Stars
Journal-ref: ASP Conference Series, 349, 301-304 (2006)

We present here a complete list of contributions to the gravitational wave frequency evolution from compact binaries on circular orbits up to the second post-Newtonian order by including the interaction of magnetic dipole moments, quadrupole-monopole interactions together with the spin-orbit, the spin-spin and the self-interaction spin contributions. We apply our results to the Manchester et al. model of the J0737-3039A-B double pulsar.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609712 [abs, ps, pdf, other] :
Title: Gravitational Faraday Rotation in Binary Pulsar Systems
Authors: Matteo Luca Ruggiero, Angelo Tartaglia
Comments: 6 pages, 3 figures, minor revision; to appear in MNRAS
Note: replaced with revised version Tue, 10 Oct 2006 10:39:24 GMT (73kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 12 Oct 06 00:00:11 GMT
0610295 -- 0610335 received


6 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610304 [abs, ps, pdf, other] :
Title: Recent Progress on Anomalous X-ray Pulsars
Authors: V. M. Kaspi (McGill University)
Comments: 10 pages, 6 figures; to appear in proceedings of the conference "Isolated Neutron Stars: From the Interior to the Surface" eds. S. Zane, R. Turolla, D. Page; Astrophysics & Space Science in press

I review recent observational progress on Anomalous X-ray Pulsars, with an emphasis on timing, variability, and spectra. Highlighted results include the recent timing and flux stabilization of the notoriously unstable AXP 1E 1048.1-5937, the remarkable glitches seen in two AXPs, the newly recognized variety of AXP variability types, including outbursts, bursts, flares, and pulse profile changes, as well as recent discoveries regarding AXP spectra, including their surprising hard X-ray and far-infrared emission, as well as the pulsed radio emission seen in one source. Much has been learned about these enigmatic objects over the past few years, with the pace of discoveries remaining steady. However additional work on both observational and theoretical fronts is needed before we have a comprehensive understanding of AXPs and their place in the zoo of manifestations of young neutron stars.

 
astro-ph/0610307 [abs, ps, pdf, other] :
Title: High Energy Processes in Pulsar Wind Nebulae
Authors: W. Bednarek
Comments: 9 pages, 1 figure, Proc. Multimessenger approach to high energy gamma-ray sources

Young pulsars produce relativistic winds which interact with matter ejected during the supernova explosion and the surrounding interstellar gas. Particles are accelerated to very high energies somewhere in the pulsar winds or at the shocks produced in collisions of the winds with the surrounding medium. As a result of interactions of relativistic leptons with the magnetic field and low energy radiation (of synchrotron origin, thermal, or microwave background), the non-thermal radiation is produced with the lowest possible energies up to $\sim$100 TeV. The high energy (TeV) gamma-ray emission has been originally observed from the Crab Nebula and recently from several other objects. Recent observations by the HESS Cherenkov telescopes allow to study for the first time morphology of the sources of high energy emission, showing unexpected spectral features. They might be also interpreted as due to acceleration of hadrons. However, theory of particle acceleration in the PWNe and models for production of radiation are still at their early stage of development since it becomes clear that realistic modeling of these objects should include their time evolution and three-dimensional geometry. In this paper we concentrate on the attempts to create a model for the high energy processes inside the PWNe which includes existence not only relativistic leptons but also hadrons inside the nebula. Such model should also take into account evolution of the nebula in time. Possible high energy expectations based on such a model are discussed in the context of new observations.

 
astro-ph/0610319 [abs, ps, pdf, other] :
Title: Spectral analysis of the Low-Mass X-ray Binary 4U~1705--44
Authors: M. Fiocchi, A. Bazzano, P. Ubertini, M. federici
Comments: The 6th INTEGRAL Workshop 2006. The 6th INTEGRAL Workshop 2006, submitted

\integral and \sax observations of the neutron-star LMXB 4U~1705--44 have been analysed to deeply investigate the spectral state transitions nature. Its energy spectrum can be described as the sum of one or two blackbody, a 6.4-keV Fe line and a component due to thermal Comptonization. For the first time in this source, we find a strong signature of Compton reflection, presumably due to illumination of the optically-thick accretion disk by the Comptonized spectrum. Detection of two blackbody component in the soft states could originate in the disk and the neutron-star surface, and the Comptonized component arises from a hot inner flow with the seed photons coming from the disk and/or the neutron-star surface. The spectral transitions are shown to be associated with variations in the accretion rate, which changes in turn the temperature of the Comptonizing electrons and the strength of Compton reflection.

 
astro-ph/0610320 [abs, ps, pdf, other] :
Title: Hard tail detection in the LMXB 4U1636-53 from INTEGRAL
Authors: M. Fiocchi, A. Bazzano, P. Ubertini, M. federici
Comments: The 6th INTEGRAL Workshop 2006. The 6th INTEGRAL Workshop 2006, submitted

Recent INTEGRAL observations and archival BeppoSAX data have been analyzed to deeply investigate the hard X-ray behavior of the neutron star, atoll type, low mass X-ray Binary 4U1636-53. Our investigation in three different periods outline three corresponding different sates. Infact, the source was detected in both the canonical high and low state and moreover in one occasion \integral spectrum shows, for first time in this source, a hard tail dominating the emission above 30 keV. This spectrum is fitted as the sum of a Comptonized component similar to soft state and a power-law component ($\Gamma=2.76$), indicating the presence of a non thermal electron distribution of velocities.

 
astro-ph/0610323 [abs, ps, pdf, other] :
Title: A New Young Galactic Supernova Remnant Containing a Compact Object: G15.9+0.2
Authors: S.P. Reynolds, K.J. Borkowski, U. Hwang, I. Harrus, R. Petre, G. Dubner
Comments: 4 pages, 3 figures. Accepted by ApJ Letters

We identify the radio-emitting shell-type supernova remnant G15.9+0.2 as a relatively young remnant containing an X-ray point source that may be its associated neutron star. The integrated spectrum of the remnant shell obtained from our 30 ks exploratory Chandra observation shows very strong lines that require elevated element abundances from ejecta, in particular of sulfur. A plane-shock model fit gives a temperature $kT = 0.9 (0.8, 1.0)$ keV, an ionization timescale $n_et = 6 (4, 9) \times 10^{10}$ cm$^{-3}$ s, and a sulfur abundance of 2.1 (1.7, 2.7) times solar (90% confidence limits). Two-component models with one solar and one enriched component are also plausible, but are not well constrained by the data. Various estimates give a remnant age of order $10^3$ yr, which would make G15.9+0.2 among the dozen or so youngest remnants in the Galaxy. The sparse point source spectrum is consistent with either a steep $\Gamma \sim$ 4 power law or a $kT \sim$ 0.4 keV blackbody. The spectrum is absorbed by a H column density $N_H \sim 4 \times 10^{22}$ cm$^{-2}$ similar to that required for the remnant shell. The implied 2--9.5 keV source luminosity is about $10^{33}$ ergs s$^{-1}$ for an assumed distance of 8.5 kpc consistent with the high absorption column. We suggest that the point source is either a rotation-powered pulsar or a compact central object (CCO).

 
astro-ph/0610335 [abs, ps, pdf, other] :
Title: Determining the neutron star equation of state using the narrow-band gravitational wave detector Schenberg
Authors: G. F. Marranghello, J. C. N. de Araujo

We briefly review the properties of quasi-normal modes of neutron stars and black holes. We analyse the consequences of a possible detection of such modes via the gravitational waves associated with them, especially addressing our study to the Brazilian spherical antenna, on which a possible detection would occur at 3.0-3.4 kHz. A question related to any putative gravitational wave detection concerns the source that produces it. We argue that, since the characteristic damping times for the gravitational waves of neutron stars and black holes are different, a detection can distinguish between them, and also distinguish the neutron stars oscillating modes. Moreover, since the source can be identified by its characteristic damping time, we are able to extract information about the neutron star or black hole. This information would lead, for example, to a strong constraint in the nuclear matter equation of state, namely the compression modulus should be K=220 MeV.

 

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astro-ph new abstracts, Fri, 13 Oct 06 00:00:11 GMT
0610336 -- 0610375 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610348 [abs, ps, pdf, other] :
Title: Polarization of high-energy emissions from the Crab pulsar
Authors: J. Takata, H.-K. Chang, K.S.Cheng
Comments: 32pages, 8 figures. Accepted for publication in ApJ

We investigate polarization of high-energy emissions from the Crab pulsar in the frame work of the outer gap accelerator, following previous works of Cheng and coworkers. The recent version of the outer gap, which extends from inside the null charge surface to the light cylinder, is used for examining the synchrotron radiations from the secondary and the tertiary pairs, which are produced outside the gap. We calculate the light curve, the spectrum and the polarization characteristics, simultaneously, by taking into account gyration motion of the particles. The polarization position angle curve and the polarization degree are calculated to compare with the Crab optical data. We demonstrate that the radiations from inside the null charge surface make outer-wing and off-pulse emissions in the light curve, and the tertiary pairs contribute to bridge emissions. The emissions from the secondary pairs explain the main features of the observed light curve and spectrum.
On the other hand, both emissions from inside the null charge surface and from the tertiary pairs are required to explain the optical polarization behavior of the Crab pulsar. The energy dependence of the polarization features is expected by the present model. For the Crab pulsar, the polarization position angle curve indicates that the viewing angle of the observer measured from the rotational axis is greater than $90^{\circ}$.

 
astro-ph/0610375 [abs, ps, pdf, other] :
Title: Pulsar Spin, Magnetic Fields, and Glitches
Authors: M. Ruderman (Columbia University)
Comments: 9 Pages, 21 Figures, Latex, he_symp.cls. To appear in the proceedings of the 363rd Heraeus Seminar on Neutron Stars and Pulsars, held in Bad Honnef, May 14-19 2006

In the core of a canonical spinning magnetized neutron star(NS) a nearly uniform superfluid neutron vortex-array interacts strongly with a twisted array of magnetic flux-tubes threading the core's superconducting protons. One consequence is that changes in NS-spin alter both arrays and also the magnetic field distribution on the surface of the surrounding crust. Among predicted consequences for very young spinning-down NSs are "spin-down indices" increasing from 2 to 3, and a family of (Crab-like) spin-period "glitches" with permanent fractional jumps in spin-down torque 10E5 times greater than those in NS-spin. For older NSs, average spin-down indices increase to around 5, and an additional (Vela-like) family of giant glitches develops. NS spin-up to millesecond pulsars results in a high abundance of orthogonal and aligned rotators, and anomolously small polar cap areas. Observations do not conflict with these expectations. An epoch of NS magnetic field evolution between the onset of proton superconductivity (approx. yr) and neutron superfluidity (approx. 10E3 yrs ?) may be important for large surface magnetic field changes and needs further study. Observations generally considered evidence for NS precession seem to need reconsideration.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0610049 [abs, ps, pdf, other] :
Title: Absolute Being vs Relative Becoming
Authors: Joy Christian (Perimeter and Oxford)
Comments: 34 pages; To appear in Relativity and the Dimensionality of the World (within the series Fundamental Theories of Physics), edited by V. Petkov (Springer, NY 2007)

Contrary to our immediate and vivid sensation of past, present, and future as continually shifting non-relational modalities, time remains as tenseless and relational as space in all of the established theories of fundamental physics. Here an empirically adequate generalized theory of the inertial structure is discussed in which proper time is causally compelled to be tensed within both spacetime and dynamics. This is accomplished by introducing the inverse of the Planck time at the conjunction of special relativity and Hamiltonian mechanics, which necessitates energies and momenta to be invariantly bounded from above, and lengths and durations similarly bounded from below, by their respective Planck scale values. The resulting theory abhors any form of preferred structure, and yet captures the transience of now along timelike worldlines by causally necessitating a genuinely becoming universe. This is quite unlike the scenario in Minkowski spacetime, which is prone to a block universe interpretation. The minute deviations from the special relativistic effects such as dispersion relations and Doppler shifts predicted by the generalized theory remain quadratically suppressed by the Planck energy, but may nevertheless be testable in the near future, for example via observations of oscillating flavor ratios of ultrahigh energy cosmic neutrinos, or of altering pulse rates of extreme energy binary pulsars.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 16 Oct 06 00:00:11 GMT
0610376 -- 0610423 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610376 [abs, ps, pdf, other] :
Title: A Spin-down Power Threshold for Pulsar Wind Nebula Generation?
Authors: E. V. Gotthelf (Columbia University)
Comments: 4 Pages, 1 Figure, 1 Table. Latex, newpasp.sty. In "Young Neutron Stars and Their Environments" (IAU Symposium 218, ASP Conference Proceedings), eds. F. Camilo and B. M. Gaensler, p. 225

A systematic X-ray survey of the most energetic rotation-powered pulsars known, based on spin-down energy loss rate, $\dot E$ = $I\omega\dot\omega$, shows that all energetic pulsars with $\dot E > \dot E_{c} \approx 3.4 \times\ 10^{36}$ erg s$^{-1}$ are X-ray bright, manifest a distinct pulsar wind nebula (PWN), and are associated with a supernova event, either historically or via a thermal remnant, with over half residing in shell-like supernova remnants. Below $\dot E_c$, the 2-10 keV PWN flux ratio $F_{PWN}/F_{PSR}$ decreases by an order-of-magnitude. This threshold is predicted by the lower limit on the spectral slope $\Gamma_{min} \approx 0.5$ observed for rotation-powered pulsars (Gotthelf 2003). The apparent lack of bright pulsar nebulae below a critical Edot suggests a change in the particle injection spectrum and serves as a constraint on emission models for rotation-powered pulsars. Neither a young age nor a high density environment is found to be a sufficient condition for generating a PWN, as often suggested, instead the spin-down energy loss rate is likely the key parameter in determining the evolution of a rotation-powered pulsar.

 
astro-ph/0610382 [abs, ps, pdf, other] :
Title: Resonant Compton Upscattering in Anomalous X-ray Pulsars
Authors: Matthew G. Baring, Alice K. Harding
Comments: 9 pages, 3 embedded color figures, Accepted for publication in Astrophysics and Space Science, as part of the proceedings of the London meeting on "Isolated Neutron Stars," eds. S. Zane, R. Turolla & D. Page

A significant new development in the study of Anomalous X-ray Pulsars (AXPs) has been the recent discovery by INTEGRAL and RXTE of flat, hard X-ray components in three AXPs. These non-thermal spectral components differ dramatically from the steeper quasi-power-law tails seen in the classic X-ray band in these sources. A prime candidate mechanism for generating this new component is resonant, magnetic Compton upscattering. This process is very efficient in the strong magnetic fields present in AXPs. Here an introductory exploration of an inner magnetospheric model for upscattering of surface thermal X-rays in AXPs is offered, preparing the way for an investigation of whether such resonant upscattering can explain the 20-150 keV spectra seen by INTEGRAL. Characteristically flat emission spectra produced by non-thermal electrons injected in the emission region are computed using collision integrals. A relativistic QED scattering cross section is employed so that Klein-Nishina reductions are influential in determining the photon spectra and fluxes. Spectral results depend strongly on the magnetospheric locale of the scattering and the observer's orientation, which couple directly to the angular distributions of photons sampled.

 
astro-ph/0610408 [abs, ps, pdf, other] :
Title: Short GRBs: Rates and luminosity function implications
Authors: Dafne Guetta
Comments: 6 pages, 2figures. Submitted to the proceedings of the Swift-Venice 2006 meeting to be published by "Il Nuovo Cimento"

We compare the luminosity function and rate inferred from the BATSE short hard bursts (SHBs) peak flux distribution with the redshift and luminosity distributions of SHBs observed by Swift/HETE II. The Swift/HETE II SHB sample is incompatible with SHB population that follows the star formation rate. However, it is compatible with a distribution of delay times after the SFR. This would be the case if SHBs are associated with the mergers of double neutron star (DNS) systems. DNS may be ``primordial'' or can form dynamically by binary exchange interaction in globular clusters during core collapse. The implied SHB rates that we find range from \sim 8 to \sim 30h_(70)^3 Gpc^(-3)yr^(-1). This rate is a much higher than what was previously estimated and, when beaming is taken into account, it is comparable to the rate of neutron star mergers estimated from statistics of binary pulsars. If GRBs are produced in mergers the implied rate practically guarantees detection by LIGO II and possibly even by LIGO I.

 
astro-ph/0610412 [abs, ps, pdf, other] :
Title: r-Process Enhanced Halo Stars
Authors: J. J. Cowan, C. Sneden, J. E. Lawler, E. A. Den Hartog
Comments: 10 pages, 5 figures, To appear in the Proceedings of the International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX (2006)

Abundance observations indicate the presence of rapid-neutron capture (i.e., r-process) elements in old Galactic halo and globular cluster stars. These observations provide insight into the nature of the earliest generations of stars in the Galaxy -- the progenitors of the halo stars -- responsible for neutron-capture synthesis of the heavy elements. The large star-to-star scatter observed in the abundances of neutron-capture element/iron ratios at low metallicities -- which diminishes with increasing metallicity or [Fe/H] -- suggests the formation of these heavy elements (presumably from certain types of supernovae) was rare in the early Galaxy. The stellar abundances also indicate a change from the r-process to the slow neutron capture (i.e., s-) process at higher metallicities in the Galaxy and provide insight into Galactic chemical evolution. Finally, the detection of thorium and uranium in halo and globular cluster stars offers an independent age-dating technique that can put lower limits on the age of the Galaxy, and hence the Universe.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 17 Oct 06 00:00:12 GMT
0610424 -- 0610482 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610448 [abs, ps, pdf, other] :
Title: Double neutron stars as double strange stars
Authors: Manjari Bagchi, Sushan Konar, Gour Bhattacharya, Mira Dey, Jishnu Dey
Comments: 4 pages, 1 figure

Double neutron star systems lead to strong tests of general relativity. The history of the double pulsar PSR J0737-3039 is also very interesting. There are claims that the younger member of this binary (pulsar B) had a light progenitor. It is possible that such double pulsar systems are double strange stars. We suggest that the collapse of the light progenitor was a phase transition to strange matter and J0737-3039B is a strange star. This would support small baryon loss implied by the small natal kick velocity for the system J0737-3039. Using equation of states for strange quark matter and neutron matter, we have calculated the stellar structure and the baryon content of the progenitor as well as the existing star - to compare with observational predictions. We have also calculated the moment of inertia using both of the equation of states to facilitate comparison with expected future measurements. The baryon number of the progenitor turns out to be ~ 2 X 10^{57} and with small baryon loss the this fits into a strange star of mass 1.25 M_sun. Double neutron stars may be double strange stars. If the moment of inertia of these stars are found in the near future as expected, then our predictions can be further tested.

 
astro-ph/0610452 [abs, ps, pdf, other] :
Title: A new type of long gamma--ray burst
Authors: Andrew King, Emma Olsson, Melvyn B. Davies
Comments: MNRAS, in press

We consider gamma--ray bursts produced by the merger of a massive white dwarf with a neutron star. We show that these are likely to produce long--duration GRBs, in some cases definitely without an accompanying supernova, as observed recently. This class of burst would have a strong correlation with star formation, and occur close to the host galaxy. However rare members of the class need not be near star--forming regions, and could have any type of host galaxy. Thus a long--duration burst far from any star--forming region would also be a signature of this class. Estimates based on the existence of a known progenitor suggest that our proposed class may be an important contributor to the observed GRB rate.

 
astro-ph/0610454 [abs, ps, pdf, other] :
Title: Three-dimensional hydrodynamic simulations of asymmetric pulsar wind bow shocks
Authors: M. Vigelius, A. Melatos, S. Chatterjee, B.M. Gaensler, P. Ghavamian
Comments: Accepted for publication in MNRAS. High resolution pdf can be found at: this http URL

We present three-dimensional, nonrelativistic, hydrodynamic simulations of bow shocks in pulsar wind nebulae. The simulations are performed for a range of initial and boundary conditions to quantify the degree of asymmetry produced by latitudinal variations in the momentum flux of the pulsar wind, radiative cooling in the postshock flow, and density gradients in the interstellar medium (ISM). We find that the bow shock is stable even when travelling through a strong ISM gradient. We demonstrate how the shape of the bow shock changes when the pulsar encounters density variations in the ISM. We show that a density wall can account for the peculiar bow shock shapes of the nebulae around PSR J2124-3358 and PSR B0740-28. A wall produces kinks in the shock, whereas a smooth ISM density gradient tilts the shock. We conclude that the anisotropy of the wind momentum flux alone cannot explain the observed bow shock morphologies but it is instead necessary to take into account external effects. We show that the analytic (single layer, thin shell) solution is a good approximation when the momentum flux is anisotropic, fails for a steep ISM density gradient, and ap- proaches the numerical solution for efficient cooling. We provide analytic expressions for the latitudinal dependence of a vacuum-dipole wind and the associated shock shape, and compare the results to a split-monopole wind. We find that we are unable to distinguish between these two wind models purely from the bow shock morphology.

 
astro-ph/0610467 [abs, ps, pdf, other] :
Title: Spectroscopic Analysis of Subluminous B Stars in Binaries - Four Candidate Systems with Neutron Star/Black Hole Companions Discovered
Authors: S. Geier, C. Karl, H. Edelmann, U. Heber, R. Napiwotzki
Comments: 10 pages, 4 figures, To appear in the Proceedings of the International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX (2006)

The masses of compact objects like white dwarfs, neutron stars and black holes are fundamental to astrophysics, but very difficult to measure. We present the results of an analysis of subluminous B (sdB) stars in close binary systems with unseen compact companions to derive their masses and clarify their nature. Radial velocity curves were obtained from time resolved spectroscopy. The atmospheric parameters were determined in a quantitative spectral analysis. With high resolution spectra we were able to measure the projected rotational velocity of the stars with high accuracy. The assumption of orbital synchronization made it possible to constrain inclination angle and companion mass of the binaries. Five invisible companions have masses that are compatible with white dwarfs or late type main sequence stars. But four sdBs have very massive companions like heavy white dwarfs, neutron stars or even black holes. Such a high fraction of massive compact companions can not be explained with current models of binary evolution.

 
astro-ph/0610476 [abs, ps, pdf, other] :
Title: Pulse profiles and cyclotron line energy dependence on X-ray pulsars luminosity
Authors: S. Tsygankov (1), A. Lutovinov (1), E. Churazov (1 and 2), R. Sunyaev (1 and 2) ((1) Space Research Institute, Moscow, Russia, (2) Max-Planck-Institut fur Astrophysik, Garching, Germany)
Comments: 5 pages, submitted proceeding of the 6th INTEGRAL Workshop "The Obscured Universe" July 2-8, 2006 Space Research Institute Moscow, Russia

We present the results of broad band (3-100 keV) observations of several X-ray pulsars with the INTEGRAL and RXTE observatories. We concentrate on the luminosity and energy dependence of the pulse profile and the variations of the cyclotron line energy. In V0332+53 the line energy changes nearly linearly with the source luminosity, while in 4U0115+63 its behavior is more complicated. Strong variations of the pulse profile with the energy and source intensity were found for both of pulsars; in V0332+53 the changes of the pulse profile near the cyclotron line are especially drastic. The preliminary results obtained for Her X-1 and GX 301-2 in a high intensity state show the absence of significant pulse profile changes with the energy. Results and possible emission mechanisms are briefly discussed in terms of theoretical models of accreting pulsars.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0606259 [abs, ps, pdf, other] :
Title: The Anomalous X-Ray Pulsar 4u 0142+61: A Neutron Star with a Gaseous Fallback Disk
Authors: U. Ertan, M. H. Erkut, K.Y. Eksi, M.A. Alpar
Comments: 21 pages, 3 figures, minor revisons, accepted for publication in Apj
Note: replaced with revised version Mon, 16 Oct 2006 18:01:35 GMT (31kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 18 Oct 06 00:00:11 GMT
0610483 -- 0610523 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610505 [abs, ps, pdf, other] :
Title: X-ray emission properties of the old pulsar PSR B2224+65
Authors: C. Y. Hui, W. Becker
Comments: submitted to A&A

Using archival Chandra data we studied the X-ray emission properties of PSR B2224+65 and its environment. Albeit limited by photon statistics the spectral analysis suggests that the bulk of the emission from PSR B2224+65 is non-thermal. Fitting a power-law to the observed energy spectrum yields a photon index of $\Gamma=1.58^{+0.43}_{-0.33}$. The possible origin of the non-thermal pulsar emission is discussed in the context of the outer-gap model. We did not find any evidence for a compact nebula around PSR B2224+65 though the Chandra data reveal the existence of an extended feature which appears to be associated with PSR B2224+65. It extends from the pulsar position about 2 arcmin to the north-west. Its orientation deviates by $\sim118^{\circ}$ from the pulsar's proper motion direction. Investigating its energy spectrum shows that the emission of this extended feature is much harder than that of the pulsar itself and is non-thermal in nature.

 
astro-ph/0610522 [abs, ps, pdf, other] :
Title: PSR J1119-6127 and the X-ray Emission from High Magnetic Field Radio Pulsars
Authors: M. E. Gonzalez, V. M. Kaspi, F. Camilo, B. M. Gaensler, M. J. Pivovaroff
Comments: 6 pages, 2 figures. To be published in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface" (April 24-28, 2006, London, UK), eds. S. Zane, R. Turolla & D. Page

The existence of radio pulsars having inferred magnetic elds in the magnetar regime suggests that possible transition objects could be found in the radio pulsar population. The discovery of such an object would contribute greatly to our understanding of neutron star physics. Here we report on unusual X-ray emission detected from the radio pulsar PSR J1119-6127 using XMM-Newton. The pulsar has a characteristic age of 1,700 yrs and inferred surface dipole magnetic eld strength of 4.1x10^13 G. In the 0.5-2.0 keV range, the emission shows a single, narrow pulse with an unusually high pulsed fraction of ~70%. No pulsations are detected in the 2.0-10.0 keV range, where we derive an upper limit at the 99% level for the pulsed fraction of 28%. The pulsed emission is well described by a thermal blackbody model with a high temperature of 2.4x10^6 K. While no unambiguous signature of magnetar-like emission has been found in high-magnetic-eld radio pulsars, the X-ray characteristics of PSR J1119-6127 require alternate models from those of conventional thermal emission from neutron stars. In addition, PSR J1119-6127 is now the radio pulsar with the smallest characteristic age from which thermal X-ray emission has been detected.

 
astro-ph/0610523 [abs, ps, pdf, other] :
Title: Chandra and XMM-Newton Observations of the Vela-like Pulsar B1046-58
Authors: M. E. Gonzalez, V. M. Kaspi1, M. J. Pivovaroff, B. M. Gaensler
Comments: 8 pages, 4 figures. Accepted to ApJ

We present results from Chandra and XMM-Newton observations pulsar B1046-58. A high-resolution spatial analysis reveals pulsar wind nebula (PWN) ~6"x11" in size. The combined emission pulsar and its PWN is faint, with a best-fit power-law photon index and unabsorbed luminosity of ~10^32 ergs/s in the 0.5-10.0 keV a distance of 2.7 kpc). A spatially resolved imaging analysis presence of softer emission from the pulsar. No pulsations are PSR B1046-58; assuming a worst-case sinusoidal pulse profile, upper limit for the pulsed fraction in the 0.5-10.0 keV range of 53%. PWN emission is seen within 2" of the pulsar; the additional structures asymmetric and extend predominantly to the south-east. We discuss from the PWN as resulting from material downstream of the wind shock, as outflow from the pulsar or as structures confined by a velocity. The first two interpretations imply equipartition fields in structures of & 40-100 uG, while the latter case implies a velocity & 190 n^{-1/2} km/s (where n is the ambient number density in emission from an associated supernova remnant is detected.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609265 [abs, ps, pdf, other] :
Title: Neutron Star Asteroseismology. Axial Crust Oscillations in the Cowling Approximation
Authors: Lars Samuelsson, Nils Andersson
Comments: 14 pages, 1 table, 4 figures. v2: Typos corrected, references added and a bug in the code was fixed which slightly modifies the figures but leaves the conclusions unchanged
Note: replaced with revised version Tue, 17 Oct 2006 11:19:58 GMT (281kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 19 Oct 06 00:00:11 GMT
0610524 -- 0610564 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610549 [abs, ps, pdf, other] :
Title: Equation of state of neutron star cores and spin down of isolated pulsars
Authors: P. Haensel, J.L.Zdunik
Comments: 7 pages, 11 figures, to appear in Astrophysics and Space Science, in the proceedings of "Isolated Neutron Stars: from the Interior to the Surface", edited by D. Page, R. Turolla and S. Zane

We study possible impact of a softening of the equation of state by a phase transition, or appearance of hyperons, on the spin evolution of of isolated pulsars. Numerical simulations are performed using exact 2-D simulations in general relativity. The equation of state of dense matter at supranuclear densities is poorly known. Therefore, the accent is put on the general correlations between evolution and equation of state, and mathematical strictness. General conjectures referring to the structure of the one-parameter families of stationary configurations are formulated. The interplay of the back bending phenomenon and stability with respect to axisymmetric perturbations is described. Changes of pulsar parameters in a corequake following instability are discussed, for a broad choice of phase transitions predicted by different theories of dense matter. The energy release in a corequake, at a given initial pressure, is shown to be independent of the angular momentum of collapsing configuration. This result holds for various types of phases transition, with and without metastability. We critically review observations of pulsars that could be relevant for the detection of the signatures of the phase transition in neutron star cores.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 20 Oct 06 00:00:09 GMT
0610565 -- 0610599 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610593 [abs, ps, pdf, other] :
Title: The Zoo of Neutron Stars
Authors: S.B. Popov (Sternberg Astronomical Institute)
Comments: 12 pages, no figures. To appear in the proceedings of the summer school "Dense Matter In Heavy Ion Collisions and Astrophysics"

In these lecture notes I briefly discuss the present day situation and new discoveries in astrophysics of neutron stars focusing on isolated objects. The latter include soft gamma repeaters, anomalous X-ray pulsars, central compact objects in supernova remnants, the Magnificent seven, and rotating radio transients. In the last part of the paper I describe available tests of cooling curves of neutron stars and discuss different additional constraints which can help to confront theoretical calculations of cooling with observational data.

 
astro-ph/0610594 [abs, ps, pdf, other] :
Title: Intensity-hardness correlation and deep infrared observation of the anomalous X-ray pulsar 1RXS J170849-400910
Authors: N. Rea, G.L. Israel, T. Oosterbroek, S. Campana, S. Zane, R. Turolla, V. Testa, M. Mendez, L. Stella
Comments: 7 pages, 5 color figures; Astrophysics & Space Science, in press ("Isolated Neutron Stars"; London, UK)

We report here on X-ray and IR observations of the Anomalous X-ray Pulsar 1RXS J170849-400910. First, we report on new XMM-Newton, Swift-XRT and Chandra observations of this AXP, which confirm the intensity-hardness correlation observed in the long term X-ray monitoring of this source by Rea et al. (2005). These new X-ray observations show that the AXP flux is rising again, and the spectrum hardening. If the increase in the source intensity is indeed connected with the glitches and a possible bursting activity, we expect this source to enter in a bursting active phase around 2006-2007. Second, we report on deep IR observations of 1RXS J170849-400910, taken with the VLT-NACO adaptive optics, showing that there are many weak sources consistent with the AXP position. Neither star A or B, previously proposed by different authors, might yet be conclusively recognised as the IR counterpart of 1RXS J170849-400910. Third, using Monte Carlo simulations, we re-address the calculation of the significance of the absorption line found in a phase-resolved spectrum of this source by Rea et al. (2003), and interpreted as a resonant scattering cyclotron feature.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609082 [abs, ps, pdf, other] :
Title: Further Evidence for Collimated Particle Beams from Pulsars, and Precession
Authors: Avinash A. Deshpande (1,2), V. Radhakrishnan (2) ((1) Arecibo Observatory, NAIC, Arecibo; (2) Raman Research Institute, Bangalore)
Comments: Minor revision; 12 (9+3) pages, 3 figures; To appear in ApJ
Note: replaced with revised version Thu, 19 Oct 2006 11:50:11 GMT (33kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 23 Oct 06 00:00:11 GMT
0610600 -- 0610636 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610612 [abs, ps, pdf, other] :
Title: Phase and Intensity Distributions of Individual Pulses of PSR B0950+08
Authors: T.V. Smirnova

The distribution of the intensities of individual pulses of PSR B0950+08 as a function of the longitudes at which they appear is analyzed. The flux density of the pulsar at 111 MHz varies strongly from day to day (by up to a factor of 13) due to the passage of the radiation through the interstellar plasma (interstellar scintillation). The intensities of individual pulses can exceed the amplitude of the mean pulse profile, obtained by accumulating 770 pulses, by more than an order of magnitude. The intensity distribution along the mean profile is very different for weak and strong pulses. The differential distribution function for the intensities is a power law with index n = -1.1 +- 0.06 up to peak flux densities for individual pulses of the order of 160 Jy.

 
astro-ph/0610635 [abs, pdf] :
Title: Swift detects a remarkable gamma-ray burst, GRB 060614, that introduces a new classification scheme
Authors: N. Gehrels, J. P. Norris, V. Mangano, S. D. Barthelmy, D. N. Burrows, J. Granot, Y. Kaneko, C. Kouveliotou, C. B. Markwardt, P. Meszaros, E. Nakar, J. A. Nousek, P. T. O'Brien, M. Page, D. M. Palmer, A. M. Parsons, P. W. A. Roming, T. Sakamoto, C. L. Sarazin, P. Schady, M. Stamatikos, S. E. Woosley
Comments: 13 pages, 2 figures, accepted in Nature

Gamma ray bursts (GRBs) are known to come in two duration classes, separated at ~2 s. Long bursts originate from star forming regions in galaxies, have accompanying supernovae (SNe) when near enough to observe and are likely caused by massive-star collapsars. Recent observations show that short bursts originate in regions within their host galaxies with lower star formation rates consistent with binary neutron star (NS) or NS - black hole (BH) mergers. Moreover, although their hosts are predominantly nearby galaxies, no SNe have been so far associated with short GRBs. We report here on the bright, nearby GRB 060614 that does not fit in either class. Its ~102 s duration groups it with long GRBs, while its temporal lag and peak luminosity fall entirely within the short GRB subclass. Moreover, very deep optical observations exclude an accompanying supernova, similar to short GRBs. This combination of a long duration event without accompanying SN poses a challenge to both a collapsar and merging NS interpretation and opens the door on a new GRB classification scheme that straddles both long and short bursts.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607666 [abs, ps, pdf, other] :
Title: Spin-Kick Correlation in Neutron Stars: Alignment Conditions and Implications
Authors: Chen Wang, Dong Lai, JinLin Han
Comments: 17 pages, 8 figures. Accepted by ApJ
Note: replaced with revised version Fri, 20 Oct 2006 16:09:19 GMT (68kb)
 
astro-ph/0610448 [abs, ps, pdf, other] :
Title: Double neutron stars as double strange stars
Authors: Manjari Bagchi, Sushan Konar, Gour Bhattacharya, Mira Dey, Jishnu Dey
Comments: 4 pages, 1 figure
Note: replaced with revised version Fri, 20 Oct 2006 11:33:58 GMT (21kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 24 Oct 06 00:00:14 GMT
0610637 -- 0610684 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610681 [abs, ps, pdf, other] :
Title: Weak microlensing effect and stability of pulsar time scale
Authors: M. S. Pshirkov, M. V. Sazhin
Comments: 11 pages, 7 figures

An influence of the weak microlensing effect on the pulsar timing is investigated for pulsar B1937+21. Average residuals of Time of Arrival (TOA) due to the effect would be as large as 10 ns in 20 years observation span. These residuals can be much greater (up to 1 ms in 20 years span) if pulsar is located in globular cluster (or behind it).

 
astro-ph/0610684 [abs, ps, pdf, other] :
Title: Chandra View of the Unidentified TeV Gamma-ray Source HESS J1804-216
Authors: Wei Cui, Alexander Konopelko (Purdue Univ.)
Comments: 14 pages including 4 figures. Accepted by ApJ Letters

We present high-resolution X-ray images taken with the {\em Chandra X-ray Observatory} of the field that contains the unidentified TeV gamma-ray source HESS J1804-216. A total of eleven discrete sources were detected with {\it a posteriori} significance of $> 5\sigma$ over the entire field of view. Among them, only one, designated as CXOU J180351.4-213707, is significantly extended. The source is about 40\arcsec away from the radio pulsar PSR J1803-2137, which was the target of the {\em Chandra} observation but was not detected in X-rays. A natural question is whether the two sources are physically related. While it is conceivable that CXOU J180351.4-213707 could be associated with a previously unknown supernova remnant (SNR), in which the pulsar was born, it seems equally plausible that it might be a pulsar wind nebula (PWN) that is powered by a different pulsar whose emission is beamed away from us. In either case, we argue that CXOU J180351.4-213707 is likely the X-ray counterpart of HESS J1804-216, based on the fact that the Galactic TeV gamma-ray sources are predominantly SNRs or PWNe. The X-ray spectrum of the source can be fitted well with a power law, although the model is not well constrained due to large statistical uncertainties. The spectrum seems to be very hard, with the best-fit photon index about $\sim 1.2$. Under the assumption that CXOU J180351.4-213707 is the X-ray counterpart of HESS J1804-216, we attempted to model the X-ray and TeV emission as synchrotron and inverse Compton scattered radiation from relativistic electrons. We briefly discuss the results.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607459 [abs, ps, pdf, other] :
Title: Proper Motion of Pulsar B1800-21
Authors: W. F. Brisken, M. Carrillo-Barragan, S. Kurtz, J. P. Finley
Comments: 13 pages, 1 color figure. Replaced with version accepted for publication in Astrophysical Journal
Note: replaced with revised version Fri, 20 Oct 2006 22:43:50 GMT (240kb)
 
gr-qc/0511136 [abs, ps, pdf, other] :
Title: Binary neutron stars: Equilibrium models beyond spatial conformal flatness
Authors: Koji Uryu, Francois Limousin, John L. Friedman, Eric Gourgoulhon, Masaru Shibata
Comments: 4 pages, 6 figures, revised version, PRL in press
Note: replaced with revised version Sat, 21 Oct 2006 16:13:04 GMT (55kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 25 Oct 06 00:00:12 GMT
0610685 -- 0610720 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610685 [abs, ps, pdf, other] :
Title: The magnetar XTE J1810-197: variations in torque, radio flux density and pulse profile morphology
Authors: F. Camilo (1), I. Cognard (2), S. M. Ransom (3), J. P. Halpern (1), J. Reynolds (4), N. Zimmerman (1), E. V. Gotthelf (1), D. J. Helfand (1), P. Demorest (5), G. Theureau (2), D. C. Backer (5) ((1) Columbia, (2) CNRS, (3) NRAO, (4) ATNF, (5) Berkeley)
Comments: Submitted to ApJ; 7 pages, 5 figures. For high-resolution version of Fig. 1, see this http URL

We report on observations of the radio-emitting anomalous X-ray pulsar XTE J1810-197 during 2006 May-October using the Nancay, Parkes, GBT, and VLA telescopes at a frequency of 1.4 GHz. The torque experienced by the neutron star during this period, as inferred from a measurement of its rotational frequency derivative, decreased by 30%, although not in a steady manner. We have also observed very large ongoing fluctuations in flux density and pulse shape. Superimposed on these, a general diminution of flux density and a broadening of the pulse profile components occurred nearly contemporaneously with a decrease in torque of about 10% that took place in late July over an interval of two weeks. In addition, a simultaneous observation of the pulsar with the Chandra X-ray Observatory and the GBT allows us to show how the X-ray and radio profiles are aligned. We discuss briefly the implications of these results for the magnetospheric currents in this remarkable object.

 
astro-ph/0610696 [abs, ps, pdf, other] :
Title: Fragmentation of Collapsar Disks and the Production of Gravitational Waves
Authors: Anthony L. Piro, Eric Pfahl (KITP)
Comments: Submitted for publication in The Astrophysical Journal Letters, 4 pages, 2 figures

We argue that gravitational instability in the outer parts of collapsar disks may lead to fragmentation near the radius where helium photodisintegrates, because of the strong cooling provided by this process. This physics sets clear physical scales for the fragmentation conditions and the properties of gravitationally bound clumps. Collapse of a fragment proceeds until the neutrons become degenerate; a neutron star of mass ~0.1-1Msun may result. We find that tidal disruption of a fragment and accretion by the central black hole are too rapid to account for the durations of observed X-ray flares from long gamma-ray bursts. Prior to disruption, migration of the fragment is driven by gravitational radiation and disk viscosity, which act together to produce a unique gravitational-wave signature. Advanced LIGO may be able to detect such sources within ~100 Mpc.

 
astro-ph/0610707 [abs, ps, pdf, other] :
Title: Gamma-ray binaries
Authors: I.F. Mirabel
Comments: 4 pages, 3 figures. Invited talk to appear in Proceedings of the conference "The Multi-Messenger Approach to High-Energy Gamma-ray Sources", Barcelona, 4-7 July 2006

Recent observations have shown that some compact stellar binaries radiate the highest energy light in the universe. The challenge has been to determine the nature of the compact object and whether the very high energy gamma-rays are ultimately powered by pulsar winds or relativistic jets. Multiwavelength observations have shown that one of the three gamma-ray binaries known so far, PSR B1259-63, is a neutron star binary and that the very energetic gamma-rays from this source and from another gamma-ray binary, LS I +61 303, may be produced by the interaction of pulsar winds with the wind from the companion star. At this time it is an open question whether the third gamma-ray binary, LS 5039, is also powered by a pulsar wind or a microquasar jet, where relativistic particles in collimated jets would boost the energy of the wind from the stellar companion to TeV energies.

 
astro-ph/0610708 [abs, ps, pdf, other] :
Title: XMM observation of the SNR G337.2+0.1
Authors: Jorge A. Combi, Juan F. Albacete Colombo, Gustavo E. Romero, Paula Benaglia
Comments: 13 pages, 5 figures, Accepted for publication in Astrophysical Journal Letters

We report the first XMM detection of the SNR candidate G337.2+0.1 (=AX J1635.9-4719). The object shows centrally filled and diffuse X-ray emission. The emission peaks in the hard 3.0-10.0 keV band. A spatially resolved spectral study confirms that the column density of the central part of the SNR is about N_{H}~5.9 +/- 1.5*10^{22} cm^{-2} and its X-ray spectrum is well represented by a single power-law with a photon index Gamma=0.96 +/- 0.56. The non-detection of line emission in the central spectrum is consistent with synchrotron radiation from a population of relativistic electrons. Detailed spectral analysis indicates that the outer region is highly absorbed and quite softer than the inner region, with N_{H}~16.2(+/-5.2)*10^{22} cm^{-2} and kT=4.4(+/-2.8) keV. Such characteristics are already observed in other X-ray plerions. Based on the morphological and spectral X-ray information, we confirm the SNR nature of G337.2+0.1, and suggest that the central region of the source is a pulsar wind nebula (PWN), originated by an energetic though yet undetected pulsar, that is currently losing energy at a rate of ~ 10^{36} erg s^{-1}.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0601063 [abs, ps, pdf, other] :
Title: On the origins of part-time radio pulsars
Authors: Bing Zhang (UNLV), Janusz Gil (Zielona Gora Univ), Jaroslaw Dyks (Nicolaus Copernicus Center)
Comments: Expanded version to include more general discussion of part-time pulsars. Accepted to MNRAS
Note: replaced with revised version Mon, 23 Oct 2006 21:15:34 GMT (12kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 26 Oct 06 00:00:12 GMT
0610721 -- 0610760 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610737 [abs, ps, pdf, other] :
Title: Extreme Scattering Events: insights into the interstellar medium on AU-scales
Authors: Mark A. Walker (MAW Technology Pty Ltd)
Comments: 8 Pages, 4 figures, Proceedings of Small Ionised and Neutral Structures conference (Socorro, 21st-24th May 2006)

Several radio-wave scintillation phenomena exhibit properties which are difficult to accommodate within the standard propagation model based on distributed Kolmogorov turbulence in the ionised ISM; here we discuss one such phenomenon, namely Extreme Scattering Events. By analysis of the data we demonstrate that these events are caused by ionised gas associated with self-gravitating, AU-sized gas clouds. The data also show that the ionised gas is confined by ram pressure, with the clouds moving at hundreds of km/s relative to the diffuse ISM and causing strong shocks. These conclusions are supported by a quantitative model in which heat from the shocked ISM evaporates gas from the surface of a cold cloud; this model readily explains the physical conditions which are required for Extreme Scattering and yields passable reproductions of the light-curves. The magnetotail of the cloud provides a site in which two other ``anomalous'' radio-wave propagation phenomena -- IntraDay Variability of quasars, and pulsar parabolic arcs -- can plausibly arise, thus linking three anomalous propagation phenomena in a single physical model. Locally there must be thousands of these neutral clouds per cubic parsec and by mass they are the primary constituent of interstellar matter.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0610103 [abs, ps, pdf, other] :
Title: Collapse and black hole formation in magnetized, differentially rotating neutron stars
Authors: Branson C. Stephens, Matthew D. Duez, Yuk Tung Liu, Stuart L. Shapiro, Masaru Shibata
Comments: Submitted to a special issue of Classical and Quantum Gravity based around the New Frontiers in Numerical Relativity meeting at the Albert Einstein Institute, Potsdam, July 17-21, 2006

The capacity to model magnetohydrodynamical (MHD) flows in dynamical, strongly curved spacetimes significantly extends the reach of numerical relativity in addressing many problems at the forefront of theoretical astrophysics. We have developed and tested an evolution code for the coupled Einstein-Maxwell-MHD equations which combines a BSSN solver with a high resolution shock capturing scheme. As one application, we evolve magnetized, differentially rotating neutron stars under the influence of a small seed magnetic field. Of particular significance is the behavior found for hypermassive neutron stars (HMNSs), which have rest masses greater the mass limit allowed by uniform rotation for a given equation of state. The remnant of a binary neutron star merger is likely to be a HMNS. We find that magnetic braking and the magnetorotational instability lead to the collapse of HMNSs and the formation of rotating black holes surrounded by massive, hot accretion tori and collimated magnetic field lines. Such tori radiate strongly in neutrinos, and the resulting neutrino-antineutrino annihilation (possibly in concert with energy extraction by MHD effects) could provide enough energy to power short-hard gamma-ray bursts. To explore the range of outcomes, we also evolve differentially rotating neutron stars with lower masses and angular momenta than the HMNS models. Instead of collapsing, the non-hypermassive models form nearly uniformly rotating central objects which, in cases with significant angular momentum, are surrounded by massive tori.

 

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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 27 Oct 06 00:00:09 GMT
0610761 -- 0610800 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610768 [abs, ps, pdf, other] :
Title: A Possible Magnetar Nature for IGR J16358-4726
Authors: S. K. Patel, J. Zurita, M. Del Santo, M. Finger, C. Kouveliotou, D. Eichler, E. Gogus, P. Ubertini, R. Walter, P. Woods, C. A. Wilson, S. Wachter, A. Bazzano
Comments: Accepted for publication in ApJ, 34 pgs, 14 figures, 4 tables

We present detailed spectral and timing analysis of the hard x-ray transient IGR J16358-4726 using multi-satellite archival observations. A study of the source flux time history over 6 years, suggests that lower luminosity transient outbursts can be occuring in intervals of at most 1 year. Joint spectral fits of the higher luminosity outburst using simultaneous Chandra/ACIS and INTEGRAL/ISGRI data reveal a spectrum well described by an absorbed power law model with a high energy cut-off plus an Fe line. We detected the 1.6 hour pulsations initially reported using Chandra/ACIS also in the INTEGRAL/ISGRI light curve and in subsequent XMM-Newton observations. Using the INTEGRAL data we identified a spin up of 94 s (dP/dt = 1.6E-4), which strongly points to a neutron star nature for IGR J16358-4726. Assuming that the spin up is due to disc accretion, we estimate that the source magnetic field ranges between 10^13 - 10^15 G, depending on its distance, possibly supporting a magnetar nature for IGR J16358-4726.

 
astro-ph/0610770 [abs, ps, pdf, other] :
Title: Constraining Galactic Neutrino Production in $p\gamma$ Interactions with Cosmic Ray Electron and Positron Spectra
Authors: Nayantara Gupta (UNLV), Bing Zhang (UNLV)
Comments: 8 pages, no figure

High energy neutrinos are expected to be produced inside astrophysical sources of cosmic rays {\it e.g.} supernova remnants, pulsar wind nebulae, active galactic nuclei and gamma-ray bursts by the decay of charged pions produced in $p\gamma$ and $pp$ interactions. Although $pp$ interactions may be the dominant mechanism in our Galaxy, it is unclear how important $p\gamma$ process is for neutrino production. We show that it is possible to put a lower limit on the contribution of $p\gamma$ interactions to high energy neutrino production from all Galactic astrophysical cosmic ray sources using the observed cosmic ray electron and positron spectra. Assuming equal injection powers of electrons and nucleons, the contribution of $p\gamma$ interactions to high energy neutrino production is found to be at least $\sim 6%$. Their contribution could be even larger if there is a large number of sources from which electrons and positrons can not escape due to their radiation losses, or the optical depths of both $pp$ and $p\gamma$ processes are small.

 
astro-ph/0610782 [abs, ps, pdf, other] :
Title: Spectral analysis of X-ray pulsars with the INTEGRAL observatory
Authors: E.V. Filippova (1), S.S. Tsygankov (1), A.A. Lutovinov (1), R.A. Sunyaev (1,2) ((1) Space Research Institute, Moscow, Russia, (2) Max Plank Institute fur Astrophysics, Garching, Germany)
Comments: 4 pages, 1 figure, submitted proceeding of the 6th INTEGRAL Workshop "The Obscured Universe" July 2-8, 2006 Space Research Institute Moscow, Russia

We studied spectra for 34 accretion-powered X-ray and one millisecond pulsars that were within the field of view of the INTEGRAL observatory over two years (December 2002 - January 2005) of its in-orbit operation and that were detected by its instruments at a statistically significant level (>8 sigma in the energy range 18-60 keV). There are seven recently discovered objects of this class among the pulsars studied: 2RXP J130159.6-635806, IGR/AX J16320-4751, IGR J16358-4726, AX J163904-4642, IGR J16465-4507, SAX/IGR J18027-2017 and AX J1841.0-0535. We analyze the evolution of spectral parameters as a function of the intensity of the sources and compare these with the results of previous studies.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 30 Oct 06 01:00:10 GMT
0610801 -- 0610839 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610802 [abs, ps, pdf, other] :
Title: On the nature of the intermittent pulsar PSR B1931+24: X-ray and optical observations
Authors: N. Rea (1), M. Kramer (2), L. Stella (3), P. Jonker (1,4,5), C. Bassa (5), P. Groot (6), G. Israel (3), M. Mendez (1,7), A. Possenti (8), A. Lyne (2) ((1) SRON-Utrecht, (2) Jodrell Bank Observatory, (3) INAF-OAR, (4) CfA, (5) Utrecht University, (6) Nijmegen University, (7) Amsterdam University, (8) INAF-OAC)
Comments: 5 pages, 2 figures; submitted to MNRAS Letter

PSR B1931+24 is a 813 ms radio pulsar which has been recently discovered to display peculiar intermittent radio emission. This source is observable in the radio band for ~5-10 days and remains radio quiet for the following 25-35 days, periodically. Even more remarkable is its spin-down behaviour: the pulsar slows down at a rate a factor of ~1.5 faster in the radio-on than during the radio-off phase. We report here on new X-ray and optical observations of PSR B1931+24, performed with the Chandra X-ray Observatory and the Isaac Newton Telescope. Furthermore, we present here the possibility that this radio pulsar is hosted in an eccentric binary system with a very low mass companion. We then discuss our results in the intermittent isolated radio pulsar scenario and in the binary picture.

 
astro-ph/0610803 [abs, ps, pdf, other] :
Title: RXTE observations of the first transient Z source XTE J1701-462: shedding new light on mass accretion in luminous neutron star LMXBs
Authors: Jeroen Homan, Michiel van der Klis, Rudy Wijnands, Tomaso Belloni, Rob Fender, Marc Klein-Wolt, Piergiorgio Casella, Mariano Mendez, Elena Gallo, Walter H.G. Lewin, Neil Gehrels
Comments: Accepted for publication in ApJ, 11 pages

(Abridged) We report on ten weeks of RXTE observations of the X-ray transient XTE J1701-462. Comparisons with other sources suggest it had all the characteristics of the neutron star Z sources (the brightest persistent neutron star LMXBs). These include Z tracks in X-ray color diagrams and typical variability components detected in the power spectra. XTE J1701-462 is the first transient Z source and provides unique insights into mass accretion rate (Mdot) and luminosity dependencies in neutron star LMXBs. As its overall luminosity decreased, we observed a switch between two types of Z-source behavior, with most of the branches of the Z-track changing their shape and/or orientation. We interpret this switch as an extreme case of the longterm changes seen in the persistent Z sources and suggest that these result from changes in Mdot. We also suggest that the Cyg-like Z sources (Cyg X-2, GX 5-1, and GX 340+0) might be more luminous (> 50%) than the Sco-like Z sources (Sco X-1, GX 17+2, and GX 349+2). Adopting a possible explanation for the behavior of kHz QPOs, which involves a prompt as well as a filtered response to changes in Mdot, we propose that changes in Mdot can explain both movement along the Z track and changes in the shape of the Z track. We discuss some consequences of this and consider the possibility that the branches of the Z will evolve into the branches observed in the X-ray color diagrams of the less luminous atoll sources, but not in a way that was previously suggested.

 
astro-ph/0610809 [abs, ps, pdf, other] :
Title: XMM-Newton survey of the central region of M31. Spectral properties and variability of bright X-ray sources and source classification
Authors: Sergey Trudolyubov (IGPP/UCR, IKI), William Priedhorsky (LANL), France Cordova (UCR)
Comments: 36 pages, 16 figures, uses emulateapj style. Submitted to ApJ

(Abridged) We present the results of the systematic survey of X-ray sources in the central region of M31 using the data from XMM-Newton observations performed in the years 2000-2004. The spectral properties and variability of 123 bright X-ray sources with apparent luminosities between ~10^{36} and \~5x10^{38} ergs/s were studied in detail. The spectral distribution of M31 X-ray sources, based on the spectral fitting with a power law model is clearly bimodal with a main peak corresponding to a photon index Gamma ~ 1.75 and a shoulder at Gamma ~ 2.0-2.2 extending to the soft spectral region, and shows clear evolution with source luminosity. The distribution of absorbing columns towards M31 sources derived from spectral analysis has a peak at N_H~1.2x10^{21} cm^{-2} extending up to 1.3x10^{22} cm^{-2}, with an average value of (1.52 +/- 0.02)x10^{21} cm^{-2}. More than 80% of sources observed in two or more observations show significant variability on the time scales of days to years. About 50% of the sources in our sample are spectrally variable. The spectral evolution of a number of sources is correlated with the level of their X-ray flux, while some sources demonstrate complex patterns of evolution on the hardness-intensity diagram. Based on the similarity of the properties of M31 X-ray sources and their Galactic counterparts, we expect most of the X-ray sources in our sample to be accreting binary systems with neutron star and black hole primaries. A total of 44 X-ray sources can be identified as probable X-ray binaries. Combining the results of X-ray analysis with available data at other wavelengths, we classify 7% and 24% of sources in our sample as, respectively, probable black hole and neutron star candidates.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 31 Oct 06 01:00:12 GMT
0610840 -- 0610911 received


8 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610840 [abs, ps, pdf, other] :
Title: Magnetorotational collapse of massive stellar cores to neutron stars: Simulations in full general relativity
Authors: Masaru Shibata, Yuk Tung Liu, Stuart L. Shapiro, Branson C. Stephens
Comments: 28 pages, 20 figures, accepted for publication in Phys. Rev. D

We study magnetohydrodynamic (MHD) effects arising in the collapse of magnetized, rotating, massive stellar cores to proto-neutron stars (PNSs). We perform axisymmetric numerical simulations in full general relativity with a hybrid equation of state. The formation and early evolution of a PNS are followed with a grid of 2500 x 2500 zones, which provides better resolution than in previous (Newtonian) studies. We confirm that significant differential rotation results even when the rotation of the progenitor is initially uniform. Consequently, the magnetic field is amplified both by magnetic winding and the magnetorotational instability (MRI). Even if the magnetic energy E_EM is much smaller than the rotational kinetic energy T_rot at the time of PNS formation, the ratio E_EM/T_rot increases to 0.1-0.2 by the magnetic winding. Following PNS formation, MHD outflows lead to losses of rest mass, energy, and angular momentum from the system. The earliest outflow is produced primarily by the increasing magnetic stress caused by magnetic winding. The MRI amplifies the poloidal field and increases the magnetic stress, causing further angular momentum transport and helping to drive the outflow. After the magnetic field saturates, a nearly stationary, collimated magnetic field forms near the rotation axis and a Blandford-Payne type outflow develops along the field lines. These outflows remove angular momentum from the PNS at a rate given by \dot{J} \sim \eta E_EM C_B, where \eta is a constant of order 0.1 and C_B is a typical ratio of poloidal to toroidal field strength. As a result, the rotation period quickly increases for a strongly magnetized PNS until the degree of differential rotation decreases. Our simulations suggest that rapidly rotating, magnetized PNSs may not give rise to rapidly rotating neutron stars.

 
astro-ph/0610867 [abs, ps, pdf, other] :
Title: Low-Luminosity GRB 060218: A Collapsar Jet from a Neutron Star, Leaving a Magnetar as a Remnant?
Authors: Kenji Toma, Kunihito Ioka, Takanori Sakamoto, Takashi Nakamura
Comments: 12 pages, 3 figures; submitted to the Astrophysical Journal

The gamma-ray burst (GRB) 060218 has ~10^5 times lower luminosity than typical long GRBs, and is associated with a supernova (SN). The radio afterglow displays no jet break, so that this burst might arise from a mildly-relativistic spherical outflow produced by the SN shock sweeping the stellar surface. Since this model is energetically difficult, we propose that the radio afterglow is produced by a non-relativistic phase of an initially collimated outflow (jet). Our jet model is supported by the detection of optical linear polarization in the SN component. We also show analytically that the jet can penetrate a progenitor star. Furthermore, we analyzed the observational data of the prompt emission of this burst and obtained the implications that it may last longer than 10^6 s, which prefers a neutron star engine to a black hole engine. The collimation-corrected event rate of such low-luminosity GRBs is ~10 times higher than that of typical long GRBs, and they might form a different GRB population: low-luminosity GRBs are produced by mildly-relativistic jets from neutron stars at the collapses of massive stars, while typical long GRBs by highly-relativistic jets from black holes. We suggest that the central engine of GRB 060218 is a pulsar (or a magnetar) with the initial rotation period P_0 ~10 ms and the magnetic field B ~10^{16} G. A giant flare from the magnetar might be observed in future.

 
astro-ph/0610883 [abs, ps, pdf, other] :
Title: A model for double notches and bifurcated components in radio profiles of pulsars and magnetars - Evidence for the parallel acceleration maser in pulsar magnetosphere
Authors: J. Dyks, B. Rudak, Joanna M. Rankin
Comments: 15 pages, 10 figures, submitted to A&A

Averaged pulse profiles of three nearby pulsars: B1929+10, J0437-4715 and B0950+08 exhibit unusual `double notches'. These W-like looking features consist of two adjacent V-shaped dips that approach each other at increasing observation frequency nuobs roughly at a rate sep \propto nuobs^{-1/2}, where sep is the separation between the notches' minima. We show that basic properties of the notches, namely their W-like look and the rate of their converging can be understood within a narrow class of models of coherent radio emission from pulsars: the free electron maser models based on coherent inverse Compton scattering of parallel oscillations of ambient electric field. The observed properties of the pulsars imply that the Fourier spectrum of the wiggler-like oscillations is narrow and that the broad-band character of the radio emission reflects the width of the electron energy distribution. Such a model provides a natural explanation for the frequency-independent separation between the main pulse and interpulse of B0950+08 as well as for the lack of radius to frequency mapping in the conal-like emission of J0437-4715. The frequency behaviour of the main pulse in the profile of the first radio magnetar XTE J1810-197 can also be explained within this model.

 
astro-ph/0610887 [abs, ps, pdf, other] :
Title: Transient pulsar dynamics in hard x-rays: Prognoz 9 and GRIF "Mir" space experiments data
Authors: M. I. Kudryavtsev, S. I. Svertilov, V. V. Bogomolov

The long-term observations of the Galactic Centre as well as the Galactic anti-Centre regions in hard X-rays (10-300 keV) were made in experiments on board Prognoz-9 satellite and "Mir" orbital station (GRIF experiment). Some transient pulsars including A0535+262, GS1722-36, 4U1145-619, A1118-615, EXO2030+37, Sct X-1, SAX J2103.5+4545, IGR 16320-4751, IGR 16465-4507 were observed. The pulsation flux components of A0535+26 and GS1722-36 X-ray emission were revealed at significant level. For other observed pulsars the upper limits of pulsation intensity were obtained. The mean pulsation profiles of A0535+26 in different energy ranges as well as the energy spectra were obtained at different stages of outburst decreasing. The pulsation intensity-period behavior does not contradict the well-known correlation between spin-up rate and X-ray flux, while the stable character of the energy spectrum power index indicates on the absence of thermal component. The energy spectrum and mean pulsation profiles were also obtained for one time interval of GS1722-36 observations. The upper limits of pulsation fluxes obtained for other observed transient pulsars at the orbital phases more than 0.14 correspond the quiescent state or final stage of the first type outburst.

 
astro-ph/0610890 [abs, ps, pdf, other] :
Title: INTEGRAL observations of IGRJ11215-5952: the first Supergiant Fast X-ray Transient displaying periodic outbursts
Authors: Lara Sidoli, Ada Paizis, Sandro Mereghetti (INAF-IASF Milano)
Comments: To be published in the proceedings of the conference "The Multicoloured Landscape of Compact Objects and their Explosive Origins", eds.L.Burderi et al., held in Cefalu', Sicily (Italy), June 11-24, 2006. Submitted

The hard X-ray source IGRJ11215-5952, discovered with INTEGRAL during a brief outburst in 2005, has been proposed as a new member of the class of Supergiant Fast X-ray Transients. Analysing archival INTEGRAL observations of the source field,we have discovered two previously unnoticed outbursts (in July 2003 and in May 2004),spaced by intervals of ~330 days, suggesting a possible orbital period.The 5-100keV spectrum is well described by a cut-off power law, with a photon index of 0.5, and a cut-off energy 15-20keV, typical of High Mass X-ray Binaries containing a neutron star. The luminosity is ~3E36erg/s assuming 6.2kpc, the distance of the likely optical counterpart, the blue supergiant HD306414.A fourth outburst was discovered in 2006 with XTE/PCA, 329 days after the third one, confirming the periodic nature of the source outbursts.Follow-up observations with Swift/XRT refined the source position and confirmed the association with HD306414.The 5-100keV spectrum, the recurrent nature of the outbursts, the blue supergiant companion star HD 306414, support the hypothesis that IGRJ11215-5952 is a Supergiant Fast X-ray Transient, and it is the first object of this class of High Mass X-ray Binaries displaying periodic outbursts.

 
astro-ph/0610896 [abs, ps, pdf, other] :
Title: Accretion by Isolated Neutron Stars
Authors: N.R. Ikhsanov
Comments: 3 pages, to appear in Astrophysics and Space Science, in the proceedings of "Isolated Neutron Stars: from the Interior to the Surface", edited by D. Page, R. Turolla and S. Zane

Accretion of interstellar material by an isolated neutron star is discussed. The point I address here is the interaction between the accretion flow and the stellar magnetosphere. I show that the interchange instabilities of the magnetospheric boundary under the conditions of interest are basically suppressed. The entry of the material into the magnetosphere is governed by diffusion. Due to this reason the persistent accretion luminosity of isolated neutron stars is limited to < 4E+26 erg/s. These objects can also appear as X-ray bursters with the burst durations of about 30 minutes and repetition time of about 1E+5 yr. This indicates that the number of the accreting isolated neutron stars which could be observed with recent and modern X-ray missions is a few orders of magnitude smaller than that previously estimated.

 
astro-ph/0610898 [abs, ps, pdf, other] :
Title: Joint H-alpha and X-ray Observations of Massive X-ray Binaries. I. The B-Supergiant System LS I +65 010 = 2S 0114+650
Authors: E. D. Grundstrom, J. L. Blair, D. R. Gies, W. Huang, M. V. McSwain, D. Raghavan, R. L. Riddle, J. P. Subasavage, D. W. Wingert, A. M. Levine, R. A. Remillard
Comments: accepted to ApJ, 19 pages including 6 figures and 3 tables

We report on a three year spectroscopic monitoring program of the H-alpha emission in the massive X-ray binary LS I +65 010 = 2S 0114+650, which consists of a B-supergiant and a slowly rotating X-ray pulsar. We present revised orbital elements that yield a period of P=11.5983 +/- 0.0006 d and confirm that the orbit has a non-zero eccentricity e=0.18 +/- 0.05. The H-alpha emission profile is formed in the base of the wind of the B-supergiant primary, and we show how this spectral feature varies on timescales that are probably related to the rotational period of the B-supergiant. We also examine the X-ray fluxes from the Rossi X-ray Timing Explorer All-Sky Monitor instrument, and we show that the X-ray orbital light curve has a maximum at periastron and a minimum at the inferior conjunction of the B-supergiant. We also show that the wind emission strength and the high energy X-ray flux appear to vary in tandem on timescales of approximately a year.

 
astro-ph/0610902 [abs, ps, pdf, other] :
Title: Accreting millisecond pulsars: one on each hand
Authors: Manuel Linares, Michiel van der Klis, Rudy Wijnands (Amsterdam)
Comments: To appear in the proceedings of the conference `The Multicoloured Landscape of Compact Objects and their Explosive Origins' (Cefalu, Sicily, June 2006), AIP

We report on the X-ray aperiodic timing analysis of two accreting millisecond pulsars: XTE J1807-294 and IGR J00291+5934. On the one hand, we discovered in XTE J1807-294 seven pairs of simultaneous kilohertz quasi-periodic oscillations (kHz QPOs) separated in frequency by nearly the spin frequency of the neutron star. This confirms the suspected dichotomy in the frequency separation of kHz QPOs: sometimes once and sometimes half the spin frequency. On the other hand, we found an extreme behavior in the power spectra of IGR J00291+5934: very strong variability at very low frequencies. Namely, the fractional amplitude of the variability was ~50%, the highest value found so far in a neutron star system.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0610131 [abs, ps, pdf, other] :
Title: On the accretion-induced QNM excitation of a Schwarzschild black hole
Authors: Alessandro Nagar, Olindo Zanotti, Jose A. Font, Luciano Rezzolla
Comments: 15 pages, 12 figures, submitted to Phys. Rev. D

By combining the numerical solution of the nonlinear hydrodynamics equations with the solution of the linear inhomogeneous Zerilli-Moncrief and Regge-Wheeler equations we investigate the properties of the gravitational radiation emitted during the axisymmetric accretion of matter onto a Schwarzschild black hole. The matter models considered include quadrupolar dust shells and thick accretion disks, permitting us to simulate situations which may be encountered at the end stages of stellar gravitational collapse or binary neutron star merger. We focus on the interference pattern appearing in the energy spectra of the emitted gravitational waves and on the amount of excitation of the quasi-normal modes of the accreting black hole. We show that, quite generically in the presence of accretion, the black hole ringdown is not a simple superposition of quasi-normal modes, although the fundamental mode is usually present and often dominates the gravitational-wave signal. We interpret this as due to backscattering of waves off the non-exponentially decaying part of the black-hole potential and to the finite spatial extension of the accreting matter. Our results suggest that the black-hole QNM contributions to the full gravitational-wave signal should be extremely small and possibly not detectable in generic astrophysical scenarios involving the accretion of extended distributions of matter.

 

Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 1 Nov 06 01:00:15 GMT
0610912 -- 0610962 received


6 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610914 [abs, ps, pdf, other] :
Title: The Effects of Finite Emission Height in Precision Pulsar Timing
Authors: Caroline D'Angelo (1,2), Roman R. Rafikov (3) ((1) University of Toronto, (2) MPA, (3) CITA)
Comments: 12 pages, 3 figures, submitted to Physical Review D

Precision timing is the key ingredient of ongoing pulsar-based gravitational wave searches and tests of general relativity using binary pulsars. The conventional approach to timing explicitly assumes that the radio emitting region is located at the center of the pulsar, while polarimetric observations suggest that radio emission is in fact produced at altitudes ranging from tens to thousands of kilometers above the neutron star surface. Here we present a calculation of the effects of finite emission height on the timing of binary pulsars using a simple model for the emitting region geometry. Finite height of emission changes the propagation path of radio photons through the binary and gives rise to a large spin velocity of the emission region co-rotating with the neutron star. Under favorable conditions these two effects introduce corrections to the conventional time delays at the microsecond level (for a millisecond pulsar in a double neutron star binary with a period of several hours and assuming the emission height of 100 km). Exploiting the dependence of the emission height on frequency (radius-to-frequency mapping) and using multi-frequency observations one should be able to detect these timing corrections even though they are formally degenerate with conventional time delays. Although even in the most accurately timed systems the magnitude of the finite emission height effects is currently somewhat below timing precision, longer-term observations and future facilities like SKA will make measurement of these effects possible, providing an independent check of existing emission height estimates.

 
astro-ph/0610920 [abs, ps, pdf, other] :
Title: Gravitational wave stochastic background from cosmic (super)strings
Authors: Xavier Siemens, Vuk Mandic, Jolien Creighton
Comments: 4 pages, 2 figures

We consider the stochastic background of gravitational waves produced by a network of cosmic strings and assess their accessibility to current and planned gravitational wave detectors, as well as to the big bang nucleosynthesis (BBN), cosmic microwave background (CMB), and pulsar timing constraints. We find that current data from interferometric gravitational wave detectors, such as LIGO, are sensitive to areas of parameter space of cosmic string models complementary to those accessible to pulsar, BBN, and CMB bounds. Future more sensitive LIGO runs and interferometers such as Advanced LIGO and LISA will be able to explore substantial parts of the parameter space.

 
astro-ph/0610925 [abs, ps, pdf, other] :
Title: Discovery of microquasar LS I +61 303 at very high energy gamma-rays with MAGIC
Authors: Nuria Sidro (for the MAGIC Collaboration)
Comments: 6 pages, 3 figures. Prepared for "VII reunion cientifica de la SEA 2006", Barcelona (Spain) 12-15 September 2006

Here we report the discovery of very high energy gamma-ray emission from the radio emitting X-ray binary LS I +61 303 with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope. This high energy emission has been found to be variable, detected 4 days after the periastron passage and lasting for several days. The data have been taken along different orbital cycles, and the fact that the detections occur at similar orbital phases, suggests that the emission is periodic. Two different scenarios have been involved to explain this high energy emission: the microquasar scenario where the gamma-rays are produced in a radio-emitting jet; or the pulsar binary scenario, where they are produced in the shock which is generated by the interaction of a pulsar wind and the wind of the massive companion.

 
astro-ph/0610929 [abs, ps, pdf, other] :
Title: Simultaneous Single-Pulse Observations of Radio Pulsars: V. On the Broadband Nature of The Pulse Nulling Phenomenon in PSR B1133+16
Authors: N. D. R. Bhat, Y. Gupta, M. Kramer, A. Karastergiou, A. G. Lyne, S. Johnston
Comments: 12 pages, 13 figures, Accepted for publication in A&A

We revisit the phenomenon of pulse nulling using high-quality single-pulse data of PSR B1133+16 from simultaneous multifrequency observations. Observations were made at 325, 610, 1400 and 4850 MHz as part of a joint program between the European Pulsar Network and the Giant Metrewave Radio Telescope. The pulse energy time series are analysed to derive improved statistics of nulling pulses as well as to investigate the frequency dependence of the phenomenon. The pulsar is observed to be in null state for approximately 15% of the time; however, we find that nulling does not always occur simultaneously at all four frequencies of observation. We characterise this "selective nulling'' as a function of frequency, separation in frequency, and combination of frequencies. The most remarkable case is a significantly large number of nulls ($\approx$6%) at lower frequencies, that are marked by the presence of a fairly narrow emission feature at the highest frequency of 4850 MHz. We refer to these as "low frequency (LF) nulls." Our analysis shows that this high frequency emission tends to occur preferentially over a narrow range in longitude and with pulse widths typically of the order of a few milliseconds. We discuss the implications of our results for the pulsar emission mechanism in general and for the broadbandness of nulling phenomenon in particular. Our results signify the presence of an additional process of emission which does not turn off when the pulsar nulls at low frequencies, and becomes more prominent at higher frequencies. Our analysis also hints at a possible outer gap origin for this new population of pulses, and thus a likely connection to some high-energy emission processes that occur in the outer parts of the pulsar magnetosphere.

 
astro-ph/0610932 [abs, ps, pdf, other] :
Title: 10 Years of RXTE Monitoring of Anomalous X-ray Pulsar 4U 0142+61: Long-Term Variability
Authors: Rim Dib, Victoria M. Kaspi, Fotis P. Gavriil
Comments: 6 pages, 6 figures, To appear in the proceedings of Isolated Neutron Stars: From the Interior to the Surface. eds. D. Page, R. Turolla, and S. Zane

We report on 10 yr of monitoring of the 8.7-s Anomalous X-ray Pulsar 4U 0142+61 using the Rossi X-Ray Timing Explorer (RXTE). This pulsar exhibited stable rotation from 2000 until February 2006: the RMS phase residual for a spin-down model which includes nu, nudot, and nuddot is 2.3%. We report a possible phase-coherent timing solution valid over a 10-yr span extending back to March 1996. A glitch may have occured between 1998 and 2000, but it is not required by the existing data. We also report that the source's pulse profile has been evolving in the past 6 years, such that the dip of emission between its two peaks has been getting shallower since 2000, almost as if the profile is recovering to its pre-2000 morphology, in which there was no clear distinction between the peaks. These profile variations are seen in the 2-4 keV band but not in 6-8 keV. Finally, we present the pulsed flux time series of the source in 2-10 keV. There is evidence of a slow but steady increase in the source's pulsed flux since 2000. The pulsed flux variability and the narrow-band pulse profile changes present interesting challenges to aspects of the magnetar model.

 
astro-ph/0610955 [abs, ps, pdf, other] :
Title: Internal heating and thermal emission from old neutron stars: Constraints on dense-matter and gravitational physics
Authors: Andreas Reisenegger, Rodrigo Fernandez, Paula Jofre
Comments: 6 pages, 7 figures. To appear in the proceedings of "Isolated Neutron Stars: from the Interior to the Surface", a conference held in London in April 2006 (special issue of Astrophysics and Space Science, edited by Dany Page, Roberto Turolla, & Silvia Zane)

The equilibrium composition of neutron star matter is achieved through weak interactions (direct and inverse beta decays), which proceed on relatively long time scales. If the density of a matter element is perturbed, it will relax to the new chemical equilibrium through non-equilibrium reactions, which produce entropy that is partly released through neutrino emission, while a similar fraction heats the matter and is eventually radiated as thermal photons. We examined two possible mechanisms causing such density perturbations: 1) the reduction in centrifugal force caused by spin-down (particularly in millisecond pulsars), leading to "rotochemical heating", and 2) a hypothetical time-variation of the gravitational constant, as predicted by some theories of gravity and current cosmological models, leading to "gravitochemical heating". If only slow weak interactions are allowed in the neutron star (modified Urca reactions, with or without Cooper pairing), rotochemical heating can account for the observed ultraviolet emission from the closest millisecond pulsar, PSR J0437-4715, which also provides a constraint on |dG/dt| of the same order as the best available in the literature.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610167 [abs, ps, pdf, other] :
Title: INTEGRAL observation of the accreting pulsar GX 1+4
Authors: Carlo Ferrigno, Alberto Segreto, Andrea Santangelo, Joern Wilms, Ingo Kreykenbohm, Miroslav Denis, Ruediger Staubert
Comments: 15 pages, 13 figures. Accepted for publication on Astronomy and Astrophysics. Introduced language editing corrections
Note: replaced with revised version Tue, 31 Oct 2006 15:10:12 GMT (515kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 2 Nov 06 01:00:14 GMT
0611001 -- 0611035 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611014 [abs, ps, pdf, other] :
Title: Heat blanketing envelopes and thermal radiation of strongly magnetized neutron stars
Authors: A. Y. Potekhin (1), G. Chabrier (2), D. G. Yakovlev (1) ((1) Ioffe Institute, St. Petersburg; (2) CRAL, ENS-Lyon)
Comments: 9 pages, 7 figures. Proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface" (April 24-28, 2006, London, UK). ApSS (accepted)

Strong (B >> 10^9 G) and superstrong (B > 10^{14} G) magnetic fields profoundly affect many thermodynamic and kinetic characteristics of dense plasmas in neutron star envelopes. In particular, they produce strongly anisotropic thermal conductivity in the neutron star crust and modify the equation of state and radiative opacities in the atmosphere, which are major ingredients of the cooling theory and spectral atmosphere models. As a result, both the radiation spectrum and the thermal luminosity of a neutron star can be affected by the magnetic field. We briefly review these effects and demonstrate the influence of magnetic field strength on the thermal structure of an isolated neutron star, putting emphasis on the differences brought about by the superstrong fields and high temperatures of magnetars. For the latter objects, it is important to take proper account of a combined effect of the magnetic field on thermal conduction and neutrino emission at densities \rho > 10^{10} g cm^{-3}. We show that the neutrino emission puts a B-dependent upper limit on the effective surface temperature of a cooling neutron star.

 
astro-ph/0611019 [abs, ps, pdf, other] :
Title: To Constrain the Parameter Space of the ICS Model
Authors: X. H. Cui, K. J. Lee, G. J. Qiao, Y. L. Yue, R. X. Xu, H. G. Wang
Comments: 7 pages, 6 figures, submitted to "Advances in Space Research" (Proceedings of COSPAR 2006)

The pulse profile of pulsar gives geometric information about pulsar's radiation model. After investigating the pulse profiles of PSR B1642-03 and PSR B0950+08, we calculate the ratios of beam width and the emission height between different frequencies. We find that the ratios are almost constants as inclination angle $\alpha$ changes from $0^{\circ}$ to $90^{\circ}$. The ratios can be used to test pulsar's radiation model. In particular it can well constrain the parameter space of the inverse Compton scattering (ICS) model. These constrained parameters indicate some physical implication for the ICS model.

 
astro-ph/0611022 [abs, ps, pdf, other] :
Title: What can the braking indices tell us about pulsars' nature?
Authors: Y. L. Yue, R. X. Xu, W. W. Zhu
Comments: 10 pages, 4 figures, submitted to "Advances in Space Research" (Proceedings of COSPAR 2006)

As a result of observational difficulties, braking indices of only six rotation-powered pulsars are obtained with certainty, all of which are remarkably smaller than the value ($n=3$) expected for pure magnetodipole radiation model. This is still a real fundamental question not being well answered after nearly forty years of the discovery of pulsar. The main problem is that we are shamefully not sure about the dominant mechanisms that result in pulsars' spin-down. Based on the previous works, the braking index is re-examined, with a conclusion of suggesting a constant gap potential drop for pulsars with magnetospheric activities. New constrains on model parameters from observed braking indices are presented.

 
astro-ph/0611035 [abs, ps, pdf, other] :
Title: An investigation of uniform expansions of large order Bessel functions in Gravitational Wave Signals from Pulsars
Authors: F.A. Chishtie, K.M. Rao, I.S. Kotsireas, S.R. Valluri

In this work, we extend the analytic treatment of Bessel functions of large order and/or argument. We examine uniform asymptotic Bessel function expansions and show their accuracy and range of validity. Such situations arise in a variety of applications, in particular the Fourier transform of the gravitational wave signal from a pulsar. The uniform expansion we consider here is found to be valid in the entire range of the argument.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0602282 [abs, ps, pdf, other] :
Title: Temperature-dependent pulsations of superfluid neutron stars
Authors: M.E. Gusakov (1,2), N. Andersson (2) ((1) Ioffe Institute, (2) University of Southampton)
Comments: 29 pages, 1 table, 4 figures
Journal-ref: Mon.Not.Roy.Astron.Soc. 372 (2006) 1776-1790
Note: replaced with revised version Wed, 1 Nov 2006 15:14:40 GMT (44kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 3 Nov 06 01:00:12 GMT
0611036 -- 0611076 received


6 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611041 [abs, ps, pdf, other] :
Title: "High-field" pulsars torqued by accretion disk?
Authors: Y. L. Yue, W. W. Zhu, R. X. Xu
Comments: 6 pages, 1 figures, submitted to "Advances in Space Research" (Proceedings of COSPAR 2006)

The nature of AXPs/SGRs (anomalous X-ray pulsars/soft $\gamma$-ray repeaters) and high field radio pulsars is still unclear even in the magnetar and/or accretion models. The detection of radio emission from AXP XTE J1810$-$197 and the discovery of a debris disk around AXP 4U 0142+61 might shed light on the problem. We propose that AXPs/SGRs could be pulsars that have magnetic field $B\lesssim 10^{13} \mathrm{G}$ as normal pulsars, but in accretion environments. We investigate these issues under the accretion model and find that two of the AXPs/SGRs might be low mass quark stars if all AXPs and SGRs are likely grouped together.

 
astro-ph/0611047 [abs, ps, pdf, other] :
Title: Relativistic neutron star merger simulations with non-zero temperature equations of state I. Variation of binary parameters and equation of state
Authors: R. Oechslin, H.-T. Janka, A. Marek (MPA Garching)
Comments: 18 pages, 15 figures, submitted to Astronomy & Astrophysics

An extended set of binary neutron star (NS) merger simulations is performed with an approximative conformally flat treatment of general relativity to systematically investigate the influence of the nuclear equation of state (EoS), the neutron star masses, and the NS spin states prior to merging. We employ the two non-zero temperature EoSs of Shen et al. (1998a,b) and Lattimer & Swesty (1991). In addition, we use the cold EoS of Akmal et al. (1998) with a simple ideal-gas-like extension according to Shibata & Taniguchi (2006), and an ideal-gas EoS with parameters fitted to the supernuclear part of the Shen-EoS. We estimate the mass sitting in a dilute high-angular momentum ``torus'' around the future black hole (BH). The dynamics and outcome of the models is found to depend strongly on the EoS and on the binary parameters. Larger torus masses are found for asymmetric systems (up to ~0.3 M_sun for a mass ratio of 0.55), for large initial NSs, and for a NS spin state which corresponds to a larger total angular momentum. We find that the postmerger remnant collapses either immediately or after a short time when employing the soft EoS of Lattimer& Swesty, whereas no sign of post-merging collapse is found within tens of dynamical timescales for all other EoSs used. The typical temperatures in the torus are found to be about 3-10 MeV depending on the strength of the shear motion at the collision interface between the NSs and thus depending on the initial NS spins. About 10^{-3}-10^{-2} M_sun of NS matter become gravitationally unbound during or right after the merging process. This matter consists of a hot/high-entropy component from the collision interface and (only in case of asymmetric systems) of a cool/low-entropy component from the spiral arm tips. (abridged)

 
astro-ph/0611050 [abs, ps, pdf, other] :
Title: The first detection of Compton Reflection in the Low-Mass X-ray Binary 4U1705-44 with INTEGRAL and BeppoSAX
Authors: Mariateresa Fiocchi, Angela Bazzano, Pietro Ubertini, Andrzej A. Zdziarski
Comments: accepted ApJ

We present data from INTEGRAL and BeppoSAX satellites showing spectral state transitions of the neutron-star, atoll-type, low-mass X-ray binary 1705-44. Its energy spectrum can be described as the sum of one or two blackbody components, a 6.4-keV Fe line, and a component due to thermal Comptonization. In addition, and for the first time in this source, we find a strong signature of Compton reflection, presumably due to illumination of the optically-thick accretion disk by the Comptonization spectrum. The two blackbody components, which the soft-state data require, presumably arise from both the disk and the neutron-star surface. The Comptonization probably takes place in a hot inner flow irradiated by some of the blackbody photons. The spectral transitions are shown to be associated with variations in the bolometric luminosity, most likely proportional to the accretion rate. Indipendentely from the spectral state, we also see changes in the temperature of the Comptonizing electrons and the strength of Compton reflection.

 
astro-ph/0611057 [abs, ps, pdf, other] :
Title: Jet-powered optical nebulae from X-ray binaries
Authors: David M. Russell (1), Rob P. Fender (1), Elena Gallo (2), James C. A. Miller-Jones (3), Christian R. Kaiser (1) ((1) Southampton, (2) California, (3) Amsterdam)
Comments: 9 pages, 6 figures; will appear in the proceedings of the Sixth Microquasar workshop: Microquasars and Beyond, 18-22 September 2006 in Como, Italy (eds: T. Belloni et al. 2006; higher resolution figures will be available from the open-access Proceedings of Science website this http URL)

Accreting black holes and neutron stars release an unknown fraction of the infalling particles and energy in the form of collimated jets. The jets themselves are radiatively inefficient, but their power can be constrained by observing their interaction with the surrounding environment. Here we present observations of X-ray binary jet-ISM interactions which produce optical line emission, using the ESO/MPI 2.2m and Isaac Newton Telescopes. We constrain the time-averaged power of the Cyg X-1 jet-powered nebula, and present a number of new candidate nebulae discovered. Comparisons are made to the large scale lobes of extragalactic AGN. We also speculate that some emission line emitters close to X-ray binaries in M31 are likely to be microquasar jet-powered nebulae.

 
astro-ph/0611068 [abs, ps, pdf, other] :
Title: The Origin and Motion of PSR J0538+2817 in S147
Authors: C.-Y. Ng, Roger W. Romani, Walter F. Brisken, Shami Chatterjee, Michael Kramer
Comments: 20 pages, 6 figures, ApJ accepted

We report on VLBA astrometry and CXO imaging of PSR J0538+2817 in the supernova remnant S147. We measure a parallax distance of $1.47^{+0.42}_{-0.27}$kpc along with a high-precision proper motion, giving a transverse velocity $V_\perp=400^{+114}_{-73}$km/s. A small extended wind nebula is detected around the pulsar; the symmetry axis of this structure suggests that the spin axis lies $12\arcdeg\pm4\arcdeg$ from the velocity vector (2-D), but the emission is too faint for robust model independent statements. The neutron star is hot, consistent with the young ~40kyr kinematic age. The pulsar progenitor is likely a runaway from a nearby cluster, with NGC 1960 (M36) a leading candidate.

 
astro-ph/0611076 [abs, ps, pdf, other] :
Title: Type I X-ray Bursts at Low Accretion Rates
Authors: Peng, F., Brown, E.F., Truran, J.W
Comments: 6 pages, 2 figures, submitted to the proceedings of the conference "The Multicoloured Landscape of Compact Objects and Their Explosive Origins'', 2006 June 11--24, Cefalu, Sicily (Italy), to be published by AIP

Neutron stars, with their strong surface gravity, have interestingly short timescales for the sedimentation of heavy elements. Recent observations of unstable thermonuclear burning (observed as X-ray bursts) on the surfaces of slowly accreting neutron stars ($< 0.01$ of the Eddington rate) motivate us to examine how sedimentation of CNO isotopes affects the ignition of these bursts. We further estimate the burst development using a simple one-zone model with a full reaction network. We report a region of mass accretion rates for weak H flashes. Such flashes can lead to a large reservoir of He, the unstable burning of which may explain some observed long bursts (duration $\sim 1000$ s).

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 6 Nov 06 01:00:12 GMT
0611077 -- 0611127 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611082 [abs, ps, pdf, other] :
Title: A search for radio pulsars around low-mass white dwarfs
Authors: Joeri van Leeuwen, Robert D. Ferdman, Sol Meyer, Ingrid Stairs (UBC)
Comments: 4 pages, accepted for publication in MNRAS

Low-mass white dwarfs can either be produced in low-mass X-ray binaries by stable mass transfer to a neutron star, or in a common-envelope phase with a heavier white dwarf companion. We have searched 8 low-mass white dwarf candidates recently identified in the Sloan Digital Sky Survey for radio pulsations from pulsar companions, using the Green Bank Telescope at 340MHz. We have found no pulsations down to flux densities of 0.6-0.8 mJy/kpc^2 and conclude that a given low-mass helium-core white dwarf has a probability of < 0.18+-0.05 of being in a binary with a radio pulsar.

 
astro-ph/0611100 [abs, ps, pdf, other] :
Title: Spitzer Mid-infrared Upper Limits on Anomalous X-Ray Pulsars 1E 1048.1-5937, 1RXS J170849-400910, and XTE J1810-197
Authors: Z. Wang, V. M. Kaspi, S. J. U. Higdon
Comments: 7 pages, 5 figures, submitted to ApJ

We report on mid-infrared imaging observations of the anomalous X-ray pulsars (AXPs) 1E 1048.1-5937, 1RXS J170849-400910, and XTE J1810-197. The observations were carried out at 4.5 and 8.0 microns with the Infrared Array Camera and at 24 microns with the Multiband Imaging Photometer on the Spitzer Space Telescope. No mid-infrared counterparts were detected. As infrared emission from AXPs may be related to their X-ray emission either via the magnetosphere or via a dust disk, we compare the derived upper limits on the infrared/X-ray flux ratios of the AXPs to the same ratio for 4U 0142+61, an AXP previously detected in the mid-infrared range. The comparison indicates that our three non-detections are consistent with their relatively low X-ray fluxes. For XTE J1810-197, our upper limits set a constraint on its rising radio/millimeter energy spectrum, suggesting a spectral break between 1.5$\times 10^{11}$--6$\times10^{13}$ Hz.

 
astro-ph/0611101 [abs, ps, pdf, other] :
Title: Normal Modes of Black Hole Accretion Disks
Authors: Manuel Ortega-Rodriguez, Alexander S. Silbergleit, Robert V. Wagoner
Comments: 51 pages, 3 figures

This paper studies the hydrodynamical problem of normal modes of small adiabatic oscillations of relativistic barotropic thin accretion disks around black holes (and compact weakly magnetic neutron stars). Employing WKB techniques, we obtain the eigenfrequencies and eigenfunctions of the modes for different values of the mass and angular momentum of the central black hole. We discuss the properties of the various types of modes and examine the role of viscosity, as it appears to render some of the modes unstable to rapid growth.

 
astro-ph/0611115 [abs, ps, pdf, other] :
Title: Nucleon superfluidity versus thermal states of isolated and transiently accreting neutron stars
Authors: K. P. Levenfish (1), P. Haensel (2) ((1) Ioffe Physical-Technical Inst., St.Petersburg, (2) N.Copernicus Astronomical Center, Warsaw)
Comments: 8 pages, 7 Figs, to be published in the proc. of "Isolated Neutron Stars: From the Interior to the Surface", eds. D.Page, S.Zane, R.Turolla

The properties of superdense matter in neutron star (NS) cores control NS thermal states by affecting the efficiency of neutrino emission from NS interiors. To probe these properties we confront the theory of thermal evolution of NSs with observations of their thermal radiation. Our observational basis includes cooling isolated NSs (INSs) and NSs in quiescent states of soft X-ray transients (SXTs). We find that the data on SXTs support the conclusions obtained from the analysis of INSs: strong proton superfluidity with T_{cp,max} >= 10^9 K should be present, while mild neutron superfluidity with T_{cn,max} =(2*10^8 -- 2*10^9) K is ruled out in the outer NS core. Here T_{cn,max} and T_{cp,max} are the maximum values of the density dependent critical temperatures of neutrons and protons. The data on SXTs suggest also that: (i) cooling of massive NSs is enhanced by neutrino emission more powerful than the emission due to Cooper pairing of neutrons; (ii) mild neutron superfluidity, if available, might be present only in inner cores of massive NSs. In the latter case SXTs would exhibit dichotomy, i.e. very similar SXTs may evolve to very different thermal states.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 7 Nov 06 01:00:14 GMT
0611128 -- 0611190 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611140 [abs, ps, pdf, other] :
Title: Presupernova evolution and explosion of massive stars with mass loss
Authors: Marco Limongi (INAF-OAR), Alessandro Chieffi (INASF-IASF)
Comments: 8 pages, 5 figures. invited review talk at the Workshop "The multicoloured landscape of compact objects and their explosive origin", Cefalu' (Sicily), 11-24 June 2006, to be published by AIP

We review the main properties of solar metallicity massive stars in the range 11-120 Msun. The influence of the mass loss on the hydrostatic burning stages as well as the final explosion is discussed in some detail. We find that the minimum masses that enter the WNL, WNE and WC stages are 30 Msun, 35 Msun and 40 Msun respectively; the limiting mass between stars exploding as SNII and SNIb/c is between 30 and 35 Msun; the limiting mass between stars forming neutron stars and black holes after the explosion is between 25-30 Msun. We also discuss the properties of the chemical yields integrated over a Salpeter IMF and we find that stars with M>=35 Msun contribute for ~60% to the production of C, N and for ~40% to the production Sc and s-process elements up to Zr, while they do not produce any intermediate mass element because of the large remnant masses

 
astro-ph/0611145 [abs, ps, pdf, other] :
Title: Modelling mid-Z element atmospheres for strongly-magnetized neutron stars
Authors: Kaya Mori (1,2), Wynn C.G. Ho (3,4) ((1) University of Toronto, (2) CITA, (3) Harvard-Smithsonian CfA, (4) MIT)
Comments: 16 pages, 23 figures, submitted to MNRAS

We construct models for strongly-magnetized neutron star atmospheres composed of mid-Z elements (carbon, oxygen and neon) with magnetic fields B=10^{12}-10^{13} G and effective temperatures Teff=(1-5)*10^6 K; this is done by first addressing the physics relevant to strongly-magnetized plasmas and calculating the equation of state and polarization-dependent opacities. We then obtain the atmosphere structure and spectrum by solving the radiative transfer equations in hydrostatic and radiative equilibrium. In contrast to hydrogen opacities at the relevant temperatures, mid-Z element opacities are dominated by numerous bound-bound and bound-free transitions. Consequently, temperature profiles are closer to grey profiles, and photosphere densities are lower than in the hydrogen case. Mid-Z element atmosphere spectra are significantly softer than hydrogen atmosphere spectra and show numerous absorption lines and edges. The atmosphere spectra depend strongly on surface composition and magnetic field but weakly on surface gravity. Absorption lines are primarily broadened by motional Stark effects and the (unknown) surface magnetic field distribution. Given the multiple absorption features observed from several isolated neutron stars, it is possible to determine, with existing X-ray data, the surface composition, magnetic field, temperature, and gravitational redshift; we present qualitative comparisons between our model spectra and the neutron stars 1E1207.4-5209 and RX J1605.3+3249. Future high-resolution X-ray missions such as Constellation-X will measure the gravitational redshift with high accuracy by resolving narrow absorption features, and when combined with radius measurements, it will be possible to uniquely determine the mass and radius of isolated neutron stars. (Abridged)

 
astro-ph/0611175 [abs, ps, pdf, other] :
Title: The first multi-wavelength campaign of AXP 4U 0142+61 from radio to hard X-rays
Authors: P.R. den Hartog (1), L. Kuiper (1), W. Hermsen (1,2), N. Rea (1), M. Durant (3), B. Stappers (2,4) V.M. Kaspi (5), R. Dib (5) ((1) SRON Netherlands Institute for Space Research; (2) Astronomical Institute, University of Amsterdam; (3) Department of Astronomy & Astrophysics, University of Toronto; (4) ASTRON The Netherlands Foundation for Research in Astronomy; (5) Physics Department, McGill University)
Comments: 6 pages, 1 figure. To be published in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface" (April 24-28, 2006, London, UK), eds. S. Zane, R. Turolla and D. Page

For the first time a quasi-simultaneous multi-wavelength campaign has been performed on an Anomalous X-ray Pulsar from the radio to the hard X-ray band. 4U 0142+61 was an INTEGRAL target for 1 Ms in July 2005. During these observations it was also observed in the X-ray band with Swift and RXTE, in the optical and NIR with Gemini North and in the radio with the WSRT. In this paper we present the source-energy distribution. The spectral results obtained in the individual wave bands do not connect smoothly; apparently components of different origin contribute to the total spectrum. Remarkable is that the INTEGRAL hard X-ray spectrum (power-law index 0.79 +/- 0.10) is now measured up to an energy of ~230 keV with no indication of a spectral break. Extrapolation of the INTEGRAL power-law spectrum to lower energies passes orders of magnitude underneath the NIR and optical fluxes, as well as the low ~30 microJy (2 sigma) upper limit in the radio band.

 
astro-ph/0611177 [abs, ps, pdf, other] :
Title: Galactic centre X-ray sources
Authors: Andrew J. Gosling, Reba M. Bandyopadhyay, Katherine M. Blundell
Comments: 4 pages, 3 figures; Poster to appear in AIP Conf. Proc.: `The Multicoloured Landscape of Compact Objects and their Explosive Origins'; Cefalu, Sicily, 2006 June 11-24

We report on a campaign to identify the counterparts to the population of X-ray sources discovered at the centre of our Galaxy by Wang et al.(2002) using Chandra. We have used deep, near infrared images obtained on VLT/ISAAC to identify candidate counterparts as astrometric matches to the X-ray positions. Follow up Ks-band spectroscopic observations of the candidate counterparts are used to search for accretions signatures in the spectrum, namely the Brackett-Gamma emission line (Bandyopadhyay et al.1997). From our small initial sample, it appears that only a small percentage, ~2-3% of the ~1000 X-ray sources are high mass X-ray binaries or wind accreting neutron stars, and that the vast majority will be shown to be canonical low mass X-ray binaries and cataclysmic variables.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0605514 [abs, ps, pdf, other] :
Title: An algorithm for solving the pulsar equation
Authors: Lukasz Bratek, Marcin Kolonko
Comments: 4 pages, 4 figures, accepted for publication in ApSS (a shortened version of the previous one)
Subj-class: Astrophysics; Numerical Analysis
Note: replaced with revised version Mon, 6 Nov 2006 14:56:31 GMT (234kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 8 Nov 06 01:00:20 GMT
0611191 -- 0611236 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611213 [abs, ps, pdf, other] :
Title: The Galactic distribution of magnetic fields in molecular clouds and HII regions
Authors: J.L. Han (NAOC), J.S. Zhang (GuangZhouUni)
Comments: 17 pages with two long tables of collected data. Submited to A&A. Comments welcome!

Aims: Magnetic fields exist on all scales in our Galaxy. There is a controversy on whether the magnetic fields in molecular clouds are preserved from the permeated magnetic fields in the interstellar medium (ISM). We want to check this controversy using available data in the light of the newly revealed magnetic field structure of the Galactic disk obtained from pulsar rotation measures (RMs). Methods: We collected the measurements of the magnetic fields in molecular clouds, including Zeeman splitting data of OH masers in clouds and OH or HI absorption or emission lines of clouds themselves. Results: These Zeeman data show structures in the sign distribution of line-of-sight component of magnetic field. Comparing with the large- scale Galactic magnetic fields from pulsar RMs we found that the sign-distribution show similar large-scale field reversals. Previous such examinations were flawed by the over-simplified global model for the large-scale magnetic fields in the Galactic disk. Conclusions: We conclude that the magnetic fields in the clouds may still "remember" the directions of magnetic fields in the Galactic ISM to some extent, and could be used as completementary tracer for the large-scale magnetic structure. More Zeeman data of OH masers in widerly distributed clouds are desired for such a study.

 
astro-ph/0611216 [abs, ps, pdf, other] :
Title: Swift and Chandra confirm the intensity-hardness correlation of the AXP 1RXS J170849.0-400910
Authors: S. Campana (Brera Obs.), N. Rea (SRON), G.L. Israel (Roma Obs.), R. Turolla (Padova Univ.), S. Zane (MSSL)
Comments: 6 pages, 5 figures, accepted for publication on A&A

Convincing evidence for long-term variations in the emission properties of the anomalous X-ray pulsar 1RXS J170849.0-400910 has been gathered in the last few years. In particular, and following the pulsar glitches of 1999 and 2001, XMM-Newton witnessed in 2003 a decline of the X-ray flux accompanied by a definite spectral softening. This suggested the existence of a correlation between the luminosity and the spectral hardness in this source, similar to that seen in the soft gamma-repeater SGR 1806-20. Here we report on new Chandra and Swift observations of 1RXS J170849.0-400910 performed in 2004 and 2005, respectively. These observations confirm and strengthen the proposed correlation. The trend appears to have now reversed: the flux increased and the spectrum is now harder. The consequences of these observations for the twisted magnetosphere scenario for anomalous X-ray pulsars are briefly discussed.

 
astro-ph/0611222 [abs, ps, pdf, other] :
Title: Timing an Accreting Millisecond Pulsar: Measuring the Accretion Torque in IGR J00291+5934
Authors: L. Burderi, T. Di Salvo, G. Lavagetto, M.T. Menna, A. Papitto, A. Riggio, R. Iaria, F. D'antona, N. R. Robba, L. Stella
Comments: 7 pages including 1 figure. Accepted for publication by ApJ

We performed a timing analysis of the fastest accreting millisecond pulsar IGR J00291+5934 using RXTE data taken during the outburst of December 2004. We corrected the arrival times of all the events for the orbital (Doppler) effects and performed a timing analysis of the resulting phase delays. In this way we have the possibility to study, for the first time in this class of sources, the spin-up of a millisecond pulsar as a consequence of accretion torques during the X-ray outburst. The accretion torque gives us for the first time an independent estimate of the mass accretion rate onto the neutron star, which can be compared with the observed X-ray luminosity. We also report a revised value of the spin period of the pulsar.

 
astro-ph/0611236 [abs, ps, pdf, other] :
Title: Developing radio beam geometry and luminosity models of pulsars
Authors: P.L. Gonthier, S.A. Story, B.M. Giacherio, R.A. Arevalo, A.K. Harding
Comments: 10 pages, 6 figures, The 2005 Lake Hanas International Pulsar Symposium. Accepted in Chinese Journal of Astronomy & Astrophysics

Our recent studies of pulsar population statistics suggest that improvements of radio and gamma-ray beam geometry and luminosity models require further refinement. The goal of this project is to constrain the viewing geometry for some radio pulsars, especially three-peaked pulse profiles, in order to limit the uncertainty of the magnetic inclination and impact angles. We perform fits of the pulse profile and position angle sweep of radio pulsars for the available frequencies. We assume a single core and conal beams described by Gaussians. We incorporate three different size cones with frequency dependence from the work of Mitra & Deshpande (1999). We obtain separate spectral indices for the core and cone beams and explore the trends of the ratio of core to cone peak fluxes. This ratio is observed to have some dependence with period. However, we cannot establish the suggested functional form of this ratio as indicated by the work of Arzoumanian, Chernoff & Cordes (2002).

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 9 Nov 06 01:00:18 GMT
0611237 -- 0611268 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611237 [abs, ps, pdf, other] :
Title: The Low-Mass X-ray Binary and Globular Cluster Connection in Virgo Cluster Early-type Galaxies: Optical Properties
Authors: Gregory R. Sivakoff (1,2), Andrés Jordán (3), Craig L. Sarazin (1), John P. Blakeslee (4), Patrick C{\^ o}t{\' e} (5), Laura Ferrarese (5), Adrienne M. Juett (1), Simona Mei (6,7), Eric W. Peng (5) ((1) University of Virginia, (2) The Ohio State University, (3) European Southern Observatory, (4) Washington State University, (5) Herzberg Institute of Astrophysics, (6) Observatoire de Paris, (7) Johns Hopkins University)
Comments: Submitted to Astrophysical Journal, 18 pages, 5 Color Figures (degraded), 6 B & W Figures: Full resolution paper available at this http URL

(Abridged) Chandra and Hubble ACS observations of 11 early-type galaxies probe the low-mass X-ray binary (LMXB) - globular cluster (GC) connection. We explore the optical properties of 270 GCs with LMXBs and 6,488 GCs without LMXBs. More massive, redder, and more compact GCs are more likely to contain LMXBs. Unlike Galactic GCs, a large number of GCs with LMXBs have half-mass relaxation times > 2.5 Gyr. We fit the dependence of the expected number of LMXBs per GC, \lambda_t, on the GC mass M, color (g-z), and half-mass radius r_{h,cor}, and find that \lambda_t \propto M^{1.24\pm0.08} 10^{0.9^{+0.2}_{-0.1} (g-z)} r_{h,cor}^{-2.2^{+0.3}_{-0.4}}. Our fit rules out that the number of LMXBs per GC is linearly proportional to GC mass and that most GCs with high X-ray luminosities contain a single LMXB. The detailed dependence of \lambda_t on GC properties appears essentially equivalent to a dependence on the encounter rate \Gamma_h and the metallicity Z, \lambda_t \propto \Gamma_h^{0.82\pm0.05} Z^{0.39\pm0.07}. Our analysis provides strong evidence that dynamical formation and metallicity play the primary roles in determining the presence of an LMXB in extragalactic GCs. The shallower than linear dependence for our sample, as well as Galactic X-ray sources and radio pulsars in GCs, requires an explanation by theories of dynamical binary formation. The abundance dependence is consistent with a metallicity-dependent variation in the number of neutron stars and black holes per unit mass GC or effects from irradiation induced winds.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 10 Nov 06 01:00:14 GMT
0611269 -- 0611311 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611273 [abs, ps, pdf, other] :
Title: Population Studies of the Unidentified EGRET Sources
Authors: J. M. Siegal-Gaskins, V. Pavlidou, A. V. Olinto, C. Brown, B. D. Fields
Comments: 6 pages, 2 figures, to appear in proceedings of "The Multi-Messenger Approach to High Energy Gamma-Ray Sources", Barcelona, 4-7 July, 2006; comments welcome

The third EGRET catalog contains a large number of unidentified sources. This subset of objects is expected to include known gamma-ray emitters of Galactic origin such as pulsars and supernova remnants, in addition to an extragalactic population of blazars. However, current data allows the intriguing possibility that some of these objects may represent a new class of yet undiscovered gamma-ray sources. Many theoretically motivated candidate emitters (e.g. clumps of annihilating dark matter particles) have been suggested to account for these detections. We take a new approach to determine to what extent this population is Galactic and to investigate the nature of the possible Galactic component. By assuming that galaxies similar to the Milky Way should host comparable populations of objects, we constrain the allowed Galactic abundance and distribution of various classes of gamma-ray sources using the EGRET data set. We find it is highly improbable that a large number of the unidentified sources are members of a Galactic halo population, but that a distribution of the sources entirely in the disk and bulge is plausible. Finally, we discuss the additional constraints and new insights that GLAST will provide.

 
astro-ph/0611291 [abs, ps, pdf, other] :
Title: GeV-TeV gamma-ray light curves expected in the IC electron-positron pair cascade model for massive binaries: Application to LS 5039
Authors: W. Bednarek
Comments: 5 pages, 4 figures, A&A accepted

TeV gamma-ray emission from two massive binaries of the microquasar type, LS 5039 and LS I +61$^{\rm o}$ 303, show clear variability with their orbital periods. Our purpose is to calculate the GeV and TeV $\gamma$-ray light curves from the massive binary LS 5039 which are expected in the specific Inverse Compton $e^\pm$ pair cascade model. This model successfully predicted the basic features of the high energy $\gamma$-ray emission from LS 5039 and LS I +61 303. In the calculations we apply the Monte Carlo code which follows the IC $e^\pm$ pair cascade in the anisotropic radiation of the massive star. The $\gamma$-ray light curves and spectra are obtained for different parameters of the acceleration scenario and the inclination angles of the binary system. It is found that the GeV and TeV $\gamma$-ray light curves should be anti-correlated. This feature can be tested in the near future by the simultaneous observations of LS 5039 with the AGILE and GLAST telescopes in GeV energies and the Cherenkov telescopes in the TeV energies. Considered model also predicts a broad maximum in the TeV $\gamma$-ray light curve between the phases $\sim 0.4-0.8$ consistently with the observations of LS 5039 by the HESS telescopes. Moreover, we predict additional dip in the TeV light curve for large inclination angles $\sim 60^{\rm o}$. This feature could serve as a diagnostic for independent measuring of the inclination angle of this binary system indicating also on the presence of a neutron star in LS 5039.

 
astro-ph/0611309 [abs, ps, pdf, other] :
Title: Production and evolution of millisecond X-ray and radio pulsars
Authors: Frederick K. Lamb
Comments: 13 pages, 1 figure, to appear in Spectra and Timing of Compact X-ray Binaries, ed. P. Ghosh, & E.P.J. van den Heuvel, Advances in Space Research (Elsevier Science) [doi:10.1016/j.asr.2006.08.003], in press (2006)

Observations using the Rossi X-ray Timing Explorer have discovered dozens of accreting neutron stars with millisecond spin periods in low-mass binary star systems. Eighteen are millisecond X-ray pulsars powered by accretion or nuclear burning or both. These stars have magnetic fields strong enough for them to become millisecond rotation-powered (radio) pulsars when accretion ceases. Few, if any, accretion- or rotation-powered pulsars have spin rates higher than 750 Hz. There is strong evidence that the spin-up of some accreting neutron stars is limited by magnetic spin equilibrium whereas the spin-up of others is halted when accretion ends. Further study will show whether the spin rates of some accretion- or rotation-powered pulsars are or were limited by emission of gravitational radiation.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 13 Nov 06 01:00:13 GMT
0611312 -- 0611351 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611319 [abs, pdf] :
Title: Rubidium-Rich Asymptotic Giant Branch Stars
Authors: D. A. Garcia-Hernandez, P. Garcia-Lario, B. Plez, F. D'Antona, A. Manchado, J. M. Trigo-Rodriguez
Comments: 17 pages, 2 figures and 1 table. 3 figures of supporting online material are also included. Accepted 2006 Oct 19 for publication in Science; Published online in 2006 Nov 9 edition of Science Express

A long debated issue concerning the nucleosynthesis of neutron-rich elements in Asymptotic Giant Branch (AGB) stars is the identification of the neutron source. We report intermediate-mass (4 to 8 solar masses) AGB stars in our Galaxy that are rubidium-rich owing to overproduction of the long-lived radioactive isotope 87Rb, as predicted theoretically 40 years ago. This represents a direct observational evidence that the 22Ne(alpha,n)25Mg reaction must be the dominant neutron source in these stars. These stars then challenge our understanding of the late stages of the evolution of intermediate-mass stars and would promote a highly variable Rb/Sr environment in the early solar nebula.

 
astro-ph/0611320 [abs, ps, pdf, other] :
Title: Be born slow or die fast: spin evolution of neutron stars with alignment or counteralignment
Authors: S.A. Eliseeva, S.B. Popov, V.S. Beskin
Comments: 12 pages, 7 figures

We revisit the case of magneto-rotational evolution of neutron stars (NSs) with accounting for changes of the angle \chi between spin and magnetic axes. This element of the evolution of NSs is very important for age estimates and population modeling, but usually it is neglected. In the framework of two models of energy losses we demonstrate that unless NSs are born with the inclination angle \chi_0 very close (within 1 degree) to the position of maximal losses, pulsars with short initial periods quickly reach regions of small energy losses (aligned rotators in the case of magneto-dipole losses and orthogonal rotators -- in the case of current losses) without significant spin-down. This means that either most of known NSs should be born with relatively long periods close to presently observed values, or the initial inclination angles should be large (close to 90) for the magnetodipole model and very small (close to 0) for the current losses model, or that both models cannot be applied for the whole evolutionary track of a typical NS. In particular, magnetar candidates should be born with periods close to the observed ones within the scope of both models of energy losses. We discuss how these considerations can influence population synthesis models and age estimates for different types of isolated NSs. Focusing on the model of current losses we illustrate our conclusion with evolutionary track reconstructions on the P--\sin \chi plane. We conclude, that most probably both existing models of energy losses -- magneto-dipole and longitudinal current -- require serious modifications, on the other hand, estimates obtained under the standard assumption of \sin \chi=1=const does not have solid theoretical ground and should be taken with care.

 
astro-ph/0611331 [abs, ps, pdf, other] :
Title: A software baseband receiver for pulsar astronomy at GMRT
Authors: Bhal Chandra Joshi (1), Sunil Ramakrishna (2 and 3) ((1) National Centre for Radio Astrophysics (TIFR), India, (2) International Institute of Information Technology, India, (3) Intoto Software (I) Pvt Ltd., India)
Comments: 13 pages, 6 figures, accepted for publication in Bulletin of Astronomical Society of India

A variety of pulsar studies, ranging from high precision astrometry to tests for theories of gravity, require high time resolution data. Few such observations at more than two frequencies below 1 GHz are available. Giant Meterwave Radio Telescope (GMRT) has the unique capability to provide such multi-frequency pulsar data at low observation frequencies, but the quality and time resolution of pulsar radio signals is degraded due to dispersion in the inter-stellar medium at these frequencies. Such degradation is usually taken care of by employing specialized digital hardware, which implement coherent dedispersion algorithm. In recent years, a new alternative is provided by the availability of cheap computer hardware. In this approach, the required signal processing is implemented in software using commercially off-the-shelf available computing hardware. This makes such a receiver flexible and upgradeable unlike a hardware implementation. The salient features and the modes of operation of a high time resolution pulsar instrument for GMRT based on this approach is described in this paper. The capability of the instrument is demonstrated by illustrations of test observations. We have obtained the average profile of PSR B1937+21 at 235 MHz for the first time and this profile indicates a scattering timescale of about 300 us. Lastly, the possible future extensions of this concept are discussed.

 
astro-ph/0611345 [abs, ps, pdf, other] :
Title: X-rays from cusps of compact remnants near galactic centres
Authors: Sergei Nayakshin (U of Leicester), Rashid Sunyaev (MPA-Garching)
Comments: submitted to MNRAS; 5 pages

Compact remnants -- stellar mass black holes and neutron stars formed in the inner few parsec of galactic centres are predicted to sink into the central parsec due to dynamical friction on low mass stars, forming a high concentration cusp (Morris 1993). Same physical region may also contain very high density molecular clouds and accretion discs that are needed to fuel SMBH activity. Here we estimate gas capture rates onto the cusp of stellar remnants, and the resulting X-ray luminosity, as a function of the accretion disc mass. At low disc masses, most compact objects are too dim to be observable, whereas in the high disc case most of them are accreting at their Eddington rates. We find that for low accretion disc masses, compact remnant cusps may be more luminous than the central SMBHs. This ``diffuse'' emission may be of importance for local moderately bright AGN, especially Low Luminosity AGN. We also briefly discuss how this expected emission can be used to put constraints on the black hole cusp near our Galactic Centre.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0611030 [abs, ps, pdf, other] :
Title: Cold uniform matter and neutron stars in the quark-mesons-coupling model
Authors: J. Rikovska-Stone (1), P.A.M. Guichon (2), H.H. Matevosyan (3), A.W. Thomas (3) ((1) Un. of Oxford (2) CEA Saclay (3) JLab USA)

A new density dependent effective baryon-baryon interaction has been recently derived from the quark-meson-coupling (QMC) model, offering impressive results in application to finite nuclei and dense baryon matter. This self-consistent, relativistic quark-level approach is used to construct the Equation of State (EoS) and to calculate key properties of high density matter and cold, slowly rotating neutron stars. The results include predictions for the maximum mass of neutron star models, together with the corresponding radius and central density, as well the properties of neutron stars with mass of order 1.4 $M_\odot$. The cooling mechanism allowed by the QMC EoS is explored and the parameters relevant to slow rotation, namely the moment of inertia and the period of rotation investigated. The results of the calculation, which are found to be in good agreement with available observational data, are compared with the predictions of more traditional EoS. The QMC EoS provides cold neutron star models with maximum mass 1.9--2.1 M$_\odot$, with central density less than 6 times nuclear saturation density ($n_{0}= 0.16 {\rm fm}^{-3}$) and offers a consistent description of the stellar mass up to this density limit. In contrast with other models, QMC predicts no hyperon contribution at densities lower than $3n_0$, for matter in $\beta$-equilibrium. At higher densities, $\Xi^{-,0}$ and $\Lambda$ hyperons are present.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609693 [abs, ps, pdf, other] :
Title: Intermittent pulsations in an accretion-powered millisecond pulsar
Authors: Duncan K. Galloway (1), Edward H. Morgan (2), Miriam I. Krauss (2,3), Philip Kaaret (4), Deepto Chakrabarty (2,3) ((1) University of Melbourne, (2) MIT Kavli Institute, (3) Department of Physics, MIT, (4) University of Iowa)
Comments: 5 pages, 3 figures, accepted by ApJL following minor revisions suggested by referee
Note: replaced with revised version Fri, 10 Nov 2006 00:06:43 GMT (34kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 14 Nov 06 01:00:14 GMT
0611352 -- 0611404 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611368 [abs, ps, pdf, other] :
Title: Assessing Millisecond Proto-Magnetars as GRB Central Engines
Authors: Todd A. Thompson
Comments: 10 pages; proceedings of the conference "Triggering Relativistic Jets," held in Cozumel, Mexico, 2005; accepted for publication in Rev. Mex. A&A

Magnetars are a sizable subclass of the neutron star census. Their very high magnetic field strengths are thought to be a consequence of rapid (millisecond) rotation at birth in a successful core-collapse supernova. In their first tens of seconds of existence, magnetars transition from hot, extended ``proto-''magnetars to the cooled and magnetically-dominated objects we identify $\sim10^4$ years later as Soft Gamma-ray Repeaters (SGRs) and Anamolous X-ray Pulsars (AXPs). Millisecond proto-magnetar winds during this cooling phase likewise transition from non-relativistic and thermally-driven to magneto-centrifugally-driven, and finally to relativistic and Poynting-flux dominated. Here we review the basic considerations associated with that transition. In particular, we discuss the spindown of millisecond proto-magnetars throughout the Kelvin-Helmholtz cooling epoch. Because of their large reservoir of rotational energy, their association with supernovae, and the fact that their winds are expected to become highly relativistic in the seconds after their birth, proto-magnetars have been suggested as the central engine of long-duration gamma ray bursts. We discuss some of the issues and outstanding questions in assessing them as such.

 
astro-ph/0611398 [abs, pdf] :
Title: Binary and recycled pulsars: 30 years after observational discovery
Authors: G S Bisnovatyi-Kogan
Journal-ref: Physics-Uspekhi 49 (1)53-61 (2006)

Binary radio pulsars, first discovered by Hulse and Taylor in 1974 [1], are a unique tool for experimentally testing general relativity (GR), whose validity has been confirmed with a precision unavailable in laboratory experiments. In particular, indirect evidence of the existence of gravitational waves has been obtained. Radio pulsars in binary systems (which have come to be known as recycled) have completed the accretion stage, during which neutron star spins reach millisecond periods and their magnetic fields decay 2 to 4 orders of magnitude more weakly than ordinary radio pulsars. Among about a hundred known recycled pulsars, many have turned out to be single neutron stars. The high concentration of single recycled pulsars in globular clusters suggests that close stellar encounters are highly instrumental in the loss of the companion. A system of one recycled pulsar and one 'normal' one discovered in 2004 is the most compact among binaries containing recycled pulsars [2]. Together with the presence of two pulsars in one system, this suggests new prospects for further essential improvements in testing GR. This paper considers theoretical predictions of binary pulsars, their evolutionary formation, and mechanisms by which their companions may be lost. The use of recycled pulsars in testing GR is discussed and their possible relation to the most intriguing objects in the universe, cosmic gamma-ray bursts, is examined.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611222 [abs, ps, pdf, other] :
Title: Timing an Accreting Millisecond Pulsar: Measuring the Accretion Torque in IGR J00291+5934
Authors: L. Burderi, T. Di Salvo, G. Lavagetto, M.T. Menna, A. Papitto, A. Riggio, R. Iaria, F. D'antona, N. R. Robba, L. Stella
Comments: 7 pages including 1 figure. Accepted for publication by ApJ; revised version including proof corrections
Note: replaced with revised version Mon, 13 Nov 2006 16:58:59 GMT (34kb)
 
gr-qc/0609044 [abs, ps, pdf, other] :
Title: Accurate and realistic initial data for black hole-neutron star binaries
Authors: Philippe Grandclement (LUTH)
Comments: Version accepted for publication in Physical Review D
Note: replaced with revised version Mon, 13 Nov 2006 08:00:39 GMT (36kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 15 Nov 06 01:00:11 GMT
0611405 -- 0611446 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611405 [abs, ps, pdf, other] :
Title: Inferring the Magnetic Fields of Magnetars from their X-ray Spectra
Authors: Tolga Guver, Feryal Ozel, Maxim Lyutikov
Comments: submitted to ApJ

We present the first self-consistent theoretical models of magnetar spectra that take into account the combined effects of the stellar atmosphere and its magnetosphere. We find that the proton cyclotron lines that are already weakened by atmospheric effects become indistinguishable from the continuum for moderate scattering optical depths in the magnetosphere. Furthermore, the hard excess becomes more pronounced due to resonant scattering and the resulting spectra closely resemble the observed magnetar spectra. We argue that while the absence of proton cyclotron lines in the observed spectra are inconclusive about the surface field strengths of magnetars, the continuum carries nearly unique signatures of the field strength and can thus be used to infer this quantity. We fit our theoretical spectra with a phenomenological two-blackbody model and compare our findings to source spectra with existing two-blackbody fits. The field strengths that we infer spectroscopically are in remarkable agreement with the values inferred from the period derivative of the sources assuming a dipole spindown. These detailed predictions of line energies and equivalent widths may provide an optimal opportunity for measuring directly the surface field strengths of magnetars with future X-ray telescopes such as {\em Constellation}-X.

 
astro-ph/0611436 [abs, ps, pdf, other] :
Title: The binary pulsar PSR J1811-1736: evidence of a low amplitude supernova kick
Authors: A.Corongiu, M.Kramer, B.W.Stappers, A.G.Lyne, A.Jessner, A.Possenti, N.D'Amico, O.Loehmer
Comments: 8 pages, 4 figures, accepted for publication on A&A. (Abridged abstract)

Aims: The binary pulsar PSR J1811-1736 has been identified, since its discovery, as a member of a double neutron star system. Observations of such binary pulsars allow the measurement of general relativistic effects, which in turn lead to information about the orbiting objects and, in a few cases, to tests of theories of gravity. Methods: Regular timing observations have been carried out with three of the largest European radio telescopes involved in pulsar research. The prospects of continued observations were studied with simulated timing data. Pulse scattering times were measured using dedicated observations at 1.4 GHz and at 3.1 GHz, and the corresponding spectral index has also been determined. The possibility of detecting the yet unseen companion as a radio pulsar was also investigated. A study of the natal kick received by the younger neutron star at birth was performed. Results: We present an up to date and improved timing solution for the binary pulsar PSR J1811-1736. One post-Keplerian parameter, the relativistic periastron advance, is measured and leads to the determination of the total mass of this binary system. The pulse profile at 1.4 GHz is heavily broadened by interstellar scattering, limiting the timing precision achievable at this frequency and the measurability of other post-keplerian parameters. Interstellar scattering is unlikely to be the reason for the continued failure to detect radio pulsations from the companion of PSR J1811-1736. The probability distribution that we derive for the amplitude of the kick imparted on the companion neutron star at its birth indicates that the kick has been of low amplitude.

 
astro-ph/0611440 [abs, ps, pdf, other] :
Title: Fallback accretion in the aftermath of a compact binary merger
Authors: S. Rosswog
Comments: submitted to MNRAS, 3 figures

Recent observations of long and short gamma-ray bursts have revealed a puzzling X-ray activity that in some cases continuous until hours after the burst. It is difficult to reconcile such time scales with the viscous time scales that an accretion disk can plausibly provide. Here I discuss the accretion activity expected from the material that during a compact binary merger coalescence is launched into eccentric, but gravitationally bound orbits. From a simple analytical model the time scales and accretion luminosities that result from fallback in the aftermath of a compact binary merger are derived. For the considered mass range double neutron star binaries are relatively homogeneous in their fallback luminosities, neutron star black hole systems show a larger spread in their fallback behaviour. While the model is too simple to make predictions about the detailed time structure of the fallback, it is expected to make reasonable predictions about its gross properties. About one hour after the coalescence the fallback accretion luminosity can still be as large as $\sim 10^{45}$ erg/s, a fraction of which will be transformed into X-rays. Large-scale amplitude variations in the X-ray luminosities can plausibly be caused by gravitational fragmentation, which for the high-eccentricity fallback should occur more easily than in an accretion disk.

 
astro-ph/0611442 [abs, ps, pdf, other] :
Title: The origin of long-period X-ray pulsars
Authors: N.R. Ikhsanov
Comments: 7 pages, 2 tables, submitted for publication in MNRAS

Several relatively bright, persistent X-ray sources display regular pulses, with periods in the range of 700-10000 s. These sources are identified with massive close binaries in which a neutron star accretes material onto its surface. The observed pulsations in all of them, but one, are unambiguously associated with the spin period of the neutron star. Analyzing possible history of these pulsars I conclude that the neutron stars in these systems undergo spherical accretion and their evolutionary tracks in a previous epoch contained three instead of two states, namely, ejector, supersonic propeller, and subsonic propeller. An assumption about a supercritical value of the initial magnetic field of the neutron stars within this scenario is not necessary. Furthermore, I show that the scenario in which the neutron star in 2S 0114+650 is assumed to be a magnetar descendant encounters major difficulties in explaining the evolution of the massive companion. An alternative interpretation of the spin evolution of the neutron star in this system is presented and the problem raised by association of the 10000 s pulsations with the spin period of the neutron star is briefly discussed.

 
astro-ph/0611445 [abs, ps, pdf, other] :
Title: Turn-over in pulsar spectra around 1 GHz
Authors: J. Kijak, Y. Gupta, K. Krzeszowski
Comments: 4 pages, to be published in Astronomy & Astrophysics

The main aim is to investigate the possibility of a high frequency turn-over in the radio spectrum of pulsars. Using the GMRT, multi-frequency flux density measurements of several candidate pulsars have been carried out and their spectra have been extended to lower frequencies. We present the first direct evidence for turn-over in pulsar radio spectra at high frequencies. A total of 3 pulsars (including 2 new ones from this study) are now shown to have a turn-over frequency > 1 GHz, and one is shown to have a turn-over at ~600 MHz.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 16 Nov 06 01:00:12 GMT
0611447 -- 0611496 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611450 [abs, ps, pdf, other] :
Title: Correlation between X-ray Lightcurve Shape and Radio Arrival Time in the Vela Pulsar
Authors: A. Lommen (Franklin and Marshall), J. Donovan (Columbia), C. Gwinn (UCSB), Z. Arzoumanian (NASA Goddard, USRA), A. Harding (NASA Goddard), M. Strickman (NRL), R. Dodson (OAN, Madrid), P. McCulloch (U. Tasmania), D. Moffett (Furman)
Comments: 6 pages, 5 figures, accepted by ApJ

We report the results of simultaneous observations of the Vela pulsar in X-rays and radio from the RXTE satellite and the Mount Pleasant Radio Observatory in Tasmania. We sought correlations between the Vela's X-ray emission and radio arrival times on a pulse by pulse basis. At a confidence level of 99.8% we have found significantly higher flux density in Vela's main X-ray peak during radio pulses that arrived early. This excess flux shifts to the 'trough' following the 2nd X-ray peak during radio pulses that arrive later. Our results suggest that the mechanism producing the radio pulses is intimately connected to the mechanism producing X-rays. Current models using resonant absorption of radio emission in the outer magnetosphere as a cause of the X-ray emission are explored as a possible explanation for the correlation.

 
astro-ph/0611460 [abs, ps, pdf, other] :
Title: Paramagnetism in color superconductivity and compact stars
Authors: Efrain J. Ferrer, Vivian de la Incera
Comments: 7 pages, presented at IRAG 2006, Barcelona, July 11-15, 2006

It is quite plausible that color superconductivity occurs in the inner regions of neutron stars. At the same time, it is known that strong magnetic fields exist in the interior of these compact objects. In this paper we discuss some important effects that can occur in the color superconducting core of compact stars due to the presence of the stars' magnetic field. In particular, we consider the modification of the gluon dynamics for a color superconductor with three massless quark flavors in the presence of an external magnetic field. We show that the long-range component of the external magnetic field that penetrates the color-flavor locked phase produces an instability for field values larger than the charged gluons' Meissner mass. As a consequence, the ground state is restructured forming a vortex state characterized by the condensation of charged gluons and the creation of magnetic flux tubes. In the vortex state the magnetic field outside the flux tubes is equal to the applied one, while inside the tubes its strength increases by an amount that depends on the amplitude of the gluon condensate. This paramagnetic behavior of the color superconductor can be relevant for the physics of compact stars.

 
astro-ph/0611469 [abs, ps, pdf, other] :
Title: The elusive Innermost Stable Circular Orbit: Now you see it, now you don't
Authors: Mariano Mendez
Comments: 8 pages, 2 figures. Uses aipproc.cls. To appear in the proceedings of the conference``The Multicoloured Landscape of Compact Objects and their Explosive Origins'', 2006 June 11--24, Cefalu, Sicily, to be published by AIP

I study the behaviour of the maximum rms fractional amplitude, $r_{\rm max}$ and the maximum coherence, $Q_{\rm max}$, of the kilohertz quasi-periodic oscillations (kHz QPOs) in a dozen low-mass X-ray binaries. I find that: (i) The maximum rms amplitudes of the lower and the upper kHz QPO, $r^{\ell}_{\rm max}$ and $r^{\rm u}_{\rm max}$, respectively, decrease more or less exponentially with increasing luminosity of the source; (ii) the maximum coherence of the lower kHz QPO, $Q^{\ell}_{\rm max}$, first increases and then decreases exponentially with luminosity; (iii) the maximum coherence of the upper kHz QPO, $Q^{\rm u}_{\rm max}$, is more or less independent of luminosity; and (iv) $r_{\rm max}$ and $Q_{\rm max}$ show the opposite behaviour with hardness of the source, consistent with the fact that there is a general anticorrelation between luminosity and spectral hardness in these sources. Both $r_{\rm max}$ and $Q_{\rm max}$ in the sample of sources, and the rms amplitude and coherence of the kHz QPOs in individual sources show a similar behaviour with hardness. This similarity argues against the interpretation that the drop of coherence and rms amplitude of the lower kHz QPO at high QPO frequencies in individual sources is a signature of the innermost stable circular orbit around a neutron star.

 
astro-ph/0611477 [abs, ps, pdf, other] :
Title: X-ray broad-band study of the symbiotic X-ray binary 4U 1954+31
Authors: N. Masetti, E. Rigon, E. Maiorano, G. Cusumano, E. Palazzi, M. Orlandini, L. Amati, F. Frontera
Comments: 13 pages, 5 figures (2 in the Appendix), 4 tables (1 in the Appendix), accepted for publication on A&A, main journal

(Abridged) We present results of several X-ray observations of the X-ray binary 4U 1954+31 performed with the satellites BeppoSAX, EXOSAT, ROSAT, RXTE, and Swift. We also studied the RXTE ASM data over a period of more than 10 years. Light curves of all observations show an erratic behaviour with sudden increases in the source emission on timescales variable from hundreds to thousands of seconds. There are no indications of changes in the source spectral hardness, with the possible exception of the RXTE pointed observation. Timing analysis does not reveal the presence of coherent pulsations or periodicities either in the pointed observations in the range from 2 ms to 2000 s or in the long-term RXTE ASM light curve on timescales from days to years. The 0.2-150 keV spectrum, afforded with BeppoSAX, is the widest for this source available up to now in terms of spectral coverage and is well described by a model consisting of a lower-energy thermal component (hot diffuse gas) plus a higher-energy (Comptonization) emission, with the latter modified by a partially-covering cold absorber plus a warm (ionized) absorber. A blackbody modelization of our BeppoSAX low-energy data is instead ruled out. The presence of a complex absorber local to the source is also supported by the 0.1-2 keV ROSAT spectrum. RXTE, EXOSAT and Swift X-ray spectroscopy is consistent with the above results, but indicates variations in the density and the ionization of the local absorber. A 6.5 keV emission line is possibly detected in the BeppoSAX and RXTE spectra. All this information suggests that the scenario which better describes 4U 1954+31 consists of a binary system in which a neutron star orbits in a highly inhomogeneus medium from a stellar wind coming from its optical companion, an M-type giant star.

 
astro-ph/0611483 [abs, ps, pdf, other] :
Title: The prospects for X-ray polarimetry and its potential use for understanding neutron stars
Authors: M.C. Weisskopf, R.F. Elsner, D. Hanna, V.M. Kaspi, S.L. O'Dell, G.G. Pavlov, B.D. Ramsey
Comments: 17 pages and 13 figures. Paper presented at the 363-rd Heraeus Seminar in Bad Honef, Germany. The paper will be published as a Springer Lecture Notes. Submitted for refereeing

We review the state of the art for measuring the X-ray polarization of neutron stars. We discuss how valuable precision measurements of the degree and position angle of polarization as a function of energy and, where relevant, of pulse phase, would provide deeper insight into the details of the emission mechanisms. We then review the current state of instrumentation and its potential for obtaining relevant data. Finally, we conclude our discussion with some opinions as to future directions.

 

Cross-listings


2 abstracts or titles contain neutron star, magnetar or pulsar


hep-ph/0611126 [abs, ps, pdf, other] :
Title: Neutral color-spin locking phase in neutron stars
Authors: Deborah N. Aguilera
Comments: 3 pages, 4 figures, contribution talk to the IVth International Conference on Quarks and Nuclear Physics(QNP06), Madrid, Spain, 5-10 Jun 2006

We present results for the spin-1 color-spin locking phase (CSL) using a NJL-type model in two flavor quark matter for compact stars applications. The CSL condensate is flavor symmetric and therefore charge and color neutrality can easily be satisfied. We find small energy gaps ~1 MeV, which make the CSL matter composition and the EoS not very different from the normal quark matter phase. We keep finite quark masses in our calculations and obtain no gapless modes that could have strong consequences in the late cooling of neutron stars. Finally, we show that the region of the phase diagram relevant for neutron star cores, when asymmetric flavor pairing is suppressed, could be covered by the CSL phase.

 
nucl-th/0611046 [abs, ps, pdf, other] :
Title: Superfluidity in neutron stars and cold atoms
Authors: A. Schwenk
Comments: 3 pages, 2 figures, talk at Quark Confinement and the Hadron Spectrum VII, Ponta Delgada, September 2006
Subj-class: Nuclear Theory; Superconductivity

We discuss superfluidity in neutron matter, with particular attention to induced interactions and to universal properties accessible with cold atoms.

 

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hep-ph/0608041 [abs, ps, pdf, other] :
Title: Spin-one color superconductivity in compact stars?- an analysis within NJL-type models
Authors: D.N. Aguilera
Comments: 7 pages, 7 figures, revised version, accepted for the Conference Proceedings of "Isolated Neutron Stars: from the Interior to the Surface", London, 24-28. April 2006
Note: replaced with revised version Wed, 15 Nov 2006 14:15:33 GMT (103kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 17 Nov 06 01:08:14 GMT
0611497 -- 0611539 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611516 [abs, ps, pdf, other] :
Title: The Be/X-ray transient 4U 0115+63/V635 Cassiopeiae. III. Quasi-cyclic variability
Authors: P. Reig (U. Crete), V. Larionov (U. St Petersburg), I. Negueruela (U. Alicante), A.A. Arkharov (Pulkovo Obs.), N.A. Kudryavtseva (U. St Petersburg)
Comments: 10 pages, 6 figures, Tables 2 and 3 in electronic form only

4u 0115+63 is one of the most active and best studied Be/X-ray transients. Previous studies of 4u0115+63 have led to the suggestion that it undergoes relatively fast quasi-cyclic activity. However, due to the lack of good coverage of the observations, the variability time scales are uncertain. Our objective is to investigate the long-term behaviour of 4u 0115+63 to confirm its quasi-cyclic nature and to explain its correlated optical/IR and X-ray variability. We have performed optical/IR photometric observations and optical spectroscopic observations of 4u 0115+63 over the last decade with unprecedented coverage. We have focused on the Halpha line variability and the long-term changes of the photometric magnitudes and colours and investigated these changes in correlation with the X-ray activity of the source. results The optical and infrared emission is characterised by cyclic changes with a period of ~ 5 years. This long-term variability is attributed to the state of the circumstellar disc around the Be star companion. Each cycle involves a low state when the disc is very weak or absent and the associated low amplitude variability is orbitally modulated and a high state when a perturbed disc precesses, giving rise to fast and large amplitude photometric changes. X-ray outbursts in 4u 0115+63 come in pairs, i.e., two in every cycle. However, sometimes the second outburst is missing. Our results can be explained within the framework of the decretion disc model. The neutron star acts as the perturbing body, truncating and distorting the disc. The first outburst would occur before the disc is strongly perturbed. The second outburst leads to the dispersal of the disc and marks the end of the perturbed phase.

 
astro-ph/0611522 [abs, ps, pdf, other] :
Title: Merger of black hole-neutron star binaries in full general relativity
Authors: Masaru Shibata, Koji Uryu
Comments: 14 pages. To appear in a special issue of Classical and Quantum Gravity: New Frontiers in Numerical Relativity

We present our latest results for simulation for merger of black hole (BH)-neutron star (NS) binaries in full general relativity which is performed preparing a quasicircular state as initial condition. The BH is modeled by a moving puncture with no spin and the NS by the $\Gamma$-law equation of state with $\Gamma=2$ and corotating velocity field as a first step. The mass of the BH is chosen to be $\approx 3.2 M_{\odot}$ or $4.0M_{\odot}$, and the rest-mass of the NS $\approx 1.4 M_{\odot}$ with relatively large radius of the NS $\approx 13$--14 km. The NS is tidally disrupted near the innermost stable orbit but $\sim 80$--90% of the material is swallowed into the BH and resulting disk mass is not very large as $\sim 0.3M_{\odot}$ even for small BH mass $\sim 3.2M_{\odot}$. The result indicates that the system of a BH and a massive disk of $\sim M_{\odot}$ is not formed from nonspinning BH-NS binaries irrespective of BH mass, although a disk of mass $\sim 0.1M_{\odot}$ is a possible outcome for this relatively small BH mass range as $\sim 3$--4$M_{\odot}$. Our results indicate that the merger of low-mass BH and NS may form a central engine of short-gamma-ray bursts.

 
astro-ph/0611524 [abs, ps, pdf, other] :
Title: Constraining the number of compact remnants near Sgr A*
Authors: Patrick Deegan, Sergei Nayakshin
Comments: 9 pages, 3 Postscript figures

Due to dynamical friction stellar mass black holes and neutron stars are expected to form high density cusps in the inner parsec of our Galaxy. These compact remnants, expected to number around 20000, may be accreting cold dense gas present there, and give rise to potentially observable X-ray emission. Here we build a simple but detailed time-dependent model of such emission. We find that at least several X-ray sources of this nature should be detectable with Chandra at any one time. Turning this issue around, we also ask a question of what current observational constraints might be telling us about the total number of compact remnants. A cusp with ~ 40 thousand black holes over-predicts the number of discrete sources and the total X-ray luminosity of the inner parsec, and is hence ruled out. Future observations of the distribution and orbits of the cold ionised gas in the inner parsec of Sgr A* will put tighter constraints on the cusp of compact remnants.

 

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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 20 Nov 06 01:00:09 GMT
0611540 -- 0611579 received


0 abstracts or titles contain neutron star, magnetar or pulsar



Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0611043 [abs, ps, pdf, other] :
Title: The crust of neutron stars
Authors: Nicolas Chamel
Comments: 9 pages, 2 figures, to appear in the Proceedings of the Tours Symposium on Nuclear Physics VI (2006)

The structure of the crust of a neutron star is completely determined by the experimentally measured nuclear masses up to a density of the order of 10^11 g.cm^{-3}. At higher densities, the composition of the crust still remains uncertain, mainly due to the presence of ``free'' superfluid neutrons which affect the properties of the nuclear ``clusters''. After briefly reviewing calculations of the equilibrium structure of the crust, we point out that the current approach based on the Wigner-Seitz approximation does not properly describe the unbound neutrons. We have recently abandoned this approximation by applying the band theory of solids. We have shown that the dynamical properties of the free neutrons are strongly affected by the clusters by performing 3D calculations with Bloch boundary conditions.

 

Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611522 [abs, ps, pdf, other] :
Title: Merger of black hole-neutron star binaries in full general relativity
Authors: Masaru Shibata, Koji Uryu
Comments: 14 pages. To appear in a special issue of Classical and Quantum Gravity: New Frontiers in Numerical Relativity
Note: replaced with revised version Fri, 17 Nov 2006 04:29:32 GMT (141kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 22 Nov 06 01:00:13 GMT
0611644 -- 0611686 received


9 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611646 [abs, ps, pdf, other] :
Title: XMM-Newton observations of HESS J1813-178 reveal a composite Supernova remnant
Authors: S. Funk, J. A. Hinton, Y. Moriguchi, F. A. Aharonian, Y. Fukui, W. Hofmann, D. Horns, G. Puehlhofer, O. Reimer, G. Rowell, R. Terrier, J. Vink, S. Wagner
Comments: Submitted to A&A

We present X-ray and 12CO(J=1-0) observations of the very-high-energy (VHE) gamma-ray source HESS J1813-178 with the aim of understanding the origin of the gamma-ray emission. Using this dataset we are able to undertake spectral and morphological studies of the X-ray emission from this object with greater precision than previous studies. NANTEN 12CO(J=1-0) data are used to search for correlations of the gamma-ray emission with molecular clouds which could act as target material for gamma-ray production in a hadronic scenario. The NANTEN 12CO(J=1-0) observations show a giant molecular cloud of mass 2.5 10^5 M$_{\sun}$ at a distance of 4 kpc in the vicinity of HESS J1813-178. Even though there is no direct positional coincidence, this giant cloud might have influenced the evolution of the gamma-ray source and its surroundings. The X-ray data show a highly absorbed non-thermal X-ray emitting object coincident with the previously known ASCA source AX J1813-178 showing a compact core and an extended tail towards the north-east, located in the centre of the radio shell-type Supernova remnant (SNR) G12.82-0.2. This central object shows morphological and spectral resemblance to a Pulsar Wind Nebula (PWN) and we therefore consider that the object is very likely to be a composite SNR. We discuss the scenario in which the gamma-rays originate in the shell of the SNR and the one in which they originate in the central object. We demonstrate, that in order to connect the core X-ray emission to the VHE gamma-ray emission electrons have to be accelerated to energies of at least 1 PeV.

 
astro-ph/0611652 [abs, ps, pdf, other] :
Title: GLAST Large Area Telescope Multiwavelength Planning
Authors: O. Reimer, P.F. Michelson, R.A. Cameron, S.W. Digel, D.J. Thompson, K.S. Wood
Comments: Comments: 4 pages, Accepted for publication in Astrophysics and Space Science, Proc. of "The Multi-Messenger Approach to High-Energy Gamma-ray Sources (Third Workshop on the Nature of Unidentified High-Energy Sources)", Barcelona, July 4-7, 2006

Gamma-ray astrophysics depends in many ways on multiwavelength studies. The Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) Collaboration has started multiwavelength planning well before the scheduled 2007 launch of the observatory. Some of the high-priority multiwavelength needs include: (1) availability of contemporaneous radio and X-ray timing of pulsars; (2) expansion of blazar catalogs, including redshift measurements; (3) improved observations of molecular clouds, especially at high galactic latitudes; (4) simultaneous broad-band blazar monitoring; (5) characterization of gamma-ray transients, including gamma ray bursts; (6) radio, optical, X-ray and TeV counterpart searches for reliable and effective sources identification and characterization. Several of these activities are needed to be in place before launch.

 
astro-ph/0611653 [abs, ps, pdf, other] :
Title: Demystifying an unidentified EGRET source by VHE gamma-ray observations
Authors: Olaf Reimer, Stefan Funk
Comments: Comments: 4 pages, 5 figures, Accepted for publication in Astrophysics and Space Science, Proc. of "The Multi-Messenger Approach to High-Energy Gamma-ray Sources (Third Workshop on the Nature of Unidentified High-Energy Sources)", Barcelona, July 4-7, 2006

In a novel approach in observational high-energy gamma-ray astronomy, observations carried out by imaging atmospheric Cherenkov telescopes provide necessary templates to pinpoint the nature of intriguing, yet unidentified EGRET gamma-ray sources. Using GeV-photons detected by CGRO EGRET and taking advantage of high spatial resolution images from H.E.S.S. observations, we were able to shed new light on the EGRET observed gamma-ray emission in the Kookaburra complex, whose previous coverage in the literature is somewhat contradictory. 3EGJ1420-6038 very likely accounts for two GeV gamma-ray sources (E>1 GeV), both in positional coincidence with the recently reported pulsar wind nebulae (PWN) by HESS in the Kookaburra/Rabbit complex. PWN associations at VHE energies, supported by accumulating evidence from observations in the radio and X-ray band, are indicative for the PSR/plerionic origin of spatially coincident, but still unidentified Galactic gamma-ray sources from EGRET. This not only supports the already suggested connection between variable, but unidentified low-latitude gamma-ray sources with pulsar wind nebulae (3EGJ1420-6038 has been suggested as PWN candidate previoulsy), it also documents the ability of resolving apparently confused EGRET sources by connecting the GeV emission as measured from a large-aperture space-based gamma-ray instrument with narrow field-of-view but superior spatial resolution observations by ground-based atmospheric Cherenkov telescopes, a very promising identification technique for achieving convincing individual source identifications in the era of GLAST-LAT.

 
astro-ph/0611659 [abs, ps, pdf, other] :
Title: Measuring Neutron Star Mass and Radius with Three Mass-Radius Relations
Authors: C. M. Zhang, H.X. Yin, Y. Kojima, H. K. Chang, R. X. Xu, X. D. Li, B. Zhang, B. Kiziltan
Comments: 8 pages, 3 figures, accepted by MNRAS

We propose to determine the mass and the radius of a neutron star (NS) using three measurable mass-radius relationships, namely the ``apparent'' radius inferred from neutron star thermal emission, the gravitational redshift inferred from the absorption lines, as well as the averaged stellar mass density inferred from the orbital Keplerian frequency derived from the kilohertz quasi periodic oscillation (kHz QPO) data. We apply the method to constrain the NS mass and the radius of the X-ray sources, 1E 1207.4-5209, Aql X-1 and EXO 0748-676.

 
astro-ph/0611666 [abs, ps, pdf, other] :
Title: Torsional Oscillations of Relativistic Stars with Dipole Magnetic Fields II. Global Alfv\'en Modes
Authors: H. Sotani, K. D. Kokkotas, N. Stergioulas, M. Vavoulidis
Comments: 13 pages, 8 figures

We investigate torsional Alfv\'{e}n modes of relativistic stars with a global dipole magnetic field. It has been noted recently (Glampedakis et al. 2006) that such oscillation modes could serve as as an alternative explanation (in contrast to torsional crustal modes) for the SGR phenomenon, if the magnetic field is not confined to the crust. We compute global Alfv\'{e}n modes for a representative sample of equations of state and magnetar masses, in the ideal MHD approximation and ignoring $\ell \pm 2$ terms in the eigenfunction. We find that the presence of a realistic crust has a negligible effect on Alfv\'{e}n modes for $B > 4\times 10^{15}$ G. Furthermore, we find strong avoided crossings between torsional Alfv\'{e}n modes and torsional crust modes. For magnetar-like magnetic field strengths, the spacing between consecutive Alfv\'{e}n modes is of the same order as the gap of avoided crossings. As a result, it is not possible to identify modes of predominantly crustal character and all oscillations are predominantly Alfv\'{e}n-like. Interestingly, we find excellent agreement between our computed frequencies and observed frequencies in two SGRs, for a maximum magnetic field strenght in the range of (0.8--1.2)$\times 10^{16}$ G.

 
astro-ph/0611672 [abs, ps, pdf, other] :
Title: Parsec-scale Constraints on the Ionized Interstellar Medium with the Terzan 5 Pulsars
Authors: Scott M. Ransom (NRAO)
Comments: 6 pages, 2 color figures. For the proceedings of the "SINS - Small Ionized and Neutral Structures in the Diffuse Interstellar Medium" meeting, edited by M. Haverkorn & W. M. Goss

Over the past two years, we used a series of GBT observations to uncover at least 33 millisecond pulsars in the globular cluster Terzan 5 located in the Galactic bulge. We now have 32 timing solutions for the pulsars which give us precise positions and dispersion measures (DMs) and indicate that the DMs are dominated by variations in the integrated electron density along the slightly different sight lines towards the pulsars. At a distance of ~8.7 kpc, angular separations between the pulsars range from 0.4"-100" and correspond to projected physical separations of 0.01-4 pc, giving us a unique probe into the ionized ISM properties on these scales. Our measurement of the DM structure function toward Terzan 5 is not inconsistent with Kolmogorov-like electron density fluctuations in the ISM on scales ranging from at least 0.2-2 pc.

 
astro-ph/0611674 [abs, ps, pdf, other] :
Title: Jet-dominated advective systems of all mass scales
Authors: Elmar Koerding, Rob Fender (Southampton)
Comments: conference proceedings of the Sixth Microquasar workshop: Microquasars and Beyond, 18-22 September 2006 in Como, Italy (eds: T. Belloni et al. 2006)

We show that the radio emission of black hole (BH) and neutron star (NS) X-ray binaries (XRBs) follows the analytical prediction of a jet model where the jet carries a constant fraction of the accretion power. The radio emission can therefore be used as a tracer of the accretion rate. This measure is normalised with efficiently radiating objects. As it is independent of the X-ray fluxes, the measure allows us to compare the accretion rate dependency of the bolometric X-ray luminosity of BHs and NSs. For NSs, it scales linearly with accretion rate while the scaling for BHs is quadratic - as expected for inefficient accretion flows. We find the same behaviour in AGN. This new approach uses the jet power to obtain the accretion rate. Thus, we know both the jet power and the radiated power of an accreting BH. This allows us to show that some accretion power is likely to be advected into the black hole, while the jet power dominates over the bolometric luminosity of a hard state BH.

 
astro-ph/0611676 [abs, ps, pdf, other] :
Title: Vertex renormalization in weak decays of Cooper pairs and cooling compact stars
Authors: Armen Sedrakian, Herbert Müther, Peter Schuck
Comments: 13 pages, 9 figures, uses RevTex

At temperatures below the critical temperature of superfluid phase transition baryonic matter emits neutrinos by breaking and recombination of Cooper pairs formed in the condensate. The strong interactions in the nuclear medium modify the weak interaction vertices and the associated neutrino loss rates. We study these modifications non-perturbatively by summing infinite series of particle-hole diagrams in the S-wave superfluid neutron matter. We argue that a consistent approach requires fulfillment of the dispersion relations for the polarization tensor, which insure the unitarity of the S-matrix. The pairing and particle-hole interactions in neutron matter are described in the framework of the BCS and Fermi-liquid theories derived from microscopic interactions. The neutrino loss rates in the vector channel are enhanced compared to the rates derived from free-space weak vertices in the temperature domain close to the critical temperature, T_c, but are suppressed by factors 5-10 for temperatures below 0.5 T_c. The vertex corrected axial vector current emission is suppressed by the ratio of the baryon to the neutrino velocity squared.

 
astro-ph/0611680 [abs, pdf] :
Title: Pulsar spins from an instability in the accretion shock of supernovae
Authors: John M. Blondin, Anthony Mezzacappa
Comments: To be published in Nature

Rotation-powered radio pulsars are born with inferred initial rotation periods of order 300 ms (some as short as 20 ms) in core-collapse supernovae. In the traditional picture, this fast rotation is the result of conservation of angular momentum during the collapse of a rotating stellar core. This leads to the inevitable conclusion that pulsar spin is directly correlated with the rotation of the progenitor star. So far, however, stellar theory has not been able to explain the distribution of pulsar spins, suggesting that the birth rotation is either too slow or too fast. Here we report a robust instability of the stalled accretion shock in core-collapse supernovae that is able to generate a strong rotational flow in the vicinity of the accreting proto-neutron star. Sufficient angular momentum is deposited on the proto-neutron star to generate a final spin period consistent with observations, even beginning with spherically symmetrical initial conditions. This provides a new mechanism for the generation of neutron star spin and weakens, if not breaks, the assumed correlation between the rotational periods of supernova progenitor cores and pulsar spin.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 23 Nov 06 01:00:10 GMT
0611687 -- 0611721 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611698 [abs, pdf] :
Title: Linear growth of spiral SASI modes in core-collapse supernovae
Authors: John M. Blondin, Samantha Shaw
Comments: To be published in The Astrophysical Journal

Two-dimensional axisymmetric simulations have shown that the post-bounce accretion shock in core collapse supernovae is subject to the Spherical Accretion Shock Instability, or SASI. Recent three-dimensional simulations have revealed the existence of a non-axisymmetric mode of the SASI as well, where the postshock flow displays a spiral pattern. Here we investigate the growth of these spiral modes using two-dimensional simulations of the post-bounce accretion flow in the equatorial plane of a core-collapse supernova. By perturbing a steady-state model we are able to excite both one, two and three-armed spiral modes that grow exponentially with time, demonstrating that these are linearly unstable modes closely related to the original axisymmetric sloshing modes. By tracking the distribution of angular momentum, we show that these modes are able to efficiently separate the angular momentum of the accretion flow (which maintains a net angular momentum of zero), leading to a significant spin-up of the underlying accreting proto-neutron star.

 
astro-ph/0611708 [abs, ps, pdf, other] :
Title: Turning Points in the Evolution of Isolated Neutron Stars' Magnetic Fields
Authors: U. Geppert
Comments: Comments: 37 pages and 14 figures. Paper presented (in part) at the 363-rd Heraeus Seminar in Bad Honef, Germany. The paper will be published as a Springer Lecture Notes. Submitted for refereeing

During the life of isolated neutron stars (NSs) their magnetic field passes through a variety of evolutionary phases. Depending on its strength and structure and on the physical state of the NS (e.g. cooling, rotation), the field looks qualitatively and quantitatively different after each of these phases. Three of them, the phase of MHD instabilities immediately after NS's birth, the phase of fallback which may take place hours to months after NS's birth, and the phase when strong temperature gradients may drive thermoelectric instabilities, are concentrated in a period lasting from the end of the proto--NS phase until 100, perhaps 1000 years, when the NS has become almost isothermal. The further evolution of the magnetic field proceeds in general inconspicuous since the star is in isolation. However, as soon as the product of Larmor frequency and electron relaxation time, the so-called magnetization parameter, locally and/or temporally considerably exceeds unity, phases, also unstable ones, of dramatic changes of the field structure and magnitude can appear. An overview is given about that field evolution phases, the outcome of which makes a qualitative decision regarding the further evolution of the magnetic field and its host NS.

 
astro-ph/0611713 [abs, ps, pdf, other] :
Title: Simultaneous radio/X-ray observations of Cir X-1
Authors: V. Tudose (1,2), P. Soleri (1), R.P. Fender (3,1), P.G. Jonker (4,5,6), M. van der Klis (1), A.K. Tzioumis (7), R.E. Spencer (8) ((1) Amsterdam, (2) Bucharest, (3) Southampton, (4) SRON, (5) Harvard, (6) Utrecht, (7) ATNF, (8) Manchester)
Comments: Accepted for publication in the proceedings of VI Microquasar Workshop: Microquasars and Beyond, 18-22 September 2006, Como (Italy), ed: T. Belloni (2006)

We present a partial analysis of a multi-wavelength study of the X-ray binary Cir X-1, a system harboring the most relativistic outflow in our galaxy so far. The data were taken (almost) simultaneously in radio and X ray during a survey carried out in October 2000 and December 2002. Cir X-1 was observed at the radio frequencies of 4.8 and 8.6 GHz with the Australia Telescope Compact Array (ATCA). In the X-ray spectral domain we used the Rossi X-Ray Timing Explorer (RXTE). We found strong evidence for flaring activity in radio not only at the periastron but also at the apoastron passages. A comparison of our data against different correlations between radio and X ray found in other neutron star systems shows that Cir X-1 does not seem to follow the general trend. However, the fact that Cir X-1 is an `exotic' X-ray binary makes any interpretation more complicated.

 
astro-ph/0611716 [abs, ps, pdf, other] :
Title: Discovery of 1122 Hz X-Ray Burst Oscillations from the Neutron-Star X-Ray Transient XTE J1739-285
Authors: P. Kaaret, Z. Prieskorn, J.J.M. in 't Zand, S. Brandt, N. Lund, S. Mereghetti, D. Gotz, E. Kuulkers, J.A. Tomsick
Comments: Submitted to ApJL, 4 pages

We report the discovery of oscillations at 1122 +/- 0.3 Hz in an X-ray burst from the X-ray transient XTE J1739-285. The signal has a peak Leahy power of 42.8 and, after consideration of the number of trials, has a chance probability of occurrence of 4E-5 equivalent to a 4.2 sigma detection. The oscillation frequency suggests that XTE J1739-285 contains the fastest rotating neutron star yet found. We also found millisecond quasiperiodic oscillations in the persistent emission with frequencies ranging from 757 Hz to 862 Hz. We detected seven X-ray bursts and derive an upper limit on the source distance of about 10.6 kpc from the brightest burst.

 
astro-ph/0611720 [abs, ps, pdf, other] :
Title: Associations of Very High Energy Gamma-Ray Sources Discovered by H.E.S.S. with Pulsar Wind Nebulae
Authors: Yves A. Gallant, for the H.E.S.S. Collaboration
Comments: 5 pages, to appear in Astrophysics and Space Science (proceedings of "The Multi-Messenger Approach to High-Energy Gamma-Ray Sources")

The H.E.S.S. array of imaging Cherenkov telescopes has discovered a number of previously unknown gamma-ray sources in the very high energy (VHE) domain above 100 GeV. The good angular resolution of H.E.S.S. (~0.1 degree per event), as well as its sensitivity (a few percent of the Crab Nebula flux) and wide 5-degree field of view, allow a much better constrained search for counterparts in comparison to previous instruments. In several cases, the association of the VHE sources revealed by H.E.S.S. with pulsar wind nebulae (PWNe) is supported by a combination of positional and morphological evidence, multi-wavelength observations, and plausible PWN model parameters. These include the plerions in the composite supernova remnants G 0.9+0.1 and MSH 15-52, the recently discovered Vela X nebula, two new sources in the Kookaburra complex, and the association of HESS J1825-137 with PSR B1823-13. The properties of these better-established associations are reviewed. A number of other sources discovered by H.E.S.S. are located near high spin-down power pulsars, but the evidence for association is less complete. These possible associations are also discussed, in the context of the available multi-wavelength data and plausible PWN scenarios.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611442 [abs, ps, pdf, other] :
Title: The origin of long-period X-ray pulsars
Authors: N.R. Ikhsanov
Comments: 7 pages, 2 tables, accepted for publication in MNRAS
Note: replaced with revised version Wed, 22 Nov 2006 11:27:43 GMT (30kb)
 
nucl-th/0611046 [abs, ps, pdf, other] :
Title: Superfluidity in neutron stars and cold atoms
Authors: A. Schwenk
Comments: 3 pages, 2 figures, talk at Quark Confinement and the Hadron Spectrum VII, Ponta Delgada, September 2006, one reference corrected
Subj-class: Nuclear Theory; Superconductivity
Note: replaced with revised version Wed, 22 Nov 2006 02:22:56 GMT (49kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 23 Nov 06 01:00:10 GMT
0611687 -- 0611721 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611698 [abs, pdf] :
Title: Linear growth of spiral SASI modes in core-collapse supernovae
Authors: John M. Blondin, Samantha Shaw
Comments: To be published in The Astrophysical Journal

Two-dimensional axisymmetric simulations have shown that the post-bounce accretion shock in core collapse supernovae is subject to the Spherical Accretion Shock Instability, or SASI. Recent three-dimensional simulations have revealed the existence of a non-axisymmetric mode of the SASI as well, where the postshock flow displays a spiral pattern. Here we investigate the growth of these spiral modes using two-dimensional simulations of the post-bounce accretion flow in the equatorial plane of a core-collapse supernova. By perturbing a steady-state model we are able to excite both one, two and three-armed spiral modes that grow exponentially with time, demonstrating that these are linearly unstable modes closely related to the original axisymmetric sloshing modes. By tracking the distribution of angular momentum, we show that these modes are able to efficiently separate the angular momentum of the accretion flow (which maintains a net angular momentum of zero), leading to a significant spin-up of the underlying accreting proto-neutron star.

 
astro-ph/0611708 [abs, ps, pdf, other] :
Title: Turning Points in the Evolution of Isolated Neutron Stars' Magnetic Fields
Authors: U. Geppert
Comments: Comments: 37 pages and 14 figures. Paper presented (in part) at the 363-rd Heraeus Seminar in Bad Honef, Germany. The paper will be published as a Springer Lecture Notes. Submitted for refereeing

During the life of isolated neutron stars (NSs) their magnetic field passes through a variety of evolutionary phases. Depending on its strength and structure and on the physical state of the NS (e.g. cooling, rotation), the field looks qualitatively and quantitatively different after each of these phases. Three of them, the phase of MHD instabilities immediately after NS's birth, the phase of fallback which may take place hours to months after NS's birth, and the phase when strong temperature gradients may drive thermoelectric instabilities, are concentrated in a period lasting from the end of the proto--NS phase until 100, perhaps 1000 years, when the NS has become almost isothermal. The further evolution of the magnetic field proceeds in general inconspicuous since the star is in isolation. However, as soon as the product of Larmor frequency and electron relaxation time, the so-called magnetization parameter, locally and/or temporally considerably exceeds unity, phases, also unstable ones, of dramatic changes of the field structure and magnitude can appear. An overview is given about that field evolution phases, the outcome of which makes a qualitative decision regarding the further evolution of the magnetic field and its host NS.

 
astro-ph/0611713 [abs, ps, pdf, other] :
Title: Simultaneous radio/X-ray observations of Cir X-1
Authors: V. Tudose (1,2), P. Soleri (1), R.P. Fender (3,1), P.G. Jonker (4,5,6), M. van der Klis (1), A.K. Tzioumis (7), R.E. Spencer (8) ((1) Amsterdam, (2) Bucharest, (3) Southampton, (4) SRON, (5) Harvard, (6) Utrecht, (7) ATNF, (8) Manchester)
Comments: Accepted for publication in the proceedings of VI Microquasar Workshop: Microquasars and Beyond, 18-22 September 2006, Como (Italy), ed: T. Belloni (2006)

We present a partial analysis of a multi-wavelength study of the X-ray binary Cir X-1, a system harboring the most relativistic outflow in our galaxy so far. The data were taken (almost) simultaneously in radio and X ray during a survey carried out in October 2000 and December 2002. Cir X-1 was observed at the radio frequencies of 4.8 and 8.6 GHz with the Australia Telescope Compact Array (ATCA). In the X-ray spectral domain we used the Rossi X-Ray Timing Explorer (RXTE). We found strong evidence for flaring activity in radio not only at the periastron but also at the apoastron passages. A comparison of our data against different correlations between radio and X ray found in other neutron star systems shows that Cir X-1 does not seem to follow the general trend. However, the fact that Cir X-1 is an `exotic' X-ray binary makes any interpretation more complicated.

 
astro-ph/0611716 [abs, ps, pdf, other] :
Title: Discovery of 1122 Hz X-Ray Burst Oscillations from the Neutron-Star X-Ray Transient XTE J1739-285
Authors: P. Kaaret, Z. Prieskorn, J.J.M. in 't Zand, S. Brandt, N. Lund, S. Mereghetti, D. Gotz, E. Kuulkers, J.A. Tomsick
Comments: Submitted to ApJL, 4 pages

We report the discovery of oscillations at 1122 +/- 0.3 Hz in an X-ray burst from the X-ray transient XTE J1739-285. The signal has a peak Leahy power of 42.8 and, after consideration of the number of trials, has a chance probability of occurrence of 4E-5 equivalent to a 4.2 sigma detection. The oscillation frequency suggests that XTE J1739-285 contains the fastest rotating neutron star yet found. We also found millisecond quasiperiodic oscillations in the persistent emission with frequencies ranging from 757 Hz to 862 Hz. We detected seven X-ray bursts and derive an upper limit on the source distance of about 10.6 kpc from the brightest burst.

 
astro-ph/0611720 [abs, ps, pdf, other] :
Title: Associations of Very High Energy Gamma-Ray Sources Discovered by H.E.S.S. with Pulsar Wind Nebulae
Authors: Yves A. Gallant, for the H.E.S.S. Collaboration
Comments: 5 pages, to appear in Astrophysics and Space Science (proceedings of "The Multi-Messenger Approach to High-Energy Gamma-Ray Sources")

The H.E.S.S. array of imaging Cherenkov telescopes has discovered a number of previously unknown gamma-ray sources in the very high energy (VHE) domain above 100 GeV. The good angular resolution of H.E.S.S. (~0.1 degree per event), as well as its sensitivity (a few percent of the Crab Nebula flux) and wide 5-degree field of view, allow a much better constrained search for counterparts in comparison to previous instruments. In several cases, the association of the VHE sources revealed by H.E.S.S. with pulsar wind nebulae (PWNe) is supported by a combination of positional and morphological evidence, multi-wavelength observations, and plausible PWN model parameters. These include the plerions in the composite supernova remnants G 0.9+0.1 and MSH 15-52, the recently discovered Vela X nebula, two new sources in the Kookaburra complex, and the association of HESS J1825-137 with PSR B1823-13. The properties of these better-established associations are reviewed. A number of other sources discovered by H.E.S.S. are located near high spin-down power pulsars, but the evidence for association is less complete. These possible associations are also discussed, in the context of the available multi-wavelength data and plausible PWN scenarios.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611442 [abs, ps, pdf, other] :
Title: The origin of long-period X-ray pulsars
Authors: N.R. Ikhsanov
Comments: 7 pages, 2 tables, accepted for publication in MNRAS
Note: replaced with revised version Wed, 22 Nov 2006 11:27:43 GMT (30kb)
 
nucl-th/0611046 [abs, ps, pdf, other] :
Title: Superfluidity in neutron stars and cold atoms
Authors: A. Schwenk
Comments: 3 pages, 2 figures, talk at Quark Confinement and the Hadron Spectrum VII, Ponta Delgada, September 2006, one reference corrected
Subj-class: Nuclear Theory; Superconductivity
Note: replaced with revised version Wed, 22 Nov 2006 02:22:56 GMT (49kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 29 Nov 06 01:00:15 GMT
0611819 -- 0611858 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611823 [abs, ps, pdf, other] :
Title: High-resolution X-ray spectroscopy of the ultracompact LMXB pulsar 4U 1626-67
Authors: Miriam I. Krauss (1, 2), Norbert S. Schulz (1), Deepto Chakrabarty (1, 2), Adrienne M. Juett (3), Jean Cottam (4) ((1) Kavli Institute for Astrophysics and Space Research, MIT; (2) Department of Physics, MIT; (3) Department of Astronomy, University of Virginia; (4) Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center)
Comments: 10 pages, 7 figures, submitted to ApJ

[abridged] We report results from four recent observations of the ultracompact LMXB pulsar 4U 1626-67. All the observations obtained high-resolution X-ray spectra of the system, two from the Chandra X-ray Observatory using the HETGS, and two from the XMM-Newton Observatory using the RGS as well as the EPIC PN and MOS. These data allow us to study in detail the prominent Ne and O emission line complexes which make 4U 1626-67 unique among LMXBs. The observations were spaced over a period of 3 years for a total observing time of 238 ks, allowing us to monitor the line regions as well as the overall source flux, continuum spectrum, and timing properties. The structure of the emission lines and the ratios of the components of the helium-like Ne IX and O VII triplets support the hypothesis that they are formed in the high-density environment of the accretion disk. We do not find any significant changes in the line widths or ratios over this time period, though we note that the line equivalent widths decrease. We are able to place constraints on the strengths of the Ne K, Fe L, and O K photoelectric absorption edges, and find that the data do not require an overabundance of Ne or O in the system relative to the expected ISM values. We find that the pulsar is still spinning down, and note that the pulse profile has changed significantly from what was found prior to the torque reversal in 1990, suggesting that this event may be linked to a change in the geometry of the accretion column. The flux of 4U 1626-67 continues to decrease, in keeping with the trend of the last approximately 30 years over which it has been observed. Taking into consideration current theory on disk stability, we expect that 4U 1626-67 will enter a period of quiescence in 2-15 years.

 
astro-ph/0611827 [abs, ps, pdf, other] :
Title: Near-Infrared Spectroscopy of Carbon-Enhanced Metal-Poor Stars. I. A SOAR/OSIRIS Pilot Study
Authors: Timothy C. Beers (1), Thirupathi Sivarani (1), Brian Marstellar (1), YoungSun Lee (1), Silvia Rossi (2), Bertrand Plez (3) ((1) Department of Physics & Astronomy, CSCE: Center for the Study of Cosmic Evolution, and JINA: Joint Institute for Nuclear Astrophysics, Michigan State University, (2) IAG, Departamento de Astronomia, Universidade de Sao Paolo, Brazil, (3) GRAAL, Universite de Montpellier, France)
Comments: 27 pages, including 5 tables, 6 figures, accepted for publication in The Astronomical Journal

We report on an abundance analysis for a pilot study of seven Carbon-Enhanced Metal-Poor (CEMP) stars, based on medium-resolution optical and near-infrared spectroscopy. The optical spectra are used to estimate [Fe/H], [C/Fe], [N/Fe], and [Ba/Fe] for our program stars. The near-infrared spectra, obtained during a limited early science run with the new SOAR 4.1m telescope and the Ohio State Infrared Imager and Spectrograph (OSIRIS), are used to obtain estimates of [O/Fe] and 12C/13C. The chemical abundances of CEMP stars are of importance for understanding the origin of CNO in the early Galaxy, as well as for placing constraints on the operation of the astrophysical s-process in very low-metallicity Asymptotic Giant Branch (AGB) stars.
This pilot study includes a few stars with previously measured [Fe/H], [C/Fe], [N/Fe],[O/Fe], 12C/13C, and [Ba/Fe], based on high-resolution optical spectra obtained with large-aperture telescopes. Our analysis demonstrates that we are able to achieve reasonably accurate determinations of these quantities for CEMP stars from moderate-resolution optical and near-infrared spectra. This opens the pathway for the study of significantly larger samples of CEMP stars in the near future. Furthermore, the ability to measure [Ba/Fe] for (at least the cooler) CEMP stars should enable one to separate stars that are likely to be associated with s-process enhancements (the CEMP-s stars) from those that do not exhibit neutron-capture enhancements (the CEMP-no stars).

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611708 [abs, ps, pdf, other] :
Title: Turning Points in the Evolution of Isolated Neutron Stars' Magnetic Fields
Authors: U. Geppert
Comments: References updated, typos corrected
Note: replaced with revised version Tue, 28 Nov 2006 15:26:22 GMT (690kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 30 Nov 06 01:00:10 GMT
0611859 -- 0611915 received


0 abstracts or titles contain neutron star, magnetar or pulsar



Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 1 Dec 06 01:00:14 GMT
0611916 -- 0611952 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611924 [abs, ps, pdf, other] :
Title: Wave Modes in the Magnetospheres of Pulsars and Magnetars
Authors: Chen Wang, Dong Lai
Comments: 18 pages, 9 figures. Submitted to MNRAS

We study the wave propagation modes in the relativistic streaming pair plasma of the magnetospheres of pulsars and magnetars, focusing on the effect of vacuum polarization. We show that the combined plasma and vacuum polarization effects give rise to a vacuum resonance, where ``avoided mode crossing'' occurs between the extraordinary mode and the (superluminous) ordinary mode. When a photon propagates from the vacuum-polarization-dominated region at small radii to the plasma-dominated region at large radii, its polarization state may undergo significant change across the vacuum resonance. We map out the parameter regimes (e.g., field strength, plasma density and Lorentz factor) under which the vacuum resonance occurs and examine how wave propagation is affected by the resonance. Some possible applications of our results are discussed, including high-frequency radio emission from pulsars and possibly magnetars, and optical/IR emission from neutron star surfaces and inner magnetospheres.

 
astro-ph/0611936 [abs, ps, pdf, other] :
Title: The diocotron instability in a pulsar cylindrical electrosphere
Authors: J. Petri
Comments: Accepted by A&A

The physics of the pulsar inner magnetosphere remains poorly constrained by observations. Although about 2000 pulsars have been discovered to date, little is known about their emission mechanism. Large vacuum gaps probably exist and a non-neutral plasma made of electrons in some regions and of positrons in some other regions fills space to form an electrosphere. The purpose of this work is to study the stability properties of the differentially rotating equatorial disk in the pulsar's electrosphere for which the magnetic field is assumed to be dipolar. In contrast to previous studies, the magnetic field is not restricted to be uniform. A pseudo-spectral Galerkin method using Tchebyshev polynomials expansion is developed to compute the spectrum of the diocotron instability in a non-neutral plasma column confined between two cylindrically conducting walls. Moreover, the inner wall carries a given charge per unit length in order to account for the presence of a charged neutron star at the centre of the electrosphere. We show several eigenfunctions and eigenspectra obtained for different initial density profiles and electromagnetic field configurations useful for laboratory plasmas. The algorithm is very efficient in computing the fastest growing modes. Applications to a cylindrical electrosphere are also shown for several differential rotation profiles. It is found that the growth rates of the diocotron instability are of the same order of magnitude as the rotation rate.

 
astro-ph/0611938 [abs, ps, pdf, other] :
Title: General Relativistic Radiative Transfer
Authors: S. Knop, P. H. Hauschildt, E. Baron

We present a general method to calculate radiative transfer including scattering in the continuum as well as in lines in spherically symmetric systems that are influenced by the effects of general relativity (GR). We utilize a comoving wavelength ansatz that allows to resolve spectral lines throughout the atmosphere. The used numerical solution is an operator splitting (OS) technique that uses a characteristic formal solution. The bending of photon paths and the wavelength shifts due to the effects of GR are fully taken into account, as is the treatment of image generation in a curved spacetime. We describe the algorithm we use and demonstrate the effects of GR on the radiative transport of a two level atom line in a neutron star like atmosphere for various combinations of continuous and line scattering coefficients. In addition, we present grey continuum models and discuss the effects of different scattering albedos on the emergent spectra and the determination of effective temperatures and radii of neutron star atmospheres.

 
astro-ph/0611942 [abs, ps, pdf, other] :
Title: Timing of the Accreting Millisecond Pulsar XTE J1814-338
Authors: A.Papitto (1,2), T.Di Salvo (3), L.Burderi (4), M.T.Menna (2), G.Lavagetto (3), A.Riggio (3,4) ((1) Universita' di Roma Tor Vergata, (2) Osservatorio Astronomico di Roma, (3) Universita' di Palermo, (4) Universita' di Cagliari)
Comments: 7 pages, 4 figures, Accepted for publication by MNRAS

We present a precise timing analysis of the accreting millisecond pulsar XTE J1814-338 during its 2003 outburst, observed by RXTE. A full orbital solution is given for the first time; Doppler effects induced by the motion of the source in the binary system were corrected, leading to a refined estimate of the orbital period, P_orb=15388.7229(2)s, and of the projected semimajor axis, a sini/c= 390.633(9) lt-ms. We could then investigate the spin behaviour of the accreting compact object during the outburst. We report here a refined value of the spin frequency (nu=314.35610879(1) Hz) and the first estimate of the spin frequency derivative of this source while accreting (nu^dot=(-6.7 +/- 0.7) 10^(-14) Hz/s). This spin down behaviour arises when both the fundamental frequency and the second harmonic are taken into consideration. We discuss this in the context of the interaction between the disc and the quickly rotating magnetosphere, at accretion rates sufficiently low to allow a threading of the accretion disc in regions where the Keplerian velocity is slower than the magnetosphere velocity. We also present indications of a jitter of the pulse phases around the mean trend, which we argue results from movements of the accreting hotspots in response to variations of the accretion rate.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 4 Dec 06 01:00:12 GMT
0612001 -- 0612039 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612007 [abs, ps, pdf, other] :
Title: Determining the nature of the faint X-ray source population near the Galactic Centre
Authors: Reba M. Bandyopadhyay, Andrew J. Gosling, Katherine M. Blundell, Philipp Podsiadlowski, Stephen E. Eikenberry, Valerie J. Mikles, James C.A. Miller-Jones, Franz E. Bauer
Comments: 9 pages, in Proceedings of "VI Microquasar Workshop: Microquasars and Beyond, 18-22 September 2006, Como, Italy; paper in PDF format with full-resolution figures available at this http URL

We present results of a multi-wavelength program to study the faint discrete X-ray source population discovered by Chandra in the Galactic Centre (GC). From IR imaging obtained with the VLT we identify candidate K-band counterparts to 75% of the X-ray sources in our sample. By combining follow-up VLT K-band spectroscopy of a subset of these candidate counterparts with the magnitude limits of our photometric survey, we suggest that only a small percentage of the sources are HMXBs, while the majority are likely to be canonical LMXBs and CVs at the distance of the GC. In addition, we present our discovery of highly structured small-scale (5-15") extinction towards the Galactic Centre. This is the finest-scale extinction study of the Galactic Centre to date. Finally, from these VLT observations we are able to place constraints on the stellar counterpart to the ``bursting pulsar'' GRO J1744-28.

 
astro-ph/0612015 [abs, ps, pdf, other] :
Title: Remnants of compact binary mergers
Authors: W. Domainko (1), M. Ruffert (2) ((1) MPIK Heidelberg, Germany, (2) School of Mathematics, University of Edinburgh, UK)
Comments: 5 pages, 1 figure, accepted for publication in AdSpR

We investigate the long-term evolution and observability of remnants originating from the merger of compact binary systems and discuss the differences to supernova remnants. Compact binary mergers expel much smaller amounts of mass at much higher velocities, as compared to supernovae, which will affect the dynamical evolution of their remnants. The ejecta of mergers consist of very neutron rich nuclei. Some of these neutron rich nuclei will produce observational signatures in form of gamma ray lines during their decay. The composition of the ejecta might even give interesting constraints about the internal structure of the neutron star. We further discuss the possibility that merger remnants appear as recently discovered 'dark accelerators' which are extended TeV sources which lack emission in other bands.

 
astro-ph/0612032 [abs, ps, pdf, other] :
Title: On the rarity of double black hole binaries: consequences for gravitational-wave detection
Authors: Krzysztof Belczynski, Vassiliki Kalogera, Frederic A. Rasio, Ronald E. Taam, Tomasz Bulik
Comments: 5 pages, submitted to ApJ Letters

Double-black-hole binaries are among the most important sources of gravitational radiation for ground-based detectors such as LIGO or Virgo. Even if formed with lower efficiency than double-neutron-star binaries, they can dominate the predicted detection rates, since black holes are more massive than neutron stars and therefore could be detected at greater distances. Here we discuss a new binary evolution process that can very significantly limit the formation of close double-black-hole binaries: the vast majority of their potential progenitors undergo a common-envelope (CE) phase while the donor, one of the massive binary components, is evolving through the Hertzsprung gap. Our latest theoretical understanding of the CE process suggests that this will always leads to a merger, preventing the double-black-hole formation. Using population synthesis calculations, we find that the corresponding reduction in the merger rate of double black holes formed in galactic fields is so great (by \~500) that their contribution to inspiral detection rates for ground-based detectors could become relatively small (~ 1 in 20) compared to double-neutron-star binaries. Our predicted detection rates for Advanced LIGO are now much lower for double black holes (~2 per yr), but are still high for double neutron stars (~40 per yr). If double black holes were found to be dominant in the detected inspiral signals, this could indicate that they mainly originate from dense star clusters (not included here) or that our theoretical modeling of the CE phase needs significant revision.

 

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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 5 Dec 06 01:00:13 GMT
0612040 -- 0612100 received


8 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612050 [abs, ps, pdf, other] :
Title: Black Hole Formation in X-Ray Binaries: The Case of XTE J1118+480
Authors: T. Fragos (1), B. Willems (1), N. Ivanova (2), V. Kalogera (1) ((1) Northwestern University, Department of Physics and Astronomy, (2) Canadian Institute for Theoretical Astrophysics)
Comments: 6 pages, 3 figures, 1 table, Submitted to Proceedings of International Astronomy Meeting "The Multicoloured Landscape of Compact Objects and their Explosive Origins" Cefalu 2006

In recent years, an increasing number of proper motions have been measured for Galactic X-ray binaries. When supplemented with accurate determinations of the component masses, orbital period, and donor luminosity and effective temperature, these kinematical constraints harbor a wealth of information on the systems' past evolution. The constraints on compact object progenitors and kicks derived from this are of immense value for understanding compact object formation and exposing common threads and fundamental differences between black hole and neutron star formation. Here, we present the results of such an analysis for the black hole X-ray binary XTE J1118+480. We present results from modeling the mass transfer phase, following the motion in the Galaxy back to the birth site of the black hole, and examining the dynamics of symmetric and asymmetric core-collapses of the black hole progenitor.

 
astro-ph/0612052 [abs, ps, pdf, other] :
Title: Rotating Boson and Boson-Fermion Stars
Authors: Claudio M. G. de Sousa
Comments: To appear in the proceedings of 10th Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories (MG X MMIII), Rio de Janeiro, Brazil, 20-26 Jul 2003

Some recent results on rotating self-gravitating configurations composed with Bosons and Fermions are reported. Given a star composed of both Bosons and Fermions without interaction, it is shown that it is possible to obtain stable slowly rotating configurations by using the same perturbative relativistic method that usually describes neutron stars.

 
astro-ph/0612054 [abs, ps, pdf, other] :
Title: Pulsars as Astrophysical Laboratories for Nuclear and Particle Physics
Authors: F. Weber (San Diego State University), R. Negreiros (San Diego State University), P. Rosenfield (San Diego State University), M. Stejner (University of Aarhus & San Diego State University)
Comments: 10 pages, 13 figures; Paper presented at the International School Of Nuclear Physics, 28th Course: Radioactive Beams, Nuclear Dynamics and Astrophysics, Erice-Sicily, 16-24 September 2006; to be published in Prog. Part. Nucl. Phys

A forefront area of research concerns the exploration of the properties of hadronic matter under extreme conditions of temperature and density, and the determination of the equation of state--the relation between pressure, temperature and density--of such matter. Experimentally, relativistic heavy-ion collision experiments enable physicists to cast a brief glance at hot and ultra-dense matter for times as little as about $10^{-22}$ seconds. Complementary to this, the matter that exists in the cores of neutron stars, observed as radio pulsars, X-ray pulsars, and magnetars, is at low temperatures but compressed permanently to ultra-high densities that may be more than an order of magnitude higher than the density of atomic nuclei. This makes pulsars superb astrophysical laboratories for medium and high-energy nuclear physics, as discussed in this paper.

 
astro-ph/0612055 [abs, ps, pdf, other] :
Title: Compact Binaries as Sources of Gravitational Radiation
Authors: M. Coleman Miller (University of Maryland)
Comments: To appear in the proceedings of the meeting "The Multicoloured Landscape of Compact Objects and their Explosive Origins", Cefalu, Italy, June 2006, to be published by AIP, Eds. L. Burderi et al

With current terrestrial gravitational wave detectors working at initial design sensitivities, and upgrades and space missions planned, it is likely that in the next five to ten years gravitational radiation will be detected directly from a variety of classes of objects. The most confidently expected of these classes is compact binaries, involving neutron stars or black holes. Detection of their coalescence, or their long-term orbits, has the potential to inform us about the evolutionary history of compact binaries and possibly even star formation over the past several billion years. We review what is currently known about compact binaries as sources of gravitational radiation, as well as the current uncertainties and what we expect to learn from future detections of gravitational waves from these systems.

 
astro-ph/0612058 [abs, ps, pdf, other] :
Title: Low-Mass X-ray Binaries and Globular Clusters in Early-Type Galaxies. I. Chandra Observations
Authors: Philip J. Humphrey, David A. Buote
Comments: 18 pages, 14 figures. Submitted to the Astrophysical Journal

We present a Chandra survey of LMXBs in 24 early-type galaxies. Correcting for detection incompleteness, the X-ray luminosity function (XLF) of each galaxy is consistent with a powerlaw with negative logarithmic differential slope, beta~2.0. However, beta strongly correlates with incompleteness, indicating the XLF flattens at low-Lx. The composite XLF is well-fitted by a powerlaw with a break at (1.8^{+0.37}_{-0.32})\times 10^{38} erg/s and beta=0.99+/-0.15 and 2.82^{+0.30}_{-0.24} below and above it, respectively. The break is close to the Eddington limit for a 1.4Msun neutron-star, but the XLF shape rules out its representing the division between neutron-star and black-hole systems. Although the XLFs are similar, we find evidence of some variation between galaxies. The high-Lz XLF slope does not correlate with age, but may correlate with [alpha/Fe]. Matching the LMXBs with globular clusters (GCs) identified in HST observations of 19 of the galaxies, we find the probability a GC hosts an LMXB is proportional to {L_{GC}^\alpha Z_{Fe}^\gamma} where alpha=0.85+/-0.16 and gamma=0.30+/-0.11. Correcting for GC luminosity and colour effects, and detection incompleteness, we find no evidence that the fraction of LMXBs in GCs (41%), or the fraction of GCs hosting LMXBs (~5.3%) varies between galaxies. The spatial distribution of LMXBs resembles that of red GCs, and the specific frequency of LMXB is proportional to the GC specific luminosity, consistent with the hypothesis that all LMXB form in GCs. Our results imply ~1.1 LMXB are formed Gyr^{-1} per GC and we place an upper limit of 1 LMXB formed in the field per 1.9E9Lsun of V-band luminosity.

 
astro-ph/0612061 [abs, ps, pdf, other] :
Title: Constraints to the EOS of ultradense matter with model-independent astrophysical observations
Authors: G. Lavagetto, I. Bombaci, A. D'Ai', I. Vidana, N.R. Robba
Comments: 4 pages, 1 colour figure, uses emulateapj class, submitted to ApJ Letters

The recent discovery of burst oscillations at 1122 Hz in the x-ray transient XTE J1739-285, together with the measurement of the mass of the binary millisecond pulsar PSR J0751+1807 (2.1 +- 0.2 solar masses) can finally allow us to put strong, model-independent observational constraints to the equation of state of compact stars. We show that the measurement of the moment of inertia of PSR J0737+3039A, together with these constraints, could allow to discriminate further the details of the inner structure of neutron stars. Moreover, we show that if XTE J1739-285 is constituted of nucleonic matter, any equation of state allows only a narrow range of very high masses, and this could explain why up to now compact stars spinning faster than a millisecond have been so difficult to detect.

 
astro-ph/0612092 [abs, ps, pdf, other] :
Title: Unmasking neutron star interiors using cooling simulations
Authors: D. Blaschke (Wroclaw U. & Dubna, JINR), H. Grigorian (Dubna, JINR & Yerevan U.)
Comments: 8 pages, 8 figures, Proceedings of the Erice School on 'Radioactive Beams, Nuclear Dynamics and Astrophysics' to be published in 'Prog. Part. Nucl. Phys.'

We introduce a new tool for 'unmasking' the composition of neutron star (NS) interiors which is based on the fact that the state of matter at high densities determines the statistics of both NS observables, the temperature-age (TA) data as well as the mass distribution. We use modern cooling simulations to extract distributions of NS masses required to reproduce those of the yet sparse data in the TA plane. By comparing the results with a mass distribution for young, nearby NSs from population synthesis we can sharpen two NS cooling problems. The direct Urca (DU) problem consists in a narrowing of the NS population at the mass value for which the DU process as the most effective cooling mechanism in the hadronic layer of the star can occur. The Vela mass problem is a broadening of the population beyond the range of the typical mass window of 1.1 - 1.5 M_sun. Applying this tool to modern EoS we discuss examples for pure hadronic stars which are in conflict with these constraints while hybrid stars with a color superconducting quark matter core can predict a satisfactory mass distribution, provided the smallest diquark pairing gap has a properly defined density dependence.

 
astro-ph/0612093 [abs, ps, pdf, other] :
Title: Order in the Chaos: Spin-up and Spin-down during the 2002 Outburst of SAX J1808.4-3658
Authors: L. Burderi, T. Di Salvo, M.T. Menna, A. Riggio, A. Papitto
Comments: 6 pages, including 3 figures. ApJ Letters, in press

We present a timing analysis of the 2002 outburst of the accreting millisecond pulsar SAX J1808.4-3658. A study of the phase delays of the entire pulse profile shows a behavior that is surprising and difficult to interpret: superposed to a general trend, a big jump by about 0.2 in phase is visible, starting at day 14 after the beginning of the outburst. An analysis of the pulse profile indicates the presence of a significant first harmonic. Studying the fundamental and the first harmonic separately, we find that the phase delays of the first harmonic are more regular, with no sign of the jump observed in the fundamental. The fitting of the phase delays of the first harmonic with a model which takes into account the observed exponential decay of the X-ray flux (and therefore of the mass accretion rate onto the neutron star) gives important information on the torque acting on the neutron star during the outburst. We find that the source shows spin-up in the first part of the outburst, while a spin-down dominates at the end. From these results we derive an estimate of the neutron star magnetic field strength.

 

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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 6 Dec 06 01:00:14 GMT
0612101 -- 0612136 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612101 [abs, ps, pdf, other] :
Title: s-Process Abundances in Planetary Nebulae
Authors: Brian Sharpee (1), Yong Zhang (2,3), Robert Williams (2), Eric Pellegrini (4), Kenneth Cavagnolo (4), Jack A. Baldwin (4), Mark Phillips (5), Xiao-Wei Liu (3) ((1) SRI International, (2) Space Telescope Science Institute, (3) Department of Astronomy, Peking University, (4) Department of Physics and Astronomy, Michigan State University, (5) Las Campanas Observatory, Carnegie Observatories)
Comments: 56 Pages, 6 figures, accepted for publication in ApJ

The s-process should occur in all but the lower mass progenitor stars of planetary nebulae, and this should be reflected in the chemical composition of the gas which is expelled to create the current planetary nebula shell. Weak forbidden emission lines are expected from several s-process elements in these shells, and have been searched for and in some cases detected in previous investigations. Here we extend these studies by combining very high signal-to-noise echelle spectra of a sample of PNe with a critical analysis of the identification of the emission lines of Z>30 ions. Emission lines of Br, Kr, Xe, Rb, Ba, and Pb are detected with a reasonable degree of certainty in at least some of the objects studied here, and we also tentatively identify lines from Te and I, each in one object. The strengths of these lines indicate enhancement of s-process elements in the central star progenitors, and we determine the abundances of Br, Kr, and Xe, elements for which atomic data relevant for abundance determination have recently become available. As representative elements of the ``light'' and ``heavy'' s-process peaks Kr and Xe exhibit similar enhancements over solar values, suggesting that PNe progenitors experience substantial neutron exposure.

 
astro-ph/0612109 [abs, ps, pdf, other] :
Title: Echoes of Giant Pulses from the Crab Pulsar
Authors: J. H. Crossley, J. A. Eilek, T. H. Hankins
Comments: to appear in proceedings of "Small Ionized and Neutral Structures in the Diffuse Interstellar Medium". 4 pages, 1 figure

We have detected occasional, short-lived ``echoes'' of giant pulses from the Crab pulsar. These echo events remind us of previously reported echoes from this pulsar, but they differ significantly in detail. Our echo events last at most only a few days; the echo emission lags the primary emission by only 40-100 musec. The echoes are consistently weaker and broader than the primary emission, and appear only at the lower of our two simultaneous observing frequencies. We suggest that these echoes are created by refraction in small plasma structures -- plasma clouds or magnetic flux ropes -- deep within the Crab nebula. If this is true, our echoes provide a new probe of small-scale structures within the inner synchrotron nebula.

 
astro-ph/0612132 [abs, ps, pdf, other] :
Title: Neutron star interiors and the equation of state of ultra-dense matter
Authors: F. Weber (San Diego State University), R. Negreiros (San Diego State University), P. Rosenfield (San Diego State University), Andreu Torres i Cuadrat (Physics Department, Universitat Autonoma de Barcelona)
Comments: 3 pages, 4 figures; Paper presented at the Int. Conf. on Quark Confinement and the Hadron Spectrum VII, Ponta Delgada, Acores, 2-7 September 2006; to be published by AIP

There has been much recent progress in our understanding of quark matter, culminating in the discovery that if such matter exists in the cores of neutron stars it ought to be in a color superconducting state. This paper explores the impact of superconducting quark matter on the properties (e.g., masses, radii, surface gravity, photon emission) of compact stars.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0609044 [abs, ps, pdf, other] :
Title: Accurate and realistic initial data for black hole-neutron star binaries
Authors: Philippe Grandclement (LUTH)
Comments: Final version appearing in Physical Review D
Journal-ref: Physical review D 74 (2006) 124002
Note: replaced with revised version Tue, 5 Dec 2006 15:39:49 GMT (36kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 7 Dec 06 01:00:23 GMT
0612137 -- 0612161 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612144 [abs, ps, pdf, other] :
Title: Formation of Double Compact Objects
Authors: V. Kalogera (1), K. Belczynski (2), C. Kim (3), R. O'Shaughnessy (1), B. Willems (1) ((1) Northwestern U., (2) New Mexico State U., (3) Cornell U.)
Comments: 55 pages, 16 figures, to appear in the Bethe Centennial Volume of Physics Reports, eds. G. E. Brown, V. Kalogera, E.P.J. van den Heuvel

Current observations of double neutron stars provide us with a wealth of information that we can use to investigate their evolutionary history and the physical conditions of neutron star formation. Understanding this history and formation conditions further allow us to make theoretical predictions for the formation of other double compact objects with one or two black hole components and assess the detectability of such systems by ground-based gravitational-wave interferometers. In this paper we summarize our group's body of work in the past few years and we place our conclusions and current understanding in the framework of other work in this area of astrophysical research.

 
astro-ph/0612145 [abs, ps, pdf, other] :
Title: Magnetic Hydrogen Atmosphere Models and the Neutron Star RX J1856.5-3754
Authors: Wynn C. G. Ho, David L. Kaplan, Philip Chang, Matthew van Adelsberg, Alexander Y. Potekhin
Comments: 11 pages, 8 figures; MNRAS, accepted

RX J1856.5-3754 is one of the brightest nearby isolated neutron stars, and considerable observational resources have been devoted to it. However, current models are unable to satisfactorily explain the data. We show that our latest models of a thin, magnetic, partially ionized hydrogen atmosphere on top of a condensed surface can fit the entire spectrum, from X-rays to optical, of RX J1856.5-3754, within the uncertainties. In our simplest model, the best-fit parameters are an interstellar column density N_H \approx 1x10^20 cm^-2 and an emitting area with R^infty \approx 17 km (assuming a distance to RX J1856.5-3754 of 140 pc), temperature T^infty \approx 4.3x10^5 K, gravitational redshift z_g \sim 0.22, atmospheric hydrogen column y_H \approx 1 g cm^-2, and magnetic field B \approx (3-4)x10^12 G; the values for the temperature and magnetic field indicate an effective average over the surface. We also calculate a more realistic model, which accounts for magnetic field and temperature variations over the neutron star surface as well as general relativistic effects, to determine pulsations; we find there exist viewing geometries that produce pulsations near the currently observed limits. The origin of the thin atmospheres required to fit the data is an important question, and we briefly discuss mechanisms for producing these atmospheres. Our model thus represents the most self-consistent picture to date for explaining all the observations of RX J1856.5-3754.

 
astro-ph/0612154 [abs, ps, pdf, other] :
Title: Late-Time Convection in the Collapse of a 23 Solar Mass Star
Authors: C.L. Fryer, P.A. Young (LANL/UArizona)
Comments: 31 pages (including 13 figures), submitted to ApJ

The results of a 3-dimensional SNSPH simulation of the core collapse of a 23 solar mass star are presented. This simulation did not launch an explosion until over 600ms after collapse, allowing an ideal opportunity to study the evolution and structure of the convection below the accretion shock to late times. This late-time convection allows us to study several of the recent claims in the literature about the role of convection: is it dominated by an l=1 mode driven by vortical-acoustic (or other) instability, does it produce strong neutron star kicks, and, finally, is it the key to a new explosion mechanism? The convective region buffets the neutron star, imparting a 150-200 km/s kick. Because the l=1 mode does not dominate the convection, the neutron star does not achieve large (>450 km/s) velocities. Finally, the neutron star in this simulation moves, but does not develop strong oscillations, the energy source for a recently proposed supernova engine. We discuss the implications these results have on supernovae, hypernovae (and gamma-ray bursts), and stellar-massed black holes.

 
astro-ph/0612160 [abs, ps, pdf, other] :
Title: Chemical Abundance Analysis of the Extremely Metal-Poor Star HE 1300+0157
Authors: Anna Frebel, John E. Norris, Wako Aoki, Satoshi Honda, Michael S. Bessell, Masahide Takada-Hidai, Timothy C. Beers, Norbert Christlieb
Comments: 35 pages (emulateapj text + 16 figures), accepted for publication in ApJ

We present a detailed chemical abundance analysis of HE 1300+0157, a subgiant with [Fe/H]=-3.9. From a high-resolution, high-S/N Subaru/HDS spectrum we find the star to be enriched in C ([C/Fe]_1D ~ +1.4) and O ([O/Fe]_1D ~ +1.8). With the exception of these species, HE 1300+0157 exhibits an elemental abundance pattern similar to that found in many other very and extremely metal-poor stars. The Li abundance is lower than the Spite-plateau value, in agreement with expectation for its evolutionary status. Of particular interest, no neutron-capture elements are detected in HE 1300+0157. This type of abundance pattern has been found by recent studies in several other metal-poor giants. We suggest that HE 1300+0157 is an unevolved example of this group of stars, which exhibit high C abundances together with low (or absent) abundances of neutron-capture elements. Several potential enrichment scenarios are presented. The low neutron-capture elements, including Sr, Ba, and Pb, suggests that the carbon excess observed in HE 1300+0157 is not due to mass transfer across a binary system. Such a scenario is applied to carbon-rich objects with excesses of s-process elements. The normal observed Li abundance supports this interpretation. Most likely, the high levels of C and O were produced prior to the birth of this star. It remains unclear whether a single hypernova is responsible for its overall chemical pattern, or whether one requires a superposition of yields from a massive Population III object and a normal Type II SN. These scenarios provide important information on the C production in the early Universe, and on the formation of C-rich stars in the early Galaxy.

 

Cross-listings


2 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0612022 [abs, ps, pdf, other] :
Title: Dynamical determination of the quadrupole mass moment of the double pulsar PSR J0737-3039 system
Authors: Lorenzo Iorio
Comments: LaTex2e, 12 pages, 1 figure, 2 tables, 21 references. Small changes in the abstract. More details released on the discrepancy between the measured orbital period and the calculated Keplerian one

In this paper we dynamically determine the quadrupole mass moment Q of the two-pulsars system PSR J0737-3039A/B by analyzing the orbital period of the relative motion occurring along a close 2.4-hr, elliptic orbit. Our result is Q=(-7.674347 +/- 4.638619) 10^45 kg m^2. It turns out that the major source of systematic error is the uncertainty in the semimajor axis a mainly due, in turn, to the error in sin i. Our result is capable to accommodate the observed discrepancy of -25.894452 +/- 15.662082 s between the phenomenologically measured orbital period P_b and the purely Keplerian period P^(0)=2pi\sqrt{a^3/G(m_A+m_B)} calculated with the system's parameters which have been determined independently of the third Kepler law.

 
nucl-th/0612021 [abs, ps, pdf, other] :
Title: Neutron stars and quark matter
Authors: Gordon Baym
Comments: To be published in the proceedings of Quark Confinement and the Hadron Spectrum VII, Sept. 2006, Ponta Delgada, Azores. 7 pages, 3 figures, aiproc

Recent observations of neutron star masses close to the maximum predicted by nucleonic equations of state begin to challenge our understanding of dense matter in neutron stars, and constrain the possible presence of quark matter in their deep interiors.

 

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hep-ph/0609081 [abs, ps, pdf, other] :
Title: Sterile neutrinos, dark matter, and the pulsar velocities in models with a Higgs singlet
Authors: Alexander Kusenko
Comments: 4 pages, one figure
Note: replaced with revised version Wed, 6 Dec 2006 01:11:09 GMT (19kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 8 Dec 06 01:00:14 GMT
0612162 -- 0612192 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612176 [abs, ps, pdf, other] :
Title: Discovering Light Pseudoscalar Bosons in Double-Pulsar Observations
Authors: Arnaud Dupays, Marco Roncadelli
Comments: Talk given by M. R. at the "Third International Workshop on Neutrino Oscillations in Venice"

The axion is just one from a general class of new particles -- called Light Pseudoscalar Bosons (LPBs) -- predicted by many realistic extensions of the Standard Model. We offer a somewhat pedagogical review of their main properties, with particular emphasis on the effects they induce in a light beam travelling in an external magnetic field, like photon-LPB oscillations, birefringence and dichroism. Moreover, we discuss a new strategy whereby LPBs can be discovered by high-precision observations of certain binary neutron-star systems. Basically, in a double pulsar seen almost edge-on, photon-LPB oscillations can give rise to a characteristic attenuation pattern of the light beam emitted by one of the pulsars when it goes through the magnetosphere of the companion. Depending on the actual values of the LPB mass and its two-photon coupling constant, the effect can be seen in the $\gamma$-ray band with the upcoming GLAST mission. We also shown that this method provides a remarkable cross-check for the recent claim by the PVLAS collaboration about the existence of a new LPB.

 
astro-ph/0612189 [abs, ps, pdf, other] :
Title: On the peculiarities in the rotational frequency evolution of isolated neutron stars
Authors: A. Biryukov, G. Beskin, S. Karpov
Comments: 4 pages, 3 figures. Accepted for publication in ApSS, in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface", London, April 2006; eds. S. Zane, R. Turolla and D. Page

The measurements of pulsar frequency second derivatives have shown that they are $10^2-10^6$ times larger than expected for standard pulsar spin-down law, and are even negative for about half of pulsars. We explain these paradoxical results on the basis of the statistical analysis of the rotational parameters $\nu$, $\dot \nu$ and $\ddot \nu$ of the subset of 295 pulsars taken mostly from the ATNF database. We have found a strong correlation between $\ddot \nu$ and $\dot \nu$ for both $\ddot\nu > 0$ and $\ddot\nu < 0$, as well as between $\nu$ and $\dot\nu$. We interpret these dependencies as evolutionary ones due to $\dot\nu$ being nearly proportional to the pulsars' age. The derived statistical relations as well as "anomalous" values of $\ddot\nu$ are well described by assuming the long-time variations of the spin-down rate. The pulsar frequency evolution, therefore, consists of secular change of $\nu_{ev}(t)$, $\dot\nu_{ev}(t)$ and $\ddot\nu_{ev}(t)$ according to the power law with $n \approx 5$, the irregularities, observed within a timespan as a timing noise, and the variations on the timescale larger than that timespan -- several tens of years.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 11 Dec 06 01:00:11 GMT
0612193 -- 0612232 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612216 [abs, ps, pdf, other] :
Title: Rotation at 1122 Hz and the neutron star structure
Authors: M. Bejger, P. Haensel, J.L. Zdunik
Comments: 4 pages, 3 figures, submitted to A&A Letters

Recent observations of XTE J1739-285 suggest that it contains a neutron star rotating at 1122 Hz. Such rotation imposes bounds on the structure of neutron star in XTE J1739-285. These bounds may be used to constrain poorly known equation of state of dense matter. One-parameter families of stationary configurations rotating rigidly at 1122 Hz are constructed, using a precise 2-D code solving Einstein equations. Hydrostatic equilibrium solutions are tested for stability with respect to axi-symmetric perturbations. A set of ten diverse EOSs of neutron stars is considered. Hypothetical strange stars are also studied. For each EOS, the family of possible neutron star models is limited by the mass shedding limit, corresponding to maximum allowed equatorial radius, R_max, and by the instability with respect to the axi-symmetric perturbations, reached at the minimum allowed equatorial radius, R_min. We get R_min \simeq 10-13km, and R_max \simeq 16-18km, with allowed mass 1.4-2.3 M_\odot. Allowed stars with hyperonic or exotic-phase core are supramassive and have a very narrow mass range. Quark star with accreted crust might be allowed, provided such a model is able to reproduce X-ray bursts from XTE J1739-285.

 
astro-ph/0612226 [abs, ps, pdf, other] :
Title: X-ray pulsar radiation from polar cap heated by back-flow bombardment
Authors: J. Gil, G. I. Melikidze, B. Zhang

We consider the problem of the thermal X-ray radiation from the hot polar cap of radio pulsars showing evidence of \EB subpulse drift in radio band. In our resent Paper I, within the partially screened gap (PSG) model of inner acceleration region we derived a simple relationship between the drift rate of subpulses observed in a radio-band and the thermal X-ray luminosity from polar caps heated by the back-flow particle bombardment. This relationship can be tested for pulsars in which the so-called carousel rotation time $P_4$, reflecting the \EB plasma drift, and the thermal X-ray luminosity $L_x$ from the hot polar cap are known. To test the model we used two only available pulsars: PSRs B0943+10 and B1133+16. They both satisfied the model prediction, although due to low photon statistics the thermal component could not be firmly identified from the X-ray data. Nevertheless, these pulsars were at least consistent with PSG pulsar model.
In the present paper we consider two more pulsars: PSRs B0656+14 and B0628-28, whose data have been recently become available. In PSR B0656+14 the thermal radiation from the hot polar cap was clearly detected, as for PSR B0628-28, it also seems to be having such a component.
It is important to note, that in all cases for which both $P_4$ and $L_x$ are presently known, the PSG pulsar model seems to be fully confirmed. Other available models of inner acceleration region fail to explain the observed relationship between radio and X-ray data. The pure vacuum gap model predicts too high $L_x$ and too low $P_4$, while the space charge limited model predicts too low $L_x$ and the origin of the subpulse drift has no natural explanation.

 
astro-ph/0612227 [abs, ps, pdf, other] :
Title: Light Pseudoscalar Bosons, PVLAS and the Double Pulsar J0737-3039
Authors: Arnaud Dupays, Marco Roncadelli
Comments: Talk given by M. R. at the "Neutrino Oscillation Workshop" (to appear in the Proceedings)

Light Pseudoscalar Bosons (LPBs) coupled to two photons are predicted by many realistic extensions of the Standard Model and give rise to birefringence and dichroism in a light beam travelling in an external magnetic field. These effects have recently been detected by the PVLAS collaboration, thereby strongly suggesting the existence of a LPB. We provide an astrophysical cross-check for such a claim. Actually, we show that in the double pulsar J0737-3039 photon-LPB conversion can give rise to a characteristic attenuation pattern of the light beam emitted by one of the pulsars when it goes through the magnetosphere of the companion. The effect under consideration shows up in the $\gamma$-ray band and can be detected by the upcoming GLAST mission.

 
astro-ph/0612232 [abs, ps, pdf, other] :
Title: Constraints on Thermal X-ray Radiation from SAX J1808.4-3658 and Implications for Neutron Star Neutrino Emission
Authors: C. O. Heinke, P. G. Jonker, R. Wijnands, R. E. Taam
Comments: 5 pages, 2 figures; submitted to ApJ

Thermal X-ray radiation from neutron star soft X-ray transients in quiescence provides the strongest constraints on the cooling rates of neutron stars, and thus on the interior composition and properties of matter in the cores of neutron stars. We analyze new (2006) and archival (2001) XMM-Newton observations of the accreting millisecond pulsar SAX J1808.4-3658 in quiescence, which provide the most stringent constraints to date. The X-ray spectrum of SAX J1808.4-3658 in the 2006 observation is consistent with a power-law of photon index 1.83\pm0.16, without requiring the presence of a blackbody-like component from a neutron star atmosphere. Our 2006 observation shows a slightly lower 0.5-10 keV X-ray luminosity, at a level of 68^{+15}_{-13}% that inferred from the 2001 observation. Simultaneous fitting of all available XMM data allows a constraint on the quiescent bolometric (0.01-10 keV) neutron star luminosity of L_{q,bol}<1.1*10^{31} erg/s. This limit excludes some current models of neutrino emission mediated by pion condensates, and provides evidence for additional cooling processes, such as neutrino emission via direct Urca processes involving protons or hyperons, in the cores of massive neutron stars.

 

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Astrophysics


astro-ph new abstracts, Tue, 12 Dec 06 01:00:12 GMT
0612233 -- 0612288 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612252 [abs, ps, pdf, other] :
Title: Neutron star oscillations and QPOs during magnetar flares
Authors: Anna L. Watts (MPA), Tod E. Strohmayer (NASA GSFC)
Comments: Proceedings of the 2006 Beijing COSPAR assembly, to appear in Advances in Space Research

The high frequency oscillations discovered in the tails of giant flares from two magnetars are thought to be the first direct detections of seismic vibrations from neutron stars. The possibility of starquakes associated with the giant flares triggering global vibrations opens up the prospect of using seismology to study the interior structure and composition of neutron stars. This is a major breakthrough in the study of the nature of matter under conditions of extreme pressure. In this paper we provide an up to date summary of the observations and the theoretical framework, including a brief discussion of gravitational wave searches for the QPOs. We summarize the status of alternative non-seismic mechanisms, and give a critique of a recent paper by Levin that argued against seismic vibrations as a viable mechanism. We conclude with an overview of current results using the seismological technique that constrain parameters such as the equation of state and crust structure.

 
astro-ph/0612282 [abs, ps, pdf, other] :
Title: Characteristics of supernova remnant G351.7+0.8 and disproof of its association with PSR J1721-3532
Authors: W.W. Tian, M. Haverkorn, H.Y. Zhang
Comments: 7 pages, 3 figures

New images of the supernova remnant (SNR) G351.7+0.8 are presented based on 21cm HI-line emission and continuum emission data from the Southern Galactic Plane Survey (SGPS). SNR G351.7+0.8 has a flux density of 8.4+-0.7 Jy at 1420 MHz. Its spectral index is 0.52+-0.25 between 1420 MHz and 843 MHz, typical of adiabatically expanding shell-like remnants. HI observations show structures possibly associated with the SNR in the radial velocity range of -10 to -18 km/s, and suggest a distance of 13.2 kpc and a radius of 30.7 pc. The estimated Sedov age for G351.7+0.8 is less than 6.8x10e4 yrs. An old radio pulsar PSR J1721-3532 lies close to the SNR G351.7+0.8 on the sky. The new distance and age of G351.7+0.8 and recent proper-motion measurements of the pulsar strongly argue against a possibility of associations between SNR G351.7+0.8 and PSR J1721-3532. There is an unidentified, faint X-ray point source 1RXS J172055.3-353937 which is close to G351.7+0.8. It may be a potential neutron star to associate with G351.7+0.8.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0612022 [abs, ps, pdf, other] :
Title: Dynamical determination of the quadrupole mass moment of the double pulsar PSR J0737-3039 system
Authors: Lorenzo Iorio
Comments: LaTex2e, 12 pages, 1 figure, 2 tables, 21 references. Small changes in the abstract. More details released on the discrepancy between the measured orbital period and the calculated Keplerian one (significant at 1.6 sigma level). Small typo fixed
Note: replaced with revised version Sun, 10 Dec 2006 11:42:57 GMT (13kb)
 

Astrophysics authors/titles "new"

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astro-ph new abstracts, Wed, 13 Dec 06 01:00:10 GMT
0612289 -- 0612324 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612302 [abs, ps, pdf, other] :
Title: Discovery of a New X-Ray Burst/Millisecond Accreting Pulsar HETE J1900.1-2455
Authors: M. Suzuki (1), N. Kawai (2 and 1), T. Tamagawa (1), A. Yoshida (3 and 1), Y. E. Nakagawa (3), K. Tanaka (3), Y. Shirasaki (4), M. Matsuoka (5), G. R. Ricker (6), R. Vanderspek (6), N. Butler (6 and 7), D. Q. Lamb (8), C. Graziani (8), G. Pizzichini (9), R. Sato (2), M. Arimoto (2), J. Kotoku (2), M. Maetou (3), M. Yamauchi (10) ((1) RIKEN, (2) Tokyo Tech, (3) Aoyama Gakuin Univ., (4) National Astronomical Observatory Japan, (5) JAXA, (6) MIT, (7) U. C. Berkeley, (8) Univ. Chicago, (9) INAF/IASF Bologna, (10) Miyazaki Univ.)
Comments: 7 pages, 4 figures

A class of low-mass X-ray binary sources are known to be both X-ray burst sources and millisecond pulsars at the same time. A new source of this class was discovered by High Energy Transient Explorer 2 (HETE-2) on 14 June 2005 as a source of type-I X-ray bursts, which was named HETE J1900.1-2455. Five X-ray bursts from HETE J1900.1-2455 were observed during the summer of 2005. The time resolved spectral analysis of these bursts have revealed that their spectra are consistent with the blackbody radiation throughout the bursts. The bursts show the indication of radius expansion. The bolometric flux remains almost constant during the photospheric radius expansion while blackbody temperature dropped during the same period. Assuming that the flux reached to the Eddington limit on a standard 1.4 solar mass neutron star with a helium atmosphere, we estimate the distance to the source to be $\sim$ 4 kpc.

 
astro-ph/0612319 [abs, ps, pdf, other] :
Title: Solving GRBs and SGRs puzzles by precessing Jets
Authors: D.Fargion, O.Lanciano, P.Oliva
Comments: 10 pages, 16 figures

A persistent, thin, micro-nano sr. beamed gamma jet, may be ejected from BH and Pulsars, powered by ultra-relativistic electron pairs. These jet while precessing and spinning are originated by Inverse Compton and-or Synchrotron Radiation at pulsars or micro-quasars sources. They are most powerful at Supernova birth, blazing, once on axis, to us and flashing GRB detector. The trembling of thin jets explains naturally the observed erratic multi-explosive structure of different GRBs. The jets are precessing and decaying on time scales of a few hours surviving as long as thousands of years, linking huge GRB-SN jet apparent Luminosity to more modest SGR relic Jets. Therefore long-life SGR may be repeating and if they are around our galaxy they might be observed again as the few known ones and a few rarer extragalactic XRFs. The orientation of the beam respect to the line of sight plays a key role in differentiating the wide GRB morphology. The relativistic cone is as small as the inverse of the electron progenitor Lorentz factor. The hardest and brightest gamma spectra are hidden inside the inner gamma jet axis. To observe the inner beamed GRB events one needs the widest SN sample and largest cosmic volumes. The most beamed are hardest.The nearest ones, within tens Mpc distances, are mostly observable on cone jet periphery leading to longest SN-GRB duration, with lowest fluency and the softest spectra, as in earliest GRB98425 and recent GRB 060218 signature. Conical shape of few nebulae describe in space the model signature. Recent X-ray precursor, like in GRB060124, ten minutes before the GRB event, or in SGR1806-20 two minutes before the main giant burst cannot be understood otherwise.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0612044 [abs, ps, pdf, other] :
Title: Isospin-dependent clusterization of Neutron-Star Matter
Authors: Camille Ducoin (GANIL, LPCC), Philippe Chomaz (GANIL), Francesca Gulminelli (LPCC)
Comments: Submitted to Nuclear Physics A

Because of the presence of a liquid-gas phase transition in nuclear matter, compact-star matter can present a region of instability against the formation of clusters. We investigate this phase separation in a matter composed of neutrons, protons and electrons, within a Skyrme-Lyon mean-field approach. Matter instability and phase properties are characterized through the study of the free-energy curvature. The effect of beta-equilibrium is also analyzed in detail, and we show that the opacity to neutrinos has an influence on the presence of clusterized matter in finite-temperature proto-neutron stars.

 

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hep-ph/0608094 [abs, ps, pdf, other] :
Title: Limits on Neutron Lorentz Violation from Pulsar Timing
Authors: B. Altschul
Comments: 10 pages, version to appear in Phys. Rev. D
Note: replaced with revised version Mon, 11 Dec 2006 21:47:40 GMT (11kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 14 Dec 06 01:00:12 GMT
0612325 -- 0612354 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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astro-ph new abstracts, Fri, 15 Dec 06 01:00:14 GMT
0612355 -- 0612402 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612371 [abs, ps, pdf, other] :
Title: Two decades of pulsar timing of Vela
Authors: Richard Dodson, Dion Lewis, Peter McCulloch
Comments: Isolated Neutron Stars conference, London, April 24-28 2006

Pulsar timing at the Mt Pleasant observatory has focused on Vela, which can be tracked for 18 hours of the day. These nearly continuous timing records extend over 24 years allowing a greater insight into details of timing noise, micro glitches and other more exotic effects. In particular we report the glitch parameters of the 2004 event, along with the reconfirmation that the spin up for the Vela pulsar occurs instantaneously to the accuracy of the data. This places a lower limit of about 30 seconds for the acceleration of the pulsar to the new rotational frequency. We also confirm of the low braking index for Vela, and the continued fall in the DM for this pulsar.

 

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astro-ph new abstracts, Mon, 18 Dec 06 01:00:10 GMT
0612403 -- 0612450 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612425 [abs, ps, pdf, other] :
Title: Non-LTE Models for Neutron Star Atmospheres and Supernova-Fallback Disks
Authors: K. Werner, T. Nagel, T. Rauch, V. Suleimanov
Comments: Accepted for publication in Advances in Space Research

We describe our recent progress in modeling supernova-fallback disks and neutron star (NS) atmospheres.
We present a first detailed spectrum synthesis calculation of a SN-fallback disk composed of iron. We assume a thin disk with a radial structure described by the alpha-disk model. The vertical structure and emission spectrum are computed self-consistently by solving the structure equations simultaneously with the radiation transfer equations under non-LTE conditions. We describe the properties of a specific disk model and discuss various effects on the emergent UV/optical spectrum.
We investigate Compton scattering effects on the thermal spectrum of NSs. In addition, we constructed a new generation of metal line-blanketed non-LTE model atmospheres for NSs. It is compared to X-ray burst spectra of EXO0748-676. It is possible that the gravitational redshift, deduced from absorption lines, is lower (z=0.24) than hitherto assumed (z=0.35). Accordingly, this would result in NS mass and radius lower limits of M>1.63Msun and R>13.8 km.

 
astro-ph/0612431 [abs, ps, pdf, other] :
Title: A detection of the donor star of Aquila X-1 during its 2004 outburst?
Authors: R. Cornelisse (Southampton Univ., IAC), J. Casares (IAC), D. Steeghs (CfA), A.D. Barnes (Southampton Univ.), P.A. Charles (SAAO, Southampton Uni), R.I. Hynes (Louisiana State Univ.), K. O'Brien (ESO)
Comments: 9 pages, 8 figures, accepted for publication in MNRAS

Phase-resolved high resolution optical spectroscopy has revealed narrow N III and He II emission lines from the soft X-ray transient Aquila X-1 during its 2004 outburst that move as a function of the orbit consistent with the phasing of the donor star. Under the assumption that these lines come from the irradiated side of the donor star, we can constrain its K_2 velocity to >247+/-8 km/s, and derive a mass function of f(M_1)>1.23+/-0.12M_sun. Estimates for the rotational broadening based on the emission components suggest a possible massive neutron star of >1.6M_sun (at 95% confidence). However, an updated ephemeris and additional high resolution spectroscopy of Aql X-1 during a future outburst are warranted in order to confirm that the narrow lines indeed originate on the donor star surface, and reliably characterise the system parameters of this important X-ray binary. Spectra taken during the end of the outburst show that the morphology of the emission lines changed dramatically. No donor star signature was present anymore, while the presence of narrow low-velocity emission lines became clear, making Aql X-1 a member of the slowly growing class of low-velocity emission line sources.

 
astro-ph/0612440 [abs, ps, pdf, other] :
Title: Neutron Star Observations: Prognosis for Equation of State Constraints
Authors: James M. Lattimer, Maddapa Prakash
Comments: 70 pages, 19 figures, submitted to Hans Bethe Centennial Physics Reports

We investigate how current and proposed observations of neutron stars can lead to an understanding of the state of their interiors and the key unknowns: the typical neutron star radius and the neutron star maximum mass. A theoretical analysis of neutron star structure, including general relativistic limits to mass, compactness, and spin rates is made. We consider observations made not only with photons, ranging from radio waves to X-rays, but also those involving neutrinos and gravity waves. We detail how precision determinations of structural properties would lead to significant restrictions on the poorly understood equation of state near and beyond the equilibrium density of nuclear matter.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0612086 [abs, ps, pdf, other] :
Title: The second post-Newtonian order generalized Kepler equation
Authors: László Á. Gergely, Zoltán Keresztes, Balázs Mikóczi
Comments: to appear in the Proceedings of the Eleventh Marcel Grossmann Meeting 2006, World Scientific, Singapore (2007)

The radial component of the motion of compact binary systems composed of neutron stars and/or black holes on eccentric orbit is integrated. We consider all type of perturbations that emerge up to second post-Newtonian order. These perturbations are either of relativistic origin or are related to the spin, mass quadrupole and magnetic dipole moments of the binary components. We derive a generalized Kepler equation and investigate its domain of validity, in which it properly describes the radial motion.

 

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astro-ph new abstracts, Tue, 19 Dec 06 01:00:19 GMT
0612451 -- 0612507 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612460 [abs, ps, pdf, other] :
Title: Multi-Dimensional Explorations in Supernova Theory
Authors: Adam Burrows, Luc Dessart, Christian D. Ott, Eli Livne
Comments: To be published in the "Centennial Festschrift for Hans Bethe," Physics Reports (Elsevier: Holland), ed. G.E. Brown, E. van den Heuvel, and V. Kalogera, 2006

In this paper, we bring together various of our published and unpublished findings from our recent 2D multi-group, flux-limited radiation hydrodynamic simulations of the collapse and explosion of the cores of massive stars. Aided by 2D and 3D graphical renditions, we motivate the acoustic mechanism of core-collapse supernova explosions and explain, as best we currently can, the phases and phenomena that attend this mechanism. Two major foci of our presentation are the outer shock instability and the inner core g-mode oscillations. The former sets the stage for the latter, which damp by the generation of sound. This sound propagates outward to energize the explosion and is relevant only if the core has not exploded earlier by some other means. Hence, it is a more delayed mechanism than the traditional neutrino mechanism that has been studied for the last twenty years since it was championed by Bethe and Wilson. We discuss protoneutron star convection, accretion-induced-collapse, gravitational wave emissions, pulsar kicks, the angular anisotropy of the neutrino emissions, a subset of numerical issues, and a new code we are designing that should supercede our current supernova code VULCAN/2D. Whatever ideas last from this current generation of numerical results, and whatever the eventual mechanism(s), we conclude that the breaking of spherical symmetry will survive as one of the crucial keys to the supernova puzzle.

 
astro-ph/0612501 [abs, ps, pdf, other] :
Title: XMM-Newton discovery of 7 s pulsations in the isolated neutron star RX J1856.5-3754
Authors: Andrea Tiengo, Sandro Mereghetti
Comments: Submitted to The Astrophysical Journal Letters

Thanks to the high counting statistics provided by a recent XMM-Newton observation of RX J1856.5-3754, we have discovered that this isolated neutron star pulsates at a period of 7.055 s. This confirms that RX J1856.5-3754 is similar in nature to the the other six thermally emitting, nearby neutron stars discovered in soft X-rays with ROSAT. The pulsations are detected at consistent periods in several XMM-Newton observations spanning from April 2002 to October 2006, yielding an upper limit of Pdot<1.9x10e-12 s/s (90% c.l.) on the period derivative. This implies a surface magnetic field smaller than 1.2x10^14 G, under the usual assumption of vacuum dipole magnetic braking. The pulse profile is nearly sinusoidal with a pulsed fraction of only ~1.5%, the smallest ever seen in an isolated X-ray pulsar.

 
astro-ph/0612503 [abs, ps, pdf, other] :
Title: A microscopic equation of state for protoneutron stars
Authors: G.F.Burgio, M. Baldo, O.E. Nicotra, H.-J. Schulze
Comments: 8 pages, 6 figures, to appear in Astrophysics and Space Science, Proceedings of "Isolated Neutron Stars: from the Interior to the Surface", edited by D. Page, R. Turolla, and S. Zane

We study the structure of protoneutron stars within the finite temperature Brueckner-Bethe-Goldstone many-body theory. If nucleons, hyperons, and leptons are present in the stellar core, we find that neutrino trapping stiffens considerably the equation of state, because hyperon onsets are shifted to larger baryon density. However, the value of the critical mass turns out to be smaller than the ``canonical'' value 1.44 $M_\odot$. We find that the inclusion of a hadron-quark phase transition increases the critical mass and stabilizes it at about 1.5--1.6 $M_\odot$.

 
astro-ph/0612507 [abs, ps, pdf, other] :
Title: The Laminar Flame Speedup by Neon-22 Enrichment in White Dwarf Supernovae
Authors: David A. Chamulak, Edward F. Brown, Francis X. Timmes
Comments: 5 pages, 2 figures, to be published in ApJ Letters. Table 2 is avalible from this http URL

Carbon-oxygen white dwarfs contain neon-22 formed from alpha-captures onto nitrogen during core He burning in the progenitor star. In a white dwarf (type Ia) supernova, the neon-22 abundance determines, in part, the neutron-to-proton ratio and hence the abundance of radioactive nickel-56 that powers the lightcurve. The neon-22 abundance also changes the burning rate and hence the laminar flame speed. We tabulate the flame speedup for different initial carbon and neon-22 abundances and for a range of densities. This increase in the laminar flame speed--about 30% for a neon-22 mass fraction of 6%--affects the deflagration just after ignition near the center of the white dwarf, where the laminar speed of the flame dominates over the buoyant rise, and in regions of lower density ~ 10^7 g/cm3 where a transition to distributed burning is conjectured to occur. The increase in flame speed will decrease the density of any transition to distributed burning.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611608 [abs, ps, pdf, other] :
Title: AXPs/SGRs: Magnetars or Quarkstars?
Authors: Renxin Xu (PKU)
Comments: 10 pages, COSPAR2006 E1.3, submitted
Note: replaced with revised version Mon, 18 Dec 2006 08:06:41 GMT (11kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 20 Dec 06 01:00:11 GMT
0612508 -- 0612558 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612533 [abs, ps, pdf, other] :
Title: Spectroscopic Analysis of subluminous B Stars in Binaries with compact Companions
Authors: S. Geier, C. Karl, H. Edelmann, U. Heber, R. Napiwotzki
Comments: 6 pages, 1 figure, To appear in the Proceedings of the 15th European Workshop on White Dwarfs, Leicester, UK, August 7-11, 2006

The masses of compact objects like white dwarfs, neutron stars and black holes are fundamental to astrophysics, but very difficult to measure. We present the results of an analysis of subluminous B (sdB) stars in close binary systems with unseen compact companions to derive their masses and clarify their nature. Radial velocity curves were obtained from time resolved spectroscopy. The atmospheric parameters were determined in a quantitative spectral analysis. Based on high resolution spectra we were able to measure the projected rotational velocity of the stars with high accuracy. The assumption of orbital synchronization makes it possible to constrain inclination angle and companion mass of the binaries. Five invisible companions have masses that are compatible with that of normal white dwarfs or late type main sequence stars. But four sdBs have very massive companions like heavy white dwarfs > 1 Mo, neutron stars or even black holes. Such a high fraction of massive compact companions is not expected from current models of binary evolution.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0612022 [abs, ps, pdf, other] :
Title: Dynamical determination of the quadrupole mass moment of the double pulsar PSR J0737-3039 system
Authors: Lorenzo Iorio
Comments: LaTex2e, 12 pages, 1 figure, 2 tables, 23 references. New results using other values for the inclination angle i. 2 references added. Typos fixed. Abstract rewritten
Note: replaced with revised version Mon, 18 Dec 2006 21:25:53 GMT (13kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 21 Dec 06 01:00:12 GMT
0612559 -- 0612605 received


6 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612561 [abs, ps, pdf, other] :
Title: Hardness-Intensity Correlations in Magnetar Afterglows
Authors: Feryal Ozel, Tolga Guver
Comments: Submitted to the Astrophysical Journal Letters

We explore the hardness-intensity correlations observed in several AXPs and SGRs within the framework of a thermally emitting magnetar model. Using our detailed atmosphere models and taking into account reprocessing of the surface emission by the magnetosphere, we show that the hardness of the surface spectra increases with increasing temperature and hence the changes in the effective temperatures of the outer layers of the star alone can account for the observed correlations. We conclude that the slow release of the heat deposited in the deep crust during a magnetar burst naturally accounts for the spectral changes during the afterglow. The correlations are further enhanced by changes in the structures of the magnetic currents during or following a burst. However, the additional hardening produced by scattering of the surface photons off the magnetospheric charges saturates at moderate values of the scattering optical depth.

 
astro-ph/0612572 [abs, ps, pdf, other] :
Title: Last moments in the life of a compact binary system: gravitational waves, gamma-ray bursts and magnetar formation
Authors: S. Rosswog
Comments: 24 pages, 18 figures, Revista Mexicana de Astronomia y Astrofisica in press higher resolution figures can be found at this http URL

The first detections of afterglows from short gamma-ray bursts (GRBs) have confirmed the previous suspicion that they are triggered by a different central engine than long bursts. In particular, the recent detections of short GRBs in galaxies without star formation lends support to the idea that an old stellar population is involved. Most prominent are mergers of either double neutron stars or of a neutron star with a stellar-mass black hole companion. Since the final identification of the central engine will only come from an integral view of several properties, we review the observable signatures that can be expected from both double neutron stars and neutron star black hole systems. We discuss the gravitational wave emission, the structure of the neutrino-cooled accretion disks, the resulting neutrino signal and possible mechanisms to launch a GRB. In addition, we address the speculative idea that in some cases a magnetar-like object may be the final outcome of a double neutron star merger. We also discuss possibilities to explain the late-time X-ray activity that has been observed in several bursts.

 
astro-ph/0612582 [abs, ps, pdf, other] :
Title: Nucleosynthesis-relevant conditions in neutrino-driven supernova outflows. I. Spherically symmetric hydrodynamic simulations
Authors: A. Arcones, H.-Th. Janka, L. Scheck (MPI for Astrophysics, Garching)
Comments: 21 pages, 13 figures; submitted to Astronomy & Astrophysics

We investigate the behavior and consequences of the reverse shock that terminates the supersonic expansion of the baryonic wind which is driven by neutrino heating off the surface of (non-magnetized) new-born neutron stars in supernova cores. To this end we perform long-time hydrodynamic simulations in spherical symmetry. In agreement with previous relativistic wind studies, we find that the neutrino-driven outflow accelerates to supersonic velocities and in case of a compact, about 1.4 solar mass (gravitational mass) neutron star with a radius of about 10 km, the wind reaches entropies of about 100 k_B per nucleon. The wind, however, is strongly influenced by the environment of the supernova core. It is decelerated and shock-heated abruptly by a termination shock that forms when the supersonic outflow collides with the slower preceding supernova ejecta. The radial position of this reverse shock varies with time and depends on the strength of the neutrino wind and the different conditions in progenitor stars with different masses and structure. Its basic properties and behavior can be understood by simple analytic considerations. We demonstrate that the entropy of matter going through the reverse shock can increase to a multiple of the asymptotic wind value. Seconds after the onset of the explosion it therefore can exceed 400 k_B per nucleon. The temperature of the shocked wind has typically dropped to about or less than 10^9 K, and density and temperature in the shock-decelerated matter continue to decrease only very slowly. Such conditions might strongly affect the important phases of supernova nucleosynthesis in a time and progenitor dependent way. (abridged)

 
astro-ph/0612587 [abs, ps, pdf, other] :
Title: Anomalous X-ray pulsars: Persistent States with Fallback Disks
Authors: Unal Ertan, M.Ali Alpar, M.Hakan Erkut, K.Yavuz Eksi, Sirin Caliskan
Comments: 6 pages, 1 figure, to appear in proceedings of the conference "Isolated Neutron Stars: From the Interior to the Surface" eds. S. Zane, R. Turolla, D. Page; Astrophysics & Space Science in press

The anomalous X-ray pulsar 4U 0142+61 was recently detected in the mid infrared bands with the SPITZER Observatory (Wang, Chakrabarty & Kaplan 2006). This observation is the first instance for a disk around an AXP. From a reanalysis of optical and infrared data, we show that the observations indicate that the disk is likely to be an active disk rather than a passive dust disk beyond the light cylinder, as proposed in the discovering paper. Furthermore, we show that the irradiated accretion disk model can also account for all the optical and infrared observations of the anomalous X-ray pulsars in the persistent state.

 
astro-ph/0612591 [abs, ps, pdf, other] :
Title: Comptonization in the X-ray Spectra of Radio Millisecond Pulsars
Authors: Slavko Bogdanov, Jonathan E. Grindlay, George B. Rybicki
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.5-8

The majority of X-ray-detected rotation-powered millisecond pulsars (MSPs) appear to exhibit predominantly thermal emission, believed to originate from the heated magnetic polar caps of the pulsar. In the nearest MSP, J0437--4715 a faint PL is also observed at >3 keV, usually associated with magnetospheric emission processes. However, the hard emission in this and other similar MSPs may instead be due to weak Comptonization of the thermal polar cap emission by energetic electrons/positrons of small optical depth most likely in the pulsar magnetosphere. This spectral model implies that all soft X-rays are of purely thermal origin, which has important implications in the study of neutron stars.

 
astro-ph/0612594 [abs, ps, pdf, other] :
Title: XMM-Newton Observations of PSR B1957+20
Authors: H.H. Huang, W. Becker
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.1-4

We report on XMM-Newton observations of the Black Widow pulsar, PSR B1957+20. The pulsar's X-ray emission is non-thermal and best modeled with a single powerlaw spectrum of photon index 2.03^{+0.51}_{-0.36}. No coherent X-ray pulsations at the pulsar's spin-period could be detected, though a strong binary-phase dependence of the X-ray flux is observed for the first time. The data suggest that the majority of the pulsar's X-radiation is emitted from a small part of the binary orbit only. We identified this part as being near to where the radio eclipse takes place. This could mean that the X-rays from PSR B1957+20 are mostly due to intra-shock emission which is strongest when the pulsar wind interacts with the ablated material from the companion star.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 22 Dec 06 01:00:13 GMT
0612606 -- 0612668 received


10 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612626 [abs, ps, pdf, other] :
Title: A Fast-Moving Central Compact Object in Puppis-A
Authors: C. Y. Hui, W. Becker
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.9-12

Utilizing two Chandra High Resolution Camera (HRC-I) observations with an epoch separation of somewhat more than five years, we have measured the proper motion of the central compact object, RX J0822-4300, in the supernova remnant Puppis-A for the first time. The position of RX J0822-4300 is found to be different by 0.574 +/- 0.184 arcsec, implying a proper motion of 107.49 +/- 34.46 mas/yr with a position angle of 241 degree +/- 24 degree. For a distance of 2.2 kpc, this proper motion is equivalent to a recoil velocity of 1121.79 +/- 359.60 km/s. Both the magnitude and the direction of the proper motion are in agreement with the birth place of RX J0822-4300 being near to the optical expansion center of the supernova remnant. Although the positional shift inferred from the current data is significant at a ~ 3 sigma level only, one or more future HRC-I observations can obtain a much larger positional separation and further constrain the measurement.

 
astro-ph/0612628 [abs, ps, pdf, other] :
Title: Discovery of an X-ray Nebula associated with PSR J2124-3358
Authors: C. Y. Hui, W. Becker
Comments: roceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.13-15

We report the discovery of an X-ray nebula associated with the nearby millisecond pulsar PSR J2124-3358. This is the first time that extended emission from a solitary millisecond pulsar is detected. The emission extends from the pulsar to the northwest by ~ 0.5 arcmin. The spectrum of the nebular emission can be modeled by a power law spectrum with photon index of 2.2 +/-0.4. This is inline with the emission being originated from accelerated particles in the post shock flow.

 
astro-ph/0612629 [abs, ps, pdf, other] :
Title: Neutrino-driven wind and wind termination shock in supernova cores
Authors: A. Arcones, L. Scheck, H.-Th. Janka (MPI for Astrophysics, Garching)
Comments: 6 pages, 3 figures, International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX, CERN, Geneva, Switzerland, 25-30 June, 2006

The neutrino-driven wind from a nascent neutron star at the center of a supernova expands into the earlier ejecta of the explosion. Upon collision with this slower matter the wind material is decelerated in a wind termination shock. By means of hydrodynamic simulations in spherical symmetry we demonstrate that this can lead to a large increase of the wind entropy, density, and temperature, and to a strong deceleration of the wind expansion. The consequences of this phenomenon for the possible r-process nucleosynthesis in the late wind still need to be explored in detail. Two-dimensional models show that the wind-ejecta collision is highly anisotropic and could lead to a directional dependence of the nucleosynthesis even if the neutrino-driven wind itself is spherically symmetric.

 
astro-ph/0612630 [abs, ps, pdf, other] :
Title: Thermal radiation from hot polar cap in pulsars
Authors: Janusz Gil, George Melikidze, Bing Zhang
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.20-23

Thermal radiation from hot polar caps is examined in radio pulsars with drifting subpulses. It is argued that if these subpulses correspond to sparking discharges of the inner acceleration region right above the polar cap surface then a simple relationship between the observed subpulse drift rate in radio and thermal X-ray luminosity from the polar cap heated by sparks should exist. This relationship is derived and tested in pulsars for which an appropriate good quality data is available.

 
astro-ph/0612631 [abs, ps, pdf, other] :
Title: Recent Observations of EGRET Pulsar Wind Nebulae
Authors: Mallory S.E. Roberts, E. V. Gotthelf, Jules P. Halpern, Crystal L. Brogan, Scott M. Ransom
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.24-27

We present recent X-ray and radio observations of pulsar wind nebulae discovered in EGRET error boxes. Two XMM-Newton observations show the X-ray extent of the rapidly moving PWN associated with the variable gamma-ray source 3EG J1809-2328, and a trail coming from the new millisecond pulsar PSR J1614-2230 at high Galactic z. We also briefly discuss three PWN that are HESS TeV sources including a new HESS source we argue is associated with the Eel nebula in 3EG J1826-1302.

 
astro-ph/0612632 [abs, ps, pdf, other] :
Title: Upper Limits on the Pulsed VHE gamma-ray Emission from Two Young Pulsars Investigated with the High Energy Stereoscopic System
Authors: A. Noutsos
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.28-31

The High Energy Stereoscopic System (H.E.S.S.) is a system of four, imaging, atmospheric Cherenkov telescopes in Namibia, designed to detect very-high-energy gamma rays above ~ 100 GeV. During 2002--2003, H.E.S.S. collected data from two, young and energetic radio pulsars: the Crab and PSR B1706-44. We searched for pulsations at the lowest energies that H.E.S.S. is capable of detecting, aiming at a detection that would potentially differentiate between the two popular models of pulsar high-energy emission: the Polar Cap and the Outer Gap. No evidence for pulsed emission was found in the data, and upperlimits were derived to a 99.95% confidence level. Our assumptions and upper limit values for the two pulsars are reported.

 
astro-ph/0612634 [abs, ps, pdf, other] :
Title: 511 keV line from millisecond pulsars in the Galactic center
Authors: Wei Wang
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.32-35

Observations of a strong and extended positron-electron annihilation line emission in the Galactic center (GC) region by the SPI/INTEGRAL are challenging to the existing models of positron sources in the Galaxy. In this paper, we study the possibility that pulsar winds from a millisecond pulsar population in the GC produce the 511 keV line. Our preliminary estimations predict that the e+/- annihilation rate in the GC is around 5 x 10E+42 sE-1, which is consistent with the present observational constraints. Therefore, the e+/- pairs from pulsar winds can contribute significantly to the positron sources in the Galactic center region. Furthermore, since the diffusion length of positrons is short in the magnetic field, we predict that the intensity distribution of the annihilation line should follow the distribution of millisecond pulsars, which should then correlate to the mass distribution in the GC.

 
astro-ph/0612637 [abs, ps, pdf, other] :
Title: Gamma-ray Pulsar Simulations for the Gamma-ray Large Area Space Telescope (GLAST)
Authors: M. Razzano
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.36-39

We present here the current status of pulsar simulations for the Large Area Telescope, the main instrument on the GLAST mission. We present "PulsarSpectrum", a pulsar simulator that can reproduce with high detail gamma-ray emission from pulsars. "PulsarSpectrum" takes into account advanced timing effects, e.g. period changes with time, barycentering effects and glitches. Other ancillary tools have been built to provide the simulator with a realistic population of pulsars and their ephemerides. All these tools are currently used in the GLAST collaboration for testing the LAT Science Analysis Tools and for studying LAT capabilities for pulsar science. They have been used also for generating a simulated pulsar population for the "Data Challenge 2 (DC2)", one of the most important milestones in the development of the GLAST software. During the DC2, scientists analyzed a set of 55 days of simulated data in order to validate LAT MonteCarlo, study instrument response functions, exercise analysis tools and study LAT capabilities. This contribution also contains results of some analysis performed during DC2 on EGRET pulsars.

 
astro-ph/0612645 [abs, ps, pdf, other] :
Title: Were most Low Mass X ray Binaries born in Globular Clusters?
Authors: Francesca D'Antona, Anamaria Teodorescu, Paolo Ventura
Comments: invited talk at the meeting: The Multicoloured Landscape of Compact Objects and their Explosive Origins: Theory vs. Observations, Cefalu', 11-24 June 2006, to be published in AIP Conf.Proc

We summarize the status of art of the secular evolution of low mass X-ray binaries (LMXBs) and take a close look at the orbital period distribution of LMXBs and of binary millisecond pulsars (MSP), in the hypothesis that this latter results from the LMXB evolution. The deficiency of systems below the period gap, which in cataclysmic binaries occurs between ~ 2 and 3 hr, points to a very different secular evolution of LMXBs with respect to their counterparts containing a white dwarf compact object. The presence of several ultrashort period LMXBs (some of which are also X-ray millisecond pulsars), the important fraction of binary MSPs at periods between 0.1 and 1 day, the periods (26 and 32hr) of two ``interacting'' MSPs in Globular Clusters are other pieces of the puzzle in the period distribution. We consider the possible explanations for these peculiarities, and point out that Grindlay's old proposal that all (most of) LMXBs in the field were originally born in globular clusters must be carefully reconsidered.

 
astro-ph/0612652 [abs, ps, pdf, other] :
Title: Constraints on the Parameters of the Unseen Pulsar in the PWN G0.9+0.1 from Radio, X-Ray, and VHE Gamma-Ray Observations
Authors: C.Venter, O.C. de Jager
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.40-43

Radio, X-ray, and HESS gamma-ray observations of the Galactic Center (GC) composite supernova remnant SNR G0.9+0.1 are used to constrain a time-dependent injection model of the downstream electron spectrum responsible for the total multiwavelength spectrum. The effect of spindown power evolution aswell as nebular field evolution is employed to reproduce the present-day multiwavelength spectrum. Assuming a nebular magnetic field decay model of typical HESS-type pulsar wind nebulae (PWN), ending with a present-day field strength of 6muG, we obtain an initial spindown power of ~ 10E+38 ergs/s if we assume a birth period and age of 43ms and 6,500 yr respectively to reproduce the properties of the SNR shell. This gives a present-day spindown power of ~ 10E+37 ergs/s, which agrees well with the present-day spindown power derived from X-ray observations.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0612090 [abs, ps, pdf, other] :
Title: The Phase Diagram of Neutral Quark Matter
Authors: Stefan B. Ruester
Comments: Ph.D. Thesis (Advisor: Dirk Rischke)

In this thesis, I study the phase diagram of dense, locally neutral three-flavor quark matter as a function of the strange quark mass, the quark chemical potential, and the temperature, employing a general nine-parameter ansatz for the gap matrix. I also study the phase diagram of dense, locally neutral three-flavor quark matter within the framework of a Nambu-Jona-Lasinio (NJL) model. In the analysis, dynamically generated quark masses are taken into account self-consistently. The phase diagram in the plane of temperature and quark chemical potential is presented. In addition, I study the effect of neutrino trapping on the phase diagram of dense, locally neutral three-flavor quark matter within the same NJL model. The phase diagrams in the plane of temperature and quark chemical potential, as well as in the plane of temperature and lepton-number chemical potential are presented. The implications of these results for the evolution of protoneutron stars are briefly discussed.

 

Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612591 [abs, ps, pdf, other] :
Title: Comptonization in the X-ray Spectra of Radio Millisecond Pulsars
Authors: Slavko Bogdanov, Jonathan E. Grindlay, George B. Rybicki
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.5-8
Note: replaced with revised version Thu, 21 Dec 2006 16:01:38 GMT (127kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 25 Dec 06 01:00:08 GMT
0612669 -- 0612698 received


12 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612675 [abs, ps, pdf, other] :
Title: Power spectra of black holes and neutron stars as a probe of hydrodynamical structure of the source. Diffusion theory and its application to Cyg X-1 and Cyg X-2 X-ray observations
Authors: Lev Titarchuk (GMU/NRL/GSFC/University of Ferrara), Nikolai Shaposhnikov (USRA/GSFC), Vadim Arefiev (IKI, Russia)
Comments: 45 pages, 12 figures, Accepted and scheduled for publication in the Astrophysical Journal, for April 10, 2007, v 659 1 issue

We present a model of Fourier Power Density Spectrum (PDS) formation in accretion powered X-ray binary systems derived from the first principles of the diffusion theory. Timing properties of X-ray emission are considered to be a result of diffusive propagation of the driving perturbations in a bounded medium. We prove that the integrated power P_x of the resulting PDS is only a small fraction of the integrated power P_dr of the driving oscillations, which is distributed over the disk. The resulting PDS continuum is a sum of two components, a low frequency (LF) component which presumably originates in an extended accretion disk and a high frequency (HF) component which originates in the innermost part of the source (Compton cloud or corona). The LF PDS component has a power-law shape with index of 1.0-1.5 at higher frequencies (``red'' noise) and a flat spectrum below a characteristic (break) frequency (``white'' noise). This white-red noise (WRN) continuum spectrum holds information about the physical parameters of the bounded extended medium, diffusion time scale and the dependence law of viscosity vs radius. We apply our model of the PDS to a sample of RXTE and EXOSAT timing data from Cyg X-1 and Cyg X-2 which describes adequately the spectral transitions in these sources.

 
astro-ph/0612676 [abs, ps, pdf, other] :
Title: Computation of Neutron Star Surface Emission Spectra for Arbitrary Magnetic Field Directions without Diffusion Approximation
Authors: L.W. Yeh, G.T. Chen, H.K. Chang
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.137-140

To derive physical properties of the neutron star surface with observed spectra, a realistic model spectrum of neutron star surface emission is essential. Limited by computing resources, a full computation of the radiative transfer equations without the diffusion approximation has been conducted up to date only for the case of local magnetic fields being perpendicular to the stellar surface. In this paper we report the full-computation result for an arbitrary field direction. For comparison we also compute the radiative transfer equation using the diffusion approximation. For a given effective temperature, the computed spectrum with the diffusion approximation is always softer than that of a full computation at a non-negligible level. It leads to an over-estimate of the effective temperature if the diffusion approximation spectrum is employed in the spectral fitting. Other characteristics for different magnetic field orientations, such as the beaming pattern of the two polarization modes and the structure of the atmosphere, are also discussed.

 
astro-ph/0612677 [abs, ps, pdf, other] :
Title: Particle acceleration in pulsar magnetospheres
Authors: P.C. Hsu, K. Hirotani, H.K. Chang
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.141-144

We investigate a pair creation cascade in the magnetosphere of a rapidly rotating neutron star. We solve the set of the Poisson equation for the electro-static potential and the Boltzmann equations for electrons, positrons, and gamma-ray photons simultaneously. In this paper, we first examine the time-dependent nature of particle accelerators by solving the non-stationary Boltzmann equations on the two-dimensional poloidal plane in which both the rotational and magnetic axes reside. Evaluating the temperature of the heated polar cap surface, which is located near the magnetic pole, by the bombardment of gap-accelerated particles, and applying the scheme to millisecond pulsar parameters, we demonstrate that the solution converges to a stationary solution of which pair-creation cascade is maintained by the heated polar-cap emission, in a wide range of three-dimensional parameter space (period, period derivative, magnetic inclination angle). We also present the deathlines of millisecond pulsars.

 
astro-ph/0612679 [abs, ps, pdf, other] :
Title: Magnetized electron-positron plasmas
Authors: C.R. Stark, D.A. Diver, A.A. da Costa
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.145-148

Electrostatic oscillations in cold electron-positron plasmas can be coupled to a propagating electromagnetic mode if the background magnetic field is inhomogeneous. Previous work considered this coupling in the quasi-linear regime, successfully simulating the electromagnetic mode. Here we present a stability analysis of the non-linear problem, perturbed from dynamical equilibrium, in order to gain some insight into the modes present in the system.

 
astro-ph/0612680 [abs, ps, pdf, other] :
Title: Is the Lack of Pulsations in Low Mass X-Ray Binaries due to Comptonizing Coronae?
Authors: Ersin Gogus (Sabanci Univ. Istanbul), M. Ali Alpar (Sabanci Univ. Istanbul), Marat Gilfanov (MPA Garching, IKI Moscow)
Comments: 11 pages, accepted for publication in ApJ

The spin periods of the neutron stars in most Low Mass X-ray Binary (LMXB) systems still remain undetected. One of the models to explain the absence of coherent pulsations has been the suppression of the beamed signal by Compton scattering of X-ray photons by electrons in a surrounding corona. We point out that simultaneously with wiping out the pulsation signal, such a corona will upscatter (pulsating or not) X-ray emission originating at and/or near the surface of the neutron star leading to appearance of a hard tail of Comptonized radiation in the source spectrum. We analyze the hard X-ray spectra of a selected set of LMXBs and demonstrate that the optical depth of the corona is not likely to be large enough to cause the pulsations to disappear.

 
astro-ph/0612681 [abs, ps, pdf, other] :
Title: Evolution of the inclination angle of radio pulsars is observable effect
Authors: Y.N. Istomin, T.V. Shabanova
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.153-156

It is shown that the slow glitches in the spin rate of the pulsar B1822-09 can be explained by the reconstruction of the neutron star shape, which is not matched with the star rotation axis. Owing to the evolution of the inclination angle, i.e. the angle between the rotation axis and the axis of the magnetic dipole, under the action of the braking torque, there appears the disagreement between the rotation axis and the symmetry axis. After the angle between the axis of symmetry and the axis of the rotation achieves the maximum value of alpha ~ 2x10^-4 the shape of the neutron star becomes matching with the rotation axis. Such reconstruction is observed as the slow glitch.

 
astro-ph/0612682 [abs, ps, pdf, other] :
Title: Relativistic MHD Winds from Rotating Neutron Stars
Authors: N. Bucciantini, T.A. Thompson, J. Arons, E. Quataert
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang

We solve the time-dependent dynamics of axisymmetric, general relativistic MHD winds from rotating neutron stars. The mass loss rate is obtained self consistently as a solution of the MHD equations, subject to a finite thermal pressure at the stellar surface. Conditions are chosen to be representative of the neutrino driven phase in newly born magnetars, which have been considered as a possible engine for GRBs. We compute the angular momentum and energy losses as a function of $\sigma$ and compare them with the analytic expectation from the classical theory of pulsar winds. We observe the convergence to the force-free limit in the energy loss and we study the evolution of the closed zone for increasing magnetization. Results also show that the dipolar magnetic field and the presence of a closed zone do not modify significantly the acceleration and collimation properties of the wind.

 
astro-ph/0612683 [abs, ps, pdf, other] :
Title: A model for unusual pulsed x-ray emission from PSR J1119-6127
Authors: G.I. Melikidze, J. Gil, A. Szary
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.157-160

We propose a model, which naturally explains an unusual thermal X-ray emission, observed from PSR J1119-6127. The model is based on the assumption that the pulsar magnetic field near the stellar surface differs significantly from the pure dipole field. We show that the structure and curvature of the field lines can be of the kind that allows the pair creation in the closed field line region. The created pairs propagate along the closed field lines and heat the stellar surface beyond the local poles. It is demonstrated that such a configuration can be easily realized.

 
astro-ph/0612684 [abs, ps, pdf, other] :
Title: The geometry of PSR B0031-07
Authors: R. Smits, D. Mitra, B. Stappers, J. Kuijpers, P. Weltevrede, A. Jessner, Y. Gupta
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.161-164

Here we present the results from an analysis of a multifrequency simultaneous observation of PSR B0031$-$07. We have constructed a geometrical model, based on an empirical relationship between height and frequency of emission, that reproduces many of the observed characteristics. The model suggests very low emission altitudes for this pulsar of only a few kilometers above the star's surface.

 
astro-ph/0612685 [abs, ps, pdf, other] :
Title: Accreting isolated neutron stars
Authors: N.R. Ikhsanov, P.L. Biermann
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.165-168

Accretion of interstellar material by a magnetized, slowly rotating isolated neutron star is discussed. We show that the average persistent X-ray luminosity of these objects is unlikely to exceed 4x10^26 erg/s. They can also appear as X-ray bursters with the burst duration of ~30 minutes and repetition time of \~10^5 yr. This indicates that the number of the accreting isolated neutron stars which could be observed with recent X-ray missions is a few orders of magnitude smaller than that previously estimated. Our findings argue against models in which the magnetic field of neutron stars is assumed to decay exponentially on a time scale shorter than 500 Myr.

 
astro-ph/0612686 [abs, ps, pdf, other] :
Title: Improved methods for modeling pulse shapes of accreting millisecond pulsars
Authors: D. Leahy, S. Morsink, C. Cadeau
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.169-172

Raytracing computations for light emitted from the surface of a rapidly rotating neutron star are carried out in order to construct light curves for accreting millisecond pulsars. These calculations are for realistic models of rapidly rotating neutron stars which take into account both the correct exterior metric and the oblate shape of the star. We find that the most important effect, comparing the full raytracing computations with simpler approximations currently in use, arises from the oblate shape of the rotating star. Approximating a rotating neutron star as a sphere introduces serious errors in fitted values of the star's radius and mass if the rotation rate is very large. However, for lower rotation rates acceptable mass and radius values can be obtained using the spherical approximation.

 
astro-ph/0612687 [abs, ps, pdf, other] :
Title: Importance of Compton scattering to radiation spectra of isolated neutron stars
Authors: V. Suleimanov, K. Werner
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.173-176

Model atmospheres of isolated neutron stars with low magnetic field are calculated with Compton scattering taking into account. Models with effective temperatures 1, 3 and 5 MK, with two values of surface gravity log(g)g = 13.9 and 14.3), and different chemical compositions are calculated. Radiation spectra computed with Compton scattering are softer than the computed with Thomson scattering at high energies (E > 5 keV) for hot (T_eff > 1 MK) atmospheres with hydrogen-helium composition. Compton scattering is more significant to hydrogen models with low surface gravity. The emergent spectra of the hottest (T_eff > 3 MK) model atmospheres can be described by diluted blackbody spectra with hardness factors ~ 1.6 - 1.9. Compton scattering is less important for models with solar abundance of heavy elements.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 25 Dec 06 01:00:08 GMT
0612669 -- 0612698 received


12 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612675 [abs, ps, pdf, other] :
Title: Power spectra of black holes and neutron stars as a probe of hydrodynamical structure of the source. Diffusion theory and its application to Cyg X-1 and Cyg X-2 X-ray observations
Authors: Lev Titarchuk (GMU/NRL/GSFC/University of Ferrara), Nikolai Shaposhnikov (USRA/GSFC), Vadim Arefiev (IKI, Russia)
Comments: 45 pages, 12 figures, Accepted and scheduled for publication in the Astrophysical Journal, for April 10, 2007, v 659 1 issue

We present a model of Fourier Power Density Spectrum (PDS) formation in accretion powered X-ray binary systems derived from the first principles of the diffusion theory. Timing properties of X-ray emission are considered to be a result of diffusive propagation of the driving perturbations in a bounded medium. We prove that the integrated power P_x of the resulting PDS is only a small fraction of the integrated power P_dr of the driving oscillations, which is distributed over the disk. The resulting PDS continuum is a sum of two components, a low frequency (LF) component which presumably originates in an extended accretion disk and a high frequency (HF) component which originates in the innermost part of the source (Compton cloud or corona). The LF PDS component has a power-law shape with index of 1.0-1.5 at higher frequencies (``red'' noise) and a flat spectrum below a characteristic (break) frequency (``white'' noise). This white-red noise (WRN) continuum spectrum holds information about the physical parameters of the bounded extended medium, diffusion time scale and the dependence law of viscosity vs radius. We apply our model of the PDS to a sample of RXTE and EXOSAT timing data from Cyg X-1 and Cyg X-2 which describes adequately the spectral transitions in these sources.

 
astro-ph/0612676 [abs, ps, pdf, other] :
Title: Computation of Neutron Star Surface Emission Spectra for Arbitrary Magnetic Field Directions without Diffusion Approximation
Authors: L.W. Yeh, G.T. Chen, H.K. Chang
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.137-140

To derive physical properties of the neutron star surface with observed spectra, a realistic model spectrum of neutron star surface emission is essential. Limited by computing resources, a full computation of the radiative transfer equations without the diffusion approximation has been conducted up to date only for the case of local magnetic fields being perpendicular to the stellar surface. In this paper we report the full-computation result for an arbitrary field direction. For comparison we also compute the radiative transfer equation using the diffusion approximation. For a given effective temperature, the computed spectrum with the diffusion approximation is always softer than that of a full computation at a non-negligible level. It leads to an over-estimate of the effective temperature if the diffusion approximation spectrum is employed in the spectral fitting. Other characteristics for different magnetic field orientations, such as the beaming pattern of the two polarization modes and the structure of the atmosphere, are also discussed.

 
astro-ph/0612677 [abs, ps, pdf, other] :
Title: Particle acceleration in pulsar magnetospheres
Authors: P.C. Hsu, K. Hirotani, H.K. Chang
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.141-144

We investigate a pair creation cascade in the magnetosphere of a rapidly rotating neutron star. We solve the set of the Poisson equation for the electro-static potential and the Boltzmann equations for electrons, positrons, and gamma-ray photons simultaneously. In this paper, we first examine the time-dependent nature of particle accelerators by solving the non-stationary Boltzmann equations on the two-dimensional poloidal plane in which both the rotational and magnetic axes reside. Evaluating the temperature of the heated polar cap surface, which is located near the magnetic pole, by the bombardment of gap-accelerated particles, and applying the scheme to millisecond pulsar parameters, we demonstrate that the solution converges to a stationary solution of which pair-creation cascade is maintained by the heated polar-cap emission, in a wide range of three-dimensional parameter space (period, period derivative, magnetic inclination angle). We also present the deathlines of millisecond pulsars.

 
astro-ph/0612679 [abs, ps, pdf, other] :
Title: Magnetized electron-positron plasmas
Authors: C.R. Stark, D.A. Diver, A.A. da Costa
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.145-148

Electrostatic oscillations in cold electron-positron plasmas can be coupled to a propagating electromagnetic mode if the background magnetic field is inhomogeneous. Previous work considered this coupling in the quasi-linear regime, successfully simulating the electromagnetic mode. Here we present a stability analysis of the non-linear problem, perturbed from dynamical equilibrium, in order to gain some insight into the modes present in the system.

 
astro-ph/0612680 [abs, ps, pdf, other] :
Title: Is the Lack of Pulsations in Low Mass X-Ray Binaries due to Comptonizing Coronae?
Authors: Ersin Gogus (Sabanci Univ. Istanbul), M. Ali Alpar (Sabanci Univ. Istanbul), Marat Gilfanov (MPA Garching, IKI Moscow)
Comments: 11 pages, accepted for publication in ApJ

The spin periods of the neutron stars in most Low Mass X-ray Binary (LMXB) systems still remain undetected. One of the models to explain the absence of coherent pulsations has been the suppression of the beamed signal by Compton scattering of X-ray photons by electrons in a surrounding corona. We point out that simultaneously with wiping out the pulsation signal, such a corona will upscatter (pulsating or not) X-ray emission originating at and/or near the surface of the neutron star leading to appearance of a hard tail of Comptonized radiation in the source spectrum. We analyze the hard X-ray spectra of a selected set of LMXBs and demonstrate that the optical depth of the corona is not likely to be large enough to cause the pulsations to disappear.

 
astro-ph/0612681 [abs, ps, pdf, other] :
Title: Evolution of the inclination angle of radio pulsars is observable effect
Authors: Y.N. Istomin, T.V. Shabanova
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.153-156

It is shown that the slow glitches in the spin rate of the pulsar B1822-09 can be explained by the reconstruction of the neutron star shape, which is not matched with the star rotation axis. Owing to the evolution of the inclination angle, i.e. the angle between the rotation axis and the axis of the magnetic dipole, under the action of the braking torque, there appears the disagreement between the rotation axis and the symmetry axis. After the angle between the axis of symmetry and the axis of the rotation achieves the maximum value of alpha ~ 2x10^-4 the shape of the neutron star becomes matching with the rotation axis. Such reconstruction is observed as the slow glitch.

 
astro-ph/0612682 [abs, ps, pdf, other] :
Title: Relativistic MHD Winds from Rotating Neutron Stars
Authors: N. Bucciantini, T.A. Thompson, J. Arons, E. Quataert
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang

We solve the time-dependent dynamics of axisymmetric, general relativistic MHD winds from rotating neutron stars. The mass loss rate is obtained self consistently as a solution of the MHD equations, subject to a finite thermal pressure at the stellar surface. Conditions are chosen to be representative of the neutrino driven phase in newly born magnetars, which have been considered as a possible engine for GRBs. We compute the angular momentum and energy losses as a function of $\sigma$ and compare them with the analytic expectation from the classical theory of pulsar winds. We observe the convergence to the force-free limit in the energy loss and we study the evolution of the closed zone for increasing magnetization. Results also show that the dipolar magnetic field and the presence of a closed zone do not modify significantly the acceleration and collimation properties of the wind.

 
astro-ph/0612683 [abs, ps, pdf, other] :
Title: A model for unusual pulsed x-ray emission from PSR J1119-6127
Authors: G.I. Melikidze, J. Gil, A. Szary
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.157-160

We propose a model, which naturally explains an unusual thermal X-ray emission, observed from PSR J1119-6127. The model is based on the assumption that the pulsar magnetic field near the stellar surface differs significantly from the pure dipole field. We show that the structure and curvature of the field lines can be of the kind that allows the pair creation in the closed field line region. The created pairs propagate along the closed field lines and heat the stellar surface beyond the local poles. It is demonstrated that such a configuration can be easily realized.

 
astro-ph/0612684 [abs, ps, pdf, other] :
Title: The geometry of PSR B0031-07
Authors: R. Smits, D. Mitra, B. Stappers, J. Kuijpers, P. Weltevrede, A. Jessner, Y. Gupta
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.161-164

Here we present the results from an analysis of a multifrequency simultaneous observation of PSR B0031$-$07. We have constructed a geometrical model, based on an empirical relationship between height and frequency of emission, that reproduces many of the observed characteristics. The model suggests very low emission altitudes for this pulsar of only a few kilometers above the star's surface.

 
astro-ph/0612685 [abs, ps, pdf, other] :
Title: Accreting isolated neutron stars
Authors: N.R. Ikhsanov, P.L. Biermann
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.165-168

Accretion of interstellar material by a magnetized, slowly rotating isolated neutron star is discussed. We show that the average persistent X-ray luminosity of these objects is unlikely to exceed 4x10^26 erg/s. They can also appear as X-ray bursters with the burst duration of ~30 minutes and repetition time of \~10^5 yr. This indicates that the number of the accreting isolated neutron stars which could be observed with recent X-ray missions is a few orders of magnitude smaller than that previously estimated. Our findings argue against models in which the magnetic field of neutron stars is assumed to decay exponentially on a time scale shorter than 500 Myr.

 
astro-ph/0612686 [abs, ps, pdf, other] :
Title: Improved methods for modeling pulse shapes of accreting millisecond pulsars
Authors: D. Leahy, S. Morsink, C. Cadeau
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.169-172

Raytracing computations for light emitted from the surface of a rapidly rotating neutron star are carried out in order to construct light curves for accreting millisecond pulsars. These calculations are for realistic models of rapidly rotating neutron stars which take into account both the correct exterior metric and the oblate shape of the star. We find that the most important effect, comparing the full raytracing computations with simpler approximations currently in use, arises from the oblate shape of the rotating star. Approximating a rotating neutron star as a sphere introduces serious errors in fitted values of the star's radius and mass if the rotation rate is very large. However, for lower rotation rates acceptable mass and radius values can be obtained using the spherical approximation.

 
astro-ph/0612687 [abs, ps, pdf, other] :
Title: Importance of Compton scattering to radiation spectra of isolated neutron stars
Authors: V. Suleimanov, K. Werner
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.173-176

Model atmospheres of isolated neutron stars with low magnetic field are calculated with Compton scattering taking into account. Models with effective temperatures 1, 3 and 5 MK, with two values of surface gravity log(g)g = 13.9 and 14.3), and different chemical compositions are calculated. Radiation spectra computed with Compton scattering are softer than the computed with Thomson scattering at high energies (E > 5 keV) for hot (T_eff > 1 MK) atmospheres with hydrogen-helium composition. Compton scattering is more significant to hydrogen models with low surface gravity. The emergent spectra of the hottest (T_eff > 3 MK) model atmospheres can be described by diluted blackbody spectra with hardness factors ~ 1.6 - 1.9. Compton scattering is less important for models with solar abundance of heavy elements.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 25 Dec 06 01:00:08 GMT
0612669 -- 0612698 received


12 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612675 [abs, ps, pdf, other] :
Title: Power spectra of black holes and neutron stars as a probe of hydrodynamical structure of the source. Diffusion theory and its application to Cyg X-1 and Cyg X-2 X-ray observations
Authors: Lev Titarchuk (GMU/NRL/GSFC/University of Ferrara), Nikolai Shaposhnikov (USRA/GSFC), Vadim Arefiev (IKI, Russia)
Comments: 45 pages, 12 figures, Accepted and scheduled for publication in the Astrophysical Journal, for April 10, 2007, v 659 1 issue

We present a model of Fourier Power Density Spectrum (PDS) formation in accretion powered X-ray binary systems derived from the first principles of the diffusion theory. Timing properties of X-ray emission are considered to be a result of diffusive propagation of the driving perturbations in a bounded medium. We prove that the integrated power P_x of the resulting PDS is only a small fraction of the integrated power P_dr of the driving oscillations, which is distributed over the disk. The resulting PDS continuum is a sum of two components, a low frequency (LF) component which presumably originates in an extended accretion disk and a high frequency (HF) component which originates in the innermost part of the source (Compton cloud or corona). The LF PDS component has a power-law shape with index of 1.0-1.5 at higher frequencies (``red'' noise) and a flat spectrum below a characteristic (break) frequency (``white'' noise). This white-red noise (WRN) continuum spectrum holds information about the physical parameters of the bounded extended medium, diffusion time scale and the dependence law of viscosity vs radius. We apply our model of the PDS to a sample of RXTE and EXOSAT timing data from Cyg X-1 and Cyg X-2 which describes adequately the spectral transitions in these sources.

 
astro-ph/0612676 [abs, ps, pdf, other] :
Title: Computation of Neutron Star Surface Emission Spectra for Arbitrary Magnetic Field Directions without Diffusion Approximation
Authors: L.W. Yeh, G.T. Chen, H.K. Chang
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.137-140

To derive physical properties of the neutron star surface with observed spectra, a realistic model spectrum of neutron star surface emission is essential. Limited by computing resources, a full computation of the radiative transfer equations without the diffusion approximation has been conducted up to date only for the case of local magnetic fields being perpendicular to the stellar surface. In this paper we report the full-computation result for an arbitrary field direction. For comparison we also compute the radiative transfer equation using the diffusion approximation. For a given effective temperature, the computed spectrum with the diffusion approximation is always softer than that of a full computation at a non-negligible level. It leads to an over-estimate of the effective temperature if the diffusion approximation spectrum is employed in the spectral fitting. Other characteristics for different magnetic field orientations, such as the beaming pattern of the two polarization modes and the structure of the atmosphere, are also discussed.

 
astro-ph/0612677 [abs, ps, pdf, other] :
Title: Particle acceleration in pulsar magnetospheres
Authors: P.C. Hsu, K. Hirotani, H.K. Chang
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.141-144

We investigate a pair creation cascade in the magnetosphere of a rapidly rotating neutron star. We solve the set of the Poisson equation for the electro-static potential and the Boltzmann equations for electrons, positrons, and gamma-ray photons simultaneously. In this paper, we first examine the time-dependent nature of particle accelerators by solving the non-stationary Boltzmann equations on the two-dimensional poloidal plane in which both the rotational and magnetic axes reside. Evaluating the temperature of the heated polar cap surface, which is located near the magnetic pole, by the bombardment of gap-accelerated particles, and applying the scheme to millisecond pulsar parameters, we demonstrate that the solution converges to a stationary solution of which pair-creation cascade is maintained by the heated polar-cap emission, in a wide range of three-dimensional parameter space (period, period derivative, magnetic inclination angle). We also present the deathlines of millisecond pulsars.

 
astro-ph/0612679 [abs, ps, pdf, other] :
Title: Magnetized electron-positron plasmas
Authors: C.R. Stark, D.A. Diver, A.A. da Costa
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.145-148

Electrostatic oscillations in cold electron-positron plasmas can be coupled to a propagating electromagnetic mode if the background magnetic field is inhomogeneous. Previous work considered this coupling in the quasi-linear regime, successfully simulating the electromagnetic mode. Here we present a stability analysis of the non-linear problem, perturbed from dynamical equilibrium, in order to gain some insight into the modes present in the system.

 
astro-ph/0612680 [abs, ps, pdf, other] :
Title: Is the Lack of Pulsations in Low Mass X-Ray Binaries due to Comptonizing Coronae?
Authors: Ersin Gogus (Sabanci Univ. Istanbul), M. Ali Alpar (Sabanci Univ. Istanbul), Marat Gilfanov (MPA Garching, IKI Moscow)
Comments: 11 pages, accepted for publication in ApJ

The spin periods of the neutron stars in most Low Mass X-ray Binary (LMXB) systems still remain undetected. One of the models to explain the absence of coherent pulsations has been the suppression of the beamed signal by Compton scattering of X-ray photons by electrons in a surrounding corona. We point out that simultaneously with wiping out the pulsation signal, such a corona will upscatter (pulsating or not) X-ray emission originating at and/or near the surface of the neutron star leading to appearance of a hard tail of Comptonized radiation in the source spectrum. We analyze the hard X-ray spectra of a selected set of LMXBs and demonstrate that the optical depth of the corona is not likely to be large enough to cause the pulsations to disappear.

 
astro-ph/0612681 [abs, ps, pdf, other] :
Title: Evolution of the inclination angle of radio pulsars is observable effect
Authors: Y.N. Istomin, T.V. Shabanova
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.153-156

It is shown that the slow glitches in the spin rate of the pulsar B1822-09 can be explained by the reconstruction of the neutron star shape, which is not matched with the star rotation axis. Owing to the evolution of the inclination angle, i.e. the angle between the rotation axis and the axis of the magnetic dipole, under the action of the braking torque, there appears the disagreement between the rotation axis and the symmetry axis. After the angle between the axis of symmetry and the axis of the rotation achieves the maximum value of alpha ~ 2x10^-4 the shape of the neutron star becomes matching with the rotation axis. Such reconstruction is observed as the slow glitch.

 
astro-ph/0612682 [abs, ps, pdf, other] :
Title: Relativistic MHD Winds from Rotating Neutron Stars
Authors: N. Bucciantini, T.A. Thompson, J. Arons, E. Quataert
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang

We solve the time-dependent dynamics of axisymmetric, general relativistic MHD winds from rotating neutron stars. The mass loss rate is obtained self consistently as a solution of the MHD equations, subject to a finite thermal pressure at the stellar surface. Conditions are chosen to be representative of the neutrino driven phase in newly born magnetars, which have been considered as a possible engine for GRBs. We compute the angular momentum and energy losses as a function of $\sigma$ and compare them with the analytic expectation from the classical theory of pulsar winds. We observe the convergence to the force-free limit in the energy loss and we study the evolution of the closed zone for increasing magnetization. Results also show that the dipolar magnetic field and the presence of a closed zone do not modify significantly the acceleration and collimation properties of the wind.

 
astro-ph/0612683 [abs, ps, pdf, other] :
Title: A model for unusual pulsed x-ray emission from PSR J1119-6127
Authors: G.I. Melikidze, J. Gil, A. Szary
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.157-160

We propose a model, which naturally explains an unusual thermal X-ray emission, observed from PSR J1119-6127. The model is based on the assumption that the pulsar magnetic field near the stellar surface differs significantly from the pure dipole field. We show that the structure and curvature of the field lines can be of the kind that allows the pair creation in the closed field line region. The created pairs propagate along the closed field lines and heat the stellar surface beyond the local poles. It is demonstrated that such a configuration can be easily realized.

 
astro-ph/0612684 [abs, ps, pdf, other] :
Title: The geometry of PSR B0031-07
Authors: R. Smits, D. Mitra, B. Stappers, J. Kuijpers, P. Weltevrede, A. Jessner, Y. Gupta
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.161-164

Here we present the results from an analysis of a multifrequency simultaneous observation of PSR B0031$-$07. We have constructed a geometrical model, based on an empirical relationship between height and frequency of emission, that reproduces many of the observed characteristics. The model suggests very low emission altitudes for this pulsar of only a few kilometers above the star's surface.

 
astro-ph/0612685 [abs, ps, pdf, other] :
Title: Accreting isolated neutron stars
Authors: N.R. Ikhsanov, P.L. Biermann
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.165-168

Accretion of interstellar material by a magnetized, slowly rotating isolated neutron star is discussed. We show that the average persistent X-ray luminosity of these objects is unlikely to exceed 4x10^26 erg/s. They can also appear as X-ray bursters with the burst duration of ~30 minutes and repetition time of \~10^5 yr. This indicates that the number of the accreting isolated neutron stars which could be observed with recent X-ray missions is a few orders of magnitude smaller than that previously estimated. Our findings argue against models in which the magnetic field of neutron stars is assumed to decay exponentially on a time scale shorter than 500 Myr.

 
astro-ph/0612686 [abs, ps, pdf, other] :
Title: Improved methods for modeling pulse shapes of accreting millisecond pulsars
Authors: D. Leahy, S. Morsink, C. Cadeau
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.169-172

Raytracing computations for light emitted from the surface of a rapidly rotating neutron star are carried out in order to construct light curves for accreting millisecond pulsars. These calculations are for realistic models of rapidly rotating neutron stars which take into account both the correct exterior metric and the oblate shape of the star. We find that the most important effect, comparing the full raytracing computations with simpler approximations currently in use, arises from the oblate shape of the rotating star. Approximating a rotating neutron star as a sphere introduces serious errors in fitted values of the star's radius and mass if the rotation rate is very large. However, for lower rotation rates acceptable mass and radius values can be obtained using the spherical approximation.

 
astro-ph/0612687 [abs, ps, pdf, other] :
Title: Importance of Compton scattering to radiation spectra of isolated neutron stars
Authors: V. Suleimanov, K. Werner
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.173-176

Model atmospheres of isolated neutron stars with low magnetic field are calculated with Compton scattering taking into account. Models with effective temperatures 1, 3 and 5 MK, with two values of surface gravity log(g)g = 13.9 and 14.3), and different chemical compositions are calculated. Radiation spectra computed with Compton scattering are softer than the computed with Thomson scattering at high energies (E > 5 keV) for hot (T_eff > 1 MK) atmospheres with hydrogen-helium composition. Compton scattering is more significant to hydrogen models with low surface gravity. The emergent spectra of the hottest (T_eff > 3 MK) model atmospheres can be described by diluted blackbody spectra with hardness factors ~ 1.6 - 1.9. Compton scattering is less important for models with solar abundance of heavy elements.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 28 Dec 06 01:00:12 GMT
0612699 -- 0612740 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612725 [abs, ps, pdf, other] :
Title: On the theory of magnetar QPOs
Authors: Yuri Levin (Leiden University)
Comments: 10 pages, submitted to MNRAS

We consider torsional oscillations of magnetars. This problem features rich dynamics due to the strong interaction between the normal modes of a magnetar's crust and a continuum of Magneto-Hydro-Dynamic (MHD) modes in its fluid core. We study the dynamics using a simple model of a magnetar possessing a uniform magnetic field and a thin spherical crust. Firstly, we show that global torsional modes only exist when one introduces unphysically large dissipative terms into the equations of motion; thus global modes are not helpful for understanding the magnetar Quasi-Periodic Oscillations (QPOs). Secondly, we solve the initial-value problem by simulating the sudden release of an initially strained crust and monitoring the subsequent crustal motion. We find that the crustal torsional modes quickly exchange their energy with the MHD continuum in the core, and decay by several orders of magnitude over the course of about 10 oscillation periods. After the initial rapid decay, the crustal motion is stabilized and several time-varying QPOs are observed. The dynamical spectrum of the simulated crustal motion is in qualitative agreement with that of the x-ray light-curve in the tail of a giant magnetar flare. The asymptotic frequencies of some of the QPOs are associated with the special spectral points--the turning points or edges--of the MHD continuum, and are not related to those of the crust. The observed steady low-frequency QPO at 18 Hz is almost certainly associated with the lowest frequency of the MHD continuum, or its first overtone. We also find that drifting QPOs get amplified when they come near the frequencies of the crustal modes. This explains why some of the observed QPOs have frequencies close to the expected crustal frequencies, and why these QPOs are highly variable with time.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607005 [abs, ps, pdf, other] :
Title: Exotic bulk viscosity and its influence on neutron star r-modes
Authors: Debarati Chatterjee, Debades Bandyopadhyay
Comments: 5 pages, 3 figure, presented in the Conference on Isolated Neutron Stars: From the Interior to The Surface, London, UK, 24-28 April, 2006; revised and final version to appear in Astrophys. Space Sci
Note: replaced with revised version Wed, 27 Dec 2006 13:06:20 GMT (181kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 29 Dec 06 01:00:09 GMT
0612741 -- 0612766 received


0 abstracts or titles contain neutron star, magnetar or pulsar



Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 1 Jan 07 01:00:09 GMT
0612767 -- 0612791 received


11 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612776 [abs, ps, pdf, other] :
Title: Asymmetric neutrino emission in quark matter and pulsar kicks
Authors: I. Sagert, J. Schaffner-Bielich
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.177-180

The puzzling phenomenon of pulsar kicks, i.e. the observed large escape velocities of pulsars out of supernova remnants, is examined for compact stars with a strange quark matter core. The direct Urca process in quark matter is studied in the presence of a strong magnetic field. Conditions for an asymmetric emission of the produced neutrinos are worked out in detail, giving constraints on the temperature, the strength of the magnetic field and the electron chemical potential in the quark matter core. In addition, the neutrino mean free paths for quark matter and a possible hadronic mantle are considered.

 
astro-ph/0612777 [abs, ps, pdf, other] :
Title: Neutron stars and quark stars: Two coexisting families of compact stars?
Authors: J. Schaffner-Bielich
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.181-184

The mass-radius relation of compact stars is discussed with relation to the presence of quark matter in the core. The existence of a new family of compact stars with quark matter besides white dwarfs and ordinary neutron stars is outlined.

 
astro-ph/0612780 [abs, ps, pdf, other] :
Title: Neutron stars in Microquasars
Authors: M. Massi
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.185-188

We discuss the "basic" condition for an accreting neutron star to become a microquasar, i.e. ejecting relativistic particles orthogonal to the accretion disk instead of confining disk-material down to the magnetic poles and creating the two emitting caps typical for a X-ray pulsar. Jet creation is prevented for B >/= 10^12 G independent of the accretion rate. This excludes the possibility for a classic X-ray pulsar to develop a "microquasar-phase" and is consistent with the lack of radio emission from such pulsar systems. Millisecond accretion-powered pulsars, on the contrary, may show a "microquasar-phase", where B < 10^7.5 G is valid, whereas the limit for Z sources is B < 10^8.2 G. The implication of our analysis is that the jet might be the suitable agent of angular momentum sink for millisecond accretion-powered pulsars.

 
astro-ph/0612782 [abs, ps, pdf, other] :
Title: Forced oscillations in relativistic accretion disks and QPOs
Authors: J. Petri
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.189-192

In this work we explore the idea that the high frequency QPOs observed in LMXBs may be explained as a resonant coupling between the neutron star spin and epicyclic modes of accretion disk oscillations. We propose a new model for these QPOs based on forced oscillations induced in the accretion disk due to a stellar asymmetric rotating gravitational or magnetic field. It is shown that particles evolving in a rotating non-axisymmetric field are subject to three kinds of resonances: a corotation resonance, a Lindblad resonance due to a driving force, and a parametric resonance due to the time varying epicyclic frequencies. These results are extends by means of 2D numerical simulations of a simplified version of the accretion disk. The simulations are performed for the Newtonian gravitational potential, as well as for a pseudo-general relativistic potential, which enables us to explore the behavior of the resonances around both rotating neutron stars and black holes. Density perturbations are only significant in the region located close to the inner edge of the disk near the ISCO where the gravitational or magnetic perturbation is maximal. It is argued that the nearly periodic motion induced in the disk will produce high quality factor QPOs.
Finally, applying this model to a typical neutron star, we found that the strongest response occurs when the frequency difference of the two modes equals either the spin frequency (for "slow rotators") or half of it (for "fast rotators"). The two main excited modes may both be connected to vertical oscillations of the disk. We emphasize that strong gravity is not needed to excite the modes.

 
astro-ph/0612783 [abs, ps, pdf, other] :
Title: Compact star constraints on the high-density EoS
Authors: H. Grigorian, D. Blaschke, T. Klaehn
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang

A new scheme for testing the nuclear matter (NM) equation of state (EoS) at high densities using constraints from compact star (CS) phenomenology is applied to neutron stars with a core of deconfined quark matter (QM). An acceptable EoS shall not to be in conflict with the mass measurement of 2.1 +/- 0.2 solar mass (1 sigma level) for PSR J0751+1807 and the mass radius relation deduced from the thermal emission of RX J1856-3754. Further constraints for the state of matter in CS interiors come from temperature-age data for young, nearby objects. The CS cooling theory shall agree not only with these data, but also with the mass distribution inferred via population synthesis models as well as with LogN-LogS data. The scheme is applied to a set of hybrid EsoS with a phase transition to stiff, color superconducting QM which fulfills all above constraints and is constrained otherwise from NM saturation properties and flow data of heavy-ion collisions. We extrapolate our description to low temperatures and draw conclusions for the QCD phase diagram to be explored in heavy-ion collision experiments.

 
astro-ph/0612785 [abs, ps, pdf, other] :
Title: Pulsar Physics without Magnetars
Authors: W. Kundt
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.197-200

Almost 40 years after the discovery of pulsars -- and despite a plethora of secured data on them -- pulsar theory is still beset by a number of fundamental inconsistencies. In this short contribution, I will argue that (i) magnetars do not exist, (ii) (ordinary) pulsars turnoff (or 'die') when their wind pressure falls short of keeping the CSM at a safe distance, exceeding 10^15 cm, whereupon they can mimic magnetars, (iii) msec pulsars are born fast (in core-collapse SNe), and are much older inside globular clusters than outside of them, (iv) neutron-star corotating magnetospheres can oscillate almost in resonance with their spin frequency, giving rise to pulse drifting, and to QPOs of accreting binary X-ray sources, and (v) the dying pulsars are the dominant sources of the cosmic rays, and of the GRBs.

 
astro-ph/0612787 [abs, ps, pdf, other] :
Title: Long term spectral variability in the soft gamma ray repeater SGR 1900+14
Authors: P. Esposito, S. Mereghetti, A. Tiengo, D. Goetz, L. Sidoli, M. Feroci
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang

We present a systematic analysis of all the BeppoSAX data of SGR 1900+14. The observations spanning five years show that the source was brighter than usual on two occasions: ~20 days after the August 1998 giant flare and during the 10^5 sec long X-ray afterglow following the April 2001 intermediate flare. In the latter case, we explore the possibility of describing the observed short term softening only with a change of the temperature of a blackbody-like component. In the only BeppoSAX observation performed before the giant flare, the spectrum of the SGR 1900+14 persistent emission was significantly harder and possibly detected also above 10 keV with the PDS instrument. In the last BeppoSAX observation (April 2002) the flux was ~25 % lower than the historical level, suggesting that the source was entering a quiescent period.

 
astro-ph/0612788 [abs, ps, pdf, other] :
Title: GEOTAIL observation of SGR 1900+14 giant flare on 27 August 1998
Authors: Y. T. Tanaka, et al
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.205-207

The soft gamma repeater (SGR) 1900+14 emitted the giant flare on 27 August 1998. Most gamma-ray detectors saturated during the initial spike of the giant flare because of the intense flux. However the plasma particle detector onboard GEOTAIL observed the first 300 ms time profile with a time resolution of 5.577 ms and the initial spike of the giant flare was first resolved. The time profile shows some similarities to that of the SGR 1806-20 giant flare in 2004: the clear exponential decay and the small hump in the decay phase around 300 or 400 ms.

 
astro-ph/0612789 [abs, ps, pdf, other] :
Title: Testing consistency of deconfinement heating of strange stars in superbursters and soft X-ray transients
Authors: M. Stejner
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.208-211

Both superbursters and soft X-ray transients probe the thermal structure of the crust on compact stars and are sensitive to the process of deep crustal heating. It was recently shown that the transfer of matter from crust to core in a strange star can heat the crust by deconfinement and ignite superbursts provided certain constraints on the strange quark matter equation of state are fulfilled. Corresponding constraints are derived for soft X-ray transients in a simple parameterized model assuming their quiescent emission is powered in the same way, and the time dependence of this heating mechanism in transient systems is discussed.

 
astro-ph/0612790 [abs, ps, pdf, other] :
Title: A precessing warped accretion disk around the X-ray pulsar Her X-1
Authors: D. Klochkov, N. Shakura, K. Postnov, R. Staubert, J. Wilms
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.212-215

We have performed an analysis and interpretation of the X-ray light curve of the accreting neutron star Her X-1 obtained with the ASM RXTE over the period 1996 February to 2004 September. The averaged X-ray light curves are constructed by means of adding up light curves corresponding to different 35 day cycles. A numerical model is introduced to explain the properties of the averaged light curves. We argue that a change of the tilt of the accretion disk over the 35 day period is necessary to account for the observed features and show that our numerical model can explain such a behavior of the disk and reproduce the details of the light curve.

 
astro-ph/0612791 [abs, ps, pdf, other] :
Title: Constraints on Neutron Star Properties from X-ray Observations of Millisecond Pulsars
Authors: Slavko Bogdanov, George B. Rybicki, Jonathan E. Grindlay
Comments: 9 pages, 8 figures; submitted for publication in the Astrophysical Journal

We present model spectra and lightcurves of thermal emission from hot spots on the surface of a compact star with an unmagnetized light-element atmosphere. An application to X-ray observations of the nearest known rotation-powered millisecond pulsar (MSP) PSR J0437--4715 reveals that the thermal emission from this pulsar is fully consistent with such a model, enabling constraints on important properties of the underlying neutron star. We demonstrate that the observed thermal X-ray pulsations from J0437--4715 are incompatible with blackbody emission and require the presence of a limb-darkened, light element (most likely hydrogen) atmosphere on the neutron star surface. The morphology of the X-ray pulse profile is consistent with a global dipole configuration of the pulsar magnetic field but suggests an off-center magnetic axis, with a displacement of $\gtrsim$1 km from the stellar center. For an assumed mass of 1.4 M$_{\odot}$, the model restricts the allowed stellar radii to R=6.8-13.8 km (90% confidence) and R>6.7 km (99.9% confidence), which is consistent with standard NS equations of state and rules out an ultra-compact star. Deeper spectroscopic and timing observations of this and other nearby radio MSPs with current and future X-ray facilities (e.g., Constellation-X and XEUS) can provide further insight into the fundamental properties of neutron stars.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0612022 [abs, ps, pdf, other] :
Title: Dynamical determination of the quadrupole mass moment of the double pulsar PSR J0737-3039 system
Authors: Lorenzo Iorio
Comments: LaTex2e, 13 pages, 1 figure, 2 tables, 23 references. Evidence of inadequacy of a purely keplerian model of P from the sum of the masses added
Note: replaced with revised version Fri, 29 Dec 2006 10:50:40 GMT (14kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 1 Jan 07 01:00:09 GMT
0612767 -- 0612791 received


11 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612776 [abs, ps, pdf, other] :
Title: Asymmetric neutrino emission in quark matter and pulsar kicks
Authors: I. Sagert, J. Schaffner-Bielich
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.177-180

The puzzling phenomenon of pulsar kicks, i.e. the observed large escape velocities of pulsars out of supernova remnants, is examined for compact stars with a strange quark matter core. The direct Urca process in quark matter is studied in the presence of a strong magnetic field. Conditions for an asymmetric emission of the produced neutrinos are worked out in detail, giving constraints on the temperature, the strength of the magnetic field and the electron chemical potential in the quark matter core. In addition, the neutrino mean free paths for quark matter and a possible hadronic mantle are considered.

 
astro-ph/0612777 [abs, ps, pdf, other] :
Title: Neutron stars and quark stars: Two coexisting families of compact stars?
Authors: J. Schaffner-Bielich
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.181-184

The mass-radius relation of compact stars is discussed with relation to the presence of quark matter in the core. The existence of a new family of compact stars with quark matter besides white dwarfs and ordinary neutron stars is outlined.

 
astro-ph/0612780 [abs, ps, pdf, other] :
Title: Neutron stars in Microquasars
Authors: M. Massi
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.185-188

We discuss the "basic" condition for an accreting neutron star to become a microquasar, i.e. ejecting relativistic particles orthogonal to the accretion disk instead of confining disk-material down to the magnetic poles and creating the two emitting caps typical for a X-ray pulsar. Jet creation is prevented for B >/= 10^12 G independent of the accretion rate. This excludes the possibility for a classic X-ray pulsar to develop a "microquasar-phase" and is consistent with the lack of radio emission from such pulsar systems. Millisecond accretion-powered pulsars, on the contrary, may show a "microquasar-phase", where B < 10^7.5 G is valid, whereas the limit for Z sources is B < 10^8.2 G. The implication of our analysis is that the jet might be the suitable agent of angular momentum sink for millisecond accretion-powered pulsars.

 
astro-ph/0612782 [abs, ps, pdf, other] :
Title: Forced oscillations in relativistic accretion disks and QPOs
Authors: J. Petri
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.189-192

In this work we explore the idea that the high frequency QPOs observed in LMXBs may be explained as a resonant coupling between the neutron star spin and epicyclic modes of accretion disk oscillations. We propose a new model for these QPOs based on forced oscillations induced in the accretion disk due to a stellar asymmetric rotating gravitational or magnetic field. It is shown that particles evolving in a rotating non-axisymmetric field are subject to three kinds of resonances: a corotation resonance, a Lindblad resonance due to a driving force, and a parametric resonance due to the time varying epicyclic frequencies. These results are extends by means of 2D numerical simulations of a simplified version of the accretion disk. The simulations are performed for the Newtonian gravitational potential, as well as for a pseudo-general relativistic potential, which enables us to explore the behavior of the resonances around both rotating neutron stars and black holes. Density perturbations are only significant in the region located close to the inner edge of the disk near the ISCO where the gravitational or magnetic perturbation is maximal. It is argued that the nearly periodic motion induced in the disk will produce high quality factor QPOs.
Finally, applying this model to a typical neutron star, we found that the strongest response occurs when the frequency difference of the two modes equals either the spin frequency (for "slow rotators") or half of it (for "fast rotators"). The two main excited modes may both be connected to vertical oscillations of the disk. We emphasize that strong gravity is not needed to excite the modes.

 
astro-ph/0612783 [abs, ps, pdf, other] :
Title: Compact star constraints on the high-density EoS
Authors: H. Grigorian, D. Blaschke, T. Klaehn
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang

A new scheme for testing the nuclear matter (NM) equation of state (EoS) at high densities using constraints from compact star (CS) phenomenology is applied to neutron stars with a core of deconfined quark matter (QM). An acceptable EoS shall not to be in conflict with the mass measurement of 2.1 +/- 0.2 solar mass (1 sigma level) for PSR J0751+1807 and the mass radius relation deduced from the thermal emission of RX J1856-3754. Further constraints for the state of matter in CS interiors come from temperature-age data for young, nearby objects. The CS cooling theory shall agree not only with these data, but also with the mass distribution inferred via population synthesis models as well as with LogN-LogS data. The scheme is applied to a set of hybrid EsoS with a phase transition to stiff, color superconducting QM which fulfills all above constraints and is constrained otherwise from NM saturation properties and flow data of heavy-ion collisions. We extrapolate our description to low temperatures and draw conclusions for the QCD phase diagram to be explored in heavy-ion collision experiments.

 
astro-ph/0612785 [abs, ps, pdf, other] :
Title: Pulsar Physics without Magnetars
Authors: W. Kundt
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.197-200

Almost 40 years after the discovery of pulsars -- and despite a plethora of secured data on them -- pulsar theory is still beset by a number of fundamental inconsistencies. In this short contribution, I will argue that (i) magnetars do not exist, (ii) (ordinary) pulsars turnoff (or 'die') when their wind pressure falls short of keeping the CSM at a safe distance, exceeding 10^15 cm, whereupon they can mimic magnetars, (iii) msec pulsars are born fast (in core-collapse SNe), and are much older inside globular clusters than outside of them, (iv) neutron-star corotating magnetospheres can oscillate almost in resonance with their spin frequency, giving rise to pulse drifting, and to QPOs of accreting binary X-ray sources, and (v) the dying pulsars are the dominant sources of the cosmic rays, and of the GRBs.

 
astro-ph/0612787 [abs, ps, pdf, other] :
Title: Long term spectral variability in the soft gamma ray repeater SGR 1900+14
Authors: P. Esposito, S. Mereghetti, A. Tiengo, D. Goetz, L. Sidoli, M. Feroci
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang

We present a systematic analysis of all the BeppoSAX data of SGR 1900+14. The observations spanning five years show that the source was brighter than usual on two occasions: ~20 days after the August 1998 giant flare and during the 10^5 sec long X-ray afterglow following the April 2001 intermediate flare. In the latter case, we explore the possibility of describing the observed short term softening only with a change of the temperature of a blackbody-like component. In the only BeppoSAX observation performed before the giant flare, the spectrum of the SGR 1900+14 persistent emission was significantly harder and possibly detected also above 10 keV with the PDS instrument. In the last BeppoSAX observation (April 2002) the flux was ~25 % lower than the historical level, suggesting that the source was entering a quiescent period.

 
astro-ph/0612788 [abs, ps, pdf, other] :
Title: GEOTAIL observation of SGR 1900+14 giant flare on 27 August 1998
Authors: Y. T. Tanaka, et al
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.205-207

The soft gamma repeater (SGR) 1900+14 emitted the giant flare on 27 August 1998. Most gamma-ray detectors saturated during the initial spike of the giant flare because of the intense flux. However the plasma particle detector onboard GEOTAIL observed the first 300 ms time profile with a time resolution of 5.577 ms and the initial spike of the giant flare was first resolved. The time profile shows some similarities to that of the SGR 1806-20 giant flare in 2004: the clear exponential decay and the small hump in the decay phase around 300 or 400 ms.

 
astro-ph/0612789 [abs, ps, pdf, other] :
Title: Testing consistency of deconfinement heating of strange stars in superbursters and soft X-ray transients
Authors: M. Stejner
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.208-211

Both superbursters and soft X-ray transients probe the thermal structure of the crust on compact stars and are sensitive to the process of deep crustal heating. It was recently shown that the transfer of matter from crust to core in a strange star can heat the crust by deconfinement and ignite superbursts provided certain constraints on the strange quark matter equation of state are fulfilled. Corresponding constraints are derived for soft X-ray transients in a simple parameterized model assuming their quiescent emission is powered in the same way, and the time dependence of this heating mechanism in transient systems is discussed.

 
astro-ph/0612790 [abs, ps, pdf, other] :
Title: A precessing warped accretion disk around the X-ray pulsar Her X-1
Authors: D. Klochkov, N. Shakura, K. Postnov, R. Staubert, J. Wilms
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.212-215

We have performed an analysis and interpretation of the X-ray light curve of the accreting neutron star Her X-1 obtained with the ASM RXTE over the period 1996 February to 2004 September. The averaged X-ray light curves are constructed by means of adding up light curves corresponding to different 35 day cycles. A numerical model is introduced to explain the properties of the averaged light curves. We argue that a change of the tilt of the accretion disk over the 35 day period is necessary to account for the observed features and show that our numerical model can explain such a behavior of the disk and reproduce the details of the light curve.

 
astro-ph/0612791 [abs, ps, pdf, other] :
Title: Constraints on Neutron Star Properties from X-ray Observations of Millisecond Pulsars
Authors: Slavko Bogdanov, George B. Rybicki, Jonathan E. Grindlay
Comments: 9 pages, 8 figures; submitted for publication in the Astrophysical Journal

We present model spectra and lightcurves of thermal emission from hot spots on the surface of a compact star with an unmagnetized light-element atmosphere. An application to X-ray observations of the nearest known rotation-powered millisecond pulsar (MSP) PSR J0437--4715 reveals that the thermal emission from this pulsar is fully consistent with such a model, enabling constraints on important properties of the underlying neutron star. We demonstrate that the observed thermal X-ray pulsations from J0437--4715 are incompatible with blackbody emission and require the presence of a limb-darkened, light element (most likely hydrogen) atmosphere on the neutron star surface. The morphology of the X-ray pulse profile is consistent with a global dipole configuration of the pulsar magnetic field but suggests an off-center magnetic axis, with a displacement of $\gtrsim$1 km from the stellar center. For an assumed mass of 1.4 M$_{\odot}$, the model restricts the allowed stellar radii to R=6.8-13.8 km (90% confidence) and R>6.7 km (99.9% confidence), which is consistent with standard NS equations of state and rules out an ultra-compact star. Deeper spectroscopic and timing observations of this and other nearby radio MSPs with current and future X-ray facilities (e.g., Constellation-X and XEUS) can provide further insight into the fundamental properties of neutron stars.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0612022 [abs, ps, pdf, other] :
Title: Dynamical determination of the quadrupole mass moment of the double pulsar PSR J0737-3039 system
Authors: Lorenzo Iorio
Comments: LaTex2e, 13 pages, 1 figure, 2 tables, 23 references. Evidence of inadequacy of a purely keplerian model of P from the sum of the masses added
Note: replaced with revised version Fri, 29 Dec 2006 10:50:40 GMT (14kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 3 Jan 07 01:00:12 GMT
0701001 -- 0701039 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701002 [abs, ps, pdf, other] :
Title: Runaway Massive Binaries and Cluster Ejection Scenarios
Authors: M. Virginia McSwain, Scott M. Ransom, Tabetha S. Boyajian, Erika D. Grundstrom, Mallory S. E. Roberts
Comments: Accepted to ApJ, 11 pages

The production of runaway massive binaries offers key insights into the evolution of close binary stars and open clusters. The stars HD 14633 and HD 15137 are rare examples of such runaway systems, and in this work we investigate the mechanism by which they were ejected from their parent open cluster, NGC 654. We discuss observational characteristics that can be used to distinguish supernova ejected systems from those ejected by dynamical interactions, and we present the results of a new radio pulsar search of these systems as well as estimates of their predicted X-ray flux assuming that each binary contains a compact object. Since neither pulsars nor X-ray emission are observed in these systems, we cannot conclude that these binaries contain compact companions. We also consider whether they may have been ejected by dynamical interactions in the dense environment where they formed, and our simulations of four-body interactions suggest that a dynamical origin is possible but unlikely. We recommend further X-ray observations that will conclusively identify whether HD 14633 or HD 15137 contain neutron stars.

 
astro-ph/0701004 [abs, ps, pdf, other] :
Title: Stochastic background from inspiralling double neutron stars
Authors: Tania Regimbau
Comments: accepted for publication in physical review D 8 pages, 3 figures

We review the contribution of extra galactic inspiralling double neutron stars, to the LISA astrophysical gravitational wave foreground. Using recent fits of the star formation rate, we show that sources beyond $z_*=0.005$ contribute to a truly continuous background, which may dominate the LISA instrumental noise in the range $3 \simeq 10^{-4}$ - $1 \times 10^{-2}$ Hz and overwhelm the galactic WD-WD confusion noise at frequencies larger than $\nu_o \simeq 2\times 10^{-3}$.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611608 [abs, ps, pdf, other] :
Title: AXPs/SGRs: Magnetars or Quark-stars?
Authors: Renxin Xu (PKU)
Comments: 10 pages, COSPAR2006 E1.3, submitted
Note: replaced with revised version Mon, 1 Jan 2007 11:36:07 GMT (11kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 4 Jan 07 01:00:13 GMT
0701040 -- 0701069 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701059 [abs, ps, pdf, other] :
Title: The Evolution of Compact Binary Star Systems
Authors: Konstantin Postnov (SAI), Lev Yungelson (Institute of Astronomy RAS)
Comments: 105 pages, 18 figures
Journal-ref: Living Reviews in Relativity, Lrr-2006-6

We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and BHs are thought to be the primary astrophysical sources of gravitational waves (GWs) within the frequency band of ground-based detectors, while compact binaries of WDs are important sources of GWs at lower frequencies to be covered by space interferometers (LISA). Major uncertainties in the current understanding of properties of NSs and BHs most relevant to the GW studies are discussed, including the treatment of the natal kicks which compact stellar remnants acquire during the core collapse of massive stars and the common envelope phase of binary evolution. We discuss the coalescence rates of binary NSs and BHs and prospects for their detections, the formation and evolution of binary WDs and their observational manifestations. Special attention is given to AM CVn-stars -- compact binaries in which the Roche lobe is filled by another WD or a low-mass partially degenerate helium-star, as these stars are thought to be the best LISA verification binary GW sources.

 
astro-ph/0701069 [abs, ps, pdf, other] :
Title: TeV source HESS J1804-216 in X-rays and other wavelengths
Authors: O. Kargaltsev, G. G. Pavlov, G. P. Garmire
Comments: 11 pages, 9 figures and 2 tables; submitted to ApJ. Version with the high-resolution figures is available at this http URL

The field of the extended TeV source HESS J1804-216 was serendipitously observed with the Chandra ACIS detector. The data reveal several X-ray sources within the bright part of HESS J1804-216. The brightest of these objects, CXOU J180432.4-214009, which has been also detected with Swift and Suzaku, is consistent with being a point-like source, with the 0.3-7 keV flux of (1.7\pm0.2)\times10^{-13} ergs s^{-1} cm^{-2}. Its hard and strongly absorbed spectrum can be fitted by the absorbed power-law model with the best-fit photon index of 0.45 and hydrogen column density of 4\times10^{22} cm^{-2}, both with large uncertainties due to the strong correlation between these parameters. A search for pulsations resulted in a 106 s period candidate, which however has a low significance of 97.9%. We found no infrared-optical counterparts for this source. The second brightest source, CXOU J180441.9-214224, which has been detected with Suzaku, is either extended or multiple, with the flux of about 10^{-13} ergs cm^{-2} s^{-1}. We found a nearby M dwarf within the X-ray source extension, which could contribute a fraction of the observed X-ray flux. The remaining sources are very faint (<3\times 10^{-14} ergs cm^{-2} s^{-1}), and at least some of them are likely associated with nearby stars. Although one or both of the two brighter X-ray sources could be faint accreting binaries or remote pulsars with pulsar wind nebulae (hence possible TeV sources), their relation to HESS J1804-216 remains elusive. The possibility that HESS J1804-216 is powered by the relativistic wind from the young pulsar B1800-21, located at a distance of about 10 pc from the TeV source, still remains a more plausible option.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611608 [abs, ps, pdf, other] :
Title: AXPs/SGRs: Magnetars or Quark-stars?
Authors: Renxin Xu (PKU)
Comments: 10 pages, COSPAR2006 E1.3, submitted
Note: replaced with revised version Wed, 3 Jan 2007 13:50:32 GMT (11kb)
 
gr-qc/0510020 [abs, ps, pdf, other] :
Title: General Relativistic Decompression of Binary Neutron Stars During Dynamic Inspiral
Authors: Mark Miller
Comments: Figure replaced, final published version. Dedicated to Rafael Sorkin on his 60th birthday
Journal-ref: Phys. Rev. D, 75, 024001 (2007)
Note: replaced with revised version Wed, 3 Jan 2007 18:49:19 GMT (123kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 5 Jan 07 01:00:09 GMT
0701070 -- 0701110 received


14 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701070 [abs, ps, pdf, other] :
Title: Chandra and XMM-Newton discovery of the transient X-ray pulsar in the nearby spiral galaxy NGC2403
Authors: Sergey Trudolyubov (IGPP/UCR, IKI), William Priedhorsky (LANL), France Cordova (UCR)
Comments: 13 pages, 6 figures, uses emulateapj style. Submitted to ApJ

We report on the discovery and analysis of the transient X-ray pulsar CXO/XMMU J073709.13+653544 detected in the 2004 August-October Chandra and XMM observations of the nearby spiral galaxy NGC2403. The source exhibits X-ray pulsations with a period P~18 s, a nearly sinusoidal pulse shape and pulsed fraction 46-70%. The source shows a rapid decrease of the pulsation period from 18.25 s on Aug. 9 to 17.93 s on Sep. 12 and 17.56 s on Oct. 3, 2004. The X-ray spectra of the source are hard and are well fitted with an absorbed simple power law of photon index 0.9~1.2. The X-ray properties of the source and the absence of an optical/UV counterpart allow us to identify CXO/XMMU J073709.13+653544 as accreting X-ray pulsar in NGC2403. The maximum unabsorbed luminosity of the source in the 0.3-7 keV range, ~2.6x10e38 erg/s at 3.2 Mpc, is at least 260 times higher than its quiescent luminosity. The corresponding luminosity in the 0.3-100 keV energy range could be as high as ~1.2x10e39 erg/s, assuming the typical pulsar energy spectrum with high-energy cut-off at 10-20 keV. The rate of decrease of the pulsation period of the source (-10e-7 s/s) is the fastest observed among accreting pulsars. The evolution of the pulsation period suggests that it is dominated by the intrinsic spin-up of the compact object. The accretion rate implied by X-ray luminosity of CXO/XMMU J073709.13+653544 could account for the observed spin-up rate, assuming that the X-ray source is powered by disk accretion onto highly magnetized neutron star. Based on the transient behavior and overall X-ray properties of the source, we conclude that it could be an X-ray pulsar belonging to either a Be binary system or a low-mass system similar to GRO J1744-28.

 
astro-ph/0701077 [abs, ps, pdf, other] :
Title: Variability of Nineteen Millisecond Pulsars in 47 Tucanae with CHANDRA/HRC-S
Authors: P. B. Cameron (Caltech), R. E. Rutledge (McGill), F. Camilo (Columbia), L. Bildsten (UCSB), S. M. Ransom (NRAO), S. R. Kulkarni (Caltech)
Comments: 21 pages, accepted for publication in ApJ

We present results from our 830 ksec observation of the globular cluster 47 Tucanae with the Chandra X-ray Observatory's High Resolution Camera-S. We limit our analysis here to the 19 previously known, localized millisecond pulsars (MSPs) in the cluster. This work more than doubles the sample of X-ray-detected MSPs observed with sensitivity to rotational variability; it is also the first survey of a large group of radio-discovered MSPs for which no previous X-ray pulsations have been detected and is therefore an unbiased survey of the X-ray properties of radio-discovered MSPs. We find that only 47 Tuc D, O and R show significant pulsations at the >~ 4-sigma level, but there is statistical evidence for rotational variability in five additional MSPs. Furthermore, we constrain the pulsed magnetospheric emission of 7 more MSPs using Monte Carlo simulations. The result is that the majority of the 47 Tuc MSPs are characterized by low pulsed fractions, <~ 50%. In cases where larger pulsed fractions are measured the folded pulse profiles show relatively large duty cycles. When considered with previous spectroscopic studies, this suggests that the X-ray emission arises from the neutron star's heated polar caps, and in some cases, from intra-binary shocks, but generally not directly from the star's magnetosphere. We discuss the impact of these results on our understanding of high energy emission from MSPs.

 
astro-ph/0701083 [abs, ps, pdf, other] :
Title: Fallback and Black Hole Production in Massive Stars
Authors: Weiqun Zhang, S. E. Woosley, A. Heger
Comments: Submitted to ApJ

The compact remnants of core collapse supernovae - neutron stars and black holes - have properties that reflect both the structure of their stellar progenitors and the physics of the explosion. In particular, the masses of these remnants are sensitive to the density structure of the presupernova star and to the explosion energy. To a considerable extent, the final mass is determined by the ``fallback'', during the explosion, of matter that initially moves outwards, yet ultimately fails to escape. We consider here the simulated explosion of a large number of massive stars (10 to 100 \Msun) of Population I (solar metallicity) and III (zero metallicity), and find systematic differences in the remnant mass distributions. As pointed out by Chevalier(1989), supernovae in more compact progenitor stars have stronger reverse shocks and experience more fallback. For Population III stars above about 25 \Msun and explosion energies less than $1.5 \times 10^{51}$ erg, black holes are a common outcome, with masses that increase monotonically with increasing main sequence mass up to a maximum hole mass of about 35 \Msun. If such stars produce primary nitrogen, however, their black holes are systematically smaller. For modern supernovae with nearly solar metallicity, black hole production is much less frequent and the typical masses, which depend sensitively on explosion energy, are smaller. We explore the neutron star initial mass function for both populations and, for reasonable assumptions about the initial mass cut of the explosion, find good agreement with the average of observed masses of neutron stars in binaries. We also find evidence for a bimodal distribution of neutron star masses with a spike around 1.2 \Msun (gravitational mass) and a broader distribution peaked around 1.4 \Msun.

 
astro-ph/0701085 [abs, ps, pdf, other] :
Title: Frequency Correlations of QPOs Based on a Disk Oscillation Model in Warped Disks
Authors: Shoji Kato
Comments: 10 pages, to be published in PASJ 59(2007), No.2

In previous papers we proposed a model that high-frequency quasi-periodic oscillations (QPOs) observed in black-hole and neutron-star X-ray binaries are disk oscillations (inertial-acoustic and/or g-mode oscillations) resonantly excited on warped disks. In this paper we examine whether time variations of the QPOs and their frequency correlations observed in neutron-star X-ray binaries can be accounted for by this disk-oscillation model. By assuming that a warp has a time-dependent precession, we can well describe observed frequency correlations among kHz QPOs and LF QPOs in a wide range of frequencies.

 
astro-ph/0701092 [abs, ps, pdf, other] :
Title: Lost and Found: A New Position and Infrared Counterpart for the X-ray Binary Scutum X-1
Authors: D. L. Kaplan, A. M. Levine, D. Chakrabarty, E. H. Morgan, D. K. Erb, B. M. Gaensler, D.-S. Moon, P. B. Cameron
Comments: 9 pages, 9 figures. Submitted to ApJ

Using archival X-ray data, we find that the catalog location of the X-ray binary Scutum X-1 (Sct X-1) is incorrect, and that the correct location is that of the X-ray source AX J183528-0737, which is 15' to the west. Our identification is made on the basis of the 112-s pulse period for this object detected in an XMM-Newton observation, as well as spatial coincidence between AX J183528-0737 and previous X-ray observations. Based on the XMM-Newton data and archival RXTE data, we confirm secular spin-down of three observations over 17 years with period derivative Pdot~3.9e-9 s/s, but do not detect a previously reported X-ray iron fluorescence line. We identify a bright (Ks=6.55), red (J-Ks=5.51), optical and infrared counterpart to AX J183528-0737 from 2MASS, a number of mid-IR surveys, and deep optical observations, which we use to constrain the extinction to and distance of Sct X-1. From these data, as well as limited near-IR spectroscopy, we conclude that Sct X-1 is most likely a binary system comprised of a late-type giant or supergiant and a neutron star.

 
astro-ph/0701095 [abs, ps, pdf, other] :
Title: Observations of the 599 Hz Accreting X-ray Pulsar IGR J00291+5934 during the 2004 Outburst and in Quiescence
Authors: M. A. P. Torres, P. G. Jonker, D. Steeghs, G. H. A. Roelofs, J. S. Bloom, J. Casares, E. E. Falco, M. R. Garcia, T. R. Marsh, M. Mendez, J. M. Miller, G. Nelemans, P. Rodriguez-Gil
Comments: 10 pages, 7 figures, 3 tables, submitted to ApJ

We report on optical and NIR observations obtained during and after the 2004 December discovery outburst of the X-ray transient and accretion-powered millisecond pulsar IGR J00291+5934. Our observations monitored the evolution of the brightness and the spectral properties of J00291 during the outburst decay towards quiescence. We also present optical, NIR and Chandra observations obtained during true quiescence. Photometry of the field during outburst reveals an optical and NIR counterpart that brightened from R~23 to R~17 and from K=19 to K~16. Spectral analysis of the RIJHK broadband photometry shows excess in the NIR bands that may be due to synchrotron emission. The Halpha emission line profile suggests the orbital inclination is ~22-32 degrees. The preferred range for the reddening towards the source is 0.7 < E(B-V) < 0.9, which is equivalent to 4.06E21 cm^-2 < NH < 5.22E21 cm^-2. The Chandra observations of the pulsar in its quiescent state gave an unabsorbed 0.5-10 keV flux for the best-fitting power-law model to the source spectrum of (7.0 +/- 0.9)E-14 ergs/cm^2/s (adopting a hydrogen column of 4.6E21 cm^-2. The fit resulted in a power-law photon index of 2.4 +/- 0.5. The (R-K)o color observed during quiescence supports an irradiated donor star and accretion disk. We estimate a distance of 2 to 4 kpc towards J00291 by using the outburst X-ray light curve and the estimated critical X-ray luminosity necessary to keep the outer parts of the accretion disk ionized. Using the quiescent X-ray luminosity and the spin period, we constrain the magnetic field of the neutron star to be < 3E8 Gauss.

 
astro-ph/0701097 [abs, ps, pdf, other] :
Title: Finding binary millisecond pulsars with the Hough transform
Authors: C. Aulbert
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.216-218

The Hough transformation has been used successfully for more than four decades. Originally used for tracking particle traces in bubble chamber images, this work shows a novel approach turning the initial idea into a powerful tool to incoherently detect millisecond pulsars in binary orbits.
This poster presents the method used, a discussion on how to treat the time domain data from radio receivers and create the input "image" for the Hough transformation, details about the advantages and disadvantages of this approach, and finally some results from pulsars in 47 Tucanae.

 
astro-ph/0701099 [abs, ps, pdf, other] :
Title: Concepts for astronomical data accessibility and analysis via relational database
Authors: L. Nicastro, G. Calderone
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.219-222

Relational databases (DBs) are ideal tools to manage bulky and structured data archives. In particular for Astronomy they can be used to fulfill all the requirements of a complex project, i.e. the management of: documents, software (s/w) packages and logs, observation schedules, object catalogues, quick-look, simulated, raw and processed data, etc. All the information gathered in a relational DB is easily and simultaneously accessible either from an interactive tool or a batch program. The user does not need to deal with traditional files I/O or editing, but has only to build the appropriate (SQL) query which will return the desired information/data, eventually producing the aforementioned files or even plots, tables, etc. in a variety of formats. What is then important for a generic user is to have the tools to easily and quickly develop, in any desired programming language, the custom s/w which can import/export the information into/from the DB. An example could be a Web interface which presents the available data and allows the user to select/retrieve (or even process) the data subset of interest.
In the last years we have been implementing a package called MCS (see dedicated paper in this proceedings) which allows users to interact with MySQL based DBs through any programming language. MCS has a multi-thread (socket) architecture which means that several clients can submit queries to a server which in turn manages the communication with the MySQL server and other MCS servers. Here we'll focus on a the real-world case of the robotic IR-optical telescope REM (placed at La Silla, Chile) which performs real time images acquisition, processing and archiving by using some of the MCS capabilities.

 
astro-ph/0701101 [abs, ps, pdf, other] :
Title: Pulsar virtual observatory
Authors: M. Keith, B. Harbulot, A. Lyne, J. Brooke
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.223-225

The Pulsar Virtual Observatory will provide a means for scientists in all fields to access and analyze the large data sets stored in pulsar surveys without specific knowledge about the data or the processing mechanisms. This is achieved by moving the data and processing tools to a grid resource where the details of the processing are seen by the users as abstract tasks. By developing intelligent scheduling middle-ware the issues of interconnecting tasks and allocating resources are removed from the user domain. This opens up large sets of radio time-series data to a wider audience, enabling greater cross field astronomy, in line with the virtual observatory concept. Implementation of the Pulsar Virtual Observatory is underway, utilising the UK National Grid Service as the principal grid resource.

 
astro-ph/0701102 [abs, ps, pdf, other] :
Title: MCS, a new approach to data treatment in astronomical projects
Authors: G. Calderone, L. Nicastro
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.226-229

Today's astronomical projects need computational systems capable to store and analyze large amounts of scientific data, to effectively share data with other research Institutes and to easily implement information services to present data for different purposes (scientific, maintenance, outreach, etc.). Due to the wide scenario of astronomical projects there isn't yet a standardized approach to implement the software needed to support all the requirements of a project. The new approach we propose here is the use of a unified model where all data are stored into the same data base becoming available in different forms, to different users with different privileges.

 
astro-ph/0701103 [abs, ps, pdf, other] :
Title: Correlations between pulsed X-ray flux and radio arrival time in the Vela pulsar
Authors: A. N. Lommen, J. Donovan, C. Gwinn, Z. Arzoumanian, A. Harding, M. Strickman, R. Dodson, P. McCulloch, D. Moffett
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.16-19

We report the results of simultaneous observations of the Vela pulsar in X-rays and radio from the RXTE satellite and the Mount Pleasant Radio Observatory in Tasmania. We sought correlations between the Vela's X-ray and radio flux densities and radio arrival times on a pulse by pulse basis. We found significantly higher flux density in Vela's main X-ray peak during radio pulses that arrived early. This excess flux shifts to the 'trough' following the 2nd X-ray peak during radio pulses that arrive later. We suggest that the mechanism producing the radio pulses is intimately connected to the mechanism producing X-rays. Current models using resonant absorption in the outer magnetosphere as a cause of the radio emission, and less directly of the X-ray emission, are explored as a possible explanation for the correlation.

 
astro-ph/0701105 [abs, ps, pdf, other] :
Title: Comparison of giant radio pulses in young pulsars and millisecond pulsars
Authors: A. Slowikowska, A. Jessner, G. Kanbach, B. Klein
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.64-67

Pulse-to-pulse intensity variations are a common property of pulsar radio emission. For some of the objects single pulses are often 10-times stronger than their average pulse. The most dramatic events are so-called giant radio pulses (GRPs). They can be thousand times stronger than the regular single pulses from the pulsar. Giant pulses are a rare phenomenon, occurring in very few pulsars which split into two groups. The first group contains very young and energetic pulsars like the Crab pulsar, and its twin (PSR B0540-69) in the Large Magellanic Cloud (LMC), while the second group is represented by old, recycled millisecond pulsars like PSR B1937+21, PSR B1821-24, PSR B1957+20 and PSR J0218+4232 (the only millisecond pulsar detected in gamma-rays). We compare the characteristics of GRPs for these two pulsar groups. Moreover, our latest findings of new features in the Crab GRPs are presented. Analysis of our Effelsberg data at 8.35 GHz shows that GRPs do occur in all phases of its ordinary radio emission, including the phases of the two high frequency components (HFCs) visible only between 5 and 9 GHz.

 
astro-ph/0701106 [abs, ps, pdf, other] :
Title: What is special about high magnetic field radio pulsars? -- First results from the multifrequency polarimetry
Authors: N. Vranevsevic, R. N. Manchester, D. B. Melrose
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.88-91

The Parkes Multibeam Survey led to the identification of a number of long-period radio pulsars with magnetic field well above the 'quantum critical field' of ~ 4.4x10^13 G (HBRPs). The HBRPs have similar spin parameters to magnetars, but their emission properties are different, and contradict those theories that predict that radio emission should be suppressed above this critical field. Our observations support the suggestion that initial neutron star spin periods depend on their magnetic fields; in particular, there is a tendency for high-field systems to be born as slow rotators. The aim of this project is to understand the emission properties of HBRPs, using multiple radio frequencies and high time resolution data. One specific objective is to identify HBRPs radio emission characteristics that are different from those of normal pulsars.

 
astro-ph/0701107 [abs, ps, pdf, other] :
Title: Observed luminosity difference between isolated and binary MSPs
Authors: A.N. Lommen, R.A. Kipphorn, D.J. Nice, E.M. Splaver, I.H. Stairs, D.C. Backer
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.96-99

We perform a brief census of velocities of isolated versus binary millisecond pulsars. We find the velocities of the two populations are indistinguishable. However, the scale height of the binary population is twice that of the isolated population and the luminosity functions of the two populations are different. We suggest that the scale height difference may be an artifact of the luminosity difference. We examine the magnetic fields of the two populations as a possible source of the luminosity difference.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0608682 [abs, ps, pdf, other] :
Title: Proto-Neutron Star Winds with Magnetic Fields and Rotation
Authors: Brian D. Metzger, Todd A. Thompson, Eliot Quataert
Comments: 21 pages, 12 figures, final version accepted to ApJ
Note: replaced with revised version Thu, 4 Jan 2007 02:15:26 GMT (95kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 8 Jan 07 01:00:12 GMT
0701111 -- 0701151 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701128 [abs, ps, pdf, other] :
Title: A Particle Simulation for the Global Pulsar Magnetosphere: the Pulsar Wind linked to the Outer Gaps
Authors: Tomohide Wada, Shinpei Shibata

Soon after the discovery of radio pulsars in 1967, the pulsars are identified as strongly magnetic (typically $10^{12}$G) rapidly rotating ($\sim 10^{2}-0.1$ Hz) neutron stars. However, the mechanism of particle acceleration in the pulsar magnetosphere has been a longstanding problem. The central problem is why the rotation power manifests itself in both gamma-ray beams and a highly relativistic wind of electron-positron plasmas, which excites surrounding nebulae observed in X-ray. Here we show with a three dimensional particle simulation for the global axisymmetric magnetosphere that a steady outflow of electron-positron pairs is formed with associated pair sources, which are the gamma-ray emitting regions within the light cylinder. The magnetic field is assumed to be dipole, and to be consistent, pair creation rate is taken to be small, so that the model might be applicable to old pulsars such as Geminga. The pair sources are charge-deficient regions around the null surface, and we identify them as the outer gap. The wind mechanism is the electromagnetic induction which brings about fast azimuthal motion and eventually trans-field drift by radiation drag in close vicinity of the light cylinder and beyond. The wind causes loss of particles from the system. This maintains charge deficiency in the outer gap and pair creation. The model is thus in a steady state, balancing loss and supply of particles. Our simulation implies how the wind coexists with the gamma-ray emitting regions in the pulsar magnetosphere.

 
astro-ph/0701144 [abs, ps, pdf, other] :
Title: Compactified pulsar wind nebula model of gamma-ray loud binary LSI +61 303
Authors: A.Neronov, M.Chernyakova
Comments: submitted to MNRAS

We show that radio-to-TeV properties of the binary system LSI +61 303 can be explained by interaction of the compact object (a young pulsar) with the inhomogeneities of the wind from companion Be star. We develop a model scenario of "compactified" pulsar wind nebula formed in result of such interaction. To test the model assumptions about geometry of the system we re-analyze the available X-ray observations to study in more details the variations of the hydrogen column density on long (orbital) and short (several kilosecond) time scales.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 9 Jan 07 01:00:10 GMT
0701152 -- 0701210 received


8 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701166 [abs, ps, pdf, other] :
Title: XMM-Newton observations reveal the X-ray counterpart of the very-high-energy gamma-ray source HESSJ1640-465
Authors: S.Funk, J.A.Hinton, G.Puehlhofer, F.A.Aharonian, W.Hofmann, O.Reimer, S.Wagner
Comments: submitted to the Astrophysical Journal

We present X-ray observations of the as of yet unidentified very high-energy (VHE) gamma-ray source HESSJ1640-465 with the aim of establishing a counterpart of this source in the keV energy range, and identifying the mechanism responsible for the VHE emission. The 21.8 ksec XMM-Newton observation of HESSJ1640-465 in September 2005 represents a significant improvement in sensitivity and angular resolution over previous ASCA studies in this region. These new data show a hard-spectrum X-ray emitting object at the centroid of the H.E.S.S. source, within the shell of the radio Supernova Remnant (SNR) G338.3-0.0. This object is consistent with the position and flux previously measured by both ASCA and Swift-XRT but is now shown to be significantly extended. We argue that this object is very likely the counterpart to HESSJ1640-465 and that both objects may represent the Pulsar Wind Nebula of an as of yet undiscovered pulsar associated with G338.3-0.0.

 
astro-ph/0701176 [abs, ps, pdf, other] :
Title: Na-O Anticorrelation and HB. VI. The chemical composition of the peculiar bulge globular cluster NGC 6388
Authors: E. Carretta, A. Bragaglia, R.G. Gratton, Y. Momany, A. Recio-Blanco, S. Cassisi, P. Francois, G. James, S. Lucatello, S. Moehler
Comments: 18 pages, 8 figures; table 3 available at CDS. Accepted for publication on A&A

We present the LTE abundance analysis of high resolution spectra for red giant stars in the peculiar bulge globular cluster NGC 6388. Spectra of seven members were taken using the UVES spectrograph at the ESO VLT2 and the multiobject FLAMES facility. We exclude any intrinsic metallicity spread in this cluster: on average, [Fe/H]=-0.44+/-0.01+/-0.03 dex on the scale of the present series of papers, where the first error bar refers to individual star-to-star errors and the second is systematic, relative to the cluster. Elements involved in H-burning at high temperatures show large spreads, exceeding the estimated errors in the analysis. In particular, the pairs Na and O, Al and Mg are anticorrelated and Na and Al are correlated among the giants in NGC 6388, the typical pattern observed in all galactic globular clusters studied so far. Stars in NGC 6388 shows an excess of alpha-process elements, similar to the one found in the twin bulge cluster NGC 6441. Mn is found underabundant in NGC 6388, in agreement with the average abundance ratio shown by clusters of any metallicity. Abundances of neutron-capture elements are homogeneously distributed within NGC 6388; the [Eu/Fe] ratio stands above the value found in field stars of similar metallicity.

 
astro-ph/0701181 [abs, ps, pdf, other] :
Title: Pulsar surveys present and future: The Arecibo pulsar-ALFA survey and projected SKA survey
Authors: J. S. Deneva, et al
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.52-55

The Arecibo Pulsar-ALFA (PALFA) survey of the Galactic plane began in 2004 when the new ALFA (Arecibo L-band Feed Array) receiver was commissioned. It is slated to continue for the next 3-5 years and is expected to discover hundreds of new pulsars. We present the goals, progress, and recent discoveries of the PALFA survey. So far preliminary data processing has found 24 new pulsars, one of which is a young 144ms pulsar in a highly relativistic binary with an orbital period of 3.98 hours. Another object exhibits sporadic bursts characteristic of a newly defined class of radio-loud neutron stars: RRATs (Rotating RAdio Transients). The PALFA survey is going to accumulate a total of 1 Petabyte (PB) of raw data which will be made available to the community via a sophisticated tape archive and database hosted at the Cornell Theory Center supercomputing facility. Web tools and services are being developed which will allow users of the archive to perform data analysis remotely.
We also discuss parameters, expected discoveries and the scientific impact of a projected pulsar survey with the Square Kilometer Array (SKA). The SKA is to become operational in 2014 and will have the capability of detecting thousands of pulsars not detectable with current instruments, allowing us to perform a comprehensive census of the Galactic pulsar population.

 
astro-ph/0701183 [abs, ps, pdf, other] :
Title: The 8gr8 Cygnus survey for new pulsars and RRATs
Authors: E. Rubio-Herrera, R. Braun, G. Janssen, J. van Leeuwen, B. W. Stappers
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.56-59

We are currently undertaking a survey to search for new pulsars and the recently found Rotating RAdio Transcients (RRATs) in the Cygnus OB complex. The survey uses the Westerbrok Synthesis Radio Telescope (WSRT) in a unique way called the 8gr8 mode, which gives it the best efficiency of any low-frequency wide-area survey. So far we have found a few new pulsars and the routines for the detection of RRATs are already implemented in the standard reduction. We expect to find a few tens of new pulsars and a similar number of RRATs. This will help us to improve our knowledge about the population and properties of the latter poorly known objects as well as provide an improved knowledge of the number of young pulsars associated with the OB complexes in the Cygnus region.

 
astro-ph/0701184 [abs, ps, pdf, other] :
Title: X-ray bright sources in the Chandra Small Magellanic Cloud Wing Survey - detection of two new pulsars
Authors: K. E. McGowan (1), M. J. Coe (1), M. Schurch (1), V. A. McBride (1), J. L. Galache (2), W. R. T. Edge (1), R. H. D. Corbet (3), S. Laycock (2), A. Udalski (4), D. A. H. Buckley (5,6) ((1) University of Southampton, (2) CfA, (3) USRA/GSFC, (4) Warsaw University Observatory, (5) SAAO, (6) SALT)
Comments: 13 pages, 7 figues, 4 tables, accepted for publication in MNRAS

We investigate the X-ray and optical properties of a sample of X-ray bright sources from the Small Magellanic Cloud (SMC) Wing Survey. We have detected two new pulsars with pulse periods of 65.8 s (CXOU J010712.6-723533) and 700 s (CXOU J010206.6-714115), and present observations of two previously known pulsars RX J0057.3-7325 (SXP101) and SAX J0103.2-7209 (SXP348). Our analysis has led to three new optical identifications for the detected pulsars. We find long-term optical periods for two of the pulsars, CXOU J010206.6-714115 and SXP101, of 267 and 21.9 d, respectively. Spectral analysis of a sub-set of the sample shows that the pulsars have harder spectra than the other sources detected. By employing a quantile-based colour-colour analysis we are able to separate the detected pulsars from the rest of the sample. Using archival catalogues we have been able to identify counterparts for the majority of the sources in our sample. Combining this with our results from the temporal analysis of the Chandra data and archival optical data, the X-ray spectral analysis, and by determining the X-ray to optical flux ratios we present preliminary classifications for the sources. In addition to the four detected pulsars, our sample includes two candidate foreground stars, 12 probable active galactic nuclei, and five unclassified sources.

 
astro-ph/0701189 [abs, ps, pdf, other] :
Title: The extreme radio emission of PSR B0656+14 -- Is B0656+14 a very nearby rotating radio transient?
Authors: P. Weltevrede, B. W. Stappers, J. M. Rankin, G. A. E. Wright
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.60-63

We present a detailed study of the single radio pulses of PSR B0656+14. The emission can be characterized by two separate populations of pulses: bright pulses have a narrow ``spiky'' appearance in contrast to the underlying weaker broad pulses. The shape of the pulse profile requires an unusually long timescale to achieve stability (over 25,000 pulses at 327 MHz) caused by spiky emission. The extreme peak-fluxes of the brightest of these pulses indicates that PSR B0656+14, were it not so near, could only have been discovered as an RRAT source. The strongest bursts represent pulses from the bright end of an extended smooth pulse-energy distribution, which is unlike giant pulses, giant micropulses or the pulses of normal pulsars. Longer observations of the RRATs may reveal that they, like PSR B0656+14, emit weaker emission in addition to the bursts.

 
astro-ph/0701190 [abs, ps, pdf, other] :
Title: Amazing properties of giant pulses and the nature of pulsar's radio emission
Authors: V. Soglasnov
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.68-71

For comprehensive studying of giant pulses (GPs) from the Crab pulsar and the original millisecond pulsar (MSP) B1937+21 (J1939+2134), we conducted multifrequency observations over the last few years. They show that giant pulses may be improbably bright, 10^5, 10^6 Jy and more, they have extra ordinal spectra and polarization. EM energy concentrated in such strong pulse is high enough to accelerate particles up to Lorenz factor gamma ~ 10^4 - 10^6, since giant pulses may play an important role in physics of pulsar's magnetosphere.

 
astro-ph/0701193 [abs, ps, pdf, other] :
Title: Giant pulses of pulsar radio emission
Authors: A. D. Kuzmin
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.72-75

Review report of giant pulses of pulsar radio emission, based on our detections of four new pulsars with giant pulses, and the comparative analysis of the previously known pulsars with giant pulses, including the Crab pulsar and millisecond pulsar PSR B1937+21.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610867 [abs, ps, pdf, other] :
Title: Low-Luminosity GRB 060218: A Collapsar Jet from a Neutron Star, Leaving a Magnetar as a Remnant?
Authors: Kenji Toma, Kunihito Ioka, Takanori Sakamoto, Takashi Nakamura
Comments: 14 pages, 3 figures, 2 tables added, references added. Accepted for publication in ApJ. Replaced with the accepted version
Note: replaced with revised version Mon, 8 Jan 2007 11:30:27 GMT (50kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 10 Jan 07 01:00:11 GMT
0701211 -- 0701264 received


17 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701214 [abs, pdf] :
Title: CU Virginis - The First Stellar Pulsar
Authors: Barry J. Kellett (1), Vito Graffagnino (1), Robert Bingham (1 and 2), Tom W. B. Muxlow (3), Alastair G. Gunn (3) ((1)Rutherford Appleton Laboratory,(2)University of Strathclyde,(3)Jodrell Bank Observatory)
Comments: 10 pages including 2 figures

CU Virginis is one of the brightest radio emitting members of the magnetic chemically peculiar (MCP) stars and also one of the fastest rotating. We have now discovered that CU Vir is unique among stellar radio sources in generating a persistent, highly collimated, beam of coherent, 100% polarised, radiation from one of its magnetic poles that sweeps across the Earth every time the star rotates. This makes the star strikingly similar to a pulsar. This similarity is further strengthened by the observation that the rotating period of the star is lengthening at a phenomenal rate (significantly faster than any other astrophysical source - including pulsars) due to a braking mechanism related to its very strong magnetic field.

 
astro-ph/0701222 [abs, ps, pdf, other] :
Title: Glitch observations in slow pulsars
Authors: G. H. Janssen, B. W. Stappers
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.80-83

We have analyzed 5.5 years of timing observations of 7 ``slowly'' rotating radio pulsars, made with the Westerbork Synthesis Radio Telescope. We present improved timing solutions and 30, mostly small new glitches. The most interesting results are: 1) The detection of glitches one to two orders of magnitude smaller than ever seen before in slow radio pulsars. 2) Resolving timing-noise looking structures in the residuals of PSR B1951+32 by using a set of small glitches. 3) The detections of three new glitches in PSR J1814-1744, a high-magnetic field pulsar. In these proceedings we present the most interesting results of our study. For a full coverage, we refer the reader to Janssen & Stappers (2006).

 
astro-ph/0701223 [abs, ps, pdf, other] :
Title: Turn-over in pulsar spectra above 1 GHz
Authors: J. Kijak, Y. Gupta, K.Krzeszowski
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.84-87

We present the first direct evidence for turn-over in pulsar radio spectra at high frequencies. Two pulsars are now shown to have a turn-over frequency > 1GHz. We also find some evidence that the peak frequency of turn-over in pulsar spectra appears to depend on dispersion measure and pulsar age.

 
astro-ph/0701227 [abs, ps, pdf, other] :
Title: Drifting subpulse survey at 21 cm
Authors: P. Weltevrede, R. T. Edwards, B. W. Stappers
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.92-95

We present the statistical results of a systematic, unbiased search for subpulse modulation of 187 pulsars performed with the Westerbork Synthesis Radio Telescope (WSRT) in the Netherlands at an observing wavelength of 21 cm (Weltevrede et al. 2006a). We have increased the list of pulsars that show the drifting subpulse phenomenon by 42, indicating that more than 55% of the pulsars that show this phenomenon. The large number of new drifters we have found allows us, for the first time, to do meaningful statistics on the drifting phenomenon. We find that the drifting phenomenon is correlated with the pulsar age such that drifting is more likely to occur in older pulsars. Pulsars that drift more coherently seem to be older and have a lower modulation index. Contrary claims from older studies, both P_3 (the repetition period of the drifting subpulse pattern) and the drift direction are found to be uncorrelated with other pulsar parameters.

 
astro-ph/0701229 [abs, ps, pdf, other] :
Title: LOFAR: A powerful tool for pulsar studies
Authors: B. W. Stappers, A. G. J. van Leeuwen, M. Kramer, D. Stinebring, J. Hessels
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.100-103

The LOw Frequency ARray, LOFAR, will have the sensitivity, bandwidth, frequency range and processing power to revolutionise low-frequency pulsar studies. We present results of simulations that indicate that a LOFAR survey will find approximately 1500 new pulsars. These new pulsars will give us a much better understanding of the low end of the luminosity function and thus allow for a much more precise estimate of the true total local pulsar population. The survey will also be very sensitive to the ultra-steep spectrum pulsars, RRATs, and the pulsed radio emission from objects like Geminga and AXPs. We will also show that by enabling us to observe single pulses from hundreds of pulsars, including many millisecond pulsars, LOFAR opens up new possibilities for the study of emission physics.

 
astro-ph/0701235 [abs, ps, pdf, other] :
Title: Pair Winds in Schwarzschild Spacetime with Application to Strange Stars
Authors: A.G. Aksenov, M. Milgrom, V.V. Usov
Comments: 3 pages, 2 figures, Invited talk at 11th Marcel Grossmann Meeting, Berlin, July 2006

We present the results of numerical simulations of stationary, spherically outflowing, electron-positron pair winds, with total luminosities in the range 10^{34}--10^{42} ergs/s. In the concrete example described here, the wind injection source is a hot, bare, strange star, predicted to be a powerful source of pairs created by the Coulomb barrier at the quark surface. We find that photons dominate in the emerging emission, and the emerging photon spectrum is rather hard and differs substantially from the thermal spectrum expected from a neutron star with the same luminosity. This might help distinguish the putative bare strange stars from neutron stars.

 
astro-ph/0701240 [abs, ps, pdf, other] :
Title: Transition to Quark Matter and long Gamma Ray Bursts
Authors: Alessandro Drago, Giuseppe Pagliara, Irene Parenti (Univ. Ferrara and INFN Sez. Ferrara, Italy)
Comments: 7 pages, 4 figures, Proceedings of "Swift and GRBs: Unveiling the Relativisitc Universe", Venice, 5-9 June 2006

The energy released by the inner engine of GRBs can originate from structural readjustments inside a compact star. In particular, the formation of deconfined quark matter can liberate enough energy to power the burst. We show that the burning of a neutron star into a quark star likely proceeds as a deflagration and not as a detonation. In that way no strong baryon contamination is produced near the surface of the star. It is tempting to associate the temporal structures observed in the light curves with specific processes taking place inside the compact star. The so-called quiescent times, during which no signal is emitted in the highest energy band, correspond to pauses during the processes of readjustment. If the quark (or hybrid) star formed after these transformations is strongly magnetized and rotates rapidly, a prolonged gamma emission can be produced, as proposed by Usov years ago. This can explain the quasi-plateau observed by Swift in several GRBs.

 
astro-ph/0701243 [abs, ps, pdf, other] :
Title: Particle accelerator in pulsar magnetospheres: A hybrid solution of inner and outer gap models
Authors: K. Hirotani
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.104-107

A self-consistent electrodynamics of a particle accelerator in a rotating neutron-star magnetosphere is investigated on the two-dimensional poloidal plane. Solving the Poisson equation for the electrostatic potential together with the Boltzmann equations for electrons, positrons and gamma-rays, it is demonstrated that the created current density increases to be super-Goldreich-Julian if the trans-field thickness of the gap becomes thick enough. This new solution exists from the neutron-star surface to the outer magnetosphere with a small-amplitude positive acceleration field in the inner part, which works to extract ions from the stellar surface as a space-charge-limited flow. The acceleration field is highly unscreened in the outer magnetosphere, in the same manner as in traditional outer-gap models.

 
astro-ph/0701244 [abs, ps, pdf, other] :
Title: The INTEGRAL Galactic bulge monitoring program: the first 1.5 years
Authors: E. Kuulkers (ESA/ESAC, Spain), S.E. Shaw (Southampton, UK/ ISDC, Switzerland), A. Paizis (INAF-IASF, Italy), J. Chenevez, S. Brandt (DNSC, Denmark), T.J.-L. Courvoisier (ISDC/ Observatoire de Geneve, Switzerland), A. Domingo (LAEFF/INTA, Spain), K. Ebisawa (ISAS, Japan), P. Kretschmar (ESA/ESAC, Spain), C.B. Markwardt (Univ.of Maryland/ NASA/GSFC, USA), N. Mowlavi (ISDC, Switzerland), T. Oosterbroek, A. Orr (ESA/ESTEC, Netherlands), D. Risquez (LAEFF/INTA, Spain), C. Sanchez-Fernandez (ESA/ESAC, Spain), R. Wijnands (Univ. of Amsterdam, The Netherlands)
Comments: 27 pages, 42 figures, accepted for publication in A&A. Abstract abridged. Tables 3,4,6,7 appear at the end. Images have been compressed and are reduced in quality; original PostScript images can be retrieved from this http URL

The Galactic bulge region is a rich host of variable high-energy point sources. Since 2005, February 17 we are monitoring the source activity in this region about every three days with INTEGRAL. Thanks to the large field of view, the imaging capabilities and the sensitivity at hard X-rays, we are able to present for the first time a detailed homogeneous (hard) X-ray view of a sample of 76 sources in the Galactic bulge region. We describe the successful monitoring program and show the first results for a period of about one and a half year. We focus on the short (hour), medium (month) and long-term (year) variability in the 20-60 keV and 60-150 keV bands. When available, we discuss the simultaneous observations in the 3-10 keV and 10-25 keV bands. Per visibility season we detect 32/33 sources in the 20-60 keV band and 8/9 sources in the 60-150 keV band. On average, we find per visibility season one active bright (>~100 mCrab, 20-60 keV) black-hole candidate X-ray transient and three active weaker (<~25 mCrab, 20-60 keV) neutron star X-ray transients. Most of the time a clear anti-correlation can be seen between the soft and hard X-ray emission in some of the X-ray bursters. Hard X-ray flares or outbursts in X-ray bursters, which have a duration of the order of weeks, are accompanied by soft X-ray drops. On the other hand, hard X-ray drops can be accompanied by soft X-ray flares/outbursts. We found a number of new sources, IGR J17354-3255, IGR 17453-2853, IGR J17454-2703, IGR J17456-2901b, IGR J17536-2339, and IGR J17541-2252. We report here on some of the high-energy properties of these sources. The high-energy light curves of all the sources in the field of view, and the high-energy images of the region, are made available through the WWW at this http URL

 
astro-ph/0701250 [abs, ps, pdf, other] :
Title: Polarisation of high-energy emission in a pulsar striped wind
Authors: J.Petri, J. Kirk
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.108-111

Recent observations of the polarisation of the optical pulses from the Crab pulsar motivated detailed comparative studies of the emission predicted by the polar cap, the outer gap and the two-pole caustics models.
In this work, we study the polarisation properties of the synchrotron emission emanating from the striped wind model. We use an explicit asymptotic solution for the large-scale field structure related to the oblique split monopole and valid for the case of an ultra-relativistic plasma. This is combined with a crude model for the emissivity of the striped wind and of the magnetic field within the dissipating stripes themselves. We calculate the polarisation properties of the high-energy pulsed emission and compare our results with optical observations of the Crab pulsar. The resulting radiation is linearly polarised. In the off-pulse region, the electric vector lies in the direction of the projection on the sky of the rotation axis of the pulsar, in good agreement with the data. Other properties such as a reduced degree of polarisation and a characteristic sweep of the polarisation angle within the pulses are also reproduced.

 
astro-ph/0701252 [abs, ps, pdf, other] :
Title: Radio emission physics in the Crab pulsar
Authors: J. A. Eilek, T. H. Hankins
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.112-115

Our high time resolution observations of individual giant pulses in the Crab pulsar show that both the time and frequency signatures of the interpulse are distinctly different from those of the main pulse. Giant main pulses can occasionally be resolved into short-lived, relatively narrow-band nanoshots. We believe these nanoshots are produced by soliton collapse in strong plasma turbulence. Giant interpulses are very different. Their dynamic spectrum contains narrow, microsecond-long emission bands. We have detected these proportionately spaced bands from 4.5 to 10.5 GHz. The bands cannot easily be explained by any current theory of pulsar radio emission; we speculate on possible new models.

 
astro-ph/0701253 [abs, ps, pdf, other] :
Title: A multicomponent model for the optical to gamma-ray emission from the Crabpulsar
Authors: R. Campana, E. Massaro, G. Cusumano, T. Mineo
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.116-119

We present a multicomponent model to explain the features of the pulsed emission and spectrum of the Crab Pulsar, on the basis of X and gamma-ray observations performed with BeppoSAX, INTEGRAL and CGRO. This model explains the evolution of the pulse shape and of the phase-resolved spectra, ranging from the optical/UV to the GeV energy band, on the assumption that the observed emission is due to several components. The first component, C_O, is assumed to have the pulsed double-peaked profile observed at the optical frequencies, while the second component, C_X, isdominant in the interpeak and second peak phase regions. The spectra of these components are modelled with log-parabolic laws. Moreover, to explain the properties of the pulsed emission in the MeV-GeV band, we introduce two more components, C_O_gamma and C_X_gamma, with phase distributions similar to those of C_O and C_X and log-parabolic spectra with the same curvature but different peak energies. This multicomponent model is able to reproduce both the broadband phase-resolved spectral behaviour and the changes of the pulse shape with energy. We also propose some possible physical interpretations in which C_O and C_X are emitted by secondary pairs via a synchrotron mechanism while C_O_gamma and C_X_gamma can originate either from Compton scattered or primary curvature photons.

 
astro-ph/0701255 [abs, ps, pdf, other] :
Title: Study on polarization of high-energy photons from the Crab pulsar
Authors: J. Takata, H. K. Chang, K. S. Cheng
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.120-123

We investigate polarization of high-energy emissions from the Crab pulsar in the frame work of the outer gap accelerator. The recent version of the outer gap, which extends from inside the null charge surface to the light cylinder, is used for examining the light curve, the spectrum and the polarization characteristics, simultaneously. The polarization position angle curve and the polarization degree are calculated to compare with the Crab optical data. We show that the outer gap model explains the general features of the observed light curve, the spectrum and the polarization by taking into account the emissions from inside of the null charge surface and from tertiary pairs, which were produced by the high-energy photons from the secondary pairs. For the Crab pulsar, the polarization position angle curve indicates that the viewing angle of the observer measured from the rotational axis is greater than 90 degrees.

 
astro-ph/0701257 [abs, ps, pdf, other] :
Title: Occurrence of concurrent `orthogonal' polarization modes in the Lienard-Wichert field of a rotating superluminal source
Authors: A. Schmidt, H. Ardavan, J. Fasel, J. Singleton, A. Ardavan
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.124-127

We evaluate the Lienard-Wiechert field of a rotating superluminal point source numerically and show that this radiation field has the following intrinsic characteristics. (i) It is sharply focused along a narrow, rigidly rotating spiral-shaped beam that embodies the cusp of the envelope of the emitted wave fronts. (ii) It consists of either one or three concurrent polarization modes (depending on the relative positions of the observer and the cusp) that constitute contributions to the field from differing retarded times. (iii) Two of the modes are comparable in strength at both edges of the signal and dominate over the third everywhere except in the middle of the pulse. (iv) The position angle of the total field swings across the beam by as much as 180$^\circ$. (v) The position angles of its two dominant modes remain approximately orthogonal throughout their excursion across the beam. Given the fundamental nature of the Lienard-Wiechert field, the coincidence of these characteristics with those of the radio emission that is received from pulsars is striking.

 
astro-ph/0701258 [abs, ps, pdf, other] :
Title: Long Gamma Ray Bursts from Quark Stars
Authors: P. Haensel, J.L. Zdunik
Comments: To be published in the proceedings of the conference "SWIFT and GRBs: Unveiling the Relativistic Universe", Venice, June 5-9, 2006. To appear in "Il Nuovo Cimento"

If strange quark matter (SQM) is the true ground state of hadronic matter, then conversion of neutron stars (NS) into quark stars (QS) could release some 10^{53} erg. We describe a scenario of burning of a NS into a hot, differentially rotating QS. Emission of released non-baryonic energy through the QS surface is discussed. The role of magnetobuoyancy of SQM is mentioned. The outflow of gamma e+ e- lasting for up to ~1000 s could be at the origin of long GRBs. Advantages of hot, differentially rotating QS as an inner engine of long GRBs are reviewed.

 
astro-ph/0701261 [abs, ps, pdf, other] :
Title: On the role of the current loss mechanism in radio pulsar evolution
Authors: V. S. Beskin, E. E. Nokhrina
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.128-131

The aim of this article is to draw attention to the importance of the electric current loss in the energy output of radio pulsars. We remind that even the losses attributed to the magneto-dipole radiation of a pulsar in vacuum can be written as a result of Ampere force action of the electric currents flowing over the neutron star surface (Michel 1991, Beskin, Gurevich & Istomin 1993). It is this force that is responsible for the transfer of angular momentum of a neutron star to an outgoing magneto-dipole wave. If a pulsar is surrounded by plasma, and there is no longitudinal current in its magnetosphere, there is no energy loss (Beskin, Gurevich & Istomin 1993, Mestel, Panagi & Shibata 1999). It is the longitudinal current closing within the pulsar polar cap that exerts the retardation torque acting on the neutron star. This torque can be determined if the structure of longitudinal current is known. Here we remind of the solution by Beskin, Gurevich & Istomin (1993) and discuss the validity of such an assumption. Finally, it is shown that the behaviour of the recently observed "part-time job" pulsar B1931+24 can be naturally explained within the model of current loss while the magneto-dipole model faces difficulties.

 
astro-ph/0701262 [abs, ps, pdf, other] :
Title: On a synthetical method to constrain 3-D structure of emission regions of pulsars
Authors: H. G. Wang, H. Zhang, X. H. Cui, G. J. Qiao, K. J. Lee, Y. Liu, R. X. Xu
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.134-136

The main idea and procedure are presented for a new synthetical method on constraining 3-D structure of emission regions of pulsars. With this method the emission regions can be synthetically constrained by fitting multi-wavelength observations features, e.g. pulse widths, phase offsets between radio pulse profiles and high energy light curves, and radio polarization properties. The main technique is based on numerically calculating the emission directions along any open field line via including aberration and retardation effects under a certain magnetic field configuration, e.g. vacuum dipole field. It can be easily extended by involving some further effects or magnetic field line configuration. The role of observed linear polarization properties in the method is discussed. The future application to known X/gamma-ray and radio pulsars will be helpful to test and improve current theoretical models on pulsar emission.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612787 [abs, ps, pdf, other] :
Title: Long term spectral variability in the soft gamma ray repeater SGR 1900+14
Authors: P. Esposito, S. Mereghetti, A. Tiengo, D. Goetz, L. Sidoli, M. Feroci
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang
Note: replaced with revised version Tue, 9 Jan 2007 16:24:05 GMT (56kb)
 
astro-ph/0612790 [abs, ps, pdf, other] :
Title: A precessing warped accretion disk around the X-ray pulsar Her X-1
Authors: D. Klochkov, N. Shakura, K. Postnov, R. Staubert, J. Wilms
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.212-215
Note: replaced with revised version Tue, 9 Jan 2007 13:22:52 GMT (141kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 11 Jan 07 01:00:11 GMT
0701265 -- 0701312 received


9 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701271 [abs, ps, pdf, other] :
Title: Cohesive property of magnetized neutron star surfaces: Computations and implications
Authors: Zach Medin Dong Lai
Comments: 12 pages, 4 figures, talk given at 36th COSPAR Scientific Assembly, Beijing, 16-23 July 2006

The cohesive energy of condensed matter in strong magnetic fields is a fundamental quantity characterizing magnetized neutron star surfaces. The cohesive energy refers to the energy required to pull an atom out of the bulk condensed matter at zero pressure. Theoretical models of pulsar and magnetar magnetospheres depend on the cohesive properties of the surface matter in strong magnetic fields. For example, depending on the cohesive energy of the surface matter, an acceleration zone ("polar gap") above the polar cap of a pulsar may or may not form. Also, condensation of the neutron star surface, if it occurs, can significantly affect thermal emission from isolated neutron stars. We describe our calculations of the cohesive property of matter in strong magnetic fields, and discuss the implications of our results to the recent observations of neutron star surface emission as well as to the detection/non-detection of radio emission from magnetars.

 
astro-ph/0701272 [abs, ps, pdf, other] :
Title: 3D Relativistic MHD Simulation of a Tilted Accretion Disk Around a Rapidly Rotating Black Hole
Authors: P. Chris Fragile, Peter Anninos, Omer M. Blaes, Jay D. Salmonson
Comments: 3 pages, 3 figures, to appear in "Proceedings of the 11th Marcel Grossmann Meeting on General Relativity", eds H. Kleinert, R. T. Jantzen, R. Ruffini

We posit that accreting compact objects, including stellar mass black holes and neutron stars as well as supermassive black holes, may undergo extended periods of accretion during which the angular momentum of the disk at large scales is misaligned with that of the compact object. In such a scenario, Lense-Thirring precession caused by the rotating compact object can dramatically affect the disk. In this presentation we describe results from a three-dimensional relativistic magnetohydrodynamic simulation of an MRI turbulent disk accreting onto a tilted rapidly rotating black hole. For this case, the disk does not achieve the commonly described Bardeen-Petterson configuration; rather, it remains nearly planar, undergoing a slow global precession. Accretion from the disk onto the hole occurs predominantly through two opposing plunging streams that start from high latitudes with respect to both the black-hole and disk midplanes. This is a consequence of the non-sphericity of the gravitational spacetime of the black hole.

 
astro-ph/0701285 [abs, ps, pdf, other] :
Title: Statistical equilibrium and ion cyclotron absorption/emission in strongly magnetized plasmas
Authors: A. Y. Potekhin (Ioffe Inst., St. Petersburg), Dong Lai (Cornell)
Comments: 17 pages, 8 figures, MNRAS, accepted

We calculate the transition rates between proton Landau levels due to non-radiative and radiative Coulomb collisions in an electron-proton plasma with strong magnetic field B. Both electron-proton collisions and proton-proton collisions are considered. The roles of the first-order cyclotron absorption and second-order free-free absorption and scattering in determining the line strength and shape as well as the continuum are analysed in detail. We solve the statistical balance equation for the populations of proton Landau levels. For temperatures \sim 10^6-10^7 K, the deviations of the proton populations from LTE are appreciable at density \rho < 0.1 B_{14}^{3.5} g cm^{-3}, where B_{14}=B/(10^{14} G). We present general formulae for the plasma emissivity and absorption coefficents under a wide range of physical conditions. Our results are useful for studying the possibility and the conditions of proton/ion cyclotron line formation in the near vicinity of highly magnetized neutron stars.

 
astro-ph/0701287 [abs, ps, pdf, other] :
Title: Electromagnetic pulsar spindown
Authors: I. Contopoulos
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.132-133

We evaluate the result of the recent pioneering numerical simulations in Spitkovsky~2006 on the spindown of an oblique relativistic magnetic dipole rotator. Our discussion is based on our experience from two idealized cases, that of an aligned dipole rotator, and that of an oblique split-monopole rotator. We conclude that the issue of electromagnetic pulsar spindown may not have been resolved yet.

 
astro-ph/0701290 [abs, ps, pdf, other] :
Title: Detailed studies of giant pulses from the millisecond pulsar B1937+21
Authors: V.I. Kondratiev, M.V. Popov, V.A. Soglasnov, Y.Y. Kovalev, N. Bartel, F. Ghigo
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.76-79

The second fastest millisecond pulsar, B1937+21, is one of several pulsars known to emit giant pulses (GPs). GPs are characterized by their huge energy, power-law cumulative energy distribution, and particular longitudes of occurrence. All these characteristics are different from those of regular pulses. Here, we present a study of GPs from our observations of the pulsar B1937+21 with the GBT at 2.1 GHz in both left and right circular polarization with a time resolution of 8 ns. The Mark5 data acquisition system was used for the first time in single-dish observations with the GBT. This allowed us to obtain continuous and uniform recording for 7.5 hours with a data rate of 512 Mbps. As a result, more than 6000 GPs were found above a detection threshold of 200 Jy. We report on instantaneous spectra of GPs, as well as on a comparison with scintillation spectra of regular emission, on the distribution of GP energies, and on polarization properties of GPs.

 
astro-ph/0701296 [abs, ps, pdf, other] :
Title: INTEGRAL observations of PSR B0540-69
Authors: A. Slowikowska, G. Kanbach, J. Borkowski, W. Becker
Comments: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.44-51

PSR B0540-69 is often called an extragalactic 'twin' of the Crab pulsar in the Large Magellanic Cloud. The pulsar is embedded in a synchrotron nebula in the center of SNR 0540-69.3. It was discovered with the Einstein satellite with P~50 ms, spin-down age of ~1500 years and a spin-down luminosity of ~10^38 erg/s. It has since been detected with all major X-ray telescopes. At X-ray energies up to ~40 keV the latest observations were reported from RXTE and from INTEGRAL (only spectrum) in the context of a survey of the LMC. Optical pulsed emission and faint radio emission have also been found from PSR B0540-69. The INTEGRAL analysis presented here is based on observations of the LMC obtained in Jan. 2003 and Jan. 2004 with a total exposure of ~1.5 Ms. In the mosaic maps from the total exposure (JEM-X and IBIS/ISGRI) a source at the location of PSR B0540-69 is clearly visible up to energies of ~200 keV. After barycentric correction and determination of the pulsar phases, based on theephemeris available from contemporaneous RXTE data, the lightcurves show the characteristic shape of a broad pulse up into the 40-100 keV band. At higher energies no significant pulsation is detectable. We derive the spectrum of the total source from the ISGRI data. The photon spectrum can be fitted with a power law of index 2.22, which is compatible with the result found by Goetz et al., 2006.

 
astro-ph/0701308 [abs, ps, pdf, other] :
Title: A Novel Mechanism for Type-I Superconductivity in Neutron Stars
Authors: James Charbonneau, Ariel Zhitnitsky
Comments: 9 pages

We suggest a mechanism that may resolve a conflict raised by Link between neutron star precession and the standard picture of the neutron star in which the core is composed of a mixture of a neutron superfluid and a proton type-II superconductor. We will show that if there is a persistent, non-dissipating current running along the magnetic flux tubes, the force between magnetic flux tubes may be attractive, resulting in a type-I, rather than a type-II, superconductor. If this is the case, the conflict between the observed precession and the canonical estimation of the Landau-Ginzburg parameter $\kappa > 1/\sqrt{2}$ (which suggests type II behaviour) will be automatically resolved. Such a current arises in some condensed matter systems and may also appear in QCD dense matter as a consequence of quantum anomalies. We calculate the interaction between two vortices carrying a current $j$ and demonstrate that when $j > {\hbar c\over 2 q \lambda}$, where $q$ is the charge of the Cooper pair and $\lambda$ is the Meissner penetration depth, a superconductor is always type-I, even when the cannonical Landau-Ginzburg parameter $\kappa$ indicates type-II behaviour. If this condition is met, the magnetic field is expelled from the superconducting regions of the neutron star leading to the formation of the intermediate state where alternating domains of superconducting matter and normal matter coexist. We also discuss some instances where anomalous induced current may play a crucial role, such as the neutron star kicks, pulsar glitches and the toroidal magnetic field.

 
astro-ph/0701310 [abs, pdf] :
Title: A black hole in a globular cluster
Authors: Thomas J. Maccarone (University of Southampton) Arunav Kundu, Stephen E. Zepf (Michigan State University) Katherine L. Rhode (Wesleyan University and Yale University)
Comments: 11 pages, 1 figure, to appear in 11 January edition of Nature. Has already appeared in online advance publications section of Nature. DOI: 10.1038/nature05434

Globular star clusters contain thousands to millions of old stars packed within a region only tens of light years across. Their high stellar densities make it very probable that their member stars will interact or collide. There has been considerable debate about whether black holes should exist in these star clusters. Some theoretical work suggests that dynamical processes in the densest inner regions of globular clusters may lead to the formation of black holes of ~1,000 solar masses. Other numerical simulations instead predict that stellar interactions will eject most or all black holes that form in globular clusters. Here we report the X-ray signature of an accreting black hole in a spectroscopically-confirmed globular cluster in the Virgo Cluster giant elliptical galaxy NGC 4472. This object has an X-ray luminosity of about 4*10^39 ergs/sec, making it brighter than any non-black hole object can be in an old stellar population. The X-ray luminosity varies by a factor of 7 in a few hours, ruling out the possibility that the object is several neutron stars superposed.

 
astro-ph/0701312 [abs, ps, pdf, other] :
Title: Supporting evidence for the signature of the innermost stable circular orbit in Rossi X-ray data from 4U1636-536
Authors: Didier Barret (CESR, Toulouse), Jean-Francois Olive (CESR, Toulouse), M. Coleman Miller (Univ. of Maryland)
Comments: Accepted for publication in MNRAS, 7 pages, 8 figures, figure 3 in color

Analysis of archival RXTE data on neutron stars binaries has shown that for several sources the quality factor (Q) of the lower kilohertz Quasi-Periodic Oscillations (QPO) drops sharply beyond a certain frequency. This is one possible signature of the approach to the general relativistic innermost stable circular orbit (ISCO), but the implications of such an interpretation for strong gravity and dense matter are important enough that it is essential to explore alternate explanations. In this spirit, Mendez has recently proposed that Q depends fundamentally on mass accretion rate (as measured by spectral hardness) rather than the frequency of the QPO. We test this hypothesis for 4U1636-536 by measuring precisely spectral colors simultaneously with the lower QPO frequency and Q after correction for the frequency drift, over a data set spanning eight years of RXTE observations. We find that in this source there is no correlation between Q and spectral hardness. In particular, no apparent changes in hardness are observed when Q reaches its maximum before dropping off. We perform a similar analysis on 4U1608-522; another source showing a sharp drop in the quality factor of its lower kHz QPO. We find that for this source, positive and negative correlations are observed between spectral hardness, frequency and Q. Consequently, if we are to search for a common explanation for the sharp drop in the quality factor seen in both sources, the spectral hardness is not a good candidate for the independent variable whereas the frequency remains. Therefore, we conclude that the ISCO explanation is viable for 4U1636-536, and thus possibly for others.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


hep-ph/0701065 [abs, ps, pdf, other] :
Title: Vacuum Energy, EoS, and the Gluon Condensate at Finite Baryon Density in QCD
Authors: Ariel Zhitnitsky
Comments: Talk at " Quark Confinement and the Hadron Spectrum VII", Ponta Delgada, September 2-7, 2006

The Equation of States (EoS) plays the crucial role in all studies of neutron star properties. Still, a microscopical understanding of EoS remains largely an unresolved problem. We use 2-color QCD as a model to study the dependence of vacuum energy (gluon condensate in QCD) as function of chemical potential \mu\ll \Lambda_{QCD} where we find very strong and unexpected dependence on $\mu$. We present the arguments suggesting that similar behavior may occur in 3-color QCD in the color superconducting phases. Such a study may be of importance for analysis of EoS when phenomenologically relevant parameters (within such models as MIT Bag model or NJL model) are fixed at zero density while the region of study lies at much higher densities not available for terrestrial tests.

 

Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607583 [abs, ps, pdf, other] :
Title: Evidence for Heating of Neutron Stars by Magnetic Field Decay
Authors: J.A. Pons, B. Link, J.A. Miralles, U. Geppert
Comments: 4 pages, 1 figures, version accepted for publication in Phys. Rev. Lett
Note: replaced with revised version Wed, 10 Jan 2007 15:54:51 GMT (18kb)
 
astro-ph/0612252 [abs, ps, pdf, other] :
Title: Neutron star oscillations and QPOs during magnetar flares
Authors: Anna L. Watts (MPA), Tod E. Strohmayer (NASA GSFC)
Comments: Proceedings of the 2006 Beijing COSPAR assembly, to appear in Advances in Space Research. Corrected minor error in gravitational wave search section
Note: replaced with revised version Wed, 10 Jan 2007 09:53:22 GMT (15kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 12 Jan 07 01:00:10 GMT
0701313 -- 0701349 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701271 [abs, ps, pdf, other] :
Title: Cohesive property of magnetized neutron star surfaces: Computations and implications
Authors: Zach Medin, Dong Lai (Cornell)
Comments: 12 pages, 4 figures. Minor changes to Author/Comments fields. To appear in Advances in Space Research
Note: replaced with revised version Thu, 11 Jan 2007 18:45:00 GMT (16kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 15 Jan 07 01:00:12 GMT
0701350 -- 0701391 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701374 [abs, ps, pdf, other] :
Title: Making up a short GRB: The bright fate of mergers of compact objects
Authors: M.A. Aloy (1), P. Mimica (1) ((1) Departamento de Astronomia y Astrofisica, Universidad de Valencia)
Comments: 3 pages, 0 figures. Proceedings of the 11th Marcel Grossman Meeting on General Relativity (Berlin, 2005)

We show some of the most important reasons why the likely fate of the merger of a neutron star with another compact object may be to yield a short gamma-ray burst (sGRB). Emphasis is made on some robust results that general relativistic (magneto)hydrodynamic simulations have established regarding the aforementioned subject.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0609685 [abs, ps, pdf, other] :
Title: An accreting millisecond pulsar with black hole-like X-ray variability: IGR J00291+5934
Authors: Manuel Linares, Michiel van der Klis, Rudy Wijnands (Amsterdam)
Comments: Accepted by The Astrophysical Journal. Scheduled for ApJ May 1, 2007, v660n1 issue. Minor changes according to referee's comments
Note: replaced with revised version Fri, 12 Jan 2007 00:04:59 GMT (227kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 16 Jan 07 01:00:11 GMT
0701392 -- 0701427 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701400 [abs, ps, pdf, other] :
Title: On the maximum efficiency of the propeller mass-ejection mechanism
Authors: M. Falanga, E. Bozzo, L. Stella, L. Burderi, T. Di Salvo, R. Perna
Comments: 5 pages, 2 figures, accepted for publication in A&A

Aims. We derive simple estimates of the maximum efficiency with which matter can be ejected by the propeller mechanism in disk-fed, rotating magnetic neutron stars. Some binary evolution scenarios envisage that this mechanism is responsible for expelling to infinity the mass inflowing at a low rate from the companion star, therefore limiting the total amount of mass that can be accreted by the neutron star. Methods. We demonstrate that, for typical neutron star parameters, a maximum of \eta_{pro} < 5.7 (P_{-3})^{1/3} times more matter than accreted can be expelled through the propeller mechanism at the expenses of the neutron star rotational energy (P_{-3} is the NS spin period in unit of 10E-3 s). Approaching this value, however, would require a great deal of fine tuning in the system parameters and the properties of the interaction of matter and magnetic field at the magnetospheric boundary. Results. We conclude that some other mechanism must be invoked in order to prevent that too much mass accretes onto the neutron stars of some low mass X-ray binaries.

 
astro-ph/0701406 [abs, ps, pdf, other] :
Title: Bright X-ray source populations in the starburst galaxies NGC 4038/4039
Authors: Xi-Wei Liu, Xiang-Dong Li (NJU)
Comments: 17 pages, 5 figures and 1 table. Submitted to Chinese Journal of Astronomy and Astrophysics. This is ONLY a first draft of the paper and some issues needs to be addressed according to the referee's report in a forthcoming revision

Assuming a naive star formation history, we construct the synthetic X-ray source populations for comparison with the X-ray luminosity function (XLF) of the interacting galaxies NGC 4038/4039 using a population synthesis code. We have considered high- and intermediate-mass X-ray binaries, young rotation-powered pulsars and fallback disc-fed black holes in modelling the bright X-ray sources detected. To examine the effects of the input parameters on the calculated results we produce a series of hybrid models. We find that for typical binary evolution parameters, it is difficult to match the observed XLF shape, and the predicted XLFs seem to be steeper than those of starburst and late type spiral galaxies. We note that the shape of the XLFs depends critically on the existence of XLF break for young populations, which seems to be a popular feature in theoretical population synthesis works. We discuss possible reasons and implications on the discrepancy of the calculated and observational XLFs.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0607583 [abs, ps, pdf, other] :
Title: Evidence for Heating of Neutron Stars by Magnetic Field Decay
Authors: J.A. Pons, B. Link, J.A. Miralles, U. Geppert
Comments: 4 pages, 1 figures, version accepted for publication in Phys. Rev. Lett
Note: replaced with revised version Mon, 15 Jan 2007 10:18:58 GMT (18kb)
 
astro-ph/0609776 [abs, ps, pdf, other] :
Title: Simultaneous INTEGRAL and RXTE observations of the accreting millisecond pulsar HETE J1900.1-2455
Authors: M. Falanga, J. Poutanen, E. W. Bonning, L. Kuiper, J. M. Bonnet-Bidaud, A. Goldwurm, W. Hermsen, L. Stella
Comments: 7 pages, 4 figures, accepted for publication in A&A
Note: replaced with revised version Sat, 13 Jan 2007 12:29:46 GMT (50kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 17 Jan 07 01:00:11 GMT
0701428 -- 0701477 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701442 [abs, ps, pdf, other] :
Title: Cooling of Neutron Stars with Strong Toroidal Magnetic Fields
Authors: Dany Page (1), Ulrich Geppert (2), Manfred Kueker (3) ((1) Instituto de Astronomia, UNAM, (2) Departament de Fisica Aplicada, Universitat d'Alacant, (3) Astrophysikalisches Institut Potsdam)
Comments: 9 pages, 10 figures; to appear in proceedings of the conference "Isolated Neutron Stars: From the Interior to the Surface", eds. S. Zane, R. Turolla, D. Page; Astrophysics & Space Science in press

We present models of temperature distribution in the crust of a neutron star in the presence of a strong toroidal component superposed to the poloidal component of the magnetic field. The presence of such a toroidal field hinders heat flow toward the surface in a large part of the crust. As a result, the neutron star surface presents two warm regions surrounded by extended cold regions and has a thermal luminosity much lower than in the case the magnetic field is purely poloidal. We apply these models to calculate the thermal evolution of such neutron stars and show that the lowered photon luminosity naturally extends their life-time as detectable thermal X-ray sources.

 
astro-ph/0701444 [abs, ps, pdf, other] :
Title: The birth properties of Galactic millisecond radio pulsars
Authors: Lilia Ferrario, Dayal Wickramasinghe
Comments: 8 pages, 2 figures, accepted for publication in the MNRAS

We model the population characteristics of the sample of millisecond pulsars within a distance of 1.5kpc.We find that for a braking index n=3, the birth magnetic field distribution of the neutron stars as they switch on as radio MSPs can be represented by a Gaussian with mean $\log B(G)= 8.1$ and $\sigma_{\log B}=0.4$ and their birth spin period by a Gaussian with mean $P_0=4$ ms and $\sigma_{P_0}=1.3$ ms. Our study, which takes into consideration acceleration effects on the observed spin-down rate, shows that most MSPs are born with periods that are close to the currently observed values and with average characteristic ages typically larger by a factor 1.5 compared to the true age. The Galactic birth rate of the MSPs is deduced to be $\gsimeq 3.2 \times 10^{-6}$ yr$^{-1}$ near the upper end of previous estimates and larger than the semi-empirical birth rate $\sim 10^{-7}$ yr$^{-1}$ of the LMXBs. The mean birth spin period deduced by us for the radio MSPs is a factor 2 higher than the mean spin period observed for the accretion and nuclear powered X-ray pulsars, although this discrepancy can be resolved if we use a braking index $n=5$, the value appropriate to spin down caused by angular momentum losses by gravitational radiation or magnetic multipolar radiation. We discuss the arguments for and against the hypothesis that accretion induced collapse may constitute the main route to the formation of the MSPs, pointing out that on the AIC scenario the low magnetic fields of the MSPs may simply reflect the field distribution in isolated magnetic white dwarfs which has recently been shown to be bi-modal with a dominant component that is likely to peak at fields below $10^3$ G which would scale to neutron star fields below $10^9$ G.

 
astro-ph/0701445 [abs, ps, pdf, other] :
Title: Germanium Production in Asymptotic Giant Branch stars: Implications for Observations of Planetary Nebulae
Authors: Amanda Karakas (McMaster, Mt Stromlo Observatory ANU), Maria Lugaro (Utrecht), Roberto Gallino (Torino)
Comments: accepted for publication in the Astrophysical Journal Letters

Observations of planetary nebulae (PNe) by Sterling, Dinerstein and Bowers have revealed abundances in the neutron-capture element Germanium (Ge) from solar to factors of 3 -- 10 above solar. The enhanced Ge is an indication that the slow-neutron capture process (s process) operated in the parent star during the thermally-pulsing asymptotic giant branch (TP-AGB) phase. We compute the detailed nucleosynthesis of a series of AGB models to estimate the surface enrichment of Ge near the end of the AGB. A partial mixing zone of constant mass is included at the deepest extent of each dredge-up episode, resulting in the formation of a 13C pocket in the top ~1/10th of the He-rich intershell. All of the models show surface increases of [Ge/Fe] less than about 0.5, except the 2.5Msun, Z=0.004 case which produced a factor of 6 enhancement of Ge. Near the tip of the TP-AGB, a couple of extra TPs could occur to account for the composition of the most Ge-enriched PNe. Uncertainties in the theoretical modeling of AGB stellar evolution might account for larger Ge enhancements than we predict here. Alternatively, a possible solution could be provided by the occurrence of a late TP during the post-AGB phase. Difficulties related to spectroscopic abundance estimates also need to be taken into consideration. Further study is required to better assess how the model uncertainties affect the predictions and, consequently, if a late TP should be invoked.

 
astro-ph/0701470 [abs, ps, pdf, other] :
Title: The superorbital variability and triple nature of the X-ray source 4U 1820-303
Authors: A. A. Zdziarski, L. Wen, M. Gierlinski
Comments: submitted to MNRAS

We perform a comprehensive analysis of the superorbital modulation in the ultracompact X-ray source 4U 1820-303, consisting of a white dwarf accreting onto a neutron star. Based on XTE data, we measure the fractional amplitude of the source superorbital variability (with a 70-d quasi-period) in the folded and averaged light curves, and find it to be by a factor of 2. As proposed before, the superorbital variability can be explained by oscillations of the binary eccentricity. We now present detailed calculations of the eccentricity-dependent flow through the inner Lagrangian point, and find a maximum of the eccentricity of 0.004 is sufficient to explain the observed fractional amplitude. We then study hierarchical triple models yielding the required quasi-periodic eccentricity oscillations through the Kozai process. We find the resulting theoretical light curves to match well the observed ones. We constrain the ratio of the semimajor axes of the outer and inner systems, the component masses, and the inclination angle between the inner and outer orbits. Last but not least, we discover a remarkable and puzzling synchronization between the observed period of the superorbital variability (equal to the period of the eccentricity oscillations in our model) and the period of the general-relativistic periastron precession of the binary.

 
astro-ph/0701477 [abs, ps, pdf, other] :
Title: Density Distribution of the Warm Ionized Medium
Authors: Alex S. Hill, Ronald J. Reynolds (UW-Madison), Robert A. Benjamin (UW-Whitewater), L. Matthew Haffner (UW-Madison)
Comments: To appear in the proceedings of the "SINS - Small Ionized and Neutral Structures in the Diffuse Interstellar Medium" conference, eds. M. Haverkorn and W.M. Goss

Observations of Halpha emission measures and pulsar dispersion measures at high Galactic latitude (|b| > 10 deg) provide information about the density and distribution of the diffuse warm ionized medium (WIM). The diffuse WIM has a lognormal distribution of EM sin |b|, which is consistent with a density structure established by isothermal turbulence. The H+ responsible for most of the emission along high-EM sin |b| sightlines is clumped in high density (> 0.1 cm^{-3}) regions that occupy only a few parsecs along the line of sight, while the H+ along low-EM sightlines occupies hundreds of parsecs with considerably lower densities.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612226 [abs, ps, pdf, other] :
Title: X-ray pulsar radiation from polar cap heated by back-flow bombardment
Authors: J. Gil, G. I. Melikidze, B. Zhang
Note: replaced with revised version Tue, 16 Jan 2007 02:10:59 GMT (23kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 18 Jan 07 01:00:08 GMT
0701478 -- 0701509 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 19 Jan 07 01:00:13 GMT
0701510 -- 0701548 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701522 [abs, ps, pdf, other] :
Title: High Energy Gamma-rays from Globular Clusters
Authors: W. Bednarek, J. Sitarek
Comments: 12 pages, 10 figures, submitted to MNRAS

It is expected that specific globular clusters can contain up to a hundred of millisecond pulsars. These pulsars can accelerate leptons at the shock waves originated in collisions of the pulsar winds and/or inside the pulsar magnetospheres. Energetic leptons diffuse gradually through the globular cluster comptonizing stellar and microwave background radiation. We calculate the GeV-TeV $\gamma$-ray spectra for different models of injection of leptons and parameters of the globular clusters assuming reasonable, of the order of 1%, efficiency of energy conversion from the pulsar winds into the relativistic leptons. It is concluded that leptons accelerated in the globular cluster cores should produce well localized $\gamma$-ray sources which are concentric with these globular clusters. The results are shown for four specific globular clusters (47 Tuc, Ter 5, M13, and M15), in which significant population of millisecond pulsars have been already discovered. We argue that the best candidates, which might be potentially detected by the present Cherenkov telescopes and the planned satellite telescopes (AGILE, GLAST), are 47 Tuc on the southern hemisphere, and M13 on the northern hemisphere. We conclude that detection (or non-detection) of GeV-TeV $\gamma$-ray emission from GCs by these instruments put important constraints on the models of acceleration of leptons by millisecond pulsars.

 
astro-ph/0701524 [abs, ps, pdf, other] :
Title: Numerical solution of the linear dispersion relation in a relativistic pair plasma
Authors: J Petri, J G Kirk
Comments: Accepted by Plasma Physics and Controlled Fusion

We describe an algorithm that computes the linear dispersion relation of waves and instabilities in relativistic plasmas within a Vlasov-Maxwell description. The method used is fully relativistic and involves explicit integration of particle orbits along the unperturbed equilibrium trajectories. We check the algorithm against the dispersion curves for a single component magnetised plasma and for an unmagnetised plasma with counter-streaming components in the non-relativistic case. New results on the growth rate of the Weibel or two-stream instability in a hot unmagnetised pair plasma consisting of two counter-streaming relativistic Maxwellians are presented. These are relevant to the physics of the relativistic plasmas found in gamma-ray bursts, relativistic jets and pulsar winds.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 22 Jan 07 01:00:11 GMT
0701549 -- 0701578 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701575 [abs, ps, pdf, other] :
Title: Discovery of X-ray burst triplets in EXO 0748-676
Authors: L. Boirin (1), L. Keek (2 and 3), M. Mendez (2 and 4), A. Cumming (5), J.J.M. In 't Zand (2 and 3), J. Cottam (6), F. Paerels (7), W.H.G. Lewin (8) ((1) Observatoire Astronomique de Strasbourg, (2) SRON Utrecht, (3) Astronomical Institute Utrecht, (4) Astronomical Institute Amsterdam, (5) McGill University Montreal, (6) NASA GSFC, (7) Columbia, (8) MIT)
Comments: 23 pages, 16 figures, accepted for publication in A&A

[Abridged] Type-I X-ray bursts are thermonuclear flashes that take place on the surface of accreting neutron stars. The wait time between consecutive bursts is set by the time required to accumulate the fuel needed to trigger a new burst; this is at least one hour. Sometimes secondary bursts are observed, approximately 10 min after the main burst. These short wait-time bursts are not yet understood. We observed the low-mass X-ray binary and X-ray burster EXO 0748-676 with XMM-Newton for 158 h, during 7 uninterrupted observations lasting up to 30 h each. We detect 76 X-ray bursts. Most remarkably, 15 of these bursts occur in burst triplets, with wait times of 12 min between the three components of the triplet. We also detect 14 doublets with similar wait times between the two components of the doublet. The characteristics of the bursts indicate that possibly all bursts in this system are hydrogen-ignited, in contrast with most other frequent X-ray bursters in which bursts are helium-ignited, but consistent with the low mass accretion rate in EXO 0748-676. Possibly the hydrogen ignition is the determining factor for the occurrence of short wait-time bursts.

 
astro-ph/0701578 [abs, ps, pdf, other] :
Title: Relativistic MHD Winds from Rotating Neutron Stars
Authors: Bucciantini, N. (1), Thompson, Todd A. (2), Arons, J. (1), Quataert, E. (1), Del Zanna, L. (3) ((1) Astronomy Dep., UC Berkeley, (2) Astrophysisc Dep., Princeton, (3) Dip. Astronomia, Univ. Firenze)
Comments: 10 pages, accepted for publication in AdSR, proceedings of the 2006 Cospar Meeting in Beijing

We review here recent numerical results concerning the acceleration and collimation of relativistic outflows from neutron stars, and we discuss their implications for models of magnetars in their hypothesized initial high rotation states. New results with different injection conditions and extending to much larger distance from the central star are also presented and discussed, showing that, only in the case of weakly magnetized winds, collimated outflows are indeed possible. We finally comment on the possibility that newly born magnetars might trigger GRBs, and we show that numerical results do not support such hypothesis.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 23 Jan 07 01:00:14 GMT
0701579 -- 0701627 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701594 [abs, pdf] :
Title: Dark matter maps reveal cosmic scaffolding
Authors: Richard Massey, Jason Rhodes, Richard Ellis, Nick Scoville, Alexie Leauthaud, Alexis Finoguenov, Peter Capak, David Bacon, Herve Aussel, Jean-Paul Kneib, Anton Koekemoer, Henry McCracken, Bahram Mobasher, Sandrine Pires, Alexandre Refregier, Shunji Sasaki, Jean-Luc Starck, Yoshi Taniguchi, Andy Taylor, James Taylor
Comments: 10 pages, 5 figures... plus 6 pages, 7 figures of supplementary information. An officially typset version is available from the Nature website at this http URL and the front cover of Nature featuring the mass map is available in PDF format from this http URL
Journal-ref: Nature 445 (2007) 286

Ordinary baryonic particles (such as protons and neutrons) account for only one-sixth of the total matter in the Universe. The remainder is a mysterious "dark matter" component, which does not interact via electromagnetism and thus neither emits nor reflects light. As dark matter cannot be seen directly using traditional observations, very little is currently known about its properties. It does interact via gravity, and is most effectively probed through gravitational lensing: the deflection of light from distant galaxies by the gravitational attraction of foreground mass concentrations. This is a purely geometrical effect that is free of astrophysical assumptions and sensitive to all matter -- whether baryonic or dark. Here we show high fidelity maps of the large-scale distribution of dark matter, resolved in both angle and depth. We find a loose network of filaments, growing over time, which intersect in massive structures at the locations of clusters of galaxies. Our results are consistent with predictions of gravitationally induced structure formation, in which the initial, smooth distribution of dark matter collapses into filaments then into clusters, forming a gravitational scaffold into which gas can accumulate, and stars can be built.

 
astro-ph/0701605 [abs, ps, pdf, other] :
Title: The stationary phase point method for transitional scattering: diffractive radio scintillation for pulsar
Authors: C.M. Zhang
Comments: Hanas Meeting paper, appear in ChJAA, 2006, 6, Sup

The stationary phase point (SPP) method in one-dimensional case is introduced to treat the diffractive scintillation. From weak scattering, where the SPP number N=1, to strong scattering (N$\gg$1), via transitional scattering regime (N$\sim$2,3), we find that the modulation index of intensity experiences the monotonically increasing from 0 to 1 with the scattering strength, characterized by the ratio of Fresnel scale $\rf$ to diffractive scale $\rdiff$.

 
astro-ph/0701611 [abs, ps, pdf, other] :
Title: XMM-Newton Observations of the Black Widow Pulsar PSR B1957+20
Authors: Hsiu-Hui Huang, Werner Becker
Comments: 4 pages, 3 figures, accepted for publication in A&A Letters

We report on XMM-Newton observations of the "Black Widow pulsar", PSR B1957+20. The pulsar's X-ray emission is non-thermal and best modeled with a single powerlaw spectrum of photon index 2.03(+0.51/-0.36). No coherent X-ray pulsations at the pulsar's spin-period could be detected, though a strong binary-phase dependence of the X-ray flux is observed for the first time. The data suggest that the majority of the pulsar's X-radiation is emitted from a small part of the binary orbit only. We identified this part as being near to where the radio eclipse takes place. This could mean that the X-rays from PSR B1957+20 are mostly due to intra-shock emission which is strongest when the pulsar wind interacts with the ablated material from the companion star.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610593 [abs, ps, pdf, other] :
Title: The Zoo of Neutron Stars
Authors: S.B. Popov (Sternberg Astronomical Institute)
Comments: 12 pages, no figures. To appear in the proceedings of the summer school "Dense Matter In Heavy Ion Collisions and Astrophysics" in a separate volume of Particles and Nuclei, Letters
Note: replaced with revised version Mon, 22 Jan 2007 13:21:47 GMT (14kb)
 
astro-ph/0611924 [abs, ps, pdf, other] :
Title: Wave Modes in the Magnetospheres of Pulsars and Magnetars
Authors: Chen Wang, Dong Lai
Comments: 19 pages, 10 figures. Accepted by MNRAS
Note: replaced with revised version Mon, 22 Jan 2007 07:20:39 GMT (87kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 24 Jan 07 01:00:10 GMT
0701628 -- 0701661 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701641 [abs, pdf] :
Title: INTEGRAL Observations of the Vela Region Focusing on Vela X-1
Authors: Stephane Schanne, Diego Gotz, Lucie Gerard, Patrick Sizun, Maurizio Falanga, Clarisse Hamadache, Bertand Cordier, Andreas von Kienlin
Comments: 4 pages, 11 figures. Accepted for publication in ESA SP-622 (Proceedings of the 6th INTEGRAL Workshop, Moscow, 2006 07 03-07)

The Vela region has been observed for 1.7 Ms in November 2005 by the INTEGRAL satellite. We present preliminary spectral and temporal results of Vela X-1, an eclipsing neutron star hosted in a wind-accreting high-mass X-ray binary system. Using data from ISGRI, SPI and JEM-X, we firmly confirm the existence of cyclotron resonant scattering features (CRSF) at ~27 keV and ~54 keV, implying a neutron-star magnetic field of ~3 10^12 Gauss, and the presence of an iron emission line at ~6.5 keV. During two strong flares those parameters remained unchanged. Furthermore we measure the neutron-star spin period of 283.6 s, indicating a still constant trend.

 
astro-ph/0701643 [abs, ps, pdf, other] :
Title: The g-mode Excitation in the Proto Neutron Star by the Standing Accretion Shock Instability
Authors: Shijun Yoshida, Naofumi Ohnishi, Shoichi Yamada
Comments: 24 pages, 6 figures

The so-called "acoustic revival mechanism" of core-collapse supernova proposed recently by the Arizona group is an interesting new possibility. Aiming to understand the elementary processes involved in the mechanism, we have calculated the eigen frequencies and eigen functions for the g-mode oscillations of a non-rotating proto neutron star. The possible excitation of these modes by the standing accretion shock instability, or SASI, is discussed based on these eigen functions. We have formulated the forced oscillations of $g$-modes by the external pressure perturbations exerted on the proto neutron star surface. The driving pressure fluctuations have been adopted from our previous computations of the axisymmetric SASI in the non-linear regime. We have paid particular attention to low l modes, since these are the modes that are dominant in SASI and that the Arizona group claimed played an important role in their acoustic revival scenario. Here l is the index of the spherical harmonic functions, $Y_l^m$. Although the frequency spectrum of the non-linear SASI is broadened substantially by non-linear couplings, the typical frequency is still much smaller than those of g-modes, the fact leading to a severe impedance mismatch. As a result, the excitations of various $g$-modes are rather inefficient and the energy of the saturated g-modes is $\sim 10^{50}$erg or smaller, with the g_2-mode being the largest in our model. Here the g_2-mode has two radial nodes and is confined to the interior of the convection region. The energy transfer rate from the g-modes to out-going sound waves is estimated from the growth of the g-modes and found to be $\sim 10^{51}$erg/s in the model studied in this paper.

 
astro-ph/0701660 [abs, ps, pdf, other] :
Title: kHz QPO pairs expose the neutron star of Circinus X-1
Authors: S. Boutloukos, M. van der Klis, D. Altamirano, M. Klein-Wolt, R. Wijnands
Comments: 3 pages, 2 figures - one from astro-ph/0608089 (ApJ 653, 1435, 2006) in corrected version, to appear in the proceedings of the 11th Marcel Grossman meeting

We discovered kHz QPOs in 80 archived RXTE observations from the peculiar low mass X-ray binary Circinus X-1. In 11 cases, those appear in pairs and have frequencies of the order of several hundred Hz that vary in frequency over a factor 2. This and the fact that they follow the relation followed by observations from other neutron stars as well as that they appear simultaneously confirm that the central object is a neutron star. These relations are extended to lower frequencies as also is the one of the frequency difference against the frequency of the upper kHz QPO. The monotonic increase of the latter challenges theoretical models of kHz QPOs.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0701110 [abs, ps, pdf, other] :
Title: Quasiequilibrium black hole-neutron star binaries in general relativity
Authors: Keisuke Taniguchi, Thomas W. Baumgarte, Joshua A. Faber, Stuart L. Shapiro
Comments: 16 pages, 15 figures, submitted to Phys. Rev. D

We construct quasiequilibrium sequences of black hole-neutron star binaries in general relativity. We solve Einstein's constraint equations in the conformal thin-sandwich formalism, subject to black hole boundary conditions imposed on the surface of an excised sphere, together with the relativistic equations of hydrostatic equilibrium. In contrast to our previous calculations we adopt a flat spatial background geometry and do not assume extreme mass ratios. We adopt a Gamma=2 polytropic equation of state and focus on irrotational neutron star configurations as well as approximately nonspinning black holes. We present numerical results for ratios of the black hole's irreducible mass to the neutron star's ADM mass in isolation of M_{irr}^{BH}/M_{ADM,0}^{NS} = 1, 2, 3, 5, and 10. We consider neutron stars of baryon rest mass M_B^{NS}/M_B^{max} = 83% and 56%, where M_B^{max} is the maximum allowed rest mass of a spherical star in isolation for our equation of state. For these sequences, we locate the onset of tidal disruption and, in cases with sufficiently large mass ratios and neutron star compactions, the innermost stable circular orbit. We compare with previous results for black hole-neutron star binaries and find excellent agreement with third-order post-Newtonian results, especially for large binary separations. We also use our results to estimate the energy spectrum of the outgoing gravitational radiation emitted during the inspiral phase for these binaries.

 

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Astrophysics


astro-ph new abstracts, Thu, 25 Jan 07 01:00:12 GMT
0701662 -- 0701704 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701676 [abs, ps, pdf, other] :
Title: High-energy Emission from Pulsar Outer Magnetospheres: Two-dimensional Electrodynamics and Phase-averaged Spectra
Authors: Kouichi Hirotani
Comments: 8 pages, 5 figures; ApJ in press. The title is modified from the text to be distinguished from astro-ph/0307236 (a book chapter)

We investigate particle accelerators in rotating neutron-star magnetospheres, by simultaneously solving the Poisson equation for the electrostatic potential together with the Boltzmann equations for electrons, positrons and photons on the poloidal plane. Applying the scheme to the three pulsars, Crab, Vela and PSR B1951+32, we demonstrate that the observed phase-averaged spectra are basically reproduced from infrared to very high energies. It is found that the Vela's spectrum in 10-50 GeV is sensitive to the three-dimensional magnetic field configuration near the light cylinder; thus, a careful argument is required to discriminate the inner-gap and outer-gap emissions using a gamma-ray telescope like GLAST. It is also found that PSR B1951+32 has a large inverse-Compton flux in TeV energies, which is to be detected by ground-based air Cerenkov telescopes as a pulsed emission.

 
astro-ph/0701695 [abs, ps, pdf, other] :
Title: Very high energy gamma-ray emission from X-ray transients during major outbursts
Authors: M. Orellana, G.E. Romero, L.J. Pellizza, S. Vidrih
Comments: 8 pages, 7 figures, accepted for publication in Astronomy and Astrophysical journal

Context: Some high mass X-ray binaries (HMXB) have been recently confirmed as gamma-ray sources by ground based Cherenkov telescopes. In this work, we discuss the gamma-ray emission from X-ray transient sources formed by a Be star and a highly magnetized neutron star. This kind of systems can produce variable hadronic gamma-ray emission through the mechanism proposed by Cheng and Ruderman, where a proton beam accelerated in the pulsar magnetosphere impacts the transient accretion disk. We choose as case of study the best known system of this class: A0535+26. Aims: We aim at making quantitative predictions about the very high-energy radiation generated in Be-X ray binary systems with strongly magnetized neutron stars. Methods: We study the gamma-ray emission generated during a major X-ray outburst of a HMXB adopting for the model the parameters of A0535+26. The emerging photon signal from the disk is determined by the grammage of the disk that modulates the optical depth. The electromagnetic cascades initiated by photons absorbed in the disk are explored, making use of the so-called "Approximation A" to solve the cascade equations. Very high energy photons induce Inverse Compton cascades in the photon field of the massive star. We implemented Monte Carlo simulations of these cascades, in order to estimate the characteristics of the resulting spectrum. Results: TeV emission should be detectable by Cherenkov telescopes during a major X-ray outburst of a binary formed by a Be star and a highly magnetized neutron star. The gamma-ray light curve is found to evolve in anti-correlation with the X-ray signal.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701611 [abs, ps, pdf, other] :
Title: XMM-Newton Observations of the Black Widow Pulsar PSR B1957+20
Authors: Hsiu-Hui Huang, Werner Becker
Comments: 4 pages, 3 figures, accepted for publication in A&A Letters
Note: replaced with revised version Wed, 24 Jan 2007 13:53:54 GMT (300kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 26 Jan 07 01:00:11 GMT
0701705 -- 0701743 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701708 [abs, ps, pdf, other] :
Title: The Latitude of Type I X-Ray Burst Ignition on Rapidly Rotating Neutron Stars
Authors: Randall L. Cooper, Ramesh Narayan
Comments: 4 pages, 2 figures, accepted by ApJL

We investigate the latitude at which type I X-ray bursts are ignited on rapidly rotating accreting neutron stars. We find that, for a wide range of accretion rates, ignition occurs preferentially at the equator, in accord with the work of Spitkovsky et al. However, for a range of accretion rates below the critical rate above which bursts cease, ignition occurs preferentially at higher latitudes. The range of accretion rates over which nonequatorial ignition occurs is an increasing function of the neutron star spin frequency. These findings have significant implications for thermonuclear flame propagation, and they may explain why oscillations during the burst rise are detected predominantly when the accretion rate is high. They also support the suggestion of Bhattacharyya & Strohmayer that non-photospheric radius expansion double-peaked bursts and the unusual harmonic content of oscillations during the rise of some bursts result from ignition at or near a rotational pole.

 
astro-ph/0701734 [abs, ps, pdf, other] :
Title: Quark Stars: Features and Findings
Authors: Prashanth Jaikumar (Ohio University)
Comments: Contribution to proceedings of Hot Quarks 2006, Villasimius, Italy; 5 pages (TeX), 2 .eps figures

Under extreme conditions of temperature and/or density, quarks and gluons are expected to undergo a deconfinement phase transition. While this is an ephemeral phenomenon at the ultra-relativistic heavy-ion collider (BNL-RHIC), quark matter may exist naturally in the dense interior of neutron stars. Herein, we present an appraisal of the possible phase structure of dense quark matter inside neutron stars, and the likelihood of its existence given the current status of neutron star observations. We conclude that quark matter inside neutron stars cannot be dismissed as a possibility, although recent observational evidence rules out most soft equations of state.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0701069 [abs, pdf] :
Title: Variational Calculation for the Equation of State of Nuclear Matter at Finite Temperatures
Authors: H. Kanzawa, K. Oyamatsu, K. Sumiyoshi, M. Takano
Comments: Accepted for publication in Nucl. Phys. A

An equation of state (EOS) for uniform nuclear matter is constructed at zero and finite temperatures with the variational method starting from the realistic nuclear Hamiltonian composed of the Argonne V18 and UIX potentials. The energy is evaluated in the two-body cluster approximation with the three-body-force contribution treated phenomenologically so as to reproduce the empirical saturation conditions. The obtained energies for symmetric nuclear matter and neutron matter at zero temperature are in good agreement with those by Akmal, Pandharipande and Ravenhall at low densities. At high densities, the EOS is stiffer, and the maximum mass of the neutron star is 2.3 M . At finite temperatures, a variational method by Schmidt and Pandharipande is employed to evaluate the free energy, which is used to derive various thermodynamic quantities of nuclear matter necessary for supernova simulations. The result of this variational method at finite temperatures is found to be self-consistent.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612232 [abs, ps, pdf, other] :
Title: Constraints on Thermal X-ray Radiation from SAX J1808.4-3658 and Implications for Neutron Star Neutrino Emission
Authors: C. O. Heinke, P. G. Jonker, R. Wijnands, R. E. Taam
Comments: 5 pages, 2 figures; slight revisions, accepted by ApJ
Note: replaced with revised version Wed, 24 Jan 2007 23:30:49 GMT (28kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 29 Jan 07 01:00:09 GMT
0701744 -- 0701780 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701748 [abs, ps, pdf, other] :
Title: Short-Hard Gamma-Ray Bursts
Authors: Ehud Nakar
Comments: A review, 125 pages, 12 figures. Physics Reports - Bethe Centennial Volume, in press

Two types of Gamma-ray bursts (GRBs) are observed: short duration hard spectrum GRBs and long duration soft spectrum GRBs. For many years long GRBs were the focus of intense research while the lack of observational data limited the study of short-hard GRBs (SHBs). In 2005 a breakthrough occurred following the first detections of SHB afterglows, longer wavelength emission that follows the burst of gamma-rays. Similarly to long GRBs, afterglow detections led to the identification of SHB host galaxies and measurement of their redshifts. These observations established that SHBs are cosmological relativistic sources that, unlike long GRBs, do not originate from the collapse of massive stars, and therefore constitute a distinct physical phenomenon. One viable model for SHB origin is the coalescence of compact binary systems (double neutron stars or a neutron star and a black hole), in which case SHBs are the electromagnetic counterparts of strong gravitational-wave sources. The theoretical and observational study of SHBs following the recent pivotal discoveries is reviewed, along with new theoretical results that are presented here for the first time.

 
astro-ph/0701771 [abs, ps, pdf, other] :
Title: Pulsar Studies of Tiny-Scale Structure in the Neutral ISM
Authors: J. M. Weisberg, S. Stanimirovic
Comments: Review to be published in the proceedings of the meeting on "Small Ionized and Neutral Structures in the Diffuse Interstellar Medium" (ASP Conference Series)

We describe the use of pulsars to study small-scale neutral structure in the interstellar medium (ISM). Because pulsars are high velocity objects, the pulsar-Earth line of sight sweeps rapidly across the ISM. Multiepoch measurements of pulsar interstellar spectral line spectra therefore probe ISM structures on AU scales. We review pulsar measurements of small scale structure in HI and OH and compare these results with those obtained through other techniques.

 
astro-ph/0701772 [abs, ps, pdf, other] :
Title: The quark core of protoneutron stars in the phase diagram of quark matter
Authors: F. Sandin, D. Blaschke
Comments: 18 pages, 25 figures

We study the effect of neutrino trapping in new-born quark stars within a three-flavor Nambu-Jona-Lasinio (NJL) model with self-consistently calculated quark masses. The phase diagrams and equations of state for charge neutral quark matter in beta-equilibrium are presented, with and without trapped neutrinos. The compact star sequences for different neutrino untrapping scenarios are investigated and the energy release due to neutrino untrapping is found to be of the order of 10^53 erg. We find that hot quark stars characterized, e.g., by an entropy per baryon of 1-2 and a lepton fraction of 0.4, as models for the cores of newborn protoneutron stars are in the two-flavor color superconducting (2SC) state. High temperatures and/or neutrino chemical potentials disfavor configurations with a color-flavor-locked (CFL) phase. Stable quark star solutions with CFL cores exist only at low temperatures and neutrino chemical potentials.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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Astrophysics


astro-ph new abstracts, Tue, 30 Jan 07 01:00:16 GMT
0701781 -- 0701831 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 31 Jan 07 01:00:12 GMT
0701832 -- 0701874 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701851 [abs, ps, pdf, other] :
Title: On the validity of the Wigner-Seitz approximation in neutron star crust
Authors: N. Chamel (IAA), S. Naimi (IPNO), E. Khan (IPNO), J. Margueron (IPNO)
Comments: 7 pages, with figures

The inner crust of neutron stars formed of nuclear clusters immersed in a neutron sea has been widely studied in the framework of the Wigner-Seitz approximation since the seminal work of Negele and Vautherin. In this article, the validity of this approximation is discussed in the framework of the band theory of solids. For a typical cell of $^{200}$Zr, present in the external layers of the inner crust, it is shown that the ground state properties of the neutron gas are rather well reproduced by the Wigner-Seitz approximation, while its dynamical properties depend on the energy scale of the process of interest or on the temperature. It is concluded that the Wigner-Seitz approximation is well suited for describing the inner crust of young neutron stars and the collapsing core of massive stars during supernovae explosions. However the band theory is required for low temperature fluid dynamics.

 
astro-ph/0701856 [abs, ps, pdf, other] :
Title: Diffuse Neutrino and Gamma-ray Emissions of the Galaxy above the TeV
Authors: Carmelo Evoli (SISSA), Dario Grasso (INFN, Pisa), Luca Maccione (SISSA & INFN, Trieste)
Comments: 25 pages, 11 figures

We construct realistic maps of the expected neutrino and gamma-ray emissions above the TeV originated from the hadronic scattering of cosmic rays (CR) with the interstellar medium (ISM). Differently from previous works, where a uniform CR density was assumed, we estimate the spatial distribution of primary nuclei by means of numerical simulations considering several models of the galactic magnetic field. Assuming that CR sources are supernova remnants (SNR), we use a distribution of those objects as estimated from observations of pulsars and progenitor stars.
For the ISM distribution, we adopt most recent data both for the atomic and molecular hydrogen. With respect to previous results, we find the neutrino and gamma-ray emissions to be more peaked along the galactic equator and in the galactic centre which improves significantly the perspectives of a positive detection.
We compare our predictions with present experimental upper limits both for the gamma-rays and the neutrinos and show that air shower array experiments may soon be able to detect the gamma-ray emission from the galactic plane. Finally, we discuss the perspectives that a neutrino telescope of kilometric scale based in the North hemisphere has to measure the diffuse emission from the inner Galaxy.

 
astro-ph/0701869 [abs, ps, pdf, other] :
Title: Accreting X-ray pulsars observed with Integral
Authors: Ingo Kreykenbohm, Sonja Fritz, Nami Mowlavi, Joern Wilms, Peter Kretschmar, Ruediger Staubert, Andrea Santangelo
Comments: accepted for publication in the Proceedings of the 6th Integral Workshop "The obscured Universe", Moscow, July 3-7 2006

In this paper, we review the observational properties of two accreting X-ray pulsars, the persistent source 4U1907+09 and the transient V0332+53. Accreting X-ray pulsars are among the brightest sources in the X-ray sky and are frequently observed by Integral and other X-ray missions. Nevertheless they are still very enigmatic sources as fundamental questions on the X-ray production mechanism still remain largely unanswered. These questions are addressed by performing detailed temporal and spectral studies on several objects over a long time range.
Of vital importance is the study of cyclotron lines as they provide the only direct link to the magnetic field of the pulsar. While some objects show cyclotron lines which are extremely stable with time and with pulse phase, in other objects the lines strongly depend on the pulse phase, the luminosity of the source, or both.
Of special interest in any case are transient sources where it is possible to study the evolution of the cyclotron line and the source in general from the onset until the end of the outburst through a wide range of different luminosity states.
We present an observational review of a transient and a persistent accreting X-ray pulsar observed with Integral.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611716 [abs, ps, pdf, other] :
Title: Evidence for 1122 Hz X-Ray Burst Oscillations from the Neutron-Star X-Ray Transient XTE J1739-285
Authors: P. Kaaret, Z. Prieskorn, J.J.M. in 't Zand, S. Brandt, N. Lund, S. Mereghetti, D. Gotz, E. Kuulkers, J.A. Tomsick
Comments: To appear in ApJL, 4 pages
Note: replaced with revised version Tue, 30 Jan 2007 17:08:10 GMT (17kb)
 
astro-ph/0612216 [abs, ps, pdf, other] :
Title: Rotation at 1122 Hz and the neutron star structure
Authors: M. Bejger, P. Haensel, J.L. Zdunik
Comments: 4 pages, 3 figures, new paragraph on the constraints from the spin-up by accretion added. Accepted for publication in A&A Letters
Note: replaced with revised version Tue, 30 Jan 2007 15:27:10 GMT (34kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 1 Feb 07 01:00:14 GMT
0701875 -- 0701925 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701888 [abs, ps, pdf, other] :
Title: Pulsar's kicks and Gamma-ray bursts
Authors: X. H. Cui (PKU), H. G. Wang (GZU), R. X. Xu (PKU), G. J. Qiao (PKU)
Comments: 3 pages, 1 figure

The supernova-GRB (Gamma-ray burst) association is tested by showing the consistence of the distributions of pulsar's kick velocities and GRB energies, under the assumption that cosmic GRBs are related to supernova explosions that form pulsars. These two distributions are derived from observations, and are checked by K-S test. The deduced distribution of kick velocity from the total energy of GRBs and the observed distribution of radio pulsars are found to come from a same parent population. This result may indicate that GRBs could be really related to supernovae, and that the asymmetry of GRB fireballs would cause the kick of pulsars.

 
astro-ph/0701893 [abs, ps, pdf, other] :
Title: The Geometry of PSR B0031-07
Authors: J.M. Smits, D. Mitra, B.W. Stappers, J. Kuijpers, P. Weltevrede, A. Jessner, Y. Gupta
Comments: 15 pages, 9 figures, 8 tables, accepted for publication in A&A

PSR B0031-07 is well known to exhibit three different modes of drifting sub-pulses (mode A, B and C). It has recently been shown that in a multifrequency observation, consisting of 2700 pulses, all driftmodes were visible at low frequencies, while at 4.85 GHz only mode-A drift or non-drifting emission was detected. This suggests that modes A and B are emitted in sub-beams, rotating at a fixed distance from the magnetic axis, with the mode-B sub-beams being closer to the magnetic axis than the mode-A sub-beams. Diffuse emission between the sub-beams can account for the non-drifting emission. Using the results of an analysis of simultaneous multifrequency observations of PSR B0031-07, we set out to construct a geometrical model that includes emission from both sub-beams and diffuse emission and describes the regions of the radio emission of PSR B0031-07 at each emission frequency for driftmodes A and B. Based on the vertical spacing between driftbands, we have determined the driftmode of each sequence of drift. To restrict the model, we calculated average polarisation and intensity characteristics for each driftmode and at each frequency. The model reproduces the observed polarisation and intensity characteristics, suggesting that diffuse emission plays an important role in the emission properties of PSR B0031-07. The model further suggests that the emission heights of this pulsar range from a few kilometers to a little over 10 kilometers above the pulsar surface. We also find that the relationships between height and frequency of emission that follow from curvature radiation and from plasma-frequency emission could not be used to reproduce the observed frequency dependence of the width of the average intensity profiles.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0701145 [abs, ps, pdf, other] :
Title: The Final Fate of Binary Neutron Stars: What Happens After the Merger?
Authors: Matthew D. Duez, Yuk Tung Liu, Stuart L. Shapiro, Masaru Shibata, Branson C. Stephens
Comments: 3 pages. To appear in the Proceedings of the Eleventh Marcel Grossmann Meeting, Berlin, Germany, 23-29 July 2006, World Scientific, Singapore (2007)

The merger of two neutron stars usually produces a remnant with a mass significantly above the single (nonrotating) neutron star maximum mass. In some cases, the remnant will be stabilized against collapse by rapid, differential rotation. MHD-driven angular momentum transport eventually leads to the collapse of the remnant's core, resulting in a black hole surrounded by a massive accretion torus. Here we present simulations of this process. The plausibility of generating short duration gamma ray bursts through this scenario is discussed.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0701308 [abs, ps, pdf, other] :
Title: A Novel Mechanism for Type-I Superconductivity in Neutron Stars
Authors: James Charbonneau, Ariel Zhitnitsky
Comments: 10 pages, Additional arguments are given supporting the idea that the Abrikosov lattice will be destroyed in regions where longitudinal currents are induced
Note: replaced with revised version Wed, 31 Jan 2007 02:39:27 GMT (19kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 2 Feb 07 01:00:11 GMT
0702001 -- 0702035 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702006 [abs, ps, pdf, other] :
Title: Gamma-ray Burst UV/optical afterglow polarimetry as a probe of Quantum Gravity
Authors: Yi-Zhong Fan, Da-Ming Wei, Dong Xu
Comments: 4 pages including 3 eps figures, accepted for publication in MNRAS

A possible birefringence effect that arises in quantum gravity leads to a frequency-dependent rotation of the polarization angle of linearly polarized emission from distant sources. Here we use the UV/optical polarization data of the afterglows of GRB 020813 and GRB 021004 to constrain this effect. We find an upper limit on the Gambini & Pulin birefringence parameter $| \eta | <2\times 10^{-7}$. This limit is of 3 orders better than the previous limits from observations of AGNs and of the Crab pulsar. Much stronger limits may be obtained by the future observation of polarization of the prompt $\gamma$-rays.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


hep-ph/0607343 [abs, ps, pdf, other] :
Title: Quark matter in neutron stars within the Nambu - Jona-Lasinio model and confinement
Authors: M. Baldo, G. F. Burgio, P. Castorina, S. Plumari, D. Zappala', (Dipartimento di Fisica, Universita' di Catania, and INFN Sezione di Catania, Italy)
Comments: 5 pages,5 eps figures, title changed, references added, accepted by Phys. Rev. C (Brief Report)
Note: replaced with revised version Thu, 1 Feb 2007 09:32:37 GMT (58kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 5 Feb 07 01:00:10 GMT
0702036 -- 0702079 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702042 [abs, ps, pdf, other] :
Title: Hydrogen-Triggered Type I X-ray Bursts in a Two-Zone Model
Authors: Randall L. Cooper, Ramesh Narayan
Comments: 9 pages, 7 figures, accepted by ApJ

We use the two-zone model of Cooper & Narayan to study the onset and time evolution of hydrogen-triggered type I X-ray bursts on accreting neutron stars. At the lowest accretion rates, thermally unstable hydrogen burning ignites helium as well and produces a mixed hydrogen and helium burst. For somewhat higher accretion rates, thermally unstable hydrogen burning does not ignite helium and thus triggers only a weak hydrogen flash. The peak luminosities of weak hydrogen flashes are typically much lower than the accretion luminosity. These results are in accord with previous theoretical work. We find that a series of weak hydrogen flashes generates a massive layer of helium that eventually ignites in an energetic pure helium flash. Although previously conjectured, this is the first time such bursting behavior has been actually demonstrated in a theoretical model. For yet higher accretion rates, hydrogen burning is thermally stable and thus steadily generates a layer of helium that ultimately ignites in a pure helium flash. We find that, for a narrow range of accretion rates between the mixed hydrogen and helium burst and weak hydrogen flash regimes, unstable hydrogen burning ignites helium only after a short series of weak hydrogen flashes has generated a sufficiently deep layer of helium. These bursts have fluences that are intermediate between those of normal mixed hydrogen and helium bursts and energetic pure helium flashes.

 
astro-ph/0702049 [abs, ps, pdf, other] :
Title: Thermally Stable Nuclear Burning on Accreting White Dwarfs
Authors: Ken J. Shen, Lars Bildsten
Comments: Accepted for publication in The Astrophysical Journal, 7 pages, 4 figures

One of the challenges to increasing the mass of a white dwarf through accretion is the tendency for the accumulating hydrogen to ignite unstably and potentially trigger mass loss. It has been known for many years that there is a narrow range of accretion rates for which the hydrogen can burn stably, allowing for the white dwarf mass to increase as a pure helium layer accumulates. We first review the physics of stable burning, providing a clear explanation for why radiation pressure stabilization leads to a narrow range of accretion rates for stable burning near the Eddington limit, confirming the recent work of Nomoto and collaborators. We also explore the possibility of stabilization due to a high luminosity from beneath the burning layer. We then examine the impact of the beta-decay-limited ``hot'' CNO cycle on the stability of burning. Though this plays a significant role for accreting neutron stars, we find that for accreting white dwarfs, it can only increase the range of stably-burning accretion rates for metallicities below 0.01 solar metallicity.

 
astro-ph/0702075 [abs, ps, pdf, other] :
Title: Newborn Magnetars as sources of Gravitational Radiation: constraints from High Energy observations of Magnetar Candidates
Authors: Simone Dall'Osso (1), Luigi Stella (1) (INAF - OAR)
Comments: Proceedings of the Conference "Isolated Neutron stars: from the interior to the surface", Eds. D. Page, R. Turolla, S. Zane

Soft Gamma Repeaters and the Anomalous X-ray Pulsars are believed to contain slowly spinning "magnetars". The enormous energy liberated in the 2004 Dece 27 giant flare from SGR 1806-20, together with the likely recurrence time of such events, points to an internal magnetic field strength ~ 10^{16} G. Such strong fields are expected to be generated by a coherent alpha-Omega dynamo in the early seconds after the Neutron Star formation, if its spin period is of a few milliseconds at most. A substantial deformation of the NS is caused by such fields and a newborn millisecond-spinning magnetar would thus radiate for a few days a strong gravitational wave signal. Such a signal may be detected with Advanced LIGO-class detectors up to the distance of the Virgo cluster, where ~ 1 magnetar per year are expected to form. Recent X-ray observations reveal that SNRs around magnetar candidates do not show evidence for a larger energy content than standard SNRs (Vink & Kuiper 2006). This is at variance with what would be expected if the spin energy of the young, millisecond NS were radiated away as electromagnetic radiation andd/or relativistic particle winds and, thus, transferred quickly to the expanding gas shell. We show here that these recent findings can be reconciled with the idea of magnetars being formed with fast spins, if most of their initial spin energy is radiated thorugh GWs. In particular, we find that this occurs for essentially the same parameter range that would make such objects detectable by Advanced LIGO-class detectors up to the Virgo Cluster.

 
astro-ph/0702077 [abs, ps, pdf, other] :
Title: Constraints on the steady and pulsed VHE gamma-ray emission from observation of PSR B1951+32 / CTB 80 with the MAGIC Telescope
Authors: J. Albert, et al
Comments: 8 pages, 7 figures, submitted to ApJ

We report on VHE gamma-observations with the MAGIC telescope of the pulsar PSR B1951+32 and its associated nebula CTB 80. Our data constrain the cutoff energy of the pulsar to be <32GeV, assuming the pulsed gamma-ray emission to be exponentially cutoff. The upper limit on the flux of pulsed gamma-ray emission >75GeV is 4.3*10^-11 photons cm^-2 sec^-1 and the upper limit on the flux of steady emission >140GeV is 1.5*10^-11 photons cm^-2 sec^-1. We discuss our results in the framework of recent model predictions and other studies.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


hep-ph/0702021 [abs, ps, pdf, other] :
Title: The rigidity of crystalline color superconducting quark matter
Authors: Massimo Mannarelli, Krishna Rajagopal, Rishi Sharma
Comments: 36 pages, 5 figures
Subj-class: High Energy Physics - Phenomenology; Superconductivity

We calculate the shear modulus of crystalline color superconducting quark matter, showing that this phase of dense, but not asymptotically dense, three-flavor quark matter responds to shear stress like a very rigid solid. To evaluate the shear modulus, we derive the low energy effective Lagrangian that describes the phonons that originate from the spontaneous breaking of translation invariance by the spatial modulation of the gap parameter $\Delta$. These massless bosons describe space- and time-dependent fluctuations of the crystal structure and are analogous to the phonons in ordinary crystals. The coefficients of the spatial derivative terms of the phonon effective Lagrangian are related to the elastic moduli of the crystal; the coefficients that encode the linear response of the crystal to a shearing stress define the shear modulus. We analyze the two particular crystal structures which are energetically favored over a wide range of densities, in each case evaluating the phonon effective action and the shear modulus up to order $\Delta^2$ in a Ginzburg-Landau expansion, finding shear moduli which are 20 to 1000 times larger than those of neutron star crusts. The crystalline color superconducting phase has long been known to be a superfluid -- by picking a phase its order parameter breaks the quark-number $U(1)_B$ symmetry spontaneously. Our results demonstrate that this superfluid phase of matter is at the same time a rigid solid. We close with a rough estimate of the pinning force on the rotational vortices which would be formed embedded within this rigid superfluid upon rotation. Our results raise the possibility that (some) pulsar glitches could originate within a quark matter core deep within a neutron star.

 

Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 6 Feb 07 01:00:13 GMT
0702080 -- 0702131 received


6 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702080 [abs, ps, pdf, other] :
Title: Magnetized Hypermassive Neutron Star Collapse: a candidate central engine for short-hard GRBs
Authors: Branson C. Stephens, Matthew D. Duez, Yuk Tung Liu, Stuart L. Shapiro, Masaru Shibta
Comments: 3 pages, 1 figure, submitted to the MG11 proceedings

Hypermassive neutron stars (HMNSs) are equilibrium configurations supported against collapse by rapid differential rotation and likely form as transient remnants of binary neutron star mergers. Though HMNSs are dynamically stable, secular effects such as viscosity or magnetic fields tend to bring HMNSs into uniform rotation and thus lead to collapse. We simulate the evolution of magnetized HMNSs in axisymmetry using codes which solve the Einstein-Maxwell-MHD system of equations. We find that magnetic braking and the magnetorotational instability (MRI) both contribute to the eventual collapse of HMNSs to rotating black holes surrounded by massive, hot accretion tori and collimated magnetic fields. Such hot tori radiate strongly in neutrinos, and the resulting neutrino-antineutrino annihilation could power short-hard GRBs.

 
astro-ph/0702084 [abs, ps, pdf, other] :
Title: Modeling Pulsar Wind Nebulae
Authors: N. Bucciantini (U.C. Berkeley)
Comments: 22 pages, 7 figures, Proceedings of the 2006 COSPAR Meeting in Beijing, accepted for publication in AdSR

In the last few years, new observations by CHANDRA and XMM have shown that Pulsar Wind Nebulae present a complex but similar inner feature, with the presence of axisymmetric rings and jets, which is generally referred as {\it jet-torus structure}. Due to the rapid growth in accuracy and robustness of numerical schemes for relativistic fluid-dynamics, it is now possible to model the flow and magnetic structure of the relativistic plasma responsible for the emission. Recent results have clarified how the jet and rings are formed, suggesting that the morphology is strongly related to the wind properties, so that, in principle, it is possible to infer the conditions in the unshocked wind from the nebular emission. I will review here the current status in the modeling of Pulsar Wind Nebulae, and, in particular, how numerical simulations have increased our understanding of the flow structure, observed emission, polarization and spectral properties. I will also point to possible future developments of the present models.

 
astro-ph/0702089 [abs, ps, pdf, other] :
Title: Evaluating Spectral Models and the X-ray States of Neutron-Star X-ray Transients
Authors: Dacheng Lin, Ronald A. Remillard, Jeroen Homan (MIT Kavli Institute for Astrophysics and Space Research)
Comments: 14 pages, 15 figures, submitted to ApJ

We propose a hybrid model to fit the X-ray spectra of atoll-type X-ray transients in the soft and hard states. This model uniquely produces luminosity tracks that are proportional to T^4 for both the accretion disk and boundary layer. The model also indicates low Comptonization levels for the soft state, gaining a similarity to black holes in the relationship between Comptonization level and the strength of the continuum in the power density spectrum. The boundary layer appears small, with a surface area that is roughly constant across soft and hard states. This result is seen as a suggestion that the NS radius is smaller than its inner-most stable circular orbit.

 
astro-ph/0702097 [abs, ps, pdf, other] :
Title: Population statistics study of radio and gamma-ray pulsars in the Galactic plane
Authors: Peter L. Gonthier, Sarah A. Story, Brian D. Clow, Alice K. Harding
Comments: 6 pages, 3 figures, 1 table, accepted in Astrophysics and Space Science

We present results of our pulsar population synthesis of ordinary isolated and millisecond pulsars in the Galactic plane. Over the past several years, a program has been developed to simulate pulsar birth, evolution and emission using Monte Carlo techniques. We have added to the program the capability to simulate millisecond pulsars, which are old, recycled pulsars with extremely short periods. We model the spatial distribution of the simulated pulsars by assuming that they start with a random kick velocity and then evolve through the Galactic potential. We use a polar cap/slot gap model for $\gamma$-ray emission from both millisecond and ordinary pulsars. From our studies of radio pulsars that have clearly identifiable core and cone components, in which we fit the polarization sweep as well as the pulse profiles in order to constrain the viewing geometry, we develop a model describing the ratio of radio core-to-cone peak fluxes. In this model, short period pulsars are more cone-dominated than in our previous studies. We present the preliminary results of our recent study and the implications for observing these pulsars with GLAST and AGILE.

 
astro-ph/0702105 [abs, ps, pdf, other] :
Title: Diffusive Synchrotron Radiation from Pulsar Wind Nebulae
Authors: G. D. Fleishman, M. F. Bietenholz
Comments: 15 pages, 5 figures, accepted to MNRAS

Diffusive Synchrotron Radiation (DSR) is produced by charged particles as they random walk in a stochastic magnetic field. The spectrum of the radiation produced by particles in such fields differs substantially from those of standard synchrotron emission because the corresponding particle trajectories deviate significantly from gyration in a regular field. The Larmor radius, therefore, is no longer a good measure of the particle trajectory. In this paper we analyze a special DSR regime which arises as highly relativistic electrons move through magnetic fields which have only random structure on a wide range of spatial scales. Such stochastic fields arise in turbulent processes, and are likely present in pulsar wind nebulae (PWNe). We show that DSR generated by a single population of electrons can reproduce the observed broad-band spectra of PWNe from the radio to the X-ray, in particular producing relatively flat spectrum radio emission as is usually observed in PWNe. DSR can explain the existence of several break frequencies in the broad-band emission spectrum without recourse to breaks in the energy spectrum of the relativistic particles. The shape of the radiation spectrum depends on the spatial spectrum of the stochastic magnetic field. The implications of the presented DSR regime for PWN physics are discussed.

 
astro-ph/0702128 [abs, ps, pdf, other] :
Title: Magnetic Helicity and the Relaxation of Fossil Fields
Authors: Avery E. Broderick (1), Ramesh Narayan (1,2) ((1) Harvard-Smithsonian Center for Astrophysics, (2) Harvard University)
Comments: 10 Pages, 2 figures, submitted to MNRAS

In the absence of an active dynamo, purely poloidal magnetic field configurations are unstable to large-scale dynamical perturbations and ultimately reconnect away on Alfvenic timescales. Nevertheless, there are a number of classes of stars, including Ap stars, white dwarfs, and neutron stars which are thought to not contain active dynamos and yet do exhibit significant, large scale, surface magnetic fields. Braithwaite & Spruit (2004) have shown via simulations that the external poloidal magnetic field may be stabilized in such systems by a toroidal component in the stellar interior. We present a variational principle for computing the structure of a magnetic field within a conducting sphere surrounded by an insulating vacuum. We find a simple class of axisymmetric solutions parametrized by angular and radial quantum numbers. We discuss the implications that these may have for soft-gamma repeaters and pulsar magnetic field decay.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610883 [abs, ps, pdf, other] :
Title: A model for double notches and bifurcated components in radio profiles of pulsars and magnetars - Evidence for the parallel acceleration maser in pulsar magnetosphere
Authors: J. Dyks, B. Rudak, Joanna M. Rankin
Comments: 15 pages, 10 figures, accepted by A&A after minor changes
Note: replaced with revised version Mon, 5 Feb 2007 16:22:52 GMT (735kb)
 
gr-qc/0601029 [abs, ps, pdf, other] :
Title: Gravitomagnetic resonant excitation of Rossby modes in coalescing neutron star binaries
Authors: Éanna É. Flanagan, Étienne Racine
Comments: 23 pages, 2 figures, substantial changes to the presentation, error corrected in energy argument in Appendix B
Journal-ref: Phys. Rev. D 75, 044001 (2007)
Note: replaced with revised version Fri, 2 Feb 2007 21:47:18 GMT (62kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 7 Feb 07 01:00:11 GMT
0702132 -- 0702169 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702142 [abs, ps, pdf, other] :
Title: Orbital Evolution and orbital phase resolved spectroscopy of the HMXB pulsar 4U 1538-52 with RXTE-PCA and BeppoSAX
Authors: U. Mukherjee, H. Raichur, B. Paul, S. Naik, N. Bhatt
Comments: 7 figures, 21 Pages

We report here results from detailed timing and spectral studies of the high mass X-ray binary pulsar 4U~1538--52 over several binary periods using observations made with the Rossi X-ray Timing Explorer (RXTE) and BeppoSAX satellites. Pulse timing analysis with the 2003 RXTE data over two binary orbits confirms an eccentric orbit of the system. Combining the orbitial parameters determined from this observation with the earlier measurements we did not find any evidence of orbital decay in this X-ray binary. We have carried out orbital phase resolved spectroscopy to measure changes in the spectral parameters with orbital phase, particularly the absorption column density and the iron line flux. The RXTE-PCA spectra in the 3--20 keV energy range were fitted with a power law and a high energy cut-off alongwith a Gaussian line at $\sim$ 6.4 keV, whereas the BeppoSAX spectra needed only a power law and Gaussian emission line at $\sim$ 6.4 keV in the restricted energy range of 0.3--10.0 keV. An absorption along the line of sight was included for both the RXTE and BeppoSAX data. The variation of the free spectral parameters over the binary orbit was investigated and we found that the variation of the column density of absorbing material in the line of sight with orbital phase is in reasonable agreement with a simple model of a spherically symmetric stellar wind from the companion star.

 
astro-ph/0702157 [abs, ps, pdf, other] :
Title: On the kHz QPO frequency correlations in bright neutron star X-ray binaries
Authors: T. Belloni (INAF - Osservatorio Astronomico di Brera, Italy), M. Mendez (SRON Utrecht, the Netherlands), J. Homan (MIT Kavli Institute for Astrophysics and Space Research, USA)
Comments: Accepted for publication in MNRAS; 7 pages, 4 figures

We re-examine the correlation between the frequencies of upper and lower kHz quasi-periodic oscillations (QPO) in bright neutron-star low-mass X-ray binaries. By including the kHz QPO frequencies of the X-ray binary Cir X-1 and two accreting millisecond pulsars in our sample, we show that the full sample does not support the class of theoretical models based on a single resonance, while models based on relativistic precession or Alfven waves describe the data better. Moreover, we show that the fact that all sources follow roughly the same correlation over a finite frequency range creates a correlation between the linear parameters of the fits to any sub-sample.

 
astro-ph/0702164 [abs, ps, pdf, other] :
Title: The Nature of Dark Matter
Authors: Peter L. Biermann (1,2,3), Faustin Munyaneza (1) ((1) Max-Planck Institute for Radioastronomy, Bonn, Germany, (2) Department of Physics and Astronomy, University of Bonn, Germany, (3)Department of Physics and Astronomy, University of Alabama, USA)
Comments: 12 pages, To be published in Proceedings of the International School of Astrophysics at Ultra-high Energies, 20-27 June 2006, Erice, Sicily, Italy

Dark matter has been recognized as an essential part of matter for over 70 years now, and many suggestions have been made, what it could be. Most of these ideas have centered on Cold Dark Matter, particles that are expected in extensions of standard particle physics, such as supersymmetry. Here we explore the concept that dark matter is sterile neutrinos, a concept that is commonly referred to as Warm Dark Matter. Such particles have keV masses, and decay over a very long time, much longer than the Hubble time. In their decay they produce X-ray photons which modify the ionization balance in the early universe, increasing the fraction of molecular Hydrogen, and thus help early star formation. Sterile neutrinos may also help to understand the baryon-asymmetry, the pulsar kicks, the early growth of black holes, the minimum mass of dwarf spheroidal galaxies, as well as the shape of dark matter halos. As soon as all these tests have been quantitative in its various parameters, we may focus on the creation mechanism of these particles, and could predict the strength of the sharp X-ray emission line, expected from any large dark matter assembly. A measurement of this X-ray emission line would be definitive proof for the existence of may be called weakly interacting neutrinos, or WINs.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 8 Feb 07 01:00:12 GMT
0702170 -- 0702207 received


7 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702173 [abs, ps, pdf, other] :
Title: Dark Matter and Sterile Neutrinos
Authors: Peter L. Biermann (1,2,3), Faustin Munyaneza (1) ((1) Max Planck Institute for Radioastronomy, Germany, (2) Department of Physics and Astronomy, University of Bonn, Germany, (3) Department of Physics and Astronomy, University of Alabama, Tuscaloosa, USA)
Comments: 18 pages, To appear in Proceedings of the 11th Marcel Grossmann Meeting on General Relativity, 23-29 July 2006, Berlin, Germany

Dark matter has been recognized as an essential part of matter for over 70 years now, and many suggestions have been made, what it could be. Most of these ideas have centered on Cold Dark Matter, particles that are predicted in extensions of standard particle physics, such as supersymmetry. Here we explore the concept that dark matter is sterile neutrinos, particles that are commonly referred to as Warm Dark Matter. Such particles have keV masses, and decay over a very long time, much longer than the Hubble time. In their decay they produce X-ray photons which modify the ionization balance in the very early universe, increasing the fraction of molecular Hydrogen, and thus help early star formation. Sterile neutrinos may also help to understand the baryon-asymmetry, the pulsar kicks, the early growth of black holes, the minimum mass of dwarf spheroidal galaxies, as well as the shape and smoothness of dark matter halos. As soon as all these tests have been made quantitative in their various parameters, we may focus on the creation mechanism of these particles, and could predict the strength of the sharp X-ray emission line, expected from any large dark matter assembly. A measurement of this X-ray emission line would be definitive proof for the existence of may be called weakly interacting neutrinos, or WINs.

 
astro-ph/0702176 [abs, ps, pdf, other] :
Title: Nucleosynthesis and Remnants in Massive Stars of Solar Metallicity
Authors: S.E. Woosley (1), A. Heger (1,2) ((1)UCSC, (2)LANL)
Comments: 22 pages, 8 figures; to appear in Physics Reports, Bethe Centennial Volume

Hans Bethe contributed in many ways to our understanding of the supernovae that happen in massive stars, but, to this day, a first principles model of how the explosion is energized is lacking. Nevertheless, a quantitative theory of nucleosynthesis is possible. We present a survey of the nucleosynthesis that occurs in 32 stars of solar metallicity in the mass range 12 to 120 solar masses. The most recent set of solar abundances, opacities, mass loss rates, and current estimates of nuclear reaction rates are employed. Restrictions on the mass cut and explosion energy of the supernovae based upon nucleosynthesis, measured neutron star masses, and light curves are discussed and applied. The nucleosynthetic results, when integrated over a Salpeter initial mass function (IMF), agree quite well with what is seen in the sun. We discuss in some detail the production of the long lived radioactivities, 26Al and 60Fe, and why recent model-based estimates of the ratio 60Fe/26Al are overly large compared with what satellites have observed. A major source of the discrepancy is the uncertain nuclear cross sections for the creation and destruction of these unstable isotopes.

 
astro-ph/0702177 [abs, ps, pdf, other] :
Title: Coherence and Intermittency of Electron Density in Small-Scale Interstellar Turbulence
Authors: P.W. Terry, K.W. Smith
Comments: 30 pages, 3 figures

Spatial intermittency in decaying kinetic Alfven wave turbulence is investigated to determine if it produces non Gaussian density fluctuations in the interstellar medium. Non Gaussian density fluctuations have been inferred from pulsar scintillation scaling. Kinetic Alfven wave turbulence characterizes density evolution in magnetic turbulence at scales near the ion gyroradius. It is shown that intense localized current filaments in the tail of an initial Gaussian probability distribution function possess a sheared magnetic field that strongly refracts the random kinetic Alfven waves responsible for turbulent decorrelation. The refraction localizes turbulence to the filament periphery, hence it avoids mixing by the turbulence. As the turbulence decays these long-lived filaments create a non Gaussian tail. A condition related to the shear of the filament field determines which fluctuations become coherent and which decay as random fluctuations. The refraction also creates coherent structures in electron density. These structures are not localized. The density distribution is non Gaussian, but its fourth order moment may not differ strongly from the Gaussian value until late times when mergers reduce the number of structures.

 
astro-ph/0702180 [abs, ps, pdf, other] :
Title: Birth Kick Distributions and the Spin-Kick Correlation of Young Pulsars
Authors: C.-Y. Ng, Roger W. Romani
Comments: 37 pages, 13 figures, ApJ accepted

Evidence from pulsar wind nebula symmetry axes and radio polarization observations suggests that pulsar motions correlate with the spin directions. We assemble this evidence for young isolated pulsars and show how it can be used to quantitatively constrain birth kick scenarios. We illustrate by computing several plausible, but idealized, models where the momentum thrust is proportional to the neutrino cooling luminosity of the proto-neutron star. Our kick simulations include the effects of pulsar acceleration and spin-up and our maximum likelihood comparison with the data constrains the model parameters. The fit to the pulsar spin and velocity measurements suggests that: i) the anisotropic momentum required amounts to ~10% of the neutrino flux, ii) while a pre-kick spin of the star is required, the preferred magnitude is small 10-20rad/s, so that for the best-fit models iii) the bulk of the spin is kick-induced with $\bar \Omega$ ~120rad/s and iv) the models suggest that the anisotropy emerges on a timescale $\tau$ ~1-3s.

 
astro-ph/0702188 [abs, ps, pdf, other] :
Title: INTEGRAL and Magnetars
Authors: D. Gotz, S. Mereghetti, K. Hurley, I.F. Mirabel, P. Esposito, A. Tiengo, G. Weidenspointner, A. von Kienlin
Comments: 8 pages, 9 figures, Proceedings of the 6th INTEGRAL Workshop, Moscow, 2006 07 03-07, ESA SP-622

Thanks to INTEGRAL's long exposures of the Galactic Plane, the two brightest Soft Gamma-Ray Repeaters, SGR 1806-20 and SGR 1900+14, have been monitored and studied in detail for the first time at hard-X/soft-gamma rays. SGR 1806-20, lying close to the Galactic Centre, and being very active in the past two years, has provided a wealth of new INTEGRAL results, which we will summarise here: more than 300 short bursts have been observed from this source and their characteristics have been studied with unprecedented sensitivity in the 15-200 keV range. A hardness-intensity anticorrelation within the bursts has been discovered and the overall Number-Intensity distribution of the bursts has been determined. The increase of its bursting activity eventually led to the December 2004 Giant Flare for which a possible soft gamma-ray (>80 keV) early afterglow has been detected with INTEGRAL. The deep observations allowed us to discover the persistent emission in hard X-rays (20-150 keV) from 1806-20 and 1900+14, the latter being in quiescent state, and to directly compare the spectral characteristics of all Magnetars (two SGRs and three Anomalous X-ray Pulsars) detected with INTEGRAL.

 
astro-ph/0702195 [abs, ps, pdf, other] :
Title: Generation of Pulsar Radio Emission
Authors: G. Gogoberidze, G.Z. Machabeli, V.V. Usov
Comments: 10 pages, 1 figure, submitted to ApJ Letters

We demonstrate that nonlinear decay of obliquely propagating Langmuir waves into another Langmuir and Alfven waves is possible in a one-dimensional, highly relativistic, streaming, pair plasma. Based on this we present a new mechanism of pulsar radio emission that involves development and quasilinear relaxation of two stream instability, induced scattering of generated Langmuir waves by plasma particles and nonlinear conversion of Langmuir waves into Alfven waves. It is shown that characteristic frequency of generated Alfven waves is much less than the plasma frequency and consistent with the observational data on pulsar radio emission.

 
astro-ph/0702196 [abs, ps, pdf, other] :
Title: New Phase-coherent Measurements of Pulsar Braking Indices
Authors: Margaret A. Livingstone, Victoria M. Kaspi, Fotis P. Gavriil, Richard N. Manchester, E.V. Gotthelf, Lucien Kuiper
Comments: 7 pages, 5 figures. To be published in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface" (April 24-28, 2006, London, UK), eds. D. Page, R. Turolla, & S. Zane

Pulsar braking indices offer insight into the physics that underlies pulsar spin-down. Only five braking indices have been measured via phase-coherent timing; all measured values are less than 3, the value expected from magnetic dipole radiation. Here we present new measurements for three of the five pulsar braking indices, obtained with phase-coherent timing for PSRs J1846-0258 (n=2.65+/-0.01), B1509-58 (n=2.839+/-0.001) and B0540-69 (n=2.140+/-0.009). We discuss the implications of these results and possible physical explanations for them.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 9 Feb 07 01:00:14 GMT
0702208 -- 0702238 received


6 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702210 [abs, ps, pdf, other] :
Title: Modeling of Interstellar Scintillation Arcs from Pulsar B1133+16
Authors: Frank S. Trang, Barney J. Rickett
Comments: 14 pages, 4 figures, submitted to Astrophysical Journal

The parabolic arc phenomenon visible in the Fourier analysis of the scintillation spectra of pulsars provides a new method of investigating the small scale structure in the ionized interstellar medium (ISM). We report archival observations of the pulsar B1133+16 showing both forward and reverse parabolic arcs sampled over 14 months. These features can be understood as the mutual interference between an assembly of discrete features in the scattered brightness distribution. By model-fitting to the observed arcs at one epoch we obtain a ``snap-shot'' estimate of the scattered brightness, which we show to be highly anisotropic (axial ratio >10:1), to be centered significantly off axis and to have a small number of discrete maxima, which are coarser the speckle expected from a Kolmogorov spectrum of interstellar plasma density. The results suggest the effects of highly localized discrete scattering regions which subtend 0.1-1 mas, but can scatter (or refract) the radiation by angles that are five or more times larger.

 
astro-ph/0702220 [abs, ps, pdf, other] :
Title: Swift observations of GRB 070110: an extraordinary X-ray afterglow powered by the central engine
Authors: E. Troja, G. Cusumano, P. O'Brien, B. Zhang, B. Sbarufatti, V. Mangano, R. Willingale, G. Chincarini, J. P. Osborne, F. E. Marshall, D. N. Burrows, S. Campana, N. Gehrels, C. Guidorzi, H. A. Krimm, V. La Parola, E. W. Liang, T. Mineo, A. Moretti, K. L. Page, P. Romano, G. Tagliaferri, B. B. Zhang
Comments: 10 pages, 5 figures, submitted to ApJ

We present a detailed analysis of Swift multi-wavelength observations of GRB 070110 and its remarkable afterglow. The early X-ray light curve, interpreted as the tail of the prompt emission, displays a spectral evolution already seen in other gamma-ray bursts. The optical afterglow shows a shallow decay up to ~2 d after the burst, which is not consistent with standard afterglow models. The most intriguing feature is a very steep decay in the X-ray flux at ~20 ks after the burst, ending an apparent plateau. The abrupt drop of the X-ray light curve rules out an external shock as the origin of the plateau in this burst and implies long-lasting activity of the central engine. The temporal and spectral properties of the plateau phase point towards a continuous central engine emission rather than the episodic emission of X-ray flares. We suggest that the observed X-ray plateau is powered by a spinning down central engine, possibly a millisecond pulsar, which dissipates energy at an internal radius before depositing energy into the external shock.

 
astro-ph/0702221 [abs, ps, pdf, other] :
Title: Rotating Neutron Stars
Authors: Fridolin Weber (San Diego State University), Philip Rosenfield (San Diego State University)
Comments: 6 pages, 12 figures, paper presented at the IX International Conference on Hypernuclear and Strange Particle Physics, 10-14 October 2006, Johannes Gutenberg-Universitaet Mainz, Mainz, Germany

Because of the tremendous densities that exist in the cores of neutron stars, a significant fraction of the matter in the cores of such stars is likely to exist in the form of hyperons. Depending on spin frequency, the hyperon content changes dramatically in rotating neutron stars, as discussed in this paper.

 
astro-ph/0702228 [abs, ps, pdf, other] :
Title: Gravitational waves from relativistic neutron star mergers with nonzero-temperature equations of state
Authors: R. Oechslin, H.-T. Janka (MPI for Astrophysics, Garching, Germany)
Comments: 5 pages, 4 figures, submitted to PRL

We analyze the gravitational wave (GW) emission from our recently published set of relativistic neutron star (NS) merger simulations and determine characteristic signal features that allow one to link GW measurements to the properties of the merging binary stars. We find that the distinct peak in the GW energy spectrum that is associated with the formation of a hypermassive merger remnant has a frequency that depends strongly on the properties of the nuclear equation of state (EoS) and on the total mass of the binary system, whereas the mass ratio and the NS spins have a weak influence. If the total mass can be determined from the inspiral chirp signal, the peak frequency of the postmerger signal is a sensitive indicator of the EoS.

 
astro-ph/0702234 [abs, ps, pdf, other] :
Title: RX J1856.5-3754 as a possible Strange Star candidate
Authors: Jillian Anne Henderson (1), Dany Page (1) ((1) Instituto de Astronomia, Universidad Nacional Autonoma de Mexico)
Comments: 4 pages, 4 figures; to appear in proceedings of the conference "Isolated Neutron Stars: From the Interior to the Surface", eds. S. Zane, R. Turolla, D. Page; Astrophysics & Space Science in press

RX J1856.5-3754 has been proposed as a strange star candidate due to its very small apparent radius measured from its X-ray thermal spectrum. However, its optical emission requires a much larger radius and thus most of the stellar surface must be cold and undetectable in X-rays. In the case the star is a neutron star such a surface temperature distribution can be explained by the presence of a strong toroidal field in the crust (Perez-Azorin et al. 2006, Geppert et al. 2006). We consider a similar scenario for a strange star with a thin baryonic crust to determine if such a magnetic field induced effect is still possible.

 
astro-ph/0702235 [abs, ps, pdf, other] :
Title: Structure and cooling of compact stars
Authors: Hovik Grigorian (JINR, Dubna)
Comments: 22 pages, 9 figures, Lecture notes for the Helmholtz International Summer School on "Dense Matter in Heavy-Ion Collisions and Astrophysics", JINR, Dubna, August 21 - September 1, 2006

We study the structure and evolution of neutron stars (NS) the interiors of which are modeled using microscopic approaches and constrained by the condition that the equation of state (EoS) of matter extrapolated to high densities should not contradict known observational data from compact stars and experimental data from heavy-ion collisions (HIC). We use modern cooling simulations to extract distributions of NS masses required to reproduce those of the yet sparse data in the Temperature-Age (TA) plane. By comparing the results with a mass distribution for young, nearby NSs used in population synthesis we can sharpen the NS cooling constraints.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0702039 [abs, ps, pdf, other] :
Title: Upper limits on gravitational wave emission from 78 radio pulsars
Authors: The LIGO Scientific Collaboration: B. Abbott, et al, M. Kramer, A. G. Lyne
Comments: 21 pages

We present upper limits on the gravitational wave emission from 78 radio pulsars based on data from the third and fourth science runs of the LIGO and GEO600 gravitational wave detectors. The data from both runs have been combined coherently to maximise sensitivity. For the first time pulsars within binary (or multiple) systems have been included in the search by taking into account the signal modulation due to their orbits. Our upper limits are therefore the first measured for 56 of these pulsars. For the remaining 22, our results improve on previous upper limits by up to a factor of 10. For example, our tightest upper limit on the gravitational strain is 3.2e-25 for PSRJ1603-7202, and the equatorial ellipticity of PSRJ2124-3358 is less than 10e-6. Furthermore, our strain upper limit for the Crab pulsar is only three times greater than the fiducial spin-down limit.

 

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Astrophysics


astro-ph new abstracts, Mon, 12 Feb 07 01:00:12 GMT
0702239 -- 0702270 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702243 [abs, ps, pdf, other] :
Title: Pulsar Emission and Force-Free Electrodynamics
Authors: A. Gruzinov (CCPP, Nyu)
Comments: 6 pages

Pulsar emission should primarily come from the magnetic separatrix... Combining theory and observations, we show that force-free electrodynamics (FFE) gives an accurate description of the large-scale electromagnetic field in the magnetospheres of Crab-like pulsars. A robust prediction of FFE is the existence and stability of a singular current layer on the magnetic separatrix. We argue that most of the observed pulsar emission comes from this singular current layer.

 
astro-ph/0702246 [abs, ps, pdf, other] :
Title: Similar phenomena at different scales: Black Holes, the Sun, Gamma-ray Bursts, Supernovae, Galaxies and Galaxy Clusters
Authors: Shuang Nan Zhang
Comments: 21 pages, 13 figures, invited discourse for the 26th IAU GA, Prague, Czech Republic, Aug. 2006, to be published in Vol. 14 IAU Highlights of Astronomy, Ed. K.A. van der Hucht. Final submission will be made on Feb. 17, 2007. Criticisms, Comments and suggestions are welcome

Many similar phenomena occur in astrophysical systems with spatial and mass scales different by many orders of magnitudes. For examples, collimated outflows are produced from the Sun, proto-stellar systems, gamma-ray bursts, neutron star and black hole X-ray binaries, and supermassive black holes; various kinds of flares occur from the Sun, stellar coronae, X-ray binaries and active galactic nuclei; shocks and particle acceleration exist in supernova remnants, gamma-ray bursts, clusters of galaxies, etc. In this report I summarize briefly these phenomena and possible physical mechanisms responsible for them. I emphasize the importance of using the Sun as an astrophysical laboratory in studying these physical processes, especially the roles magnetic fields play in them; it is quite likely that magnetic activities dominate the fundamental physical processes in all these systems.
As a case study, I show that X-ray light curves from solar flares, black hole binaries and gamma-ray bursts exhibit a common scaling law of non-linear dynamical properties, over a dynamical range of several orders of magnitudes in intensities, implying that many basic X-ray emission nodes or elements are interconnected over multi-scales. A future high timing and imaging resolution solar X-ray instrument, aimed at isolating and resolving the fundamental elements of solar X-ray lightcurves, may shed new lights onto the fundamental physical mechanisms, which are common in astrophysical systems with vastly different mass and spatial scales. Using the Sun as an astrophysical laboratory, "Applied Solar Astrophysics" will deepen our understanding of many important astrophysical problems.

 
astro-ph/0702248 [abs, ps, pdf, other] :
Title: Finding Periods in High Mass X-Ray Binaries
Authors: Gordon E. Sarty, Laszlo L. Kiss, Helen M. Johnston, Richard Huziak, Kinwah Wu
Comments: Accepted: JAAVSO

This is a call for amateur astronomers who have the equipment and experience for producing high quality photometry to contribute to a program of finding periods in the optical light curves of high mass X-ray binaries (HMXB). HMXBs are binary stars in which the lighter star is a neutron star or a black hole and the more massive star is an O type supergiant or a Be type main sequence star. Matter is transferred from the ordinary star to the compact object and X-rays are produced as the the gravitational energy of the accreting gas is converted into light. HMXBs are very bright, many are brighter than 10th magnitude, and so make perfect targets for experienced amateur astronomers with photometry capable CCD equipment coupled with almost any size telescope.

 
astro-ph/0702254 [abs, ps, pdf, other] :
Title: On the Present and Future of Pulsar Astronomy
Authors: W.Becker (MPE), J.Gil (Uni. of Zielona Gora), B. Rudak (CAMK Torun)
Comments: Summary of the Joined Discussion (JD02) held at the XXVI IAU General Assembly in 2006 August in Prague. To appear in "Highlights of Astronomy, Volume 14", ed. K.A. van der Hucht

To face recent observational results obtained in multi-wavelength studies from neutron stars and pulsars with the various theoretical models and to discuss on future perspectives on neutron star astronomy we organized a Joined Discussion (JD02) during the XXVI IAU General Assembly which took place in 2006 August in Prague. More than 150 scientists took actively part in this Joint Discussion. Fourteen invited review talks were presented to view the present and future of pulsar astronomy. Fifty three poster contributions displayed new and exciting results. In this summary we give an overview of the invited review talks and contributed posters. The review talks are subject of review articles which will be published elsewhere. More information on this will be available at this http URL in the near future.

 
astro-ph/0702259 [abs, ps, pdf, other] :
Title: Bulk viscosity in kaon condensed matter
Authors: Debarati Chatterjee, Debades Bandyopadhyay
Comments: LaTeX, 26 pages, 8 figures

We investigate the effect of $K^-$ condensed matter on bulk viscosity and r-mode instability in neutron stars. The bulk viscosity coefficient due to the non-leptonic process $n \rightleftharpoons p + K^-$ is studied here. In this connection the equation of state is constructed within the framework of relativistic field theoretical models where nucleon-nucleon and kaon-nucleon interactions are mediated by the exchange of scalar and vector mesons. We find that the bulk viscosity coefficient due to the non-leptonic weak process in the condensate is suppressed by several orders of magnitude. Consequently, kaon bulk viscosity may not damp the r-mode instability in neutron stars.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0702040 [abs, ps, pdf, other] :
Title: Relativistic r-modes and shear viscosity
Authors: L. Gualtieri, J.A. Pons, J.A. Miralles, V. Ferrari
Comments: 8 pages, 7 figures, to appear in the Proceedings of the Albert Einstein Century International Conference, Paris, France, July 2005
Journal-ref: AIP Conf. Proc., 861, 2006, 638

We derive the relativistic equations for stellar perturbations, including in a consistent way shear viscosity in the stress-energy tensor, and we numerically integrate our equations in the case of large viscosity. We consider the slow rotation approximation, and we neglect the coupling between polar and axial perturbations. In our approach, the frequency and damping time of the emitted gravitational radiation are directly obtained. We find that, approaching the inviscid limit from the finite viscosity case, the continuous spectrum is regularized. Constant density stars, polytropic stars, and stars with realistic equations of state are considered. In the case of constant density stars and polytropic stars, our results for the viscous damping times agree, within a factor two, with the usual estimates obtained by using the eigenfunctions of the inviscid limit. For realistic neutron stars, our numerical results give viscous damping times with the same dependence on mass and radius as previously estimated, but systematically larger of about 60%.

 

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astro-ph new abstracts, Tue, 13 Feb 07 01:00:16 GMT
0702271 -- 0702318 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702283 [abs, ps, pdf, other] :
Title: Joint H-alpha and X-Ray Observations of Massive X-Ray Binaries. III. The Be X-ray Binaries HDE 245770 = A 0535+26 and X Persei
Authors: E. D. Grundstrom, T. S. Boyajian, C. Finch, D. R. Gies, W. Huang, M. V. McSwain, D. P. O'Brien, R. L. Riddle, M. L. Trippe, S. J. Williams, D. W. Wingert, R. A. Zaballa
Comments: accepted to ApJ, 24 pages including 3 tables & 10 figures

We present results from an H-alpha monitoring campaign of the Be X-ray binary systems HDE 245770 = A 0535+26 and X Per. We use the H-alpha equivalent widths together with adopted values of the Be star effective temperature, disk inclination, and disk outer boundary to determine the half-maximum emission radius of the disk as a function of time. The observations of HDE 245770 document the rapid spectral variability that apparently accompanied the regeneration of a new circumstellar disk. This disk grew rapidly during the years 1998 - 2000, but then slowed in growth in subsequent years. The outer disk radius is probably truncated by resonances between the disk gas and neutron star orbital periods. Two recent X-ray outbursts appear to coincide with the largest disk half-maximum emission radius attained over the last decade. Our observations of X Per indicate that its circumstellar disk has recently grown to near record proportions, and concurrently the system has dramatically increased in X-ray flux, presumably the result of enhanced mass accretion from the disk. We find that the H-alpha half-maximum emission radius of the disk surrounding X Per reached a size about six times larger than the stellar radius, a value, however, that is well below the minimum separation between the Be star and neutron star. We suggest that spiral arms excited by tidal interaction at periastron may help lift disk gas out to radii where accretion by the neutron star companion becomes more effective.

 
astro-ph/0702305 [abs, ps, pdf, other] :
Title: Generic Gravitational Wave Signals from the Collapse of Rotating Stellar Cores
Authors: Harald Dimmelmeier, Christian D. Ott, Hans-Thomas Janka, Andreas Marek, Ewald Mueller
Comments: 4 pages, 3 figures

We perform general relativistic simulations of stellar core collapse to a proto-neutron star, using a microphysical equation of state as well as an approximate description of deleptonization. We show that for a wide variety of rotation rates and profiles the gravitational wave burst signals from the core bounce are of a generic type, known as Type I in the literature. In our systematic study, using both general relativity and Newtonian gravity, we identify and individually quantify the micro- and macrophysical mechanisms leading to this result, i.e. the effects of rotation, the equation of state, and deleptonization. Such a generic type of signal templates will likely facilitate a more efficient search in current and future gravitational wave detectors of both interferometric and resonant type.

 
astro-ph/0702307 [abs, ps, pdf, other] :
Title: The Optical Polarisation of the Vela Pulsar revisited
Authors: R.P. Mignani (MSSL), S. Bagnulo (ESO), J. Dyks (NCAC), G.Lo Curto (ESO), A.Slowikowska (NCAC)
Comments: 8 pages, 4 figures

In this work we present a revised measurement of the phase-averaged optical polarisation of the Vela pulsar (PSR B0833-45), for which only one value has been published so far (Wagner & Seifert 2000). Our measurement has been obtained through an accurate reanalysis of archival polarisation observations obtained with the FORS instrument at the VLT. We have measured a phase-averaged linear polarisation degree P=9.4% +/- 4% and a position angle 146 +/- 11 deg, very close to the ones of the axis of symmetry of the X-ray arcs and jets detected by Chandra and of the pulsar proper motion.We have compared the measured phase-averaged optical polarisation with the expectations of different pulsars' magnetosphere models. We have found that all models consistently predict too large values of the phase-averaged linear polarization with respect to the observed one. This is probably a consequence of present models' limitations which neglect the contributions of various depolarisation effects. Interestingly, for the outer gap model we have found that, assuming synchrotron radiation for the optical emission, the observed polarisation position angle also implies an alignment between the pulsar rotational axis and the axis of symmetry of the X-ray arcs and jets.

 

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astro-ph new abstracts, Wed, 14 Feb 07 01:00:11 GMT
0702319 -- 0702350 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702335 [abs, ps, pdf, other] :
Title: Stochastic Gravitational Wave Background from Light Cosmic Strings
Authors: Matthew R. DePies, Craig J. Hogan (University of Washington)
Comments: 13 pages, 7 figures

Spectra of the stochastic gravitational wave backgrounds from cosmic strings are calculated and compared with present and future experimental limits. Background spectra are calculated numerically for dimensionless string tensions G mu/c^2 between 10^{-7} and 10^{-18}, and initial loop sizes as a fraction of the Hubble radius, alpha, from 0.1 to 10^{-6}. The spectra of the cosmic string backgrounds are compared with current millisecond pulsar limits and LISA sensitivity curves. For models with large stable loops (alpha=0.1), current pulsar-timing limits exclude G mu/c^2>10^{-9} and within the range of current models based on brane inflation. LISA may detect a background from strings as light as G mu/c^2 10^{-16}, corresponding to field-theory strings formed at roughly 10^{11} GeV.

 
astro-ph/0702336 [abs, ps, pdf, other] :
Title: Search for Pulsed VHE Gamma-Ray Emission from Young Pulsars with H.E.S.S
Authors: The HESS Collaboration: F.Aharonian, et al
Comments: 13 pages, 11 figures, accepted for publication in A&A

We present the results of a search for pulsed very-high-energy (VHE) gamma-ray emission from young pulsars using data taken with the H.E.S.S. imaging atmospheric Cherenkov telescope system. Data on eleven pulsars, selected according to their spin-down luminosity relative to distance, are searched for gamma-ray signals with periodicity at the respective pulsar spin period. Special analysis efforts were made to improve the sensitivity in the 100 GeV gamma-ray energy domain in an attempt to reduce the gap between satellite and ground-based gamma-ray instruments. No significant evidence for pulsed emission is found in any data set. Differential upper limits on pulsed energy flux are determined for all selected pulsars in the approximate gamma-ray energy range between 100 GeV and 50 TeV, using different limit determination methods, testing a wide range of possible pulsar light curves and energy spectra. The limits derived here imply that the magnetospheric VHE gamma-ray production efficiency in young pulsars is less than 10^-4 of the pulsar spin-down luminosity, requiring spectral turnovers for the high-energy emission of four established gamma-ray pulsars, and constrain the inverse Compton radiation component predicted by several outer gap models.

 
astro-ph/0702347 [abs, ps, pdf, other] :
Title: The Unusual Binary Pulsar PSR J1744-3922: Radio Flux Variability, Near-infrared Observation and Evolution
Authors: R. P. Breton (1), M. S. E. Roberts (2), S. M. Ransom (3), V. M. Kaspi (1), M. Durant (4), P. Bergeron (5), A. J. Faulkner (6) ((1) McGill, (2) Eureka Scientific, (3) NRAO, (4) UofT, (5) UdeM, (6) JBO)
Comments: 18 pages, 8 figures, accepted for publication of ApJ

PSR J1744-3922 is a binary pulsar exhibiting highly variable pulsed radio emission. We report on a statistical multi-frequency study of the pulsed radio flux variability which suggests that this phenomenon is extrinsic to the pulsar and possibly tied to the companion, although not strongly correlated with orbital phase. The pulsar has an unusual combination of characteristics compared to typical recycled pulsars: a long spin period (172 ms); a relatively high magnetic field strength (1.7x10^10 G); a very circular, compact orbit of 4.6 hours; and a low-mass companion (0.08 Msun). These spin and orbital properties are likely inconsistent with standard evolutionary models. We find similarities between the properties of the PSR J1744-3922 system and those of several other known binary pulsar systems, motivating the identification of a new class of binary pulsars. We suggest that this new class could result from either: a standard accretion scenario of a magnetar or a high-magnetic field pulsar; common envelope evolution with a low-mass star and a neutron star, similar to what is expected for ultra-compact X-ray binaries; or, accretion induced collapse of a white dwarf. We also report the detection of a possible K'=19.30(15) infrared counterpart at the position of the pulsar, which is relatively bright if the companion is a helium white dwarf at the nominal distance, and discuss its implications for the pulsar's companion and evolutionary history.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0702027 [abs, ps, pdf, other] :
Title: Interplay between kaon condensation and hyperons in highly dense matter
Authors: Takumi Muto
Comments: 31 pages, 16 figures

Possible coexistence and/or competition of kaon condensation with hyperons are investigated in hyperonic matter, where hyperons are mixed in the ground state of neutron-star matter. The formulation is based on the effective chiral Lagrangian for the kaon-baryon interaction and the nonrelativistic baryon-baryon interaction model. First, the onset condition of the s-wave kaon condensation realized from hyperonic matter is reexamined. It is shown that the usual assumption of the continuous phase transition is not always kept valid in the presence of the negatively charged hyperons. Second, the equation of state (EOS) of the kaon-condensed phase in hyperonic matter is discussed. In the case of the stronger kaon-baryon attractive interaction, it is shown that a local energy minimum with respect to the baryon number density appears as a result of considerable softening of the EOS due to both kaon condensation and hyperon-mixing and recovering of the stiffness of the EOS at very high densities. This result implies a possible existence of self-bound objects with kaon condensates on any scale from an atomic nucleus to a neutron star.

 

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astro-ph/0608689 [abs, ps, pdf, other] :
Title: On the role of the current loss in radio pulsar evolution
Authors: V.S.Beskin, E.E.Nokhrina
Comments: 4 pages, to appear in Astrophysics and Space Science, Special Issue: Isolated Neutron Stars. In the replaced paper we amended several misprints (coefficients in equations 12,14,15) and removed the excessive explanation for the boundary condition (4)
Note: replaced with revised version Tue, 13 Feb 2007 11:47:07 GMT (22kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 15 Feb 07 01:00:11 GMT
0702351 -- 0702390 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702364 [abs, ps, pdf, other] :
Title: Quantum Electrodynamical Photon Splitting in Magnetized Nonlinear Pair Plasmas
Authors: G. Brodin, M. Marklund, B. Eliasson, P. K. Shukla
Comments: 5 pages, 3 figures, to appear in Physical Review Letters

We present for the first time the nonlinear dynamics of quantum electrodynamic (QED) photon splitting in a strongly magnetized electron-positron (pair) plasma. By using a QED corrected Maxwell equation, we derive a set of equations that exhibit nonlinear couplings between electromagnetic (EM) waves due to nonlinear plasma currents and QED polarization and magnetization effects. Numerical analyses of our coupled nonlinear EM wave equations reveal the possibility of a more efficient decay channel, as well as new features of energy exchange among the three EM modes that are nonlinearly interacting in magnetized pair plasmas. Possible applications of our investigation to astrophysical settings, such as magnetars, are pointed out.

 
astro-ph/0702365 [abs, ps, pdf, other] :
Title: Polarized radio emission from a magnetar
Authors: M.Kramer (1), B.W.Stappers (2), A.Jessner (3), A.G.Lyne (1), C.A.Jordan (1) ((1) University of Manchester, Jodrell Bank Observatory, UK, (2) Stichting ASTRON, The Netherlands, (3) MPI fuer Radioastronomie, Germany)
Comments: accepted paged for publication in MNRAS, 15 pages, 11 figures. Figure 9 in reduced quality, full resolution preprint at this ftp URL

We present polarization observations of the radio emitting magnetar AXP J1810-197. Using simultaneous multi-frequency observations performed at 1.4, 4.9 and 8.4 GHz, we obtained polarization information for single pulses and the average pulse profile at several epochs. We find that in several respects this magnetar source shows similarities to the emission properties of normal radio pulsars while simultaneously showing striking differences. The emission is nearly 80-95% polarized, often with a low but significant degree of circular polarization at all frequencies which can be much greater in selected single pulses. The position angle swing has a low average slope of only 1 deg/deg, deviating significantly from an S-like swing as often seen in radio pulsars which is usually interpreted in terms of a rotating vector model and a dipolar magnetic field. The observed position angle is consistent at all frequencies while showing significant secular variations. On average the interpulse is less linearly polarized but shows a higher degree of circular polarization. Some epochs reveal the existence of non-orthogonal emission modes in the main pulse and systematic wiggles in the PA swing, while the interpulse shows a large variety of position angle values. We interprete many of the emission properties as propagation effects in a non-dipolar magnetic field configuration where emission from different multipole components is observed.

 
astro-ph/0702366 [abs, ps, pdf, other] :
Title: Dispersion Measure Variations and their Effect on Precision Pulsar Timing
Authors: X. P. You, G. Hobbs, W. A. Coles, R. N. Manchester, R. Edwards, M. Bailes, J. Sarkissian, J. P. W. Verbiest, W. van Straten, A. Hotan, S. Ord, F. Jenet, N. D. R. Bhat, A. Teoh
Comments: 16 pages, 6 figures, 5 tables, accepted by MNRAS

We present an analysis of the variations seen in the dispersion measures (DMs) of 20 millisecond pulsars observed as part of the Parkes Pulsar Timing Array project. We carry out a statistically rigorous structure function analysis for each pulsar and show that the variations seen for most pulsars are consistent with those expected for an interstellar medium characterised by a Kolmogorov turbulence spectrum. The structure functions for PSRs J1045-4509 and J1909-3744 provide the first clear evidence for a large inner scale, possibly due to ion-neutral damping. We also show the effect of the solar wind on the DMs and show that the simple models presently implemented into pulsar timing packages cannot reliably correct for this effect. For the first time we clearly show how DM variations affect pulsar timing residuals and how they can be corrected in order to obtain the highest possible timing precision. Even with our presently limited data span, the residuals (and all parameters derived from the timing) for six of our pulsars have been significantly improved by correcting for the DM variations.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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Astrophysics


astro-ph new abstracts, Fri, 16 Feb 07 01:00:14 GMT
0702391 -- 0702422 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702402 [abs, ps, pdf, other] :
Title: Discovery of a remarkable subpulse drift pattern in PSR B0818-41
Authors: B. Bhattacharyya (NCRA, TIFR, India), Y. Gupta (NCRA, TIFR, India), J. Gil (Zielona Gora University, Poland), M. Sendyk (Zielona Gora University, Poland)
Comments: 5 pages and 7 figures, Accepted for publication in MNRAS Letters

We report the discovery of a remarkable subpulse drift pattern in the relatively less studied wide profile pulsar, B0818-41, using high sensitivity GMRT observations. We find simultaneous occurrence of three drift regions with two different drift rates: an inner region with steeper apparent drift rate flanked on each side by a region of slower apparent drift rate. Furthermore, these closely spaced drift bands always maintain a constant phase relationship. Though these drift regions have significantly different values for the measured P2, the measured P3 value is the same and equal to 18.3 P1. We interpret the unique drift pattern of this pulsar as being created by the intersection of our line of sight (LOS) with two conal rings on the polar cap of a fairly aligned rotator (inclination angle alpha ~ 11 deg), with an ``inner'' LOS geometry (impact angle beta ~ -5.4 deg). We argue that both the rings have the same values for the carousel rotation periodicity P4 and the number of sparks Nsp. We find that Nsp is 19-21 and show that it is very likely that, P4 is the same as the measured P3, making it a truly unique pulsar. We present results from simulations of the radiation pattern using the inferred parameters, that support our interpretations and reproduce the average profile as well as the observed features in the drift pattern quite well.

 
astro-ph/0702407 [abs, ps, pdf, other] :
Title: Importance of Compton scattering for radiation spectra of isolated neutron stars with weak magnetic fields
Authors: V.Suleimanov (1,2), K.Werner (1) ((1) - IAAT, Germany, (2) - Kazan State University, Russia)
Comments: 7 pages, 1 table, 6 figures, Accepted for publication in A&A

Emergent model spectra of neutron star atmospheres are widely used to fit the observed soft X-ray spectra of different types of isolated neutron stars. We investigate the effect of Compton scattering on the emergent spectra of hot (T_eff > 10^6 K) isolated neutron stars with weak magnetic fields. In order to compute model atmospheres in hydrostatic and radiative equilibrium we solve the radiation transfer equation with the Kompaneets operator. We calculate a set of models with effective temperatures in the range 1 - 5 * 10^6 K, with two values of surface gravity (log g = 13.9 and 14.3) and different chemical compositions. Radiation spectra computed with Compton scattering are softer than those computed without Compton scattering at high energies (E > 5 keV) for light elements (H or He) model atmospheres. The Compton effect is more significant in H model atmospheres and models with low surface gravity. The emergent spectra of the hottest (T_eff > 3 * 10^6 K) model atmospheres can be described by diluted blackbody spectra with hardness factors ~ 1.6 - 1.9. Compton scattering is less important in models with solar abundance of heavy elements.

 
astro-ph/0702412 [abs, ps, pdf, other] :
Title: Experimental measurements of the O15(alpha,gamma)Ne19 reaction rate vs. observations of type I X-ray bursts
Authors: Jacob Lund Fisker, Wanpeng Tan, Joachim Goerres, Michael Wiescher, Randall L. Cooper
Comments: 7 pages, 4 figures, submitted to Astrophys. J

Neutron stars in close binary star systems often accrete matter from their companion stars. Thermonuclear ignition of the accreted material in the atmosphere of the neutron star leads to a thermonuclear explosion which is observed as an X-ray burst occurring periodically between hours and days depending on the accretion rate. The ignition conditions are characterized by a sensitive interplay between the continuously accreting fuel supply and depletion by nuclear burning via the hot CNO cycles. Therefore the ignition depends critically on the hot CNO breakout reaction O15(alpha,gamma)Ne19 that regulates the flow between the beta-limited hot CNO cycle and the rapid proton capture process. Until recently, the O15(alpha,gamma)Ne19 reaction rate was not known experimentally and the theoretical estimates carried significant uncertainties. In this paper we report on the astrophysical consequences of the first measurement of this reaction rate on the thermonuclear instability that leads to type I X-ray bursts on accreting neutron stars.

 
astro-ph/0702421 [abs, ps, pdf, other] :
Title: Abundance analysis of barium and mild barium stars
Authors: R. Smiljanic, G. F. Porto de Mello, L. da Silva
Comments: 34 pages, 18 figures, A&A accepted

High signal to noise, high resolution spectra were obtained for a sample of normal, mild barium, and barium giants. Atmospheric parameters were determined from the FeI and FeII lines. Abundances for Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, Eu, and Gd, were determined from equivalent widths and model atmospheres in a differential analysis, with the red giant Eps Vir as the standard star. The different levels of s-process overabundances of barium and mild barium stars were earlier suggested to be related to the stellar metallicity. Contrary to this suggestion, we found in this work no evidence for barium and mild barium to have a different range in metallicity. However, comparing the ratio of abundances of heavy to light s-process elements, we found some evidence that they do not share the same neutron exposure parameter. The exact mechanism controlling this difference is still not clear. As a by-product of this analysis we identify two normal red giants misclassified as mild barium stars. The relevance of this finding is discussed. Concerning the suggested nucleosynthetic effects possibly related to the s-process, for elements like Cu, Mn, V and Sc, we found no evidence for an anomalous behavior in any of the s-process enriched stars here analyzed. However, we stress that further work is still needed since a clear [Cu/Fe] vs. [Ba/H] anticorrelation exists for other s-process enriched objects.

 

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astro-ph new abstracts, Mon, 19 Feb 07 01:00:10 GMT
0702423 -- 0702449 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702426 [abs, ps, pdf, other] :
Title: Thermal emission from isolated neutron stars: theoretical and observational aspects
Authors: Vyacheslav E. Zavlin
Comments: Review lecture given at the 363-rd Heraeus Seminar on Neutron Stars and Pulsars held on May 14-19, 2006 in Bad Honnef (Germany); to be published as a Springer Lecture Notes; 37 pages, 14 figures; comments are very welcome

The possibility for direct investigation of thermal emission from isolated neutron stars was opened about 25 years ago with the launch of the first X-ray observatory, Einstein. A significant contribution to this study was provided by ROSAT in 1990's. The outstanding capabilities of the currently operating observatories, Chandra and XMM-Newton, have greatly increased the potential to observe and analyze thermal radiation from the neutron star surfaces. Confronting observational data with theoretical models of thermal emission, presumably formed in neutron star atmospheres, allows one to infer the surface temperatures, magnetic fields, chemical composition, and neutron star masses and radii. This information, supplemented with model equations of state and neutron star cooling models, provides an opportunity to understand the fundamental properties of the superdense matter in the neutron star interiors. I review the current status and most important results obtained from modeling neutron star thermal emission and present selected Chandra and XMM-Newton results on thermal radiation from various types of these objects: ordinary radio pulsars with ages ranging from about 2 kyr to 20 Myr (J1119-6127, Vela, B1706-44, J0538+2817, B2334+61, B0656+14, B1055-52, Geminga, B0950+08, J2043+2740), millisecond pulsars (J0030+0451, J2124-3358, J1024-0719, J0437-4715), putative pulsars (CXOU J061705.3+222127, RX J0007.0+7302), central compact objects in supernova remnats (in particular, 1E 1207.4-5209), and isolated radio-quiet neutron stars.

 
astro-ph/0702440 [abs, ps, pdf, other] :
Title: The effect of Pulse profile evolution on Pulsar Dispersion Measure
Authors: Amrit Lal Ahuja (1), Dipanjan Mitra (2), Yashwant Gupta (2) ((1) Inter-University Centre for Astronomy and Astrophysics, Pune, India, (2) National Center for Radio Astrophysics, TIFR, Pune, India)
Comments: 14 pages, 14 figures, 5 tables, to be published in MNRAS

In an earlier paper (Ahuja, et al, 2005), based on simultaneous multi-frequency observations with the Giant Metrewave Radio Telescope (GMRT), we reported the variation of pulsar dispersion measures (DMs) with frequency. A few different explanations are possible for such frequency dependence, and a possible candidate is the effect of pulse shape evolution on the DM estimation technique. In this paper we describe extensive simulations we have done to investigate the effect of pulse profile evolution on pulsar DM estimates. We find that it is only for asymmetric pulse shapes that the DM estimate is significantly affected due to profile evolution with frequency. Using multi-frequency data sets from our earlier observations, we have carried out systematic analyses of PSR B0329+54 and PSR B1642-03. Both these pulsars have central core dominated emission which does not show significant asymmetric profile evolution with frequency. Even so, we find that the estimated DM shows significant variation with frequency for these pulsars. We also report results from new, simultaneous multi-frequency observations of PSR B1133+16 carried out using the GMRT in phased array mode. This pulsar has an asymmetric pulse profile with significant evolution with frequency. We show that in such a case, amplitude of the observed DM variations can be attributed to profile evolution with frequency. We suggest that genuine DM variations with frequency could arise due to propagation effects through the interstellar medium and/or the pulsar magnetosphere.

 
astro-ph/0702441 [abs, ps, pdf, other] :
Title: GRB Precursors in the Fallback Collapsar Scenario
Authors: Xiang-Yu Wang, Peter Meszaros
Comments: 6 pages, submitted to ApJ

Precursor emission has been observed in a non-negligible fraction of gamma-ray bursts, the time gap between the precursor and the main burst extending up to hundreds of seconds in some cases, such as in GRB041219A, GRB050820A and GRB060124. We have investigated the maximum possible time gaps arising from the jet propagation inside the progenitor star, in models which assume that the precursor is produced by the jet bow shock or the cocoon breaking out of the progenitor. Due to the pressure drop ahead of the jet head after it reaches the stellar surface, a rarefaction wave propagates back into the jet at the sound speed, which re-accelerates the jet to a relativistic velocity and therefore limits the gap period to within about ten seconds. This scenario therefore cannot explain gaps which are hundreds of seconds long. Instead, we ascribe such long time gaps to the behavior of the central engine, and suggest a fallback collapsar scenario for these bursts. In this scenario, the precursor is produced by a weak jet formed during the initial core collapse, possibly related to MHD process associated with a short-lived proto-neutron star, while the main burst is produced by a stronger jet fed by the fallback disk accreting onto the black hole resulting from the collapse of the neutron star. We have examined the propagation times of the weak precursor jet through the stellar progenitor. We find that the initial weak jet can break out of the progenitor in a time less than ten seconds provided that it has a moderately high relativistic Lorentz factor (Gamma>10). The longer time gap following this is dictated by the fall-back timescale, which is long enough for the exit channel to close after the precursor activity ceases, allowing for the collimation of the main jet by the cocoon pressure as it propagates outward.

 

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astro-ph new abstracts, Tue, 20 Feb 07 01:00:12 GMT
0702450 -- 0702493 received


6 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702453 [abs, ps, pdf, other] :
Title: Energy dependent ~100 \mu s time lags as observational evidence of Comptonization effects in the neutron star plasma environment
Authors: Maurizio Falanga, Lev Titarchuk
Comments: 4 pages, 3 figures, ApJ accepted

We present a Comptonization model for the observed properties of the energy-dependent soft/hard time lags and pulsed fraction (amplitude) associated with the pulsed emission of a neutron star (NS). We account for the soft lags by downscattering of hard X-ray photons in the relatively cold plasma of the disk or NS surface. A fraction of the soft X-ray photons coming from the disk or NS surface upscatter off hot electrons in the accretion column. This effect leads to hard lags as a result of thermal Comptonization of the soft photons. This model reproduces the observed soft and hard lags due to the down- and upscattered radiation as a function of the electron number densities of the reflector, n_{e}^{ref}, and the accretion column, n_{e}^{hot}. In the case of the accretion-powered millisecond pulsars IGR J00291+5934, XTE J1751-305, and SAX J1808.4-3658, the observed time lags agree well with the model. Soft lags are observed only if n_e^{ref} << n_e^{hot}. Scattering of the pulsed emission in the NS environment may account for the observed time lags as a non-monotonic function of energy. The time lag measurements can be used as a probe of the innermost parts of the NS and accretion disk. We determine the upper and lower limits of the density variation in this region using the observed time lags. The observed energy-dependent pulsed amplitude allows us to infer a variation of the Thomson optical depth of the Compton cloud in which the accretion column is embedded.

 
astro-ph/0702454 [abs, ps, pdf, other] :
Title: Accreting X-ray millisecond pulsars observed with INTEGRAL
Authors: Maurizio Falanga
Comments: 8 pages, 7 figures, 1 table, accepted for publication in ESA SP-622. Proceeding of the 6th INTEGRAL Workshop, July 3-7, 2006 Moscow, Russia

I review the properties of three X-ray accreting millisecond pulsars observed with INTEGRAL. Out of seven recently discovered accretion-powered pulsars (one discovered by INTEGRAL), three were observed with the INTEGRAL satellite up to 300 keV. Detailed timing and spectral results will be presented, including data obtained during the most recent outburst of the pulsar HETE J1900.1-2455. Accreting X-ray millisecond pulsars are key systems to understand the spin and accretion history of neutron stars. They are also a good laboratory in which to study the source spectra, pulse profile, and phase shift between X-ray pulses in different energy ranges which give additional information of the X-ray production processes and emission environment.

 
astro-ph/0702472 [abs, ps, pdf, other] :
Title: Diversity of the Supernova - Gamma-Ray Burst Connection
Authors: K. Nomoto, N. Tominaga, M. Tanaka, K. Maeda, T. Suzuki, J.S. Deng, P.A. Mazzali
Comments: 16 pages, 12 figures. To be published in the proceedings of the conference "SWIFT and GRBs: Unveiling the Relativistic Universe", Venice, June 5-9, 2006. To appear in "Il Nuovo Cimento"

The connection between the long Gamma Ray Bursts (GRBs) and Type Ic Supernovae (SNe) has revealed interesting diversity. We review the following types of the GRB-SN connection. (1) GRB-SNe: The three SNe all explode with energies much larger than those of typical SNe, thus being called Hypernovae (HNe). They are massive enough for forming black holes. (2) Non-GRB HNe/SNe: Some HNe are not associated with GRBs. (3) XRF-SN: SN 2006aj associated with X-Ray Flash 060218 is dimmer than GRB-SNe and has very weak oxygen lines. Its progenitor mass is estimated to be small enough to form a neutron star rather than a black hole. (4) Non-SN GRB: Two nearby long GRBs were not associated SNe. Such ``dark HNe'' have been predicted in this talk (i.e., just before the discoveries) in order to explain the origin of C-rich (hyper) metal-poor stars. This would be an important confirmation of the Hypernova-First Star connection. We will show our attempt to explain the diversity in a unified manner with the jet-induced explosion model.

 
astro-ph/0702476 [abs, ps, pdf, other] :
Title: Effects of QCD phase transition on gravitational radiation from two-dimensional collapse and bounce of massive stars
Authors: Nobutoshi Yasutake, Kei Kotake, Masa-aki Hashimoto, Shoichi Yamada
Comments: 12 pages, 12 figures. Resubmitted to Phys.Rev.D

We perform two-dimensional, magnetohydrodynamical core-collapse simulations of massive stars accompanying the QCD phase transition. We study how the phase transition affects the gravitational waveforms near the epoch of core-bounce. As for initial models, we change the strength of rotation and magnetic fields. Particularly, the degree of differential rotation in the iron core (Fe-core) is changed parametrically. As for the microphysics, we adopt a phenomenological equation of state above the nuclear density, including two parameters to change the hardness before the transition. We assume the first order phase transition, where the conversion of bulk nuclear matter to a chirally symmetric quark-gluon phase is described by the MIT bag model. Based on these computations, we find that the phase transition can make the maximum amplitudes larger up to $\sim$ 10 percents than the ones without the phase transition. On the other hand, the maximum amplitudes become smaller up to $\sim$ 10 percents owing to the phase transition, when the degree of the differential rotation becomes larger. We find that even extremely strong magnetic fields $\sim 10^{17}$ G in the protoneutron star do not affect these results.

 
astro-ph/0702477 [abs, ps, pdf, other] :
Title: IGR J18483-0311: an accreting X-ray pulsar observed by INTEGRAL
Authors: V. Sguera, A. B. Hill, A. J. Bird, A. J. Dean, A. Bazzano, P. Ubertini, N. Masetti, R. Landi, A. Malizia, D. J. Clark, M. Molina
Comments: accepted for publication in A&A, 10 pages, 17 figures, 4 tables

IGR J18483-0311 is a poorly known transient hard X-ray source discovered by INTEGRAL during observations of the Galactic Center region performed between 23--28 April 2003. Aims: To detect new outbursts from IGR J18483-0311 using INTEGRAL and archival Swift XRT observations and finally to characterize the nature of this source using the optical/near-infrared (NIR) information available through catalogue searches. Results: We report on 5 newly discovered outbursts from IGR J18483-0311 detected by INTEGRAL.For two of them it was possible to constrain a duration of the order of a few days. The strongest outburst reached a peak flux of 120 mCrab (20--100 keV): its broad band JEM--X/ISGRI spectrum (3--50 keV) is best fitted by an absorbed cutoff power law with photon index=1.4+/-0.3, cutoff energy of ~22 keV and Nh ~9x10^22 cm^-2. Timing analysis of INTEGRAL data allowed us to identify periodicities of 18.52 days and 21.0526 seconds which are likely the orbital period of the system and the spin period of the X-ray pulsar respectively. Swift XRT observations of IGR J18483$-$0311 provided a very accurate source position which strongly indicates a highly reddened star in the USNO--B1.0 and 2MASS catalogues as its possible optical/NIR counterpart. Conclusions: The X-ray spectral shape, the periods of 18.52 days and 21.0526 seconds, the high intrinsic absorption, the location in the direction of the Scutum spiral arm and the highly reddened optical object as possible counterpart, all favour the hypothesis that IGR J18483-0311 is a HMXB with a neutron star as compact companion. The system is most likely a Be X-ray binary, but a Supergiant Fast X-ray Transient nature can not be entirely excluded.

 
astro-ph/0702490 [abs, ps, pdf, other] :
Title: Discovery of a flux-related change of the cyclotron line energy in Her X-1
Authors: R.Staubert, N.I.Shakura, K.Postnov, J.Wilms, R.E.Rothschild, W.Coburn, L.Rodina, D.Klochkov
Comments: 4 pages, 2 figures, accepted by A&A Letters

We present the results of ten years of repeated measurements of the Cyclotron Resonance Scattering Feature (CRSF) in the spectrum of the binary X-ray pulsar Her X-1 and report the discovery of a positive correlation of the centroid energy of this absorption feature in pulse phase averaged spectra with source luminosity.Our results are based on a uniform analysis of observations bythe RXTE satellite from 1996 to 2005, using sufficiently long observations of 12 individual 35-day Main-On states of the source. The mean centroid energy E_c of the CRSF in pulse phase averaged spectra of Her X-1 during this time is around 40 keV, with significant variations from one Main-On state to the next. We find that the centroid energy of the CRSF in Her X-1 changes by ~5% in energy for a factor of 2 in luminosity. The correlation is positive, contrary to what is observed in some high luminosity transient pulsars. Our finding is the first significant measurement of a positive correlation between E_c and luminosity in any X-ray pulsar. We suggest that this behaviour is expected in the case of sub-Eddington accretion and present a calculation of a quantitative estimate, which is very consistent with the effect observed in Her X-1.We urge that Her X-1 is regularly monitored further and that other X-ray pulsars are investigated for a similar behaviour.

 

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astro-ph new abstracts, Wed, 21 Feb 07 01:00:10 GMT
0702494 -- 0702540 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702512 [abs, ps, pdf, other] :
Title: Polarization of the Crab Nebula with disordered magnetic components
Authors: Yuji Nakamura, Shinpei Shibata
Comments: 7 pages, 25 figures, submitted to MNRAS

In this paper, we present an expanding disc model to derive polarization properties of the Crab nebula. The distribution function of the plasma and the energy density of the magnetic field are prescribed as function of the distance from the pulsar by using the model by Kennel and Coroniti (1984) with $\sigma = 0.003$, where $\sigma$ is the ratio of Poynting flux to the kinetic energy flux in the bulk motion just before the termination shock. Unlike previous models, we introduce disordered magnetic field, which is parameterized by the fractional energy density of the disordered component. Flow dynamics is not solved. The mean field is toroidal. Averaged polarization degree over the disc is obtained as a function of inclination angle and fractional energy density of the disordered magnetic field. It is found for the Crab that the disordered component has about 60 percent of the magnetic field energy. This value is also supported by the facts that the disc appears not `lip-shape' but as `rings' in the intensity map as was observed, and that the highest polarization degree of $\sim 40$ percent is reproduced for rings, being consistent with the observation. We suggest that because the disordered field contributes rather pressure than tension, the pinch force may be over-estimated in previous relativistic magnetohydrodynamic simulations. Disruption of the toroidal magnetic field with alternating direction, which is proposed by Lyubarski (2003), may actually takes place. The relativistic flow speed, which is indicated by the front-back contrast, can be detected in asymmetry in distributions of the position angle and depolarization.

 
astro-ph/0702528 [abs, ps, pdf, other] :
Title: Long-term developments in Her X-1: Correlation between the histories of the 35 day turn-on cycle and the 1.24 sec pulse period
Authors: R. Staubert, S. Schandl, D. Klochkov, J Wilms, K. Postnov, N. Shakura
Comments: 6 pages, 4 figures, In: The transient Milky Way: a perspective for MIRAX, AIP Conf. Proc. 840 (2006) 65-70
Journal-ref: AIP Conf. Proc. 2006

We have studied the long-term (1971-2005) behaviour of the 1.24 sec pulse period and the 35 day precession period of Her X-1 and show that both periods vary in a highly correlated way (see also Staubert et al. 1997 and 2000). When the spin-up rate decreases, the 35 day turn-on period shortens.This correlation is most evident on long time scales (~2000 days),e.g.around four extended spin-down episodes, but also on shorter time scales (a few 100 days) on which quasi-periodic variations are apparent. We argue that the likely common cause is variations of the mass accretion rate onto the neutron star.The data since 1991 allow a continuous sampling and indicate a lag between the turn-on behaviour and the spin behaviour, in the sense that changes are first seen in the spin, about one cycle later in the turn-on. Both the coronal wind model (Schandl & Meyer 1994) as well as the stream-disk model (Shakura et al.999) predict this kind of behaviour.

 
astro-ph/0702533 [abs, ps, pdf, other] :
Title: Hybrid protoneutron stars within a static approach
Authors: O. E. Nicotra
Comments: 5 pages, 3 figures, Prepared for XI Convegno su Problemi di Fisica Nucleare Teorica (Cortona 2006), Cortona, Italy, 11-14 Oct 2006

We study the hadron-quark phase transition in the interior of protoneutron stars. For the hadronic sector, we use a microscopic equation of state involving nucleons and hyperons derived within the finite-temperature Brueckner-Bethe-Goldstone many-body theory, with realistic two-body and three-body forces. For the description of quark matter, we employ the MIT bag model both with a constant and a density-dependent bag parameter. We calculate the structure of protostars within a static approach. In particular we focus on a suitable temperature profile, suggested by dynamical calculations, which plays a fundamental role in determining the value of the minimum gravitational mass. The maximum mass instead depends only upon the equation of state employed.

 
astro-ph/0702539 [abs, ps, pdf, other] :
Title: Simulations of Magnetically-Driven Supernova and Hypernova Explosions in the Context of Rapid Rotation
Authors: Adam Burrows, Luc Dessart, Eli Livne, Christian D. Ott, Jeremiah Murphy
Comments: 26 pages, including 16 color figures; submitted to the Astrophysical Journal February 20, 2007; higher-resolution figures available at this http URL

We present here the first 2D rotating, multi-group, radiation magnetohydrodynamics (RMHD) simulations of supernova core collapse, bounce, and explosion. In the context of rapid rotation, we focus on the dynamical effects of magnetic stresses and the creation and propagation of MHD jets. We find that a quasi-steady state can be quickly established after bounce, during which a well-collimated MHD jet is maintained by continuous pumping of power from the differentially rotating core. If the initial spin period of the progenitor core is $\sles$ 2 seconds, the free energy reservoir in the secularly evolving protoneutron star is adequate to power a supernova explosion, and may be enough for a hypernova. The jets are well collimated by the infalling material and magnetic hoop stresses, and maintain a small opening angle. We see evidence of sausage instabilities in the emerging jet stream. Neutrino heating is sub-dominant in the rapidly rotating models we explore, but can contribute 10$-$25% to the final explosion energy. Our simulations suggest that even in the case of modest or slow rotation, a supernova explosion might be followed by a secondary, weak MHD jet explosion, which, because of its weakness may to date have gone unnoticed in supernova debris. Furthermore, we suggest that the generation of a non-relativistic MHD precursor jet during the early protoneutron star/supernova phase is implicit in both the collapsar and "millisecond magnetar" models of GRBs. The multi-D, multi-group, rapidly rotating RMHD simulations we describe here are a start along the path towards more realistic simulations of the possible role of magnetic fields in some of Nature's most dramatic events.

 

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astro-ph new abstracts, Thu, 22 Feb 07 01:00:12 GMT
0702541 -- 0702582 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702546 [abs, ps, pdf, other] :
Title: Probing Dark Matter Substructure with Pulsar Timing
Authors: E. R. Siegel, M. P. Hertzberg, J. N. Fry
Comments: 8 pages, 4 figures, submitted to MNRAS

We demonstrate that pulsar timing measurements may be able to detect the presence of dark matter substructure within our own galaxy. As dark matter substructure transits near the line-of-sight between a pulsar and an observer, the change in the gravitational field will result in a delay of the light-travel-time of photons. We calculate the effect of this delay due to transiting dark matter substructure and find that the effect on pulsar timing ought to be observable for a wide range of substructure masses and density profiles. We find that transiting dark matter substructure with masses above 0.01 solar masses ought to be detectable at present by these means. With small improvements, this method may be able to distinguish between baryonic, thermal non-baryonic, and non-thermal non-baryonic types of dark matter. Additionally, information about structure formation on small scales and the density profiles of galactic dark matter substructure can be extracted via this method.

 
astro-ph/0702571 [abs, ps, pdf, other] :
Title: Magnetospheric particle acceleration and X-ray emission of pulsars
Authors: Sevinc O. Tagieva (Academy of Science, Physics Institute, Baku), Askin Ankay (Bogazici University, Physics Department, Istanbul), Arzu M. Ankay (Bogazici University, Physics Department, Istanbul)
Comments: 20 pages (4 figures, 1 table), submitted to International Journal of Modern Physics D

The available data on isolated X-ray pulsars, their wind nebulae, and the supernova remnants which are connected to some of these sources are analyzed. It is shown that electric fields of neutron stars tear off charged particles from the surface of neutron star and trigger the acceleration of particles. The charged particles are accelerated mainly in the field of magneto-dipole radiation wave. Power and energy spectra of the charged particles depend on the strength of the magneto-dipole radiation. Therefore, the X-ray radiation is strongly dependent on the rate of rotational energy loss and weakly dependent on the electric field intensity. Coulomb interaction between the charged particles is the main factor for the energy loss and the X-ray spectra of the charged particles.

 

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astro-ph new abstracts, Fri, 23 Feb 07 01:00:13 GMT
0702583 -- 0702613 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702586 [abs, ps, pdf, other] :
Title: Searching for primordial black hole dark matter with pulsar timing arrays
Authors: Naoki Seto, Asantha Cooray
Comments: 4 pages, 2 figures, Accepted for publication in ApJL

We discuss the possibility of detecting the presence of primordial black holes (PBHs), such as those that might account for galactic dark matter, using modification of pulsar timing residuals when PBHs pass within ~1000 AU and impart impulse accelerations to the Earth. With this technique, PBHs with masses around 10^{25} g (~0.1 lunar mass) can be detected. Currently, the constraints on the abundance of such dark matter candidates are weak. A 30 year-long monitoring campaign with the proposed Square Kilometer Array (SKA) can rule out a PBH fraction more than ~1/10 in the solar neighborhood in the form of dark matter with mass ~10^{25} g.

 
astro-ph/0702598 [abs, ps, pdf, other] :
Title: SGR1806-20: evidence for a superstrong Magnetic Field from Quasi Periodic Oscillations
Authors: M. Vietri, L. Stella, G. Israel
Comments: Accepted for publication in the Astrophysical Journal, Part I

Fast Quasi-Periodic Oscillations (QPOs, frequencies of $\sim 20 - 1840$ Hz) have been recently discovered in the ringing tail of giant flares from Soft Gamma Repeaters (SGRs), when the luminosity was of order $10^{41}-10^{41.5}$ erg/s. These oscillations persisted for many tens of seconds, remained coherent for up to hundreds of cycles and were observed over a wide range of rotational phases of the neutron stars believed to host SGRs. Therefore these QPOs must have originated from a compact, virtually non-expanding region inside the star's magnetosphere, emitting with a very moderate degree of beaming (if at all). The fastest QPOs imply a luminosity variation of $\Delta L/\Delta t \simeq 6 \times 10^{43}$ erg s$^{-2}$, the largest luminosity variation ever observed from a compact source. It exceeds by over an order of magnitude the usual Cavallo-Fabian-Rees (CFR) luminosity variability limit for a matter-to-radiation conversion efficiency of 100%. We show that such an extreme variability can be reconciled with the CFR limit if the emitting region is immersed in a magnetic field $\gtrsim 10^{15}$ G at the star surface, providing independent evidence for the superstrong magnetic fields of magnetars.

 

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astro-ph/0702365 [abs, ps, pdf, other] :
Title: Polarized radio emission from a magnetar
Authors: M.Kramer (1), B.W.Stappers (2), A.Jessner (3), A.G.Lyne (1), C.A.Jordan (1) ((1) University of Manchester, Jodrell Bank Observatory, UK, (2) Stichting ASTRON, The Netherlands, (3) MPI fuer Radioastronomie, Germany)
Comments: accepted for publication in MNRAS, 15 pages, 11 figures. Figure 9 in reduced quality, full resolution preprint at this ftp URL, typos fixed
Note: replaced with revised version Wed, 21 Feb 2007 23:58:35 GMT (1202kb)
 

Astrophysics authors/titles "new"

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astro-ph new abstracts, Mon, 26 Feb 07 01:00:11 GMT
0702614 -- 0702641 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702616 [abs, ps, pdf, other] :
Title: Polarized radio emission from the magnetar XTE J1810-197
Authors: F. Camilo (Columbia), J. Reynolds (ATNF), S. Johnston (ATNF), J. P. Halpern (Columbia), S. M. Ransom (NRAO), W. van Straten (U. Texas Brownsville)
Comments: Accepted for publication in ApJ Letters. Six pages with 4 figures

We have used the Parkes radio telescope to study the polarized emission from the anomalous X-ray pulsar XTE J1810-197 at frequencies of 1.4, 3.2, and 8.4 GHz. We find that the pulsed emission is nearly 100% linearly polarized. The position angle of linear polarization varies gently across the observed pulse profiles, varying little with observing frequency or time, even as the pulse profiles have changed dramatically over a period of 7 months. In the context of the standard pulsar "rotating vector model," there are two possible interpretations of the observed position angle swing coupled with the wide profile. In the first, the magnetic and rotation axes are substantially misaligned and the emission originates high in the magnetosphere, as seen for other young radio pulsars, and the beaming fraction is large. In the second interpretation, the magnetic and rotation axes are nearly aligned and the line of sight remains in the emission zone over almost the entire pulse phase. We deprecate this possibility because of the observed large modulation of thermal X-ray flux. We have also measured the Faraday rotation caused by the Galactic magnetic field, RM = +77 rad/m^2, implying an average magnetic field component along the line of sight of 0.5 microG.

 
astro-ph/0702624 [abs, ps, pdf, other] :
Title: The hard X-ray tails in neutron star low mass X-ray binaries: BeppoSAX observations and possible theoretical explanation of the GX 17+2 case
Authors: R. Farinelli, L. Titarchuk, F. Frontera
Comments: 6 pages, 3 figures, Accepted for publication in ApJ

We report results of a new spectral analysis of two BeppoSAX observations of the Z source GX 17+2. In one of the two observations the source exhibits a powerlaw-like hard (> 30 keV) X-ray tail which was described in a previous work by a hybrid Comptonization model. Recent high-energy observations with INTEGRAL of a sample of Low Mass X-Ray Binaries including both Z and atoll classes have shown that bulk (dynamical) Comptonization of soft photons can be a possible alternative mechanism for producing hard X-ray tails in such systems. We start from the INTEGRAL results and we exploit the broad-band capability of BeppoSAX to better investigate the physical processes at work. We use GX 17+2 as a representative case. Moreover, we suggest that weakening (or disappearance) of the hard X-ray tail can be explained by increasing radiation pressure originated at the surface of the neutron star (NS). As a result the high radiation pressure stops the bulk inflow and consequently this radiation feedback of the NS surface leads to quenching the bulk Comptonization.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611145 [abs, ps, pdf, other] :
Title: Modelling mid-Z element atmospheres for strongly-magnetized neutron stars
Authors: Kaya Mori (1,2), Wynn C.G. Ho (3,4) ((1) University of Toronto, (2) CITA, (3) Harvard-Smithsonian CfA, (4) MIT)
Comments: 16 pages, 22 figures, accepted for publication in MNRAS
Note: replaced with revised version Fri, 23 Feb 2007 12:53:57 GMT (300kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 27 Feb 07 01:00:12 GMT
0702642 -- 0702690 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702648 [abs, ps, pdf, other] :
Title: Observing cosmic string loops with gravitational lensing surveys
Authors: Katherine J. Mack, Daniel H. Wesley, Lindsay J. King
Comments: 18 pages, 3 figures

We show that the existence of cosmic strings can be strongly constrained by the next generation of gravitational lensing surveys at radio frequencies. We focus on cosmic string loops, which we expect to be far more numerous than long (horizon-sized) strings, as suggested by simulations. Using simple models of the loop population and minimal assumptions about the lensing cross-section per loop, we estimate the optical depth to lensing and show that extant radio surveys such as CLASS have already ruled out a portion of the cosmic string model parameter space. Future radio interferometers, such as LOFAR and especially SKA, may constrain $G\mu/c^2 < 10^{-9}$ in some regions of parameter space, outperforming current constraints from pulsar timing and the CMB by up to two orders of magnitude. A fundamental advantage of this approach is that it is based on direct detections of cosmic strings; whereas lensing requires only that the loop have a mass, other constraints must rely on estimates of theoretical uncertainties such as the gravitational wave emission of loops or the population dynamics of string networks. This difference is essential since the properties of cosmic strings are essentially unknown.

 
astro-ph/0702671 [abs, ps, pdf, other] :
Title: Do Black Holes End up as Quark Stars ?
Authors: R.K.Thakur
Comments: 6 pages

The possibility of the existence of quark stars has been discussed by several authors since 1970. Recently, it has been pointed out that two putative neutron stars, RXJ 1856.5 - 3754 in Corona Australis and 3C58 in Cassiopeia are too small and too dense to be neutron stars; they show evidence of being quark stars. Apart from these two objects, there are several other compact objects which fit neither in the category of neutron stars nor in that of black holes. It has been suggested that they may be quark stars.In this paper it is shown that a black hole cannot collapse to a singularity, instead it may end up as a quark star. In this context it is shown that a gravitationally collapsing black hole acts as an ultrahigh energy particle accelerator, hitherto inconceivable in any terrestrial laboratory, that continually accelerates particles comprising the matter in the black hole. When the energy \textit{E} of the particles in the black hole is $\geq 10^{2}$GeV, or equivalently the temperature \textit{T} of the matter in the black holes is $\geq 10^{15}$K, the entire matter in the black hole will be converted into quark-gluon plasma permeated by leptons. Since quarks and leptons are spin 1/2 particles,they are governed by Pauli's exclusion principle. Consequently, one of the two possibilities will occur; either Pauli's exclusion principle would be violated and the black hole would collapse to a singularity, or the collapse of the black hole to a singularity would be inhibited by Pauli's exclusion principle, and the black hole would eventually explode with a mini bang of a sort. After explosion, the remnant core would stabilize as a quark star.

 
astro-ph/0702676 [abs, ps, pdf, other] :
Title: Investigation for the puzzling abundance pattern of the neutron-capture elements in the ultra metal-poor star: CS 30322-023
Authors: W. Y. Cui (1 and 2), B. Zhang (1 and 2), K. Ma (1), L. Zhang (3) ((1) Department of Physics, Hebei Normal University, China, (2) National Astronomical observatories, Chinese Academy of Sciences, China, (3) Department of Modern Physics, University of Science and Technology of China, China)
Comments: 13 pages, 2 figures
Journal-ref: ApJ 657 (2007) 1037

The s-enhanced and very metal-poor star CS 30322-023 shows a puzzling abundance pattern of the neutron-capture elements, i.e. several neutron-capture elements such as Ba, Pb etc. show enhancement, but other neutron-capture elements such as Sr, Eu etc. exhibit deficient with respect to iron. The study to this sample star could make people gain a better understanding of s- and r-process nucleosynthesis at low metallicity. Using a parametric model, we find that the abundance pattern of the neutron-capture elements could be best explained by a star that was polluted by an AGB star and the CS 30322-023 binary system formed in a molecular cloud which had never been polluted by r-process material. The lack of r-process material also indicates that the AGB companion cannot have undergone a type-1.5 supernova, and thus must have had an initial mass below 4.0M$_\odot$, while the strong N overabundance and the absence of a strong C overabundance indicate that the companion's initial mass was larger than 2.0M$_\odot$. The smaller s-process component coefficient of this star illustrates that there is less accreted material of this star from the AGB companion, and the sample star should be formed in the binary system with larger initial orbital separation where the accretion-induced collapse (AIC) mechanism can not work.

 
astro-ph/0702677 [abs, ps, pdf, other] :
Title: Investigation of the single neutron exposure model for the s-process: the primary nature of the neutron source
Authors: Kun Ma (1), W. Y. Cui (1 and 2), B. Zhang (1) ((1) Department of Physics, Hebei Normal University, China, (2) National Astronomical observatories, Chinese Academy of Sciences, China)
Comments: 6 pages, 2 figures
Journal-ref: MNRAS (2007) v.375, p.1418

The primary nature of the $^{13}$C neutron source is very significant for the studies of the s-process nucleosynthesis. In this paper we present an attempt to fit the element abundances observed in 16 s-rich stars using parametric model of the single neutron exposure. The calculated results indicate that almost all s-elements were made in a single neutron exposure for 9 sample stars. Although a large spread of neutron exposure is obtained, the maximum value of the neutron exposure will reach about 7.0 mbarn$^{-1}$, which is close to the theoretical predictions by the AGB model. The calculated result is a significant evidence for the primary nature of the neutron source. Combining the result obtained in this work and the neutron exposure-initial mass relations, a large spread of neutron exposure can be explained by the different initial stellar mass and their time evolution. The possibility that the rotationally induced mixing process can lead to a spread of the neutron exposure in AGB stars is also existent.

 
astro-ph/0702690 [abs, ps, pdf, other] :
Title: Generation of Type I X-ray Burst Oscillations by Unstable Surface Modes
Authors: Ramesh Narayan, Randall L. Cooper
Comments: 9 pages, submitted to ApJ

The Rossi X-ray Timing Explorer has detected nearly coherent oscillations in the tails of type I X-ray bursts from 17 low-mass X-ray binaries. The oscillations are thought to be generated by brightness fluctuations associated with a surface mode on the rotating neutron star. The mechanism that drives the modes is, however, not understood, since the burning layer is stable to thermal perturbations. We show here via a linear perturbation analysis that, even under conditions when pure thermal perturbations are stable, nonradial surface modes may still be unstable. Specifically, we find that, if helium-burning reactions supply a reasonable fraction of the outgoing flux during burst decay, nonradial surface modes will grow in time. On the other hand, these modes are stable in the presence of hydrogen burning via the rp-process. The result naturally explain why oscillations in the decay phase of type I X-ray bursts are detected only from short-duration bursts.

 

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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702571 [abs, ps, pdf, other] :
Title: Magnetospheric particle acceleration and X-ray emission of pulsars
Authors: Sevinc O. Tagieva (Academy of Science, Physics Institute, Baku), Askin Ankay (Bogazici University, Physics Department, Istanbul), Arzu M. Ankay (Bogazici University, Physics Department, Istanbul)
Comments: minor correction on table format, 20 pages (4 figures, 1 table), submitted to International Journal of Modern Physics D
Note: replaced with revised version Mon, 26 Feb 2007 11:36:28 GMT (78kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 28 Feb 07 01:00:11 GMT
0702691 -- 0702722 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702694 [abs, ps, pdf, other] :
Title: The Prompt Gamma-Ray and Afterglow Energies of Short-Duration Gamma-Ray Bursts
Authors: E. Berger (Carnegie Observatories, Princeton)
Comments: Submitted to ApJ; 9 pages, 2 figures, 1 table

I present an analysis of the gamma-ray and afterglow energies of the complete sample of 17 short duration GRBs with prompt X-ray follow-up. I find that 80% of the bursts exhibit a linear correlation between their gamma-ray fluence and the afterglow X-ray flux normalized to t=1 d, a proxy for the kinetic energy of the blast wave ($F_{X,1}~F_{gamma}^1.01). An even tighter correlation is evident between E_{gamma,iso} and L_{X,1} for the subset of 13 bursts with measured or constrained redshifts. The remaining 20% of the bursts have values of F_{X,1}/F_{gamma} that are suppressed by about three orders of magnitude, likely because of low circumburst densities (Nakar 2007). These results have several important implications: (i) The X-ray luminosity is generally a robust proxy for the blast wave kinetic energy, indicating nu_X>nu_c and hence a circumburst density n>0.05 cm^{-3}; (ii) most short GRBs have a narrow range of gamma-ray efficiency, with <epsilon_{gamma}>~0.85 and a spread of 0.14 dex; and (iii) the isotropic-equivalent energies span 10^{48}-10^{52} erg. Furthermore, I find tentative evidence for jet collimation in the two bursts with the highest E_{gamma,iso}, perhaps indicative of the same inverse correlation that leads to a narrow distribution of true energies in long GRBs. I find no clear evidence for a relation between the overall energy release and host galaxy type, but a positive correlation with duration may be present, albeit with a large scatter. Finally, I note that the outlier fraction of 20% is similar to the proposed fraction of short GRBs from dynamically-formed neutron star binaries in globular clusters. This scenario may naturally explain the bimodality of the F_{X,1}/F_{gamma} distribution and the low circumburst densities without invoking speculative kick velocities of several hundred km/s.

 
astro-ph/0702698 [abs, ps, pdf, other] :
Title: Curious properties of the recycled pulsars and the potential of high precision timing
Authors: Matthew Bailes
Comments: 15 pages, 8 figures, To appear in proceedings of "A life with stars", a conference held in honour of Ed van den Heuvel, Amsterdam, Aug 2005), New Ast. Rev. accepted Feb 2007

Binary and Millisecond pulsars have a great deal to teach us about stellar evolution and are invaluable tools for tests of relativistic theories of gravity. Our understanding of these objects has been transformed by large-scale surveys that have uncovered a great deal of new objects, exquisitely timed by ever-improving instrumentation. Here we argue that there exists a fundamental relation between the spin period of a pulsar and its companion mass, and that this determines many of the observable properties of a binary pulsar. No recycled pulsars exist in which the minimum companion mass exceeds (P/10 ms) Solar Masses. Furthermore, the three fastest disk millisecond pulsars are either single, or possess extremely low-mass companions Mc~0.02 Mo, consistent with this relation. Finally, the four relativistic binaries for which we have actual measurements of neutron star masses, suggest that not only are their spin periods related to the companion neutron star mass, but that the kick imparted to the system depends upon it too, leading to a correlation between orbital eccentricity and spin period. The isolation of the relativistic binary pulsars in the magnetic field-period diagram is used to argue that this must be because the kicks imparted to proto-relativistic systems are usually small, leading to very few if any isolated runaway mildly-recycled pulsars. This calls into question the magnitude of supernova kicks in close binaries, which have been usually assumed to be similar to those imparted to the bulk of the pulsar population. Finally, we review some of the highlights of the Parkes precision timing efforts, which suggest 10 nanosecond timing is obtainable on PSR J1909-3744 that will aid us in searching for cosmological sources of gravitational waves.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 1 Mar 07 01:00:13 GMT
0702723 -- 0702755 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0702735 [abs, ps, pdf, other] :
Title: Hyperfast pulsars as the remnants of massive stars ejected from young star clusters
Authors: V.V.Gvaramadze, A.Gualandris, S.Portegies Zwart
Comments: 11 pages, 6 figures, 1 table

Recent proper motion and parallax measurements for the pulsar PSR B1508+55 gave the highest (transverse) velocity (~1100 km/s) ever measured for a neutron star (Chatterjee et al. 2005). The spin-down characteristics of PSR B1508+55 (typical of non-recycled pulsars) imply that the high velocity of this pulsar cannot be solely due to disruption of a tight massive binary system. A possible way to account for the high velocity of PSR B1508+55 is to assume that at least a part of this velocity is due to a natal kick or a post-natal acceleration (Chatterjee et al. 2005). We propose an alternative explanation for the origin of hyperfast pulsars based on the idea that they could be the remnants of a symmetric supernova explosion of a high-velocity massive star (or its helium core) which attained its peculiar velocity (similar to that of the pulsar) in the course of a strong three or four body dynamical encounter in the core of the parent young massive star cluster. Our proposal implies that the dense cores of young massive star clusters (located either in the Galactic disk or near the Galactic centre) could also produce the so-called hypervelocity stars (Brown et al. 2005) -- the ordinary stars moving with a speed of ~1000 km/s.

 
astro-ph/0702750 [abs, ps, pdf, other] :
Title: Further Evidence for an Elliptical Instability in Rotating Fluid Bars and Ellipsoidal Stars
Authors: Shangli Ou, Joel E. Tohline, Patrick M. Motl
Comments: 28 pages, submitted to ApJ, quicktime movies are available at: this http URL

Using a three-dimensional nonlinear hydrodynamic code, we examine the dynamical stability of more than twenty self-gravitating, compressible, ellipsoidal fluid configurations that initially have the same velocity structure as Riemann S-type ellipsoids. Our focus is on ``adjoint'' configurations, in which internal fluid motions dominate over the collective spin of the ellipsoidal figure; Dedekind-like configurations are among this group. We find that, although some models are stable and some are moderately unstable, the majority are violently unstable toward the development of $m=1$, $m=3$, and higher-order azimuthal distortions that destroy the coherent, $m=2$ bar-like structure of the initial ellipsoidal configuration on a dynamical time scale.
The parameter regime over which our models are found to be unstable generally corresponds with the regime over which incompressible Riemann S-type ellipsoids have been found to be susceptible to an elliptical strain instability \citep{LL96}. We therefore suspect that an elliptical instability is responsible for the destruction of our compressible analogs of Riemann ellipsoids. The existence of the elliptical instability raises concerns regarding the final fate of neutron stars that encounter the secular bar-mode instability and regarding the spectrum of gravitational waves that will be radiated from such systems.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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Astrophysics


astro-ph new abstracts, Fri, 2 Mar 07 01:00:14 GMT
0703001 -- 0703027 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703019 [abs, ps, pdf, other] :
Title: The Geminga Fraction
Authors: Alice K. Harding, Isabelle A. Grenier, Peter L. Gonthier
Comments: 10 pages, 7 figures, accepted for publication in Astrophysics and Space Science, as proceedings of "The Multi-Messenger Approach to High-Energy Gamma-Ray Sources", Barcelona, July 4-7, 2006, J. M. Paredes, O. Reimer, and D. F. Torres, editors

Radio-quiet gamma-ray pulsars like Geminga may account for a number of the unidentified EGRET sources in the Galaxy. The number of Geminga-like pulsars is very sensitive to the geometry of both the gamma-ray and radio beams. Recent studies of the shape and polarization of pulse profiles of young radio pulsars have provided evidence that their radio emission originates in wide cone beams at altitudes that are a significant fraction (1 -10%) of their light cylinder radius. Such wide radio emission beams will be visible at a much larger range of observer angles than the narrow core components thought to originate at lower altitude. Using 3D geometrical modeling that includes relativistic effects from pulsar rotation, we study the visibility of such radio cone beams as well as that of the gamma-ray beams predicted by slot gap and outer gap models. From the results of this study one can obtain revised predictions for the fraction of Geminga-like, radio quiet pulsars present in the gamma-ray pulsar population.

 
astro-ph/0703020 [abs, ps, pdf, other] :
Title: The quasi-persistent neutron star soft X-ray transient 1M 1716-315 in quiescence
Authors: P.G. Jonker, C.G. Bassa, S. Wachter
Comments: 7 pages, 4 figures, accepted to MNRAS

We report on our analysis of a 20 ksec Chandra X-ray observation of the quasi-persistent neutron star soft X-ray transient (SXT) 1M1716-315 in quiescence. Only one source was detected in the HEAO-I error region. Its luminosity is 1.6E32-1.3E33 erg s-1. In this the range is dominated by the uncertainty in the source distance. The source spectrum is well described by an absorbed soft spectrum, e.g. a neutron star atmosphere or black body model. No optical or near-infrared counterpart is present at the location of the X-ray source, down to a magnitude limit of I> 23.5 and K_s> 19.5. The positional evidence, the soft X-ray spectrum together with the optical and near-infrared non-detections provide strong evidence that this source is the quiescent neutron star SXT. The source is 10-100 times too bright in X-rays in order to be explained by stellar coronal X-ray emission. Together with the interstellar extinction measured in outburst and estimates for the source distance, the reported optical and near-infrared limit give an upper limit on the absolute magnitude of the counterpart of I>8.6 and K_s>5.1. This implies that the system is either an ultra-compact X-ray binary having P_orb<1 hr or the companion star is an M-dwarf. We reconstructed the long term X-ray lightcurve of the source. 1M1716-315 has been active for more than 12 years before returning to quiescence, the reported Chandra observation started 16.9+-4.1 years after the outburst ended.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


nucl-th/0702080 [abs, ps, pdf, other] :
Title: Constraining a possible time variation of the gravitational constant G with terrestrial nuclear laboratory data
Authors: P. G. Krastev, B. A. Li (Texas A&M University-Commerce)
Comments: 7 pages, 7 figures, 1 table

Testing the constancy of the gravitational constant G has been a longstanding fundamental question in natural science. As first suggested by Jofr\'{e}, Reisenegger and Fern\'{a}ndez [1], Dirac's hypothesis of a decreasing gravitational constant $G$ with time due to the expansion of the Universe would induce changes in the composition of neutron stars, causing dissipation and internal heating. Eventually, neutron stars reach their quasi-stationary states where cooling due to neutrino and photon emissions balances the internal heating. The correlation of surface temperatures and radii of some old neutron stars may thus carry useful information about the changing rate of G. Using the density dependence of the nuclear symmetry energy constrained by recent terrestrial laboratory data on isospin diffusion in heavy-ion reactions at intermediate energies and the size of neutron skin in $^{208}Pb$ within the gravitochemical heating formalism, we obtain an upper limit of the relative changing rate of $|\dot{G}/G|\le4\times 10^{-12}yr^{-1}$ consistent with the best available estimates in the literature.

 

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Astrophysics


astro-ph new abstracts, Mon, 5 Mar 07 01:00:16 GMT
0703028 -- 0703052 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703043 [abs, ps, pdf, other] :
Title: A description of sources detected by INTEGRAL during the first 4 years of observations
Authors: A. Bodaghee, T.J.-L. Courvoisier, J. Rodriguez, V. Beckmann, N. Produit, D. Hannikainen, E. Kuulkers, D.R. Willis, G. Wendt
Comments: 36 pages, 16 figures, 1 long table, accepted for publication in A&A (as of 23-2-07)

Parameters from the literature, such as positions, photoelectric absorption (nH), spin and orbital periods, and distances or redshifts, were collected for all ~500 sources detected by INTEGRAL-ISGRI so far. We investigate where new and previously-known sources detected by ISGRI fit in the parameter space of high-energy objects, and we use the parameters to test correlations expected from theoretical predictions. For example, the influence of the local absorbing matter on periodic modulations is studied for Galactic High-Mass X-ray Binaries (HMXBs) with OB supergiant and Be companions. We examine the spatial distribution of different types of sources in the Milky Way using various projections of the Galactic plane, in order to highlight signatures of stellar evolution and to speculate on the origin of the group of sources whose classifications are still uncertain. ISGRI has detected similar numbers of X-ray Binaries and Active Galactic Nuclei (AGN). The former group contains new members of the class of HMXBs with supergiant stellar companions. Thanks to these additional systems, we are able to show that HMXBs are generally segregated in plots of intrinsic nH versus the orbital period of the system and versus the spin period of the pulsar, based on whether the companion is a Be or an OB supergiant star. We also find a tentative but expected anti-correlation between nH and the orbital period, and a possible and unexpected correlation between the nH and the spin period. While only a handful of new Low-Mass X-ray Binaries (LMXBs) have been discovered, there are many sources that remain unclassified and they appear to follow a spatial distribution typical of Galactic sources (especially LMXBs) rather than extragalactic sources.

 
astro-ph/0703046 [abs, ps, pdf, other] :
Title: Probing cosmic plasma with giant radio pulses
Authors: V.I. Kondratiev (ASC LPI, WVU, York University), M.V. Popov, V.A. Soglasnov (ASC LPI), Y.Y. Kovalev (ASC LPI, NRAO GB, MPIfR), N. Bartel, W. Cannon, A. Yu. Novikov (York University)
Comments: 16 pages, 5 figures, Proceedings of the International Colloq. "Scattering and Scintillation in Radio Astronomy", June 23-26, 2006, Puschino, Russia (to be published in Astronomical and Astrophysical Transactions)

VLBI observations of the Crab pulsar with the 64-m radio telescope at Kalyazin (Russia) and the 46-m radio telescope of the Algonquin Radio Observatory (Canada) at 2.2 GHz and single-dish observations of the millisecond pulsar B1937+21 with the GBT (USA) at 2.1 GHz were conducted to probe the interstellar medium and study the properties of giant pulses. The VLBI data were processed with a dedicated software correlator, which allowed us to obtain the visibility of single giant pulses. Two frequency scales of 50 and 450 kHz were found in the diffraction spectra of giant pulses from the Crab pulsar. The location of the scattering region was estimated to be close to the outer edge of the nebula. No correlation was found between the power spectra of giant pulses at left- and right-hand circular polarization. We explain this lack of correlation through the influence of the strong magnetic field on circularly polarized emission in the region close to the Crab pulsar.
Combining the measurement of the decorrelation bandwidth with that of the scattering time of giant pulses for B1937+21, we found three frequency scales of 1.7, 3.8, and 16.5 MHz. The scattering time of giant pulses of B1937+21 at 2.1 GHz was found to be 40+-4 ns. We obtained an upper limit of the intrinsic width of giant pulses from B1937+21 of less than 8 ns. The frequency dependences of the scattering times for the Crab pulsar and PSR B1937+21 were found to be different. They are characterized by exponents of -3.5 and -4.2, respectively. We attribute the difference to the large influence of scattering in the Crab nebula.

 
astro-ph/0703051 [abs, ps, pdf, other] :
Title: Timing the Eccentric Binary Millisecond Pulsar in NGC 1851
Authors: Paulo C. Freire, Scott M. Ransom, Yashwant Gupta
Comments: Accepted for publication in the Astrophysical Journal

We have used the Green Bank Telescope to observe the millisecond pulsar PSR J0514-4002A on 43 occasions spread over 2 years. This 5-ms pulsar is located in the globular cluster NGC 1851; it belongs to a binary system and has a highly eccentric (e = 0.888) orbit. We have obtained a phase-coherent timing solution for this object, including very precise position, spin and orbital parameters. The pulsar is located 4.6" (about 1.3 core radii) from the center of the cluster, and is likely to lie on its more distant half. The non-detection of eclipses at superior conjunction can be used, given the peculiar geometry of this system, to rule out the possibility of an extended companion. We have measured the rate of advance of periastron for this binary system to be $\dot{\omega}$ = 0.01289(4) degrees per year, which if due completely to general relativity, implies a total system mass of 2.453(14) solar masses. Given the known mass function, the pulsar mass has to be < 1.5 solar masses, and the mass of the companion has to be > 0.96 solar masses, implying that it is a heavy white dwarf. The 350-MHz flux density of this pulsar varies between 0.2 and 1.4 mJy; the origin of these variations is not known.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0703001 [abs, ps, pdf, other] :
Title: Elastic stars in general relativity: IV. Axial perturbations
Authors: Max Karlovini, Lars Samuelsson
Comments: 18 pages, no figures

This is the fourth paper in a series that attempt to put forward a consistent framework for modelling solid regions in neutron stars. Here we turn our attention to axial perturbations of spherically symmetric spacetimes using a gauge invariant approach due to one of us. Using the formalism developed in the first paper in the series it turns out that the matter perturbations are neatly expressible in terms of a ``metric'' tensor field depending only on the speeds of shear wave propagation along the principal directions in the solid. The results are applicable to a wide class of elastic materials and does not assume material isotropy nor quasi-Hookean behaviour. The perturbation equations are then specialised to a static background and are given by two coupled wave equations. Our formalism is thus slightly simpler than the previously existing results of Shumaker & Thorne, where an additional initial value equation needs to be solved. The simplification is mainly due to the gauge invariance of our approach and shows up also in somewhat simpler boundary conditions. We also give a first order formulation suitable for numerical integration of the quasi-normal mode problem of a neutron star. The relations between the gauge independent variables and the, in general, gauge dependent perturbed metric and strain tensor are explicitly given.

 

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Astrophysics


astro-ph new abstracts, Tue, 6 Mar 07 01:00:18 GMT
0703053 -- 0703085 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703060 [abs, ps, pdf, other] :
Title: Long-term pulse profile study of the Be/X-ray pulsar SAX J2103.5+4545
Authors: A. Camero Arranz, C.A. Wilson, M.H. Finger, V. Reglero
Comments: 9 pages, 11 figures, submitted to Astronomy & Astrophysics

Aims. We present the first long-term pulse profile study of the X-ray pulsar SAX J2103.5+4545. Our main goal is to study the pulse shape correlation either with luminosity, time or energy.
Methods. This Be/X-ray binary system was observed from 1999 to 2004 by RXTE PCA, and by INTEGRAL from 2002 to 2005, during the Performance and Verification (PV) phase and the Galactic Plane Scan survey (GPS). X-ray pulse profiles were obtained in different energy ranges. The long-term spectral variability of this source is studied. The long-term flux, frequency and spin-up rate histories are computed. A new set of orbital parameters are also determined.
Results. The pulse shape is complex and highly variable either with time or luminosity. However, an energy dependence pattern was found. Single, double, triple or even quadruple peaks pulse profile structure was obtained. It was confirmed that SAX J2103.5+4545 becomes harder when the flux is higher. The new orbital solution obtained is: P_orb= 12.66528+-0.00051 days, e = 0.401+-0.018, w = 241.36+-2.18 and a_xsin i = 80.81+-0.67 lt-s.

 
astro-ph/0703062 [abs, ps, pdf, other] :
Title: Phase separation in the crust of accreting neutron stars
Authors: C. J. Horowitz, D. K. Berry, E. F. Brown
Comments: 7 pages, 6 figures

Nucleosynthesis, on the surface of accreting neutron stars, produces a range of chemical elements. We perform molecular dynamics simulations of crystallization to see how this complex composition forms new neutron star crust. We find chemical separation, with the liquid ocean phase greatly enriched in low atomic number elements compared to the solid crust. This phase separation should change many crust properties such as the thermal conductivity and shear modulus. The concentration of carbon, if present, is enriched in the ocean. This may allow unstable thermonuclear burning of the carbon and help explain the ignition of the very energetic explosions known as superbursts.

 
astro-ph/0703073 [abs, ps, pdf, other] :
Title: On the neutron star-disc interaction in Be/X-ray binaries
Authors: P. Reig (FORTH/University of Crete)
Comments: accepted for publication in MNRAS

We have investigated the long-term X-ray variability, defined as the root-mean-square (rms) of the ASM RXTE light curves, of a set of galactic Be/X-ray binaries and searched for correlations with system parameters, such as the spin period of the neutron star and the orbital period and eccentricity of the binary. We find that systems with larger rms are those harbouring fast rotating neutron stars, low eccentric and narrow orbits. These relationships can be explained as the result of the truncation of the circumstellar disc. We also present an updated version of the Halpha equivalent width-orbital period diagram, including sources in the SMC. This diagram provides strong observational evidence of the interaction of neutron star with the circumstellar envelope of its massive companion.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0603126 [abs, ps, pdf, other] :
Title: Analysing the atolls: X-ray spectral transitions of accreting neutron stars
Authors: Jeanette Gladstone, Chris Done, Marek Gierlinski
Comments: Accepted for publication in MNRAS
Note: replaced with revised version Mon, 5 Mar 2007 09:10:00 GMT (775kb)
 
astro-ph/0606259 [abs, ps, pdf, other] :
Title: The Anomalous X-Ray Pulsar 4U 0142+61: A Neutron Star with a Gaseous Fallback Disk
Authors: U. Ertan, M. H. Erkut, K.Y. Eksi, M.A. Alpar
Comments: 22 pages, 3 figures, minor revisons, appeared in Apj
Journal-ref: The Astrophysical Journal, 657, 441, 2007 March 1
Note: replaced with revised version Mon, 5 Mar 2007 15:05:34 GMT (32kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 7 Mar 07 01:00:10 GMT
0703086 -- 0703123 received


6 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703091 [abs, ps, pdf, other] :
Title: Explorations of the r-Processes: Comparisons between Calculations and Observations of Low-Metallicity Stars
Authors: Karl-Ludwig Kratz, Khalil Farouqi, Bernd Pfeiffer, James W. Truran, Christopher Sneden, John J. Cowan
Comments: 42 pages, 2 tables, 12 figures; To appear in the Astrophysical Journal

Abundances of heavier elements (barium and beyond) in many neutron-capture-element-rich halo stars accurately replicate the solar system r-process pattern. However, abundances of lighter neutron-capture elements in these stars are not consistent with the solar system pattern. These comparisons suggest contributions from two distinct types of r-process synthesis events -- a so called main r-process for the elements above the 2nd r-process peak and a weak r-process for the lighter neutron-capture elements. We have performed r-process theoretical predictions to further explore the implications of the solar and stellar observations. We find that the isotopic composition of barium and the elemental Ba/Eu abundance ratios in r-process-rich low metallicity stars can only be matched by computations in which the neutron densities are in the range 23< log n_n < 28, values typical of the main r-process. For r-process conditions that successfully generate the heavy element pattern extending down to A=135, the relative abundance of I129 produced in this mass region appears to be at least 90% of the observed solar value. Finally, in the neutron number density ranges required for production of the observed solar/stellar 3rd r-process-peak (A~200), the predicted abundances of inter-peak element hafnium (Z=72, A~180) follow closely those of 3rd-peak elements and lead. Hf, observable from the ground and close in mass number to the 3rd r-process-peak elements, might also be utilized as part of a new nuclear chronometer pair, Th/Hf, for stellar age determinations.

 
astro-ph/0703107 [abs, ps, pdf, other] :
Title: SN 2006aj Associated with XRF 060218 At Late Phases: Nucleosynthesis-Signature of A Neutron Star-Driven Explosion
Authors: Keiichi Maeda, Koji Kawabata, Masaomi Tanaka, Ken'ichi Nomoto, Nozomu Tominaga, Takashi Hattori, Takeo Minezaki, Takami Kuroda, Tomoharu Suzuki, Jinsong Deng, Paolo A. Mazzali, Elena Pian
Comments: Accepted for Publication in the Astrophysical Journal Letters (2007 March 20 issue). 8 pages, including 1 table and 3 figures

Optical spectroscopy and photometry of SN 2006aj have been performed with the Subaru telescope at t > 200 days after GRB060218, the X-ray Flash with which it was associated. Strong nebular emission-lines with an expansion velocity of v ~ 7,300 km/s were detected. The peaked but relatively broad [OI]6300,6363 suggests the existence of ~ 2 Msun of materials in which ~1.3 Msun is oxygen. The core might be produced by a mildly asymmetric explosion. The spectra are unique among SNe Ic in (1) the absence of [CaII]7291,7324 emission, and (2) a strong emission feature at ~ 7400A, which requires ~ 0.05 Msun of newly-synthesized 58Ni. Such a large amount of stable neutron-rich Ni strongly indicates the formation of a neutron star. The progenitor and the explosion energy are constrained to 18 Msun < Mms < 22 Msun and E ~ (1 - 3) 10^{51} erg, respectively.

 
astro-ph/0703113 [abs, ps, pdf, other] :
Title: Hypernuclear Physics and Compact Stars
Authors: J. Schaffner-Bielich
Comments: 6 pages, 2 figrues, plenary talk given at the IX International Conference on Hypernuclear and Strange Particle Physics, 10-14 October 2006, Mainz, Germany

Hypernuclear physics plays a decisive role for several features of compact star physics. I review the impact of hypernuclear potential depths, two-body hyperon-nucleon and hyperon three-body forces as well as hyperon-hyperon interactions on the maximum mass, the mass-radius relation, and cooling properties of neutron stars.

 
astro-ph/0703116 [abs, ps, pdf, other] :
Title: The theory of pulsar winds and nebulae
Authors: J. G. Kirk, Y. Lyubarsky, J. Petri
Comments: 33 pages invited review, 363rd Heraeus Seminar "Neutron Stars and Pulsars", Bad Honnef, 2006

We review current theoretical ideas on pulsar winds and their surrounding nebulae. Relativistic MHD models of the wind of the aligned rotator, and of the striped wind, together with models of magnetic dissipation are discussed. It is shown that the observational signature of this dissipation is likely to be point-like, rather than extended, and that pulsed emission may be produced. The possible pulse shapes and polarisation properties are described. Particle acceleration at the termination shock of the wind is discussed, and it is argued that two distinct mechanisms must be operating, with the first-order Fermi mechanism producing the high-energy electrons (above 1 TeV) and either magnetic annihilation or resonant absorption of ion cyclotron waves responsible for the 100 MeV to 1 TeV electrons. Finally, MHD models of the morphology of the nebula are discussed and compared with observation.

 
astro-ph/0703122 [abs, ps, pdf, other] :
Title: The s-process in stellar population synthesis: a new approach to understanding AGB stars
Authors: A.A. Bonacic Marinovic, R.G. Izzard, M. Lugaro, O.R. Pols
Comments: 16 pages, 15 figures, accepted for publication in Astronomy & Astrophysics

Thermally pulsating asymptotic giant branch (AGB) stars are the main producers of slow neutron capture (s-) process elements, but there are still large uncertainties associated with the formation of the main neutron source, 13C, and with the physics of these stars in general. Observations of s-process element enhancements in stars can be used as constraints on theoretical models. For the first time we apply stellar population synthesis to the problem of s-process nucleosynthesis in AGB stars, in order to derive constraints on free parameters describing the physics behind the third dredge-up and the properties of the neutron source. We utilize a rapid evolution and nucleosynthesis code to synthesize different populations of s-enhanced stars, and compare them to their observational counterparts to find out for which values of the free parameters in the code the synthetic populations fit best to the observed populations. These free parameters are the amount of third dredge-up, the minimum core mass for third dredge-up, the effectiveness of 13C as a source of neutrons and the size in mass of the 13C pocket. We find that galactic disk objects are reproduced by a spread of a factor of two in the effectiveness of the 13C neutron source. Lower metallicity objects can be reproduced only by lowering by at least a factor of 3 the average value of the effectiveness of the 13C neutron source needed for the galactic disk objects. Using observations of s-process elements in post-AGB stars as constraints we find that dredge-up has to start at a lower core mass than predicted by current theoretical models, that it has to be substantial ($\lambda$ >~ 0.2) in stars with mass M <~ 1.5 M_sun and that the mass of the 13C pocket must be about 1/40 that of the intershell region.

 
astro-ph/0703123 [abs, ps, pdf, other] :
Title: The Oblate Schwarzschild Approximation for Light Curves of Rapidly Rotating Neutron Stars
Authors: Sharon M. Morsink, Denis A. Leahy, Coire Cadeau, John Braga
Comments: 8 pages, 4 figures. Submitted to the Astrophysical Journal

We present a simple method for including the oblateness of a rapidly rotating neutron star when fitting X-ray light curves. In previous work we showed that the oblateness induced by rotation at frequencies above 300 Hz produces a geometric effect which needs to be accounted for when modelling light curves to extract constraints on the neutron star's mass and radius. In our model X-rays are emitted from the surface of an oblate neutron star and propagate to the observer along geodesics of the Schwarzschild metric for a spherical neutron star. Doppler effects due to rotation are added in the same manner as in the case of a spherical neutron star. We show that this model captures the most important effects due to the neutron star's rotation. We also explain how the geometric oblateness effect can rival the Doppler effect for some emission geometries.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 8 Mar 07 01:00:14 GMT
0703124 -- 0703159 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703128 [abs, ps, pdf, other] :
Title: Spectral modelling of the high energy emission of the magnetar 4U 0142+614
Authors: Nanda Rea (SRON/U.Sydney), Roberto Turolla (U.Padua), Silvia Zane (MSSL), Andrea Tramacere (U.Rome), Luigi Stella, Gianluca Israel (INAF-OAR), Riccardo Campana (U.Rome)
Comments: 5 pages, 2 figures; accepted for publication in ApJ Letter

We present an empirical spectral modelling of the high energy emission of the anomalous X-ray pulsar 4U 0142+614, based on simultaneous Swift and INTEGRAL observations from X to gamma-ray energies. We adopted models contained in the XSPEC analysis package, as well as models based on recent theoretical studies, and restricted ourselves to those combinations of up to three components which produce a good fit while requiring the lowest number of free parameters. Only three models were found to fit satisfactorily the 0.5-250keV spectrum of 4U 0142+614: i) a ~0.4keV blackbody and two power-laws, ii) a resonant cyclotron scattering model plus a power-law and iii) two log-parabolic functions. We found that only the latter two models do not over-predict the infrared/optical emission observed simultaneously from this AXP, and only the log-parabolic functions can naturally account for the upper limits set by COMPTEL in the gamma-ray range. A possible interpretation of the two log-parabolae in terms of inverse Compton scattering of soft X-ray photons by very energetic particles is discussed.

 
astro-ph/0703131 [abs, ps, pdf, other] :
Title: Black Hole Spin Evolution: Implications for Short-hard Gamma Ray Bursts and Gravitational Wave Detection
Authors: Krzysztof Belczynski, Ronald E. Taam, Emmanouela Rantsiou, Marc van der Sluys
Comments: 19 pages, 3 tables, 10 figures: submitted to ApJ

The evolution of the spin and tilt of black holes in compact black hole - neutron star and black hole - black hole binary systems is investigated via the population synthesis method. Based on recent results on accretion at super Eddington rates in slim disk models, estimates of natal kicks, and the results regarding fallback in supernova models, we obtain the black hole spin and misalignment. It is found that the spin parameter, a_spin, is less than 0.5 for initially non rotating black holes and the tilt, i_tilt, is less than 40 deg for 50% of the systems in black hole - neutron star binaries. Upon comparison with the results of black hole - neutron star merger calculations we estimate that only a small fraction (~0.02) of these systems can potentially produce a short-hard gamma ray burst. Only for high initial black hole spin parameters (a_spin>0.6) can this fraction be significant (~0.35). For the majority of black holes in black hole - neutron star systems the spin magnitude is increased to a_spin>0.1 and the degree of spin misalignment (i_tilt ~ 40 deg) is sufficiently high that the predicted gravitational radiation signal significantly differs from that for non rotating black holes. However, due to the (i) insensitivity of signal detection techniques to the black hole spin and the (ii) predicted overall low contribution of black hole binaries to the signal we find that the detection of gravitational waves are not greatly inhibited by current searches with non spinning templates. It is pointed out that the detection of a black hole - black hole binary inspiral system with LIGO or VIRGO may provide a direct measurement of the initial spin of a black hole.

 
astro-ph/0703142 [abs, ps, pdf, other] :
Title: The main- interpulse interaction of PSR B1702-19
Authors: P. Weltevrede, G. A. E. Wright, B. W. Stappers
Comments: 13 pages, 12 figures, accepted for publication in A&A

This paper reports on single-pulse radio observations of PSR B1702-19 and their implications for pulsar emission theories. These observations were made with the Westerbork Synthesis Radio Telescope at 1380 and 328 MHz. The PA-swing is used to constrain possible geometries of the pulsar and the single-pulse data is analysed for subpulse modulation correlations between the main pulse and interpulse. We confirm earlier conclusions that the dipole axis of this pulsar is almost perpendicular to its rotation axis, and report that both its main pulse and interpulse are modulated with a periodicity around 10.4 times the pulsar's rotation. Allowing for the half-period delay between main pulse and interpulse the modulation is found to be precisely in phase. Despite small secular variations in the periodicity, the phase-locking continues over all timescales ranging up to several years. The precision of the phase locking is difficult for current emission theories to explain if the main pulse and interpulse originate from opposing magnetic poles. We therefore also explore the possibility of a bidirectional model, in which all the modulated emission comes from one pole, but is seen from two sides and slightly displaced by aberration and time-delay. In this model the unmodulated emission is directed to us from the opposite pole, requiring the emission of the main pulse to originate from two different poles. This is difficult to reconcile with the observed smooth PA-swing. Whichever model turns out to be correct, the answer will have important implications for emission theories.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 9 Mar 07 01:00:14 GMT
0703160 -- 0703190 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703170 [abs, ps, pdf, other] :
Title: Coupling between the 45 Hz Horizontal-Branch Oscillation and the Normal Branch Oscillation in Scorpius X-1
Authors: Wenfei Yu
Comments: 10 pages, 2 figures, accepted for publication in ApJL

The observations of the bright persistent neutron star low-mass X-ray binary (LMXB) Sco X-1 performed with the {\it Rossi X-ray Timing Explorer} (RXTE) show a $\sim$ 6 Hz normal-branch oscillation (NBO), a $\sim$ 45 Hz horizontal-branch oscillation (HBO), and twin kHz quasi-periodic oscillations (QPOs) on its normal branch simultaneously. We have found that the fractional amplitude of the HBO corresponding to the NBO phase of high flux is 1.1%, while that of the NBO phase of low flux is undetectable, with a 3$\sigma$ upper limit of 0.4%, implying that the HBO strength varies with the NBO phase in an opposite way to that of the lower kHz QPO previously found, and suggests that the condition for the generation of the HBO is met when the NBO flux is high. The 6 Hz NBO in Sco X-1 connects the 45 Hz HBO and the twin kHz QPO together, showing a unique picture indicating a coupling between the QPOs, which has never been observed in other neutron star LMXBs. We discuss the implications for current models of the 45 Hz HBO, the 6 Hz NBO, and the twin kHz QPOs.

 
astro-ph/0703181 [abs, ps, pdf, other] :
Title: Pulsed X-ray Emission from Pulsar A in the Double Pulsar System J0737-3039
Authors: S. Chatterjee, B. M. Gaensler, A. Melatos, W. F. Brisken, B. W. Stappers
Comments: 6 pages, 3 figures, emulateapj; submitted to ApJ

The double pulsar system J0737-3039 is not only a test bed for General Relativity and theories of gravity, but also provides a unique laboratory for probing the relativistic winds of neutron stars. Recent X-ray observations have revealed a point source at the position of PSR J0737-3039, but have failed to detect pulsations or orbital modulation. Here we report on Chandra X-ray Observatory High Resolution Camera observations of the double pulsar. We detect deeply modulated, double-peaked X-ray pulses at the period of PSR J0737-3039A, similar in appearance to the observed radio pulses. The pulsed fraction is approximately 70%. Although purely non-thermal emission is consistent with the data, the X-ray pulse morphology of A, in combination with previously reported spectral properties of the X-ray emission, suggests the existence of both non-thermal magnetospheric emission and a broad sinusoidal thermal emission component from the neutron star surface. No pulsations are detected from pulsar B, and there is no evidence for orbital modulation. The absence of orbital modulation is consistent with theoretical expectations of a Poynting-dominated relativistic wind at the termination shock between the magnetosphere of B and the wind from A, and with the small fraction of the energy outflow from A intercepted by the termination shock.

 
astro-ph/0703183 [abs, ps, pdf, other] :
Title: The XENON10 WIMP Search Experiment at the Gran Sasso Underground Laboratory
Authors: Laura Baudis (for the XENON Collaboration)
Comments: 7 pages, 6 figures, to be published in the Proceedings of the Third Symposium on Large TPCs for Low Energy Rare Event Detection, 11 - 12 December 2006, Paris

XENON10 is a new direct dark matter detection experiment using liquid xenon as target for weakly interacting, massive particles (WIMPs). A two-phase (liquid/gas) time projection chamber with 15 kg fiducial mass has been installed in a low-background shield at the Gran Sasso Underground Laboratory in July 2006. After initial performance tests with various calibration sources, the science data run started on August 24, 2006. The detector has been running stably since then, and a full analysis of more than 75 live days of WIMP search data is now in progress. We present first results on gamma and neutron calibration runs, as well as a preliminary analysis of a subset of the WIMP search data.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



Replacements


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703107 [abs, ps, pdf, other] :
Title: SN 2006aj Associated with XRF 060218 At Late Phases: Nucleosynthesis-Signature of A Neutron Star-Driven Explosion
Authors: Keiichi Maeda, Koji Kawabata, Masaomi Tanaka, Ken'ichi Nomoto, Nozomu Tominaga, Takashi Hattori, Takeo Minezaki, Takami Kuroda, Tomoharu Suzuki, Jinsong Deng, Paolo A. Mazzali, Elena Pian
Comments: Accepted for Publication in the Astrophysical Journal Letters (2007, ApJ, 658, L5). 8 pages, including 1 table and 3 figures. Typos corrected
Note: replaced with revised version Thu, 8 Mar 2007 05:46:12 GMT (376kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 12 Mar 07 00:00:11 GMT
0703191 -- 0703221 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703203 [abs, ps, pdf, other] :
Title: Burial of the polar magnetic field of an accreting neutron star. II. Hydromagnetic stability of axisymmetric equilibria
Authors: D. J. B. Payne, A. Melatos
Comments: 16 pages, 23 figures, accepted for publication in MNRAS

The theory of polar magnetic burial in accreting neutron stars predicts that a mountain of accreted material accumulates at the magnetic poles of the star, and that, as the mountain spreads equatorward, it is confined by, and compresses, the equatorial magnetic field. Here, we extend previous, axisymmetric, Grad-Shafranov calculations of the hydromagnetic structure of a magnetic mountain up to accreted masses as high as $\Ma = 6\times 10^{-4}\Msun$, by importing the output from previous calculations (which were limited by numerical problems and the formation of closed bubbles to $\Ma < 10^{-4}\Msun$) into the time-dependent, ideal-magnetohydrodynamic code ZEUS-3D and loading additional mass onto the star dynamically. The rise of buoyant magnetic bubbles through the accreted layer is observed in these experiments. We also investigate the stability of the resulting hydromagnetic equilibria by perturbing them in ZEUS-3D. Surprisingly, it is observed that the equilibria are marginally stable for all $\Ma\leq 6\times 10^{-4}\Msun$; the mountain oscillates persistently when perturbed, in a combination of Alfv\'en and acoustic modes, without appreciable damping or growth, and is therefore not disrupted (apart from a transient Parker instability initially, which expels $< 1 %$ of the mass and magnetic flux).

 
astro-ph/0703205 [abs, ps, pdf, other] :
Title: Quasi periodic oscillations in XTE J0111.2--7317, highest frequency among the HMXB pulsars
Authors: Ramanpreet Kaur, Biswajit Paul, Harsha Raichur, Ram Sagar
Comments: Accepted for publication in The Astrophysical Journal

We report here discovery of Quasi Periodic Oscillations (QPOs) in the High Mass X-ray Binary (HMXB) Pulsar XTE J0111.20-7317 during a transient outburst in this source in December 1998. Using observations made with the proportional counter array of the Rossi X-ray Timing Explorer during the second peak and the declining phase of this outburst we have discovered a QPO feature at a frequency of 1.27 Hz. We have ruled out the possibility that the observed QPOs can instead be from the neighbouring bright X-ray pulsar SMC X-1. This is the highest frequency QPO feature ever detected in any HMXB pulsar. In the absence of a cyclotron absorption feature in the X-ray spectrum, the QPO feature, along with the pulse period and X-ray flux measurement measurement helps us to constrain the magnetic field strength of the neutron star.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0612501 [abs, ps, pdf, other] :
Title: XMM-Newton discovery of 7 s pulsations in the isolated neutron star RX J1856.5-3754
Authors: Andrea Tiengo, Sandro Mereghetti
Comments: Revised version published on ApJ - More details on data analysis, added energy dependence of pulsed fraction, and other minor changes
Journal-ref: The Astrophysical Journal, vol. 657, part 2 (2007), pages L101-L104
Note: replaced with revised version Thu, 8 Mar 2007 21:57:32 GMT (111kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 13 Mar 07 00:00:14 GMT
0703222 -- 0703280 received


5 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703241 [abs, ps, pdf, other] :
Title: Pulsar Nulling and Mode Changing
Authors: N. Wang (1 and 2 and 3), R. N. Manchester (2), S. Johnston (2 and 3) ((1) Urumqi Observatory, NAOC, China, (2) Australia Telescope National Facility, CSIRO, Australia, (3) School of Physics, University of Sydney, Australia)
Comments: 11 pages, 8 figures, accepted by MNRAS

With its relatively long observation time per pointing, the Parkes multibeam survey was effective in detecting nulling pulsars. We have made 2-hour observations of 23 pulsars which showed evidence for pulse nulling or mode changing in the survey data. Because of the low flux density of these pulsars, in most cases averaging times of between 10 s and 60 s were necessary and so this analysis is insensitive to very short nulls. Seven of the pulsars had null fractions of more than 40% with the largest having a lower limit of 95%. Mode changes were observed in six pulsars with clear relationships between nulling and mode changing in some cases. Combined with earlier results, the data suggest that large null fractions are more related to large characteristic age than to long pulse period. The observations suggest that nulling and mode changing are different manifestations of the same phenomenon.

 
astro-ph/0703246 [abs, ps, pdf, other] :
Title: Deep Searches for Radio Pulsations and Bursts from Four Southern Anomalous X-ray Pulsars
Authors: Fronefield Crawford, Jason W. T. Hessels, Victoria M. Kaspi
Comments: 6 pages, including 1 table. Accepted for publication in ApJ

We have searched for persistent radio pulsations, bright single pulses, and bursts from four Southern anomalous X-ray pulsars (AXPs). Deep observations were conducted at 1.4 GHz in 1999 July and August with the Parkes 64-m telescope. For all of the target AXPs, the upper limits on integrated pulsed emission are ~0.02 mJy, while the limits on the flux of single pulses are ~1 Jy or better. The corresponding radio luminosity limits are significantly below the observed luminosities of the majority of the observed radio pulsars, and they are significantly below the radio luminosity of XTE J1810-197, the only AXP known thus far to emit radio pulsations, at the epoch when radio pulses were first detected from this source. Our null results support the hypothesis that pulsed radio emission from AXPs is only present in conjunction with X-ray outburst activity. However, we cannot rule out the possibility that pulsed radio emission is present, but that it is too weak to be detected in our observations, or that unfavorable viewing geometries prevent this emission from being seen by terrestrial observers. Given the possible association between the radio emission and transient X-ray behavior of XTE J1810-197, continued radio searches of these and other AXPs at different epochs are warranted, particularly after periods of X-ray burst activity.

 
astro-ph/0703257 [abs, ps, pdf, other] :
Title: Superfluid neutron star turbulence
Authors: N. Andersson, T. Sidery, G.L. Comer
Comments: 15 pages, 2 figures

We analyse the implications of superfluid turbulence for neutron star physics. We begin by extending our previous results for the mutual friction force for a straight vortex array to account for the self-induced flow which arises when the vortices are curved. We then discuss Vinen's phenomenological model for isotropic turbulence, and derive the associated (Gorter-Mellink) form for the mutual friction. We compare this derivation to a more recent analysis of Schwarz, which sheds light on various involved issues. Having discussed isotropic turbulence, we argue that this case is unlikely to be relevant for neutron stars. Instead we expect a rotating neutron star to exhibit polarised turbulence, where relative flow drives the turbulence and rotation counteracts it. Based on recent results for superfluid Helium, we construct a phenomenological model that should have the key features of such a polarised turbulent system.

 
astro-ph/0703267 [abs, ps, pdf, other] :
Title: Magnetic field dissipation in neutron star crusts: from magnetars to isolated neutron stars
Authors: J.A. Pons, U. Geppert
Comments: 14 pages, 10 figures

We study the non--linear evolution of magnetic fields in neutron star crusts with special attention to the influence of the Hall drift. Our goal is to understand the conditions for fast dissipation due to the Hall term in the induction equation. We study the interplay of Ohmic dissipation and Hall drift in order to find a timescale for the overall crustal field decay. We solve numerically the Hall induction equation by means of a hybrid method (spectral in angles but finite differences in the radial coordinate). The microphysical input consists of the most modern available crustal equation of state, composition and electrical conductivities. We present the first long term simulations of the non--linear magnetic field evolution in realistic neutron star crusts with a stratified electron number density and temperature dependent conductivity. We show that Hall drift influenced Ohmic dissipation takes place in neutron star crusts on a timescale of 1 Myr. When the initial magnetic field has magnetar strength, the fast Hall drift results in an initial rapid dissipation stage that lasts 10-50 kyr. The interplay of the Hall drift with the temporal variation and spatial gradient of conductivity tends to favor the displacement of toroidal fields toward the inner crust, where stable configurations can last for 1 Myr. We show that the thermally emitting isolated neutron stars, as the Magnificent Seven, are very likely descendants of neutron stars born as magnetars.

 
astro-ph/0703274 [abs, ps, pdf, other] :
Title: Periodicities in X-ray Binaries from Swift/BAT Observations
Authors: R. Corbet, C. Markwardt, L. Barbier, S. Barthelmy, J. Cummings, N. Gehrels, H. Krimm, D. Palmer, T. Sakamoto, G. Sato, J. Tueller (on behalf of the Swift/BAT Survey Team)
Comments: To appear in the proceedings of "The Extreme Universe in the Suzaku Era", Kyoto, Japan, December 4-8, 2006. (Progress of Theoretical Physics, Supplement)

The Burst Alert Telescope (BAT) on board Swift has accumulated extensive light curves for 265 sources (not including GRBs) in the energy range 14 to 200 keV. We present here a summary of searches for periodic modulation in the flux from X-ray binaries. Our results include: determination of the orbital periods of IGR J16418-4532 and IGR J16320-4751; the disappearance of a previously known 9.6 day period in 4U 2206+54; the detection of a 5 hour period in the symbiotic X-ray binary 4U 1954+31, which might be the slowest neutron star rotation period yet discovered; and the detection of flares in the supergiant system 1E 1145.1-6141 which occur at both periastron and apastron passage with nearly equal amplitude. We compare techniques of weighting data points in power spectra and present a method related to the semi-weighted mean which, unlike conventional weighting, works well over a wide range of source brightness.

 

Cross-listings


0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0611047 [abs, ps, pdf, other] :
Title: Relativistic neutron star merger simulations with non-zero temperature equations of state I. Variation of binary parameters and equation of state
Authors: R. Oechslin, H.-T. Janka, A. Marek (MPI for Astrophysics, Garching)
Comments: 20 pages, 15 figures, accepted for publication in A&A, included changes based on referee comments
Note: replaced with revised version Mon, 12 Mar 2007 12:50:21 GMT (934kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 14 Mar 07 00:00:12 GMT
0703281 -- 0703335 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703287 [abs, ps, pdf, other] :
Title: Limits on Mass and Radius for the ms-Period X-ray Pulsar SAX J1808.4-3658
Authors: Denis A. Leahy, Sharon M. Morsink, Coire Cadeau
Comments: 6 pages, 2 figures. Submitted to ApJ Letters

We present an analysis of the light curves of SAX J1808.4-3658 during its 1998 and 2002 outbursts. We assume a hot spot model where the X-rays are originate from the surface of the neutron star. We obtain 80%, 90%, 2 $\sigma$ and 3 $\sigma$ limits on the mass and radius, which suggest a soft equation of state. At the 3 $\sigma$ level, the radius must satisfy R<11.9 km which rules out very stiff equations of state. At the 2 $\sigma$ level, the radius must satisfy R<11.6 km, ruling out equations of state with more moderate stiffness.

 
astro-ph/0703311 [abs, ps, pdf, other] :
Title: Explosive hydrogen burning during type I X-ray bursts
Authors: Jacob Lund Fisker, Hendrik Schatz, Friedrich-Karl Thielemann
Comments: 53 pages, 24 figures, submitted to Astrophys. J

Explosive hydrogen burning in type I X-ray bursts (XRBs) comprise charged particle reactions creating isotopes with masses up to A~100. Since charged particle reactions in a stellar environment are very temperature sensitive, we use a realistic time-dependent general relativistic and self-consistent model of type I x-ray bursts to provide accurate values of the burst temperatures and densities. This allows a detailed and accurate time-dependent identification of the reaction flow from the surface layers through the convective region and the ignition region to the neutron star ocean. Using this, we determine the relative importance of specific nuclear reactions in the X-ray burst.

 
astro-ph/0703326 [abs, ps, pdf, other] :
Title: Spectral and Rotational Changes in the Isolated Neutron Star RX J0720.4-3125
Authors: Marten H. van Kerkwijk (U. Toronto), David L. Kaplan (MIT), George G. Pavlov (Penn. State), Kaya Mori (U. Toronto)
Comments: 4 pages, 2 figures, 2 tables, emulateapj format. ApJL, accepted

RX J0720.4-3125 is an isolated neutron star that, uniquely in its class, has shown changes in its thermal X-ray spectrum. We use new spectra taken with Chandra's Low Energy Transmission Grating Spectrometer, as well as archival observations, to try to understand the timescale and nature of these changes. We construct lightcurves, which show both small, slow variations on a timescale of years, and a larger event that occurred more quickly, within half a year.
From timing, we find evidence for a `glitch' coincident with this larger event, with a fractional increase in spin frequency of 5x10^{-8}. We compare the `before' and `after' spectra with those from RX J1308.6+2127, an isolated neutron star with similar temperature and magnetic field strength, but with a much stronger absorption feature in its spectrum. We find that the `after' spectrum can be represented remarkably well by the superposition of the `before' spectrum, scaled by two thirds, and the spectrum of RX J1308.6+2127, thus suggesting that the event affected approximately one third of the surface. We speculate the event reflects a change in surface composition caused by, e.g., an accretion episode.

 
astro-ph/0703334 [abs, ps, pdf, other] :
Title: Supernova neutrinos
Authors: Christian Y. Cardall (Oak Ridge National Laboratory and University of Tennessee, Knoxville)
Comments: Belated posting of contribution to the proceedings of NOW2006, Conca Specchiulla, Italy, September 9-16, 2006

A nascent neutron star resulting from stellar collapse is a prodigious source of neutrinos of all flavors. While the most basic features of this neutrino emission can be estimated from simple considerations, the detailed simulation of the neutrinos' decoupling from the hot neutron star is not yet computationally tractable in its full glory, being a time-dependent six-dimensional transport problem. Nevertheless, supernova neutrino fluxes are of great interest in connection with the core-collapse supernova explosion mechanism and supernova nucleosynthesis, and as a potential probe of the supernova environment and of some of the neutrino mixing parameters that remain unknown; hence a variety of approximate transport schemes have been used to obtain results with reduced dimensionality. However, none of these approximate schemes have addressed a recent challenge to the conventional wisdom that neutrino flavor mixing cannot impact the explosion mechanism or r-process nucleosynthesis.

 

Cross-listings


1 abstracts or titles contain neutron star, magnetar or pulsar


hep-ph/0703116 [abs, ps, pdf, other] :
Title: Sterile neutrinos
Authors: Alexander Kusenko
Comments: 11 pages, 1 figure; invited talk at the "12th Mexican School on particles and fields" and the "6th Latin American Symposium on high energy physics" (VI-Silafae/XII-MSPF)

Neutrino masses are usually described by adding to the Standard Model some SU(2)-singlet fermions that have the Yukawa couplings, as well as some Majorana mass terms. The number of such fields and the scales of their Majorana masses are not known. Several independent observations point to the possibility that some of these singlets may have masses well below the electroweak scale. A sterile neutrino with mass of a few keV can account for cosmological dark matter. The same particle would be emitted anisotropically from a cooling neutron star born in a supernova explosion. This anisotropy can be large enough to explain the observed velocities of pulsars. A lighter sterile neutrino, with mass of the order of eV, is implied by the LSND results; it can have profound implications for cosmology. We review the physics of sterile neutrinos and the roles they may play in astrophysics and cosmology.

 

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Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 15 Mar 07 00:00:10 GMT
0703336 -- 0703371 received


4 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703336 [abs, ps, pdf, other] :
Title: VLBA measurement of the transverse velocity of the magnetar XTE J1810-197
Authors: D. J. Helfand (1), S. Chatterjee (2), W. F. Brisken (3), F. Camilo (1), J. Reynolds (4), M. H. van Kerkwijk (5), J. P. Halpern (1), S. M. Ransom (3) ((1) Columbia U., (2) U. of Sydney, (3) NRAO, (4) ATNF, (5) U. of Toronto)
Comments: Accepted for publication in The Astrophysical Journal. Six pages, 2 figures

We have obtained observations of the magnetar XTE J1810-197 with the Very Long Baseline Array at two epochs separated by 106 days, at wavelengths of 6 cm and 3.6 cm. Comparison of the positions yields a proper motion value of 13.5+-1.0 mas/yr at an equatorial position angle of 209.4+-2.4 deg (east of north). This value is consistent with a lower-significance proper motion value derived from infrared observations of the source over the past three years, also reported here. Given its distance of 3.5+-0.5 kpc, the implied transverse velocity corrected to the local standard of rest is 212+-35 km/s (1 sigma). The measured velocity is slightly below the average for normal young neutron stars, indicating that the mechanism(s) of magnetar birth need not lead to high neutron star velocities. We also use Australia Telescope Compact Array, Very Large Array, and these VLBA observations to set limits on any diffuse emission associated with the source on a variety of spatial scales, concluding that the radio emission from XTE J1810-197 is >96% pulsed.

 
astro-ph/0703343 [abs, ps, pdf, other] :
Title: The Distance to the Isolated Neutron Star RX J0720.4-3125
Authors: D. L. Kaplan, M. H. van Kerkwijk, J. Anderson
Comments: 17 pages, 8 figures. To be published in ApJ

We have used a set of dedicated astrometric data from the Hubble Space Telescope to measure the parallax and proper motion of the nearby neutron star RX J0720.4-3125. At each of eight epochs over two years, we used the High Resolution Camera of the Advanced Camera for Surveys to measure the position of the B=26.6 target to a precision of ~2 mas (~0.07 pix) relative to 22 other stars. From these data we measure a parallax of pi=2.8+/-0.9 mas (for a distance of 360+170-90 pc) and a proper motion of mu=107.8+/-1.2 mas/yr. Exhaustive testing of every stage of our analysis suggests that it is robust, with a maximum systematic uncertainty on the parallax of 0.4 mas. The distance is compatible with earlier estimates made from scaling the optical emission of RX J0720.4-3125 relative to the even closer neutron star RX J1856.5-3754. The distance and proper motion imply a transverse velocity of 180+90-40 km/s, comparable to velocities observed for radio pulsars. The speed and direction suggest an origin for RX J0720.4-3125 in the Trumpler 10 OB association ~0.7 Myr ago, with a possible range of 0.5-1.0 Myr given by the uncertainty in the distance.

 
astro-ph/0703346 [abs, pdf, other] :
Title: The Birthrate of Magnetars
Authors: Ramandeep Gill, Jeremy Heyl (University of British Columbia)
Comments: will be appreciated; 7 pages, 3 figures, will be submitted to Monthly Notices of the Royal Astronomical Society

Magnetars, neutron stars with ultra strong magnetic fields ($B\sim 10^{14} - 10^{15}$G), manifest their exotic nature in the form of soft gamma-ray repeaters and anomalous X-ray pulsars. This study estimates the birthrate of magnetars to be $\sim$ 0.22 per century with a galactic population comprising of $\sim$17 objects. A population synthesis was carried out based on the five anomalous X-ray pulsars detected in the ROSAT All-Sky Survey by comparing their number to that of massive OB stars in a well defined volume. Additionally, the group of seven X-ray dim isolated neutron stars detected in the same survey were found to have a birthrate of $\sim$ 2 per century with a galactic population of $\sim$ 22,000 objects.

 
astro-ph/0703371 [abs, ps, pdf, other] :
Title: Investigating the nature of absorption lines in the Chandra X-ray spectra of the neutron star binary 4U 1820-30
Authors: E. M. Cackett, J. M. Miller (Univ. of Michigan), J. Homan (MIT), M. van der Klis (Amsterdam), M. Mendez (Amsterdam/SRON/Utrecht), J. Raymond, D. Steeghs (CfA), R. Wijnands (Amsterdam)
Comments: 7 pages, 3 figures, 3 tables, submitted to ApJ

We use four Chandra gratings spectra of the neutron star low-mass X-ray binary 4U 1820-30 to better understand the nature of certain X-ray absorption lines in X-ray binaries, including the Ne II, Ne III, Ne IX, O VII, and O VIII lines. The equivalent widths of the lines are generally consistent between the observations, as expected if these lines originate in the hot interstellar medium. No evidence was found that the lines were blueshifted, again supporting the interstellar medium origin, though this may be due to poor statistics. There may be low-level variability in the O VIII Ly-alpha line though it is not clearly correlated with the source flux as might be expected if the origin of the line is local to the source. We conclude that a high fraction of the absorption is interstellar in origin, but more sensitive observations are needed to search for low-level variability.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0502102 [abs, ps, pdf, other] :
Title: The Interpretations For the Low and High Frequency QPO Correlations of X-ray Sources Among White Dwarfs, Neutron Stars and Black Holes
Authors: C. M. Zhang, H.X. Yin, Y.H. Zhao
Comments: 11 pages, 1 figure, accepted by PASP
Note: replaced with revised version Wed, 14 Mar 2007 15:02:40 GMT (25kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 16 Mar 07 00:00:13 GMT
0703372 -- 0703416 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703384 [abs, ps, pdf, other] :
Title: Peak Luminosities of the Hard States of GX 339-4: Implications for the Accretion Geometry, Disk Mass, and Black Hole Mass
Authors: Wenfei Yu, Robert Fender, Michiel van der Klis
Comments: 15 pages, including 3 figures, submitted to ApJ

We have analyzed observations of the black hole transient {GX 339$-$4} made with the {\it Rossi} X-ray Timing Explorer (RXTE) and the Burst and Transient Source Experiment (BATSE) on board the Compton Gamma-ray Observatory (CGRO). We have found a nearly linear relation between the peak flux during the low/hard (LH) state that occurs at the beginning of an outburst and the time since the flux peak of the latest LH state identified in the previous outburst. Assuming that the rate at which mass accumulates in the accretion disk between these peaks is constant and that any mass that remains in the disk after an outburst has a negligible effect on the next outburst, this nearly linear relation suggests that the peak flux during the LH state that occurs at the beginning of an outburst is related to the mass in the disk, and thus that the entire disk is probably involved in powering these LH states. We have also found a positive correlation between the peak luminosities of the LH state in the three recent outbursts of {GX 339$-$4} and the peak luminosities of the following HS state. This correlation is similar to the correlations reported previously for {Aql X$-$1}, {4U 1705$-$44}, and {XTE J1550$-$564}, providing further support that the accretion flow that powers the LH state is related to the accretion flow that powers the following HS state. Although the luminosity of the LH-to-HS transition varies by up to an order of magnitude, the neutron stars and the black holes are distinguishable in the state transition luminosity. We discuss the implications for the mass determination of the compact stars in the Ultra-luminous X-ray sources (ULXs).

 
astro-ph/0703392 [abs, ps, pdf, other] :
Title: Triaxial nuclear models and the outer crust of nonaccreting cold neutron stars
Authors: Lu Guo, M. Hempel, J. Schaffner-Bielich, J. A. Maruhn
Comments: 4 pages

The properties and composition of the outer crust of nonaccreting cold neutron stars are studied by applying the model of Baym, Pethick and Sutherland, which was extended by the higher order corrections for the atomic binding, screening, exchange and zero-point energies, and taking into account for the first time triaxial deformations of nuclei. Experimental data of the atomic mass table from Audi, Wapstra and Thibault of 2003 are used together with two different theoretical nuclear models: the SLy6 parametrization for a Skyrme-Hartree-Fock model with BCS pairing and the parametrization D1S for a Hartree-Fock-Bogolyubov calculation with a finite-range Gogny interaction. The nuclear masses in both theoretical models were calculated under consideration of 3D triaxial deformations. The two models are compared concerning their neutron drip line, magic neutron numbers and the sequence of nuclei up to the neutron drip in the outer crust of nonaccreting cold neutron stars, with special emphasis on the effect of triaxial deformations.

 
astro-ph/0703414 [abs, ps, pdf, other] :
Title: Discovery of HE 1523-0901, a Strongly r-Process Enhanced Metal-Poor Star with Detected Uranium
Authors: Anna Frebel, Norbert Christlieb, John E. Norris, Christopher Thom, Timothy C. Beers, Jaehyon Rhee
Comments: 7 pages, 2 figures. Accepted for publication in ApJ Letters

We present age estimates for the newly discovered very r-process enhanced metal-poor star HE 1523-0901 ([Fe/H]=-2.95) based on the radioactive decay of Th and U. The bright (V=11.1) giant was found amongst a sample of bright metal-poor stars selected from the Hamburg/ESO survey. From an abundance analysis of a high-resolution (R=75,000) VLT/UVES spectrum we find HE 1523-0901 to be strongly overabundant in r-process elements ([r/Fe]=1.8). The abundances of heavy neutron-capture elements (Z>56) measured in HE 1523-0901 match the scaled solar r-process pattern extremely well. We detect the strongest optical U line at 3859.57 A. For the first time, we are able to employ several different chronometers, such as the U/Th, U/Ir, Th/Eu and Th/Os ratios to measure the age of a star. The weighted average age of HE 1523-0901 is 13.2 Gyr. Several sources of uncertainties are assessed in detail.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 19 Mar 07 00:00:11 GMT
0703417 -- 0703453 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703419 [abs, ps, pdf, other] :
Title: Search for gravitational wave radiation associated with the pulsating tail of the SGR 1806-20 hyperflare of 27 December 2004 using LIGO
Authors: The LIGO Scientific Collaboration
Comments: 13 pages, 2 tables, 3 figures

We have searched for Gravitational Waves (GWs) associated with the SGR 1806-20 hyperflare of 27 December 2004. This event, originating from a Galactic neutron star, displayed exceptional energetics. Recent investigations of the X-ray light curve's pulsating tail revealed the presence of Quasi-Periodic Oscillations (QPOs) in the 30 - 2000 Hz frequency range, most of which coincides with the bandwidth of the LIGO detectors. These QPOs, with well-characterized frequencies, can plausibly be attributed to seismic modes of the neutron star which could emit GWs. Our search targeted potential quasi-monochromatic GWs lasting for tens of seconds and emitted at the QPO frequencies. We have observed no candidate signals above a pre-determined threshold and our lowest upper limit was set by the 92.5 Hz QPO observed in the interval from 150 s to 260 s after the start of the flare. This bound corresponds to a (90% confidence) root-sum-squared amplitude h_rssdet^90% = 4.5e-22 strain Hz^-1/2 on the GW waveform strength in the detectable polarization state reaching our Hanford (WA) 4 km detector. We illustrate the astrophysical significance of the result via an estimated characteristic energy in GW emission that we would expect to be able to detect. The above result corresponds to 7.7e46 erg (= 4.3e-8 M_sun c^2), which is of the same order as the total (isotropic) energy emitted in the electromagnetic spectrum. This result provides a means to probe the energy reservoir of the source with the best upper limit on the GW waveform strength published and represents the first broadband asteroseismology measurement using a GW detector.

 
astro-ph/0703431 [abs, ps, pdf, other] :
Title: Correlations between X-ray Spectral Characteristics and Quasi-Periodic Oscillations in Sco X-1
Authors: Charles F. Bradshaw (MITRE/GMU), Lev Titarchuk (GMU/NRL/GSFC), Sergey Kuznetsov (UCR/IKI, Russia)
Comments: 7 pages, 4 figures, accepted for publication in ApJ (July 1, 2007, v663n1 issue)

Correlations between 1-10 Hz quasi-periodic oscillations (QPOs) and spectral power law index have been reported for black hole (BH) candidate sources and one neutron star source, 4U 1728-34. An examination of QPO frequency and index relationships in Sco X-1 is reported herein. We discovered that Sco X-1, representing Z-source groups, can be adequately modeled by a simple two-component model of Compton up-scattering with a soft photon electron temperature of about 0.4 keV, plus an Iron K-line. The results show a strong correlation between spectral power law index and kHz QPOs. Because Sco X-1 radiates near the Eddington limit, one can infer that the geometrical configuration of the Compton cloud (CC) is quasi-spherical because of high radiation pressure in the CC. Thus, we conclude that the high Thomson optical depth of the Compton cloud, in the range of ~5-6 from the best-fit model parameters, is consistent with the neutron star's surface being obscured by material. Moreover, a spin frequency of Sco X-1 is likely suppressed due to photon scattering off CC electrons. Additionally, we demonstrate how the power spectrum evolves when Sco X-1 transitions from the horizontal branch to the normal branch.

 
astro-ph/0703447 [abs, ps, pdf, other] :
Title: Early afterglow detection in the Swift observations of GRB 050801
Authors: Massimiliano De Pasquale, S. R. Oates, M.J.Page, D.N. Burrows, A.J.Blustin, S. Zane, K.O. Mason, P.W.A. Roming, D. Palmer, N. Gehrels, B. Zhang
Comments: 13 pages, 7 figs, Accepted for publication in MNRAS

We present results of Swift optical, UV and X-ray observations of the afterglow of GRB 050801. The source is visible over the full optical, UV and X-ray energy range of the Swift UVOT and XRT instruments.Both optical and X-ray lightcurves exhibit a broad plateau (\Delta t/t ~ 1) during the first few hundred seconds after the gamma-ray event. We investigate the multiwavelength spectral and timing properties of the afterglow, and we suggest that the behaviour at early times is compatible with an energy injection by a newly born magnetar with a period of a few tenths of a millisecond, which keeps the forward shock refreshed over this short interval by irradiation. Reverse shock emission is not observed. Its suppression might be due to GRB ejecta being permeated by high magnetic fields, as expected for outflows powered by a magnetar.Finally, the multiwavelength study allows a determination of the burst redshift, z=1.56.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610505 [abs, ps, pdf, other] :
Title: X-ray emission properties of the old pulsar PSR B2224+65
Authors: C. Y. Hui, W. Becker
Comments: Accepted by A&A, 7 pages, 6 figures, 3 tables
Note: replaced with revised version Fri, 16 Mar 2007 11:47:04 GMT (201kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Tue, 20 Mar 07 00:00:15 GMT
0703454 -- 0703502 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703499 [abs, ps, pdf, other] :
Title: Exploring the connection between the stellar wind and the non-thermal emission in LS 5039
Authors: V. Bosch-Ramon, C. Motch, M. Ribo, R. Lopes de Oliveira, E. Janot-Pacheco, I. Negueruela, J. M. Paredes, A. Martocchia
Comments: 11 pages (preprint format), 8 figures, submitted to A&A (shown abstract shortened, see paper abstract!)

New xmm observations have been performed around periastron and apastron passages in September 2005, during an epoch of presumably enhanced O star wind. Also, 2005 Chandra observations on LS 5039 are revisited. Moreover, a compilation of the Halpha EW and rxte/ASM X-ray count rate obtained since the 1990s is carried out, being both quantities compared with each other and also with historical radio data. xmm observations show higher and harder emission around apastron than around periastron. No signatures of thermal emission or a reflection iron line indicating the presence of an accretion disk are found in the spectrum, and the hydrogen column density (N_H) is compatible with a constant and with the interstellar value in both observations. The hardness ratio and the count rate seem uncorrelated at periastron and may be correlated at apastron. We find that LS 5039 was bright and hard in 2005 chandra observations. The ASM count rate shows changes by a ~80% on year timescales, and the Halpha EW shows yearly variations of a ~10%. Both quantities may be anticorrelated rather than correlated, unlike it was previously thought. At radio frequencies, the emission varies by ~20%, presenting some similarities with the X-rays. ASM, Halpha EW and radio data may hint to variability at orbital timescales. The low value and constancy of the N_H could imply that the X-ray emitter is located at >~10^12 cm from the compact object. We suggest that the non-thermal emission in LS 5039 is related to the jet and the stellar wind in a complex way and produced outside the system. However, the present data do not rule out the pulsar scenario.

 
astro-ph/0703501 [abs, ps, pdf, other] :
Title: Uncovering the Nature of the X-ray Transient 4U 1730-22: Discovery of X-ray Emission from a Neutron Star in Quiescence with Chandra
Authors: John A. Tomsick (SSL/UCB and CASS/UCSD), Dawn M. Gelino (MSS/Caltech), Philip Kaaret (Univ. of Iowa)
Comments: Accepted by the Astrophysical Journal

The X-ray transient, 4U 1730-22, has not been detected in outburst since 1972, when a single outburst was detected by the Uhuru satellite. This neutron star or black hole X-ray binary is presumably in quiescence now, and here, we report on X-ray and optical observations of the 4U 1730-22 field designed to identify the system's quiescent counterpart. Using Chandra, we have found a very likely counterpart. The candidate counterpart is close to the center of the Uhuru error region and has a thermal spectrum. The 0.3-8 keV spectrum is well-described by a neutron star atmosphere model with an effective temperature of 131+/-21 eV. For a neutron star with a 10 km radius, the implied source distance is 10(+12)(-4) kpc, and the X-ray luminosity is 1.9E33 ergs/s assuming a distance of 10 kpc. Accretion from a companion star is likely required to maintain the temperature of this neutron star, which would imply that it is an X-ray binary and therefore, almost certainly the 4U 1730-22 counterpart. We do not detect an optical source at the position of the Chandra source down to R > 22.1, and this is consistent with the system being a Low-Mass X-ray Binary at a distance greater than a few kpc. If our identification is correct, 4U 1730-22 is one of the 5 most luminous of the 20 neutron star transients that have quiescent X-ray luminosity measurements.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0610685 [abs, ps, pdf, other] :
Title: The magnetar XTE J1810-197: variations in torque, radio flux density and pulse profile morphology
Authors: F. Camilo (1), I. Cognard (2), S. M. Ransom (3), J. P. Halpern (1), J. Reynolds (4), N. Zimmerman (1), E. V. Gotthelf (1), D. J. Helfand (1), P. Demorest (5), G. Theureau (2), D. C. Backer (5) ((1) Columbia, (2) CNRS, (3) NRAO, (4) ATNF, (5) Berkeley)
Comments: Accepted for publication in ApJ. Major changes with respect to submitted (v1) version: includes an additional 4 months of timing, flux and pulse shape data, and revised discussion
Note: replaced with revised version Mon, 19 Mar 2007 16:30:30 GMT (143kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Wed, 21 Mar 07 00:00:12 GMT
0703503 -- 0703536 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703507 [abs, ps, pdf, other] :
Title: Quark core formation in spinning-down pulsars
Authors: G. F. Marranghello, T. Regimbau, J. A. de Freitas Pacheco
Comments: Proceedings of the 2nd International Workshop on Astronomy and Relativistic Astrophysics, to appear in IJMPD

Pulsars spin-down due to magnetic torque reducing its radius and increasing the central energy density. Some pulsar which are born with central densities close to the critical value of quark deconfinement may undergo a phase transition and structural re-arrengement. This process may excite oscillation modes and emmit gravitational waves. We determine the rate of quark core formation in neutron stars using a realistic population synthesis code.

 
astro-ph/0703513 [abs, ps, pdf, other] :
Title: Discovery of a Pulsar Candidate Associated with the TeV Gamma-ray Source HESS J1813-178
Authors: E. V. Gotthelf, D. J. Helfand (Columbia University)
Comments: 3 pages, 3 figures. Latex, aipproc.cls. To be published in the proceedings of the conference "First GLAST Symposium" (Febuary 5-8, 2007, Stanford Univ., USA), AIP, ed. S. Barnes

We present a Chandra X-ray observation of G12.82-0.02, a shell-like radio supernova remnant coincident with the TeV gamma-ray source HESS J1813-178. We resolve the X-ray emission from the co-located ASCA source into a compact object surrounded by structured diffuse emission that fills the interior of the radio shell. The morphology of the diffuse emission strongly resembles that of a pulsar wind nebula. The spectrum of the compact source is well-characterized by a power-law with index approx. 1.3, typical of young and energetic rotation-powered pulsars. For a distance of 4.5 kpc, consistent with the X-ray absorption, the 2-10 keV X-ray luminosity of the putative pulsar and nebula is L(PSR) = 3.2E33 erg/s and L(PWN) = 1.4E34 erg/s, respectively. Both the flux ratio of L(PWN)/L(PSR) = 4.3 and the total luminosity of this system imply a pulsar spin-down power greater then 1E37 erg/s, on a par with the top ten most energetic young pulsars in the Galaxy. We associate the putative pulsar with the radio remnant and the TeV source and discuss the origin of the gamma-ray emission.

 
astro-ph/0703523 [abs, ps, pdf, other] :
Title: Comparing P-stars with Observations
Authors: Paolo Cea
Comments: 11 pages, 3 figures

P-stars are compact stars made of up and down quarks in $\beta$-equilibrium with electrons in a chromomagnetic condensate. P-stars are able to account for compact stars as well as stars with radius comparable with canonical neutron stars. We compare p-stars with different available observations. Our results indicate that p-stars are able to reproduce in a natural manner several observations from isolated and binary pulsars. On the other hand, we argue that the standard model based on neutron stars is getting in troubles leading to the need for a drastic revision of the standard paradigm.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar



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1 abstracts or titles contain neutron star, magnetar or pulsar


gr-qc/0605044 [abs, ps, pdf, other] :
Title: Eigenmode frequency distribution of rapidly rotating neutron stars
Authors: Stratos Boutloukos, Hans-Peter Nollert
Comments: 10 pages, 6 figures, added references, improved wording, published in Physical Review D
Journal-ref: Phys.Rev. D75 (2007) 043007
Note: replaced with revised version Tue, 20 Mar 2007 19:59:51 GMT (69kb)
 

Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Thu, 22 Mar 07 00:00:12 GMT
0703537 -- 0703569 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Fri, 23 Mar 07 00:00:11 GMT
0703570 -- 0703593 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



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0 abstracts or titles contain neutron star, magnetar or pulsar



Astrophysics authors/titles "new"

Astrophysics


astro-ph new abstracts, Mon, 26 Mar 07 00:00:13 GMT
0703594 -- 0703619 received


3 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703597 [abs, ps, pdf, other] :
Title: General relativistic simulations of magneto-rotational core collapse with microphysics
Authors: P. Cerdá-Durán, J. A. Font, H. Dimmelmeier
Comments: 25 pages, 14 figures, submitted to Astronomy & Astrophysics on March 7, 2007

This paper presents results from axisymmetric simulations of magneto-rotational stellar core collapse to neutron stars in general relativity. These simulations are performed using a new general relativistic numerical code specifically designed to study this astrophysical scenario. The code is based on the conformally-flat approximation of Einstein's field equations and conservative formulations of the magneto-hydrodynamics equations. The code has been recently upgraded to incorporate a tabulated, microphysical equation of state and an approximate deleptonization scheme. This allows us to perform the most realistic simulations of magneto-rotational core collapse to date, which are compared with simulations employing a simplified (hybrid) equation of state, widely used in the relativistic core collapse community. Furthermore, state-of-the-art (unmagnetized) initial models from stellar evolution are used. In general, stellar evolution models predict weak magnetic fields in the progenitors, which justifies our simplification of performing the computations under the approach that we call the passive field approximation for the magnetic field. Our results show that for the core collapse models with microphysics the saturation of the magnetic field cannot be reached within dynamical time scales by winding up the poloidal magnetic field into a toroidal one. We estimate the effect of other amplification mechanisms including the magneto-rotational instability (MRI) and several types of dynamos.

 
astro-ph/0703599 [abs, ps, pdf, other] :
Title: Mergers of Black Hole -- Neutron Star binaries. I. Methods and First Results
Authors: Emmanouela Rantsiou (1), Shiho Kobayashi (2), Pablo Laguna (3), Frederic Rasio (1) ((1) Department of Physics and Astronomy, Northwestern University; (2) Astrophysics Research Institute, Liverpool John Moores University; (3) Department of Astronomy and Astrophysics and Department of Physics, Pennsylvania State University)
Comments: 48 pages, 17 figures

We use a 3-D relativistic SPH (Smoothed Particle Hydrodynamics) code to study mergers of black hole -- neutron star (BH--NS) binary systems with low mass ratios, adopting $M_{NS}/M_{BH} \simeq 0.1$ as a representative case. The outcome of such mergers depends sensitively on both the magnitude of the BH spin and its obliquity (i.e., the inclination of the binary orbit with respect to the equatorial plane of the BH). In particular, only systems with sufficiently high BH spin parameter $a$ and sufficiently low orbital inclinations allow any NS matter to escape or to form a long-lived disk outside the BH horizon after disruption. Mergers of binaries with orbital inclinations above $\sim60^o$ lead to complete prompt accretion of the entire NS by the BH, even for the case of an extreme Kerr BH. We find that the formation of a significant disk or torus of NS material around the BH always requires a near-maximal BH spin and a low initial inclination of the NS orbit just prior to merger.

 
astro-ph/0703611 [abs, ps, pdf, other] :
Title: The Chemistry of the Local Group
Authors: Brad K. Gibson
Comments: 4 pages, 1 figure, in Proceedings of IAU Symposium No. 241 "Stellar Populations as Building Blocks of Galaxies", eds. A. Vazdekis and R. Peletier, Cambridge: Cambridge University Press, in press

Simulations of the chemical enrichment histories of ten Local Group (LG) dwarf galaxies are presented, employing empirically-derived star formation histories (SFHs), a rich network of isotopic and elemental nucleosynthetic yields, and a range of prescriptions for supernova (SN)-driven outflows. Our main conclusions are that (i) neutron-capture element patterns (particularly that of Ba/Y) suggest a strong contribution from low- and intermediate-mass stars, (ii) neutron star mergers may play a relatively larger role in the nucleosynthesis of dwarfs, (iii) SN feedback alone can explain the observed gas fraction in dwarf irregulars (dIrrs), but dwarf spheroidals (dSphs) require almost all their gas to be removed via ram pressure and/or tidal stripping, (iv) the predicted heavy Mg isotope enhancements in the interstellar medium of dwarfs may provide an alternate solution to claims of a varying fine structure (v) the gas lost from dwarfs have O,Si/C abundances in broad agreement with intergalactic medium abundances at redshifts 2<z<4, and (vi) the chemical properties of dSphs are well-matched by preventing galactic winds from re-accreting, whilst those of dIrrs are better-matched by incorporating metallicity-dependent cooling and re-accretion of hot winds. Finally, doubts are cast upon a claimed association between LG dSph UMaII and High-Velocity Cloud Complex A.

 

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astro-ph new abstracts, Tue, 27 Mar 07 00:00:16 GMT
0703620 -- 0703660 received


1 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703641 [abs, ps, pdf, other] :
Title: Simulation of the interstellar scintillation and the extreme scattering events of pulsars
Authors: Murad Hamidouche, Jean-Francois Lestrade
Comments: Accepted for publication in Astronomy & Astrophysics

The rare and conspicuous flux density variations of some radio sources (extragalactic and pulsars) for periods of weeks to months have been denoted Extreme Scattering Events (ESE's) by Fiedler et al. (1987). Presently, there is no astrophysical mechanism that satisfactorily produces this phenomenon. In this paper, we conjecture that inhomogeneities of the electronic density in the turbulent interstellar medium might be the origin of this phenomenon. We have tested this conjecture by a simulation of the scintillation of the pulsar B1937+21 at 1.4 GHz and 1.7 GHz for a period of six months. To this end, we have constructed a large square Kolmogorov phase screen made of 131k x 131k pixels with electron inhomogeneity scales ranging from 6 x $10^6$ m to $10^{12}$ m and used the Kirchhoff-Fresnel integral to simulate dynamic spectra of a pulsar within the framework of Physical Optics.
The simulated light curves exhibit a 10 day long variation simultaneously at 1.41 and 1.7 GHz that is alike the ``ESE'' observed with the Nancay radiotelescope toward the pulsar B1937+21 in October 1989. Consequently, we conclude that ``ESE'' toward pulsars can be caused naturally by the turbulence in the ionized interstellar medium instead of invoking the crossing of discrete over pressured ionized clouds on the line of sight as in the model of Fiedler et al. (1987). We suggest that longer events could occur in a simulation of scintillation, if larger electron inhomogeneities > $10^{12}$ m were included in the construction of the Kolmogorov phase screen. This next step requires a supercomputer.

 

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astro-ph new abstracts, Wed, 28 Mar 07 00:00:24 GMT
0703661 -- 0703697 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703684 [abs, ps, pdf, other] :
Title: The Post-Burst Awakening of the Anomalous X-ray Pulsar in Westerlund 1
Authors: G.L. Israel, S. Campana, S. Dall'Osso, M. P. Muno, J. Cummings, R. Perna, L. Stella
Comments: Accepted for publication on ApJ Main Journal; 24 pages, 8 figures

On September 21, 2006, an intense (~10^39 erg/s) and short (20 ms) burst was detected by Swift BAT at a position consistent with that of the candidate Anomalous X-ray Pulsar, CXOU J164710.2-455216, discovered by Chandra in 2005. Swift follow-up observations began about 13 hours after the event and found the source at a 1-10keV flux level of about 4.5 x 10^-11 erg/s/cm^2, i.e. ~300 times brighter than measured 5 days earlier by XMM. We report the results obtained from Swift BAT observations of the burst and subsequent Swift XRT observations carried out during the first four months after the burst. These data are complemented with those from two XMM observations (carried out just before and after the BAT event) and four archival Chandra observations carried out between 2005 and 2007. We find a phase coherent solution for the source pulsations after the burst. The evolution of the pulse phase comprises an exponential component decaying with timescale of 1.4d which we interpret as the recovery stage following a large glitch (Delta nu / nu about 6 x 10^-5). We also detect a quadratic component corresponding to a spin-down rate of Pdot ~ 9 x 10^-13, implying a magnetic field strength of 10^14 Gauss.
During the first Swift XRT observation taken 0.6 days after the burst, the spectrum showed a kT = 0.65keV blackbody (R_BB = 1.5km) plus a Gamma=2.3 power-law accounting for about 60% of the 1-10 keV observed flux. Analysis of Chandra archival data, taken during 2005 when the source was in quiescence, reveal that the modulation in quiescence is 100% pulsed at energies above 4 keV and consistent with the (unusually small-sized) blackbody component being occulted by the neutron star as it rotates.

 
astro-ph/0703692 [abs, ps, pdf, other] :
Title: GRO J1744-28, search for the counterpart: infrared photometry and spectroscopy
Authors: Andrew J. Gosling (1), Reba M. Bandyopadhyay (2), S.A. Farrell (3,4), James C.A. Miller-Jones (5) ((1) University of Oxford, (2) University of Florida, (3) UNSW at ADFA, Australia, (4) CESR, (5) University of Amsterdam)
Comments: 8 pages, 6 figures, 1 table, MNRAS submitted

Using ISAAC on the VLT, we have detected 2 candidate counterparts to the bursting pulsar GRO J 1744-28, one bright and one faint, both within the X-ray error circles found using XMM-Newton and Chandra. Photometry and spectroscopy of the bright candidate indicate that it is most likely a G type giant. The spectrum does not show Brackett-gamma emission, a known indicator of accretion, and dynamical calculations and comparison with the X-ray mass-function indicate that this star is most likely not the true X-ray source counterpart. Photometry of the fainter candidate indicates it is a K5 V star at a distance of 4 kpc. This fits the LEdd distance and the measured infrared extinction. If this star is the IR counterpart, dynamical calculations would require the system to be at very low inclination; however this source cannot be excluded without follow-up spectroscopy to detect emission signatures. The mass-function remains the tightest constraint for this system. The true counterpart most likely has a mass M < 0.3Msol. Mass transfer in such a system will be by wind-accretion as the counterpart will not fill its Roche lobe given the observed Porb. In this case, the derived magnetic field strength of 2.4 x 10^11 G is sufficient to inhibit accretion of captured material by the propeller effect.

 

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astro-ph/0703513 [abs, ps, pdf, other] :
Title: Discovery of a Pulsar Candidate Associated with the TeV Gamma-ray Source HESS J1813-178
Authors: E. V. Gotthelf, D. J. Helfand (Columbia University)
Comments: 3 Pages, 3 Figures. Latex, aipproc.cls. To be published in "The Proceedings of the First International GLAST Symposium" (Held Febuary 5-8, 2007, Stanford Univ., USA), AIP, Eds. S. Ritz, P.F. Michelson, and C. Meegan. Updated coordinates
Note: replaced with revised version Mon, 26 Mar 2007 23:56:00 GMT (269kb)
 

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astro-ph new abstracts, Thu, 29 Mar 07 00:00:27 GMT
0703698 -- 0703740 received


2 abstracts or titles contain neutron star, magnetar or pulsar


astro-ph/0703712 [abs, ps, pdf, other] :
Title: Dynamics of Charged Particles in the Radio Emission Region of Pulsar Magnetosphere
Authors: R. M. C. Thomas, R. T. Gangadhara (Indian Institute of Astrophysics)
Comments: 16 pages, 11 figures, Accepted for publication in Astronomy and Astrophysics (2007)

We consider the classical picture of three dimensional motion of charged particles in pulsar magnetosphere. We adopt a perturbative method to solve the equation of motion, and find the trajectory of particles as they move along the rotating dipolar magnetic field lines. Our aim is to study the influence of rotation on the pulsar radio emission by considering the constrained motion of particles along the open dipolar magnetic field lines. We find that the rotation induces a significant curvature into the particle trajectories. Our model predicts the intensity on leading side dominates over that of trailing side. We expect that if there is any curvature induced radio emission from the region close to the magnetic axis then it must be due to the rotation induced curvature. Our model predicts the radius--to--frequency mapping (RFM) in the core emissions.

 
astro-ph/0703726 [abs, ps, pdf, other] :
Title: Accretion rate and the occurrence of multi-peaked X-ray bursts
Authors: Anna L. Watts, Immanuel Maurer (MPA Garching)
Comments: 5 pages, 4 figures, accepted for publication in A&A Letters

Most Type I X-ray bursts from accreting neutron stars have a lightcurve with a single peak, but there is a rare population of faint bursts that are double or even triple peaked. Suggested mechanisms include polar ignition with equatorial stalling, or multi-step energy release; the latter being caused by hydrodynamic instabilities or waiting points in the nuclear reaction sequence. We present an analysis of the accretion rate dependence of the multi-peak bursts, and discuss the consequences for the various models. The observations pose particular challenges for the polar ignition mechanism given current models of ignition latitude dependence.

 

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astro-ph/0701660 [abs, ps, pdf, other] :
Title: kHz QPO pairs expose the neutron star of Circinus X-1
Authors: S. Boutloukos, M. van der Klis, D. Altamirano, M. Klein-Wolt, R. Wijnands
Comments: 3 pages, 2 figures - one from astro-ph/0608089 (ApJ 653, 1435, 2006) in corrected form, to appear in the proceedings of the 11th Marcel Grossman meeting, improved wording, added reference
Note: replaced with revised version Wed, 28 Mar 2007 16:48:40 GMT (35kb)
 

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astro-ph new abstracts, Fri, 30 Mar 07 00:00:12 GMT
0703741 -- 0703768 received


0 abstracts or titles contain neutron star, magnetar or pulsar



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astro-ph/0701070 [abs, ps, pdf, other] :
Title: Chandra and XMM-Newton discovery of the transient X-ray pulsar in the nearby spiral galaxy NGC2403
Authors: Sergey Trudolyubov (IGPP/UCR, IKI), William Priedhorsky (LANL), France Cordova (UCR)
Comments: Accepted for publication in ApJ. 14 pages, 6 figures, uses emulateapj style. Updated to match the accepted version
Note: replaced with revised version Thu, 29 Mar 2007 00:50:56 GMT (508kb)
 

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[21]  arXiv:0704.0205 [ps, pdf, other] :
Title: Discovery of X-ray emission from the young radio pulsar PSR J1357-6429
Authors: P. Esposito, A. Tiengo, A. De Luca, F. Mattana
Comments: Submitted to A&A Letters on 2007 March 14 (revised version following referee's comments)

We present the first X-ray detection of the very young pulsar PSR J1357-6429 (characteristic age of 7.3 kyr) using data from the XMM-Newton and Chandra satellites. We found that the spectrum is well described by a power-law plus blackbody model, with photon index Gamma=1.4 and blackbody temperature kT=160 eV. For the estimated distance of 2.5 kpc, this corresponds to a 2-10 keV luminosity of about 1.2E+32 erg/s, thus the fraction of the spin-down energy channeled by PSR J1357-6429 into X-ray emission is one of the lowest observed. The Chandra data confirm the positional coincidence with the radio pulsar and allow to set un upper limit of 3E+31 erg/s on the 2-10 keV luminosity of a compact pulsar wind nebula. We do not detect any pulsed emission from the source and determine an upper limit of 30% for the modulation amplitude of the X-ray emission at the radio frequency of the pulsar.

 
[22]  arXiv:0704.0207 [ps, pdf, other] :
Title: Quark matter and the astrophysics of neutron stars
Authors: M Prakash
Comments: 8 pages, 6 figures, Plenary talk in Quark Matter 2006 to appear in J. Phys. G: Nucl. Part. Phys. 34 (2007)

Some of the means through which the possible presence of nearly deconfined quarks in neutron stars can be detected by astrophysical observations of neutron stars from their birth to old age are highlighted.

 
[24]  arXiv:0704.0219 [ps, pdf, other] :
Title: The Radio Emission, X-ray Emission, and Hydrodynamics of G328.4+0.2: A Comprehensive Analysis of a Luminous Pulsar Wind Nebula, its Neutron Star, and the Progenitor Supernova Explosion
Authors: Joseph D. Gelfand, B. M. Gaensler, Patrick O. Slane, Daniel J. Patnaude, John P. Hughes, Fernando Camilo
Comments: 27 pages, 11 figures, accepted for publication in The Astrophysical Journal

We present new observational results obtained for the Galactic non-thermal radio source G328.4+0.2 to determine both if this source is a pulsar wind nebula or supernova remnant, and in either case, the physical properties of this source. Using X-ray data obtained by XMM, we confirm that the X-ray emission from this source is heavily absorbed and has a spectrum best fit by a power law model of photon index=2 with no evidence for a thermal component, the X-ray emission from G328.4+0.2 comes from a region significantly smaller than the radio emission, and that the X-ray and radio emission are significantly offset from each other. We also present the results of a new high resolution (7 arcseconds) 1.4 GHz image of G328.4+0.2 obtained using the Australia Telescope Compact Array, and a deep search for radio pulsations using the Parkes Radio Telescope. We find that the radio emission has a flat spectrum, though some areas along the eastern edge of G328.4+0.2 have a steeper radio spectral index of ~-0.3. Additionally, we obtain a luminosity limit of the central pulsar of L_{1400} < 30 mJy kpc^2, assuming a distance of 17 kpc. In light of these observational results, we test if G328.4+0.2 is a pulsar wind nebula (PWN) or a large PWN inside a supernova remnant (SNR) using a simple hydrodynamic model for the evolution of a PWN inside a SNR. As a result of this analysis, we conclude that G328.4+0.2 is a young (< 10000 years old) pulsar wind nebula formed by a low magnetic field (<10^12 G) neutron star born spinning rapidly (<10 ms) expanding into an undetected SNR formed by an energetic (>10^51 ergs), low ejecta mass (M < 5 Solar Masses) supernova explosion which occurred in a low density (n~0.03 cm^{-3}) environment.

 

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[5]  arXiv:0704.0458 [ps, pdf, other] :
Title: Rotation Measures of Extragalactic Sources Behind the Southern Galactic Plane: New Insights into the Large-Scale Magnetic Field of the Inner Milky Way
Authors: J.C. Brown, M. Haverkorn, B.M. Gaensler, A.R. Taylor, N.S. Bizunok, N.M. McClure-Griffiths, J.M. Dickey, A.J. Green
Comments: 16 pages, 4 colour figures, 1 B/W figure, 1 table; Accepted for publication in ApJ on March 26, 2007

We present new Faraday rotation measures (RMs) for 148 extragalactic radio sources behind the southern Galactic plane (253o < l < 356o, |b| < 1.5o), and use these data in combination with published data to probe the large-scale structure of the Milky Way's magnetic field. We show that the magnitudes of these RMs oscillate with longitude in a manner that correlates with the locations of the Galactic spiral arms. The observed pattern in RMs requries the presence of at least one large-scale magnetic reversal in the fourth Galactic quadrant, located between the Sagittarius- Carina and Scutum-Crux spiral arms. To quantitatively compare our measurements to other recent studies, we consider all available extragalactic and pulsar RMs in the region we have surveyed, and jointly fit these data to simple models in which the large-scale field follows the spiral arms. In the best-fitting model, the magnetic field in the fourth Galactic quadrant is directed clockwise in the Sagittarius-Carina spiral arm (as viewed from the North Galactic pole), but is oriented counter- clockwise in the Scutum-Crux arm. This contrasts with recent analyses of pulsar RMs alone, in which the fourth-quadrant field was presumed to be directed counter-clockwise in the Sagittarius- Carina arm. Also in contrast to recent pulsar RM studies, our joint modeling of pulsar and extragalactic RMs demonstrates that large numbers of large-scale magnetic field reversals are not required to account for observations.

 
[19]  arXiv:0704.0536 [ps, pdf, other] :
Title: Binaries, microquasars and GLAST
Authors: Guillaume Dubus
Comments: 5 pages, invited talk to appear in Proc. of the 1st GLAST Symposium, Feb 5-8, 2007, Stanford, AIP, Eds. S. Ritz, P. F. Michelson, and C. Meegan

Radio and X-ray observations of the relativistic jets of microquasars show evidence for the acceleration of particles to very high energies. Signatures of non-thermal processes occurring closer in to the compact object can also be found. In addition, three binaries are now established emitters of high (> 100 MeV) and/or very high (> 100GeV) energy gamma-rays. High-energy emission can originate from a microquasar jet (accretion-powered) or from a shocked pulsar wind (rotation-powered). I discuss the impact GLAST will have in the very near future on studies of such binaries. GLAST is expected to shed new light on the link between accretion and ejection in microquasars and to enable to probe pulsar winds on small scales in rotation-powered binaries.

 

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[7]  arXiv:0704.0659 [pdf, other] :
Title: Long Gamma-Ray Burst Progenitors: Boundary Conditions and Binary Models
Authors: E.P.J. van den Heuvel, S.-C. Yoon
Comments: 8 pp., 2 figs, Proceedings of 5th Stromlo Symposium

The observed association of Long Gamma-Ray Bursts (LGRBs) with peculiar Type Ic supernovae gives support to Woosley`s collapsar/hypernova model, in which the GRB is produced by the collapse of the rapidly rotating core of a massive star to a black hole. The association of LGRBs with small star-forming galaxies suggests low-metallicity to be a condition for a massive star to evolve to the collapsar stage. Both completely-mixed single star models and binary star models are possible. In binary models the progenitor of the GRB is a massive helium star with a close companion. We find that tidal synchronization during core-helium burning is reached on a short timescale (less than a few millennia). However, the strong core-envelope coupling in the subsequent evolutionary stages is likely to rule out helium stars with main-sequence companions as progenitors of hypernovae/GRBs. On the other hand, helium stars in close binaries with a neutron-star or black-hole companion can, despite the strong core-envelope coupling in the post-helium burning phase, retain sufficient core angular momentum to produce a hypernova/GRB.

 
[9]  arXiv:0704.0675 [ps, pdf, other] :
Title: Proto-Neutron Star Winds, Magnetar Birth, and Gamma-Ray Bursts
Authors: B.D. Metzger, T.A. Thompson, E. Quataert
Comments: 5 pages; to appear in the AIP conference proceedings of "Supernova 1987A: 20 Years After - Supernovae and Gamma-Ray Bursters", February 19-23, 2007, Aspen, Colorado

We begin by reviewing the theory of thermal, neutrino-driven proto-neutron star (PNS) winds. Including the effects of magnetic fields and rotation, we then derive the mass and energy loss from magnetically-driven PNS winds for both relativistic and non-relativistic outflows, including important multi-dimensional considerations. With these simple analytic scalings we argue that proto-magnetars born with ~ millisecond rotation periods produce relativistic winds just a few seconds after core collapse with luminosities, timescales, mass-loading, and internal shock efficiencies favorable for producing long-duration gamma-ray bursts.

 
[14]  arXiv:0704.0689 [ps, pdf, other] :
Title: Study on Correlations between the Twin Kilohertz Quasi-periodic Oscillations in Low-mass X-ray Binaries
Authors: H. X. Yin, Y. H. Zhao
Comments: 14 pages, 3 figures, accepted by Advances of Space Research

The recently updated data of the twin kilohertz quasi-periodic oscillations (kHz QPOs) in the neutron star low-mass X-ray binaries are analyzed. The power-law fitting $\nu_{1}=a(\nu_{2}/1000)^{b}$ and linear fitting $\nu_{2}=A\nu_{1}+B$ are applied, individually, to the data points of four Z sources (GX 17+2, GX 340+0, GX 5-1 and Sco X-1) and four Atoll sources (4U 0614+09, 4U 1608-52, 4U 1636-53 and 4U 1728-34). The $\chi^{2}$-tests show that the power-law correlation and linear correlation both can fit data well. Moreover, the comparisons between the data and the theoretical models for kHz QPOs are discussed.

 

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[4]  arXiv:0704.0799 [ps, pdf, other] :
Title: Spin Evolution of Accreting Neutron Stars: Nonlinear Development of the R-mode Instability
Authors: Ruxandra Bondarescu, Saul A. Teukolsky, Ira Wasserman (Cornell University)
Comments: 17 pages, 9 figures

The nonlinear saturation of the r-mode instability and its effects on the spin evolution of Low Mass X-ray Binaries (LMXBs) are modeled using the triplet of modes at the lowest parametric instability threshold. We solve numerically the coupled equations for the three mode amplitudes in conjunction with the spin and temperature evolution equations. We observe that very quickly the mode amplitudes settle into quasi-stationary states. Once these states are reached, the mode amplitudes can be found algebraically and the system of equations is reduced from eight to two equations: spin and temperature evolution. Eventually, the system may reach thermal equilibrium and either (1) undergo a cyclic evolution with a frequency change of at most 10%, (2) evolve toward a full equilibrium state in which the accretion torque balances the gravitational radiation emission, or (3) enter a thermogravitational runaway on a very long timescale of about $10^6$ years. Alternatively, a faster thermal runaway (timescale of about 100 years) may occur. The sources of damping considered are shear viscosity, hyperon bulk viscosity and boundary layer viscosity. We vary proprieties of the star such as the hyperon superfluid transition temperature $T_c$, the fraction of the star that is above the threshold for direct URCA reactions, and slippage factor, and map the different scenarios we obtain to ranges of these parameters. For all our bound evolutions the r-mode amplitude remains small $\sim 10^{-5}$. The spin frequency is limited by boundary layer viscosity to $\nu_{max} \sim 800 Hz [S_{ns}/(M_{1.4} R_6)]^{4/11} T_8^{-2/11}$. We find that for $\nu > 700$ Hz the r-mode instability would be active for about 1 in 1000 LMXBs and that only the gravitational waves from LMXBs in the local group of galaxies could be detected by advanced LIGO interferometers.

 
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[16]  arXiv:0704.0973 [ps, pdf, other] :
Title: X-ray Timing Observations of PSR J1930+1852 in the Crab-like SNR G54.1+0.3
Authors: Fangjun Lu, Q.Daniel Wang, E. V. Gotthelf, Jinlu Qu
Comments: 14 pages with 7 figures included, accepted to ApJ

We present new X-ray timing and spectral observations of PSR J1930+1852, the young energetic pulsar at the center of the non-thermal supernova remnant G54.1+0.3. Using data obtained with the Rossi X-ray Timing Explorer and Chandra X-ray observatories we have derived an updated timing ephemeris of the 136 ms pulsar spanning 6 years. During this interval, however, the period evolution shows significant variability from the best fit constant spin-down rate of $\dot P = 7.5112(6) \times 10^{-13}$ s s$^{-1}$, suggesting strong timing noise and/or glitch activity. The X-ray emission is highly pulsed ($71\pm5%$ modulation) and is characterized by an asymmetric, broad profile ($\sim 70%$ duty cycle) which is nearly twice the radio width. The spectrum of the pulsed emission is well fitted with an absorbed power law of photon index $\Gamma = 1.2\pm0.2$; this is marginally harder than that of the unpulsed component. The total 2-10 keV flux of the pulsar is $1.7 \times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$. These results confirm PSR J1930+1852 as a typical Crab-like pulsar.

 
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[12]  arXiv:0704.1197 [ps, pdf, other] :
Title: Statistical properties of giant pulses from the Crab pulsar
Authors: M.V. Popov, B. Stappers
Comments: 5 pages, 2 figures. Accepted by Astronomy and Astrophysics

The statistics of giant pulses from the Crab pulsar was studied for the first time with particular reference to their widths. About 3.5 hours of observations conducted with the Westerbork Synthesis Radio Telescope in a tied-array mode at a frequency of 1200 MHz were analyzed. The PuMa pulsar backend provided voltage recording of X and Y linear polarization states in two conjugate 10 MHz bands. Time resolution was restricted to 4 microseconds to match the scattering on the interstellar inhomogeneities. In total about 18000 giant pulses (GP) were detected in full intensity with a threshold level of 6 sigma. Cumulative probability distributions (CPD) of giant pulse energies were analyzed for groups of GPs with different effective widths in the range 4 to 65 microseconds. The CPDs were found to manifest notable differences for the different GP width groups. The slope of a power-law fit to the high-energy portion of the CPDs evolves from -1.4 to -3.2 when going from the shortest to the longest GPs. There are breaks in the CPD power-law fits indicating flattening at low energies with indices varying from -0.6 to -1.6 for the short and long GPs respectively. GPs with a stronger peak flux density were found to be of shorter duration. We compare our results with previously published data and discuss the importance of these peculiarities in the statistical properties of GPs for the theoretical understanding of the emission mechanism responsible for GP generation.

 
[14]  arXiv:0704.1204 [ps, pdf, other] :
Title: The effect of supernova asymmetry on coalescence rates of binary neutron stars
Authors: K.A. Postnov, A.G. Kuranov (Sternberg Astronomical Institute, Moscow)
Comments: LaTeX, 4 pages, 3 figures; talk given at XLIId Rencontres de Moriond "Gravitaional Waves and Experimental Gravitation", March 11-18, La Thuile; to be published in the Proceedings; references added

We study the effect of the kick velocity -- neutron star spin alignment observed in young radio pulsars on the coalescence rate of binary neutron stars. The effect is shown to be especially strong for large kick amplitudes and tight alignments, reducing the galactic rate of binary neutron star coalescences up to an order of magnitude with respect to the rates calculated for random kicks. The spin-kick correlation also leads to much narrower NS spin-orbit misalignments compared to random kicks.

 
[17]  arXiv:0704.1215 [ps, pdf, other] :
Title: Double Neutron Stars: Evidence For Two Different Neutron-Star Formation Mechanisms
Authors: E.P.J. van den Heuvel (University of Amsterdam, University of California)
Comments: 9 pages. Invited talk at `The Multicoloured Landscape of Compact Objects and their Explosive Origins', Cefalu', 2006 June 11-24 (AIP Conf. Proc.), eds. L. Burderi et al., in press

Six of the eight double neutron stars known in the Galactic disk have low orbital eccentricities (< 0.27) indicating that their second-born neutron stars received only very small velocity kicks at birth. This is similar to the case of the B-emission X-ray binaries, where a sizable fraction of the neutron stars received hardly any velocity kick at birth (Pfahl et al. 2002). The masses of the second-born neutron stars in five of the six low-eccentricity double neutron stars are remarkably low (between 1.18 and 1.30 Msun). It is argued that these low-mass, low-kick neutron stars were formed by the electron-capture collapse of the degenerate O-Ne-Mg cores of helium stars less massive than about 3.5 Msun, whereas the higher-mass, higher kick-velocity neutron stars were formed by the collapses of the iron cores of higher initial mass. The absence of low-velocity single young radio pulsars (Hobbs et al. 2005) is consistent with the model proposed by Podsiadlowski et al. (2004), in which the electron-capture collapse of degenerate O-Ne-Mg cores can only occur in binary systems, and not in single stars.

 
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[19]  arXiv:0704.1534 [ps, pdf, other] :
Title: The Phase-resolved High Energy Spectrum of the Crab Pulsar
Authors: J.J. Jia, Anisia P.S. Tang, J. Takata, H.K. Chang, K.S.Cheng
Comments: 15 pages, 4 figures To appear in Advances in Space Science Research

We present a modified outer gap model to study the phase-resolved spectra of the Crab pulsar. A theoretical double peak profile of the light curve containing the whole phase is shown to be consistent with the observed light curve of the Crab pulsar by shifting the inner boundary of the outer gap inwardly to $\sim 10$ stellar radii above the neutron star surface. In this model, the radial distances of the photons corresponding to different phases can be determined in the numerical calculation. Also the local electrodynamics, such as the accelerating electric field, the curvature radius of the magnetic field line and the soft photon energy, are sensitive to the radial distances to the neutron star. Using a synchrotron self-Compton mechanism, the phase-resolved spectra with the energy range from 100 eV to 3 GeV of the Crab pulsar can also be explained.

 
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[19]  arXiv:0704.1732 [ps, pdf, other] :
Title: Spheroidal and torsional modes of quasistatic shear oscillations in the solid globe models of nuclear physics and pulsar astrophysics
Authors: S. Bastrukov, H-K. Chang, S. Misicu, I. Molodtsova, D. Podgainy
Comments: 34 pages; 6 figures

The past three decades of investigation on nuclear physics and pulsar astrophysics have seen gradual recognition that elastodynamic approach to the continuum mechanics of nuclear matter provides proper account of macroscopic motions of degenerate Fermi-matter constituting interior of these material objects, the densest of all known today. This paper focuses on one theoretical issue of this development which is concerned with oscillatory behavior of a viscoelastic solid globe in the regime of quasistatic, force-free, non-compressional oscillations less investigated in the literature compared to oscillations in the regime of standing shear waves. We show that in this case the problem of computing frequency and lifetime of spheroidal and torsional modes of non-radial shear vibrations damped by viscosity can be unambiguously resolved by working from the energy balance equation and taking advantage of the Rayleigh's variational method. The efficiency of this method is demonstrated by solid globe models of nuclear physics and pulsar astrophysics dealing with oscillations of a spherical mass of a viscoelastic Fermi-solid with homogeneous and non-homogeneous profiles of the bulk density, the shear modulus, and the shear viscosity.

 
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[2]  arXiv:0704.1813 [ps, pdf, other] :
Title: The Discovery of a Companion to the Lowest Mass White Dwarf
Authors: Mukremin Kilic, Warren R. Brown, Carlos Allende Prieto, M. H. Pinsonneault, S. J. Kenyon
Comments: ApJ, in press. See the Press Release at this http URL

We report the detection of a radial velocity companion to SDSS J091709.55+463821.8, the lowest mass white dwarf currently known with M~0.17Msun. The radial velocity of the white dwarf shows variations with a semi-amplitude of 148.8 km/s and a period of 7.5936 hours, which implies a companion mass of M > 0.28Msun. The lack of evidence of a companion in the optical photometry forces any main-sequence companion to be smaller than 0.1Msun, hence a low mass main sequence star companion is ruled out for this system. The companion is most likely another white dwarf, and we present tentative evidence for an evolutionary scenario which could have produced it. However, a neutron star companion cannot be ruled out and follow-up radio observations are required to search for a pulsar companion.

 
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[7]  arXiv:0704.2079 [ps, pdf, other] :
Title: X-ray emission from the planet pulsar B1257+12
Authors: G. G. Pavlov, O. Kargaltsev, G. P. Garmire, A. Wolszczan
Comments: 8 pages, 4 figures, emulateapj.sty; accepted for publication in Astrophysical Journal

We report the detection of the millisecond pulsar B1257+12 with the Chandra X-ray Observatory. In a 20 ks exposure we detected 25 photons from the pulsar, with energies between 0.4 and 2.0 keV, corresponding to the flux F_X=(4.4+/- 0.9)*10^{-15} ergs s^{-1} cm^{-2} in this energy range. The X-ray spectrum can be described by a power-law model with photon index Gamma = 2.8 and luminosity L_X \approx 2.5*10^{29} ergs s^{-1} in the 0.3--8 keV band, for a plausible distance of 500 pc and hydrogen column density N_H=3*10^{20} cm^{-2}. Alternatively, the spectrum can be fitted by a blackbody model with kT ~ 0.22 keV and projected emitting area ~2000 m^2. If the thermal X-rays are emitted from two symmetric polar caps, the bolometric luminosity of the two caps is 2 L_bol ~ 3*10^{29} ergs s^{-1}. We compared our results with the data on other 30 millisecond pulsars observed in X-rays and found that the apparent X-ray efficiency of PSR B1257+12, L_X/Edot ~ 3*10^{-5} for d=500 pc, is lower than those of most of millisecond pulsars. This might be explained by an unfavorable orientation of the X-ray pulsar beam if the radiation is magnetospheric, or by strong asymmetry of polar caps if the radiation is thermal (e.g., one of the polar caps is much brighter than the other and remains invisible for most part of the pulsar period). Alternatively, it could be attributed to absorption of X-rays in circumpulsar matter, such as a flaring debris disk left over after formation of the planetary system around the pulsar.

 
[20]  arXiv:0704.2141 [ps, pdf, other] :
Title: Differentially rotating force-free magnetosphere of an aligned rotator: analytical solutions in split-monopole approximation
Authors: Andrey Timokhin
Comments: 15 pages, 15 figures; accepted for publication in MNRAS

In this paper we consider stationary force-free magnetosphere of an aligned rotator when plasma in the open field line region rotates differentially due to presence of a zone with the accelerating electric field in the polar cap of pulsar. We study the impact of differential rotation on the current density distribution in the magnetosphere. Using split-monopole approximation we obtain analytical expressions for physical parameters of differentially rotating magnetosphere. We find the range of admitted current density distributions under the requirement that the potential drop in the polar cap is less than the vacuum potential drop. We show that the current density distribution could deviate significantly from the ``classical'' Michel distribution and could be made almost constant over the polar cap even when the potential drop in the accelerating zone is of the order of 10 per cents of the vacuum potential drop. We argue that differential rotation of the open magnetic field lines could play an important role in adjusting between the magnetosphere and the polar cap cascade zone and could affect the value of pulsar breaking index.

 
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[8]  arXiv:0704.2255 [ps, pdf, other] :
Title: Precise Timing of the X-ray Pulsar 1E 1207.4-5209: A Steady Neutron Star Weakly Magnetized at Birth
Authors: E. V. Gotthelf, J. P. Halpern (Columbia)
Comments: 5 pages, 2 figure, Latex, emulateapj style. Submitted to ApJ Letters

We analyze all X-ray timing data on 1E 1207.4-5209 in supernova remnant PKS 1209-51/52 gathered in 2000-2005, and find a highly stable rotation with P=424.130451(4) ms and period derivative of (9.6 +/- 9.4)E-17 s/s. This refutes previous claims of large timing irregularities in these data. In the dipole spin-down formalism, the 2-sigma upper limit on period derivative implies an energy loss rate < 1.5E32 ergs/s, surface magnetic field strength B_p < 3.5E11 G, and characteristic age tau > 24 Myr. This tau exceeds the remnant age by 3 orders of magnitude, requiring that the pulsar was born spinning at its present period. The X-ray luminosity of 1E 1207.4-5209, L(bol) ~= 2E33 ergs/s at 2 kpc, exceeds its spin-down energy loss, implying that L(bol) derives from residual cooling, and perhaps partly from accretion of supernova debris. The upper limit on B_p is small enough to favor the electron cyclotron model for at least one of the prominent absorption lines in its soft X-ray spectrum. This is the second demonstrable case of a pulsar born spinning slowly and with a weak B-field, after PSR J1852+0040 in Kesteven 79.

 
[22]  arXiv:0704.2318 [ps, pdf, other] :
Title: On a multi-resonant origin of high frequency quasiperiodic oscillations in the neutron-star X-ray binary 4U 1636-53
Authors: Zdenek Stuchlik, Gabriel Torok, Pavel Bakala
Comments: 7 pages, 3 figures, submitted to A&A

It was suggested that a multipeaked ratio distribution of the kHz QPOs observed in neutron star LMXBs may follow from different resonances. The atoll source 4U 1636-53 shows datapoints clustering around two distinct values (3/2 and 5/4) of the frequency ratio. The same frequency ratios correspond to the change in the sign of the twin peak QPOs amplitude difference, suggesting existence of a resonant energy overflow. We explore the idea that the two clusters of datapoints in 4U 1636-53 result from two different instances of the same orbital resonance. Assuming the neutron star external spacetime to be described by the Hartle-Thorne metric, we search for a frequency relation matching the two observed datapoints clusters. We have identified a suitable class of frequency relations well fitting the observed data. The relationship implied for so called total precession resonance between the Keplerian frequency and the total precession frequency introduced in this paper resembles the twin peak QPOs observed in 4U 1636-53 with a chi-square about 3 d.o.f. and implies for the central compact object mass M = 1.77M_sun, angular momentum j=0.05 and quadrupole momentum q = 0.003. The position of 3/2 and 5/4 resonant points implied by the total precession relationship well coincides with frequencies given by the change of the rms-amplitude difference sign. Nevertheless, if a resonance (in our opinion most likely present) is not considered, the total precession relation has a similar kinematic meaning as the periastron precession relation involved in the model of Stella and Vietri, but gives substantially better fit and lower neutron star mass.

 
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[1]  arXiv:0704.2415 [ps, pdf, other] :
Title: Near-Infrared and X-ray Observations of the Enigmatic G70.7+1.2
Authors: P. B. Cameron, S. R. Kulkarni (Caltech)
Comments: 13 pages, 4 figures. Submitted to ApJL, referee's comments incorporated

We present high resolution imaging of the puzzling radio and optical nebula G70.7+1.2 with the Keck Observatory's laser guide star adaptive optics (LGS-AO) system and the Chandra X-ray Observatory. The archival X-ray observations show a hard (Gamma ~ 1.8), low luminosity (L_X ~ 4 x 10^31 ergs/s) point source at the center of the nebula. Follow-up LGS-AO near-infrared imaging of the Chandra error circle reveals a relatively bright (K' ~ 14 magnitude) counterpart. Both its color and brightness are consistent with a heavily obscured B-star or possibly a late-G/early-K giant. The most plausible explanation is that this newly discovered X-ray source is a non-accreting B-star/pulsar binary powering the radio and optical nebula. If so, the luminous Be-star discussed in the literature seemingly embedded in the nebula is not the dominant force responsible for shaping G70.7+1.2. Thus, we suggest that G70.7+1.2 is the result of two unrelated objects (a B-star X-ray binary and a Be star) interacting with a dense molecular cloud. With this explanation we believe we have solved the mystery of the origin of G70.7+1.2.

 
[8]  arXiv:0704.2426 [ps, pdf, other] :
Title: Testing General Metric Theories of Gravity with Bursting Neutron Stars
Authors: Dimitrios Psaltis (Arizona)
Comments: 7 pages, submitted for publication in Physical Review D

I show that several observable properties of bursting neutron stars in metric theories of gravity can be calculated using only conservation laws, Killing symmetries, and the Einstein equivalence principle, without requiring the validity of the general relativistic field equations. I calculate, in particular, the gravitational redshift of a surface atomic line, the touchdown luminosity of a radius-expansion burst, which is believed to be equal to the Eddington critical luminosity, and the apparent surface area of a neutron star as measured during the cooling tails of bursts. I show that, for a general metric theory of gravity, the apparent surface area of a neutron star depends on the coordinate radius of the stellar surface and on its gravitational redshift, in the exact same way as in general relativity. On the other hand, the Eddington critical luminosity depends also on the ratio of two additional parameters that measure the degree to which the general relativistic field equations are satisfied. These results can be used in conjunction with current and future high-energy observations of bursting neutron stars to test general relativity in the strong-field regime.

 
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[7]  arXiv:0704.2608 [ps, pdf, other] :
Title: WHAM: A WENO-based general relativistic numerical scheme I: Hydrodynamics
Authors: Alexander Tchekhovskoy, Jonathan C. McKinney, Ramesh Narayan (Harvard-CfA)
Comments: 33 pages, 22 figures, accepted to MNRAS, for a version with high quality figures see this http URL

Active galactic nuclei, x-ray binaries, pulsars, and gamma-ray bursts are all believed to be powered by compact objects surrounded by relativistic plasma flows driving phenomena such as accretion, winds, and jets. These flows are often accurately modelled by the relativistic magnetohydrodynamics (MHD) approximation. Time-dependent numerical MHD simulations have proven to be especially insightful, but one regime that remains difficult to simulate is when the energy scales (kinetic, thermal, magnetic) within the plasma become disparate. We develop a numerical scheme that significantly improves the accuracy and robustness of the solution in this regime. We use a modified form of the WENO method to construct a finite-volume general relativistic hydrodynamics code called WHAM that converges at fifth order. We avoid (1) field-by-field decomposition by adaptively reducing down to 2-point stencils near discontinuities for a more accurate treatment of shocks, and (2) excessive reduction to low order stencils, as in the standard WENO formalism, by maintaining high order accuracy in smooth monotonic flows. Our scheme performs the proper surface integral of the fluxes, converts cell averaged conserved quantities to point conserved quantities before performing the reconstruction step, and correctly averages all source terms. We demonstrate that the scheme is robust in strong shocks, very accurate in smooth flows, and maintains accuracy even when the energy scales in the flow are highly disparate.

 
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[12]  arXiv:0704.2860 [pdf] :
Title: Cryptoplanet update
Authors: Robert L. Kurucz
Comments: research presentation, 85 figures

We have had several talks recently reviewing 11 years of exoplanet discoveries through radial velocity variations, or from transits, or from microlensing. More than 200 exoplanets have been found, including some around pulsars that we do not discuss here.
My physical definition for a planet is a roughly spherical, self-gravitating body more massive than 10**26 g formed from the leftover material in a protostellar disk after the protostar forms. Radiation from the protostar pushes the inner wall of the disk outward. The material agglomerates and forms planets in radial sequence. The outer planets are formed slowly by classical dynamical mechanisms acting in the snow zone. Planets have dense cores because of agglomeration.
Not one of the exoplanets discovered thus far is a planet. They are cryptoplanets formed from matter ejected by protostars. When protostars have excessive infall at high latitudes, they partially balance angular momentum through outflow at the equator as they spin up. The ejected matter is trapped in the magnetic torus formed between the star and the disk, like a tokamak. The tokamak eventully reconnects and magnetic compression forms self-gravitating remnants trapped and compressed by a closed spherical magnetic field, spheromaks. Cooled spheromaks are cryptoplanets. They orbit near the star. They can merge with each other or fall into the star or be ejected. They can grow by accreting gas. They have a low density core and abundances characteristic of the protostar. Their masses, radii, densities, and orbits are random, and are inconsistent with the parameters for planets. They tend to have lower density than planets.

 
[14]  arXiv:0704.2874 [ps, pdf, other] :
Title: 4U 0115+63 from RXTE and INTEGRAL Data: Pulse Profile and Cyclotron Line Energy
Authors: S.S. Tsygankov (1,2), A.A. Lutovinov (1,2), E.M. Churazov (2,1), R.A. Sunyaev (2,1) ((1) Space Research Institute, Moscow, Russia; (2) MPI for Astrophysik, Garching, Germany)
Comments: 30 pages, 13 figures, Astronomy Letters, 33, 368 (2007)
Journal-ref: Astron.Lett. 33 (2007) 368-384; Pisma Astron.Zh. 33 (2007) 417-434

We analyze the observations of the transient X-ray pulsar 4U 0115+63 with the RXTE and INTEGRAL observatories in a wide X-ray (3-100 keV) energy band during its intense outbursts in 1999 and 2004. The energy of the fundamental harmonic of the cyclotron resonance absorption line near the maximum of the X-ray flux from the source (luminosity range 5x10^{37} - 2x10^{38} erg/s) is ~11 keV. When the pulsar luminosity falls below ~5x10^{37} erg/s, the energy of the fundamental harmonic is displaced sharply toward the high energies, up to ~16 keV. Under the assumption of a dipole magnetic field configuration, this change in cyclotron harmonic energy corresponds to a decrease in the height of the emitting region by ~2 km, while other spectral parameters, in particular, the cutoff energy, remain essentially constant. At a luminosity ~7x10^{37} erg/s, four almost equidistant cyclotron line harmonics are clearly seen in the spectrum. This suggests that either the region where the emission originates is compact or the emergent spectrum from different (in height) segments of the accretion column is uniform. We have found significant pulse profile variations with energy, luminosity, and time. In particular, we show that the profile variations from pulse to pulse are not reduced to a simple modulation of the accretion rate specified by external conditions.

 
[18]  arXiv:0704.2906 [ps, pdf, other] :
Title: Pulsar radiation belts and transient radio emission
Authors: Q. Luo, D. B. Melrose
Comments: 11 pages, 3 figures, accepted for publication in MNRAS

It is proposed that radiation belts similar to the ones in the planetary magnetosphere can exist for a pulsar with a relatively long period and a strong magnetic field. In the belts located in the closed field line region near the light cylinder relativistic pairs are trapped and maintained at a density substantially higher than the local Goldreich-Julian corotation density. The trapped plasma can be supplied and replenished by either direct injection of relativistic pairs from acceleration of externally-supplied particles in a dormant outer gap or in situ ionization of the accreted neutral material in the trapping region. The radiation belts can be disrupted by waves that are excited in the region as the result of plasma instabilities or emitted from the surface due to starquakes or stellar oscillations. The disruption can cause an intermittent particle precipitation toward the star producing radio bursts. It is suggested that such bursts may be seen as rotating radio transients (RRATs).

 
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[16]  arXiv:0704.3104 [ps, pdf, other] :
Title: The first determination of the actinide Th abundance for a red giant of the Ursa Minor dwarf galaxy
Authors: Wako Aoki, Satoshi Honda, Kozo Sadakane, Nobuo Arimoto
Comments: 5 pages, 2 figures, 1 table, to appear in PASJ

The Thorium abundance for the red giant COS82 in the Ursa Minor dwarf spheroidal galaxy is determined based on a high resolution spectrum. This is the first detection of actinides in an extra Galactic object. A detailed abundance pattern is determined for 12 other neutron-capture elements from the atomic number 39 to 68. These elements are significantly over-abundant with respect to other metals like Fe (> 1 dex) and their abundance pattern agrees well with those of the r-process-enhanced, very metal-poor stars known in the Galactic halo, while the metallicity of this object ([Fe/H] ~ -1.5) is much higher than these field stars ([Fe/H] ~ -3.0). The results indicate that the mechanism and the astrophysical site that are responsible for neutron-capture elements in COS82 is similar to that for field r-process-enhanced stars, while the condition of low mass star formation is quite different. An estimate of the age of this object based on the Th abundance ratio is discussed.

 
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[5]  arXiv:0704.3282 [ps, pdf, other] :
Title: Production of TeV gamma-radiation in the vicinity of the supermassive black hole in the giant radiogalaxy M87
Authors: A.Neronov, F.Aharonian
Comments: 11 pages, submitted to ApJ

Although the giant radiogalaxy M 87 harbors many distinct regions of broad-band nonthermal emission, the recently reported fast variability of TeV gamma rays from M 87 on a timescale of days strongly constrains the range of speculations concerning the possible sites and scenarios of particle acceleration responsible for the observed TeV emission. A natural production site of this radiation is the immediate vicinity of the central supermassive mass black hole (BH). Because of the low bolometric luminosity, the nucleus of M 87 is effectively transparent for gamma rays up to energy of 10 TeV, which makes this source an ideal laboratory for study of particle acceleration processes close to the BH event horizon. We critically analyse different possible radiation mechanisms in this region, and argue that the observed very high-energy gamma ray emission can be explained by the inverse Compton emission of ultrarelativistic electron-positron pairs produced through the development of an electromagnetic cascade in the BH magnetosphere. We demonstrate, through detailed numerical calculations of acceleration and radiation of electrons in the magnetospheric vacuum gap, that this ``pulsar magnetosphere like'' scenario can satisfactorily explain the main properties of TeV gamma-ray emission of M 87.

 
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1 abstracts or titles contain neutron star, magnetar or pulsar


[16]  arXiv:0704.3517 [ps, pdf, other] :
Title: Gamma-ray production in young open clusters: Berk 87, Cyg OB2 and Westerlund 2
Authors: W. Bednarek
Comments: 14 pages, 7 figures, submitted to MNRAS

Young open clusters are likely sites of cosmic ray acceleration as indicated by recent detections of the TeV gamma-ray sources in the directions of two open clusters (Cyg OB2 and Westerlund 2) and their directional proximity to some unidentified EGRET sources. In fact, up to now a few different scenarios for acceleration of particles inside open clusters have been considered, i.e. shocks in massive star winds, pulsars and their nebulae, supernova shocks, massive compact binaries. Here we consider in detail the radiation processes due to both electrons and hadrons accelerated inside the open cluster. As a specific scenario, we apply the acceleration process at the shocks arising in the winds of WR type stars. Particles diffuse through the medium of the open cluster during the activity time of the acceleration scenario defined by the age of the WR star. They interact with the matter and radiation, at first inside the open cluster and, later in the dense surrounding clouds. We calculate the broad band spectrum in different processes for three example open clusters (Berk 87, Cyg OB2, Westerlund 2) for which the best observational constraints on the spectra are at present available. It is assumed that the high energy phenomena, observed from the X-ray up to the GeV-TeV gamma-ray energies, are related to each other. We conclude that the most likely description of the radiation processes in these objects is achieved in the hybrid (leptonic-hadronic) model in which leptons are responsible for the observed X-ray and GeV gamma-ray emission and hadrons are responsible for the TeV gamma-ray emission, which is produced directly inside and in dense clouds surrounding the open cluster.

 
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[ total of 38 entries: 1-25 | 26-38 ]
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1 abstracts or titles contain neutron star, magnetar or pulsar


[13]  arXiv:0704.3682 [ps, pdf, other] :
Title: IGR J16194-2810: a new symbiotic X-ray binary
Authors: N. Masetti, R. Landi, M.L. Pretorius, V. Sguera, A.J. Bird, M. Perri, P.A. Charles, J.A. Kennea, A. Malizia, P. Ubertini
Comments: 9 pages, 4 figures, 3 tables. Accepted for publication on Astronomy & Astrophysics, main journal

We here report on the multiwavelength study which led us to the identification of X-ray source IGR J16194-2810 as a new Symbiotic X-ray Binary (SyXB), that is, a rare type of Low Mass X-ray Binary (LMXB) composed of a M-type giant and a compact object. Using the accurate X-ray position allowed by Swift/XRT data, we pinpointed the optical counterpart, a M2 III star. Besides, the combined use of the spectral information afforded by XRT and INTEGRAL/IBIS shows that the 0.5-200 keV spectrum of this source can be described with an absorbed Comptonization model, usually found in LMXBs and, in particular, in SyXBs. No long-term (days to months) periodicities are detected in the IBIS data. The time coverage afforded by XRT reveals shot-noise variability typical of accreting Galactic X-ray sources, but is not good enough to explore the presence of X-ray short-term (seconds to hours) oscillations in detail. By using the above information, we infer important parameters for this source such as its distance (about 3.7 kpc) and X-ray luminosity (about 1.4e35 erg/s in the 0.5-200 keV band), and we give a description for this system (typical of SyXBs) in which a compact object (possibly a neutron star) accretes from the wind of its M-type giant companion. We also draw some comparisons between IGR J16194-2810 and other sources belonging to this subclass, finding that this object resembles SyXBs 4U 1700+24 and 4U 1954+31.

 

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[6]  arXiv:0704.3801 [ps, pdf, other] :
Title: An annular gap acceleration model for $\gamma$-ray emission of pulsars
Authors: G. J. Qiao, K. J. Lee, B. Zhang, H. G. Wang, R. X. Xu
Comments: 11 pages 2 figures, accepted by Chinese Journal of Astronomy and Astrophysics

If the binding energy of the pulsar's surface is not so high (the case of a neutron star), both the negative and positive charges will flow out freely from the surface of the star. The annular free flow model for $\gamma$-ray emission of pulsars is suggested in this paper. It is emphasized that: (1). Two kinds of acceleration regions (annular and core) need to be taken into account. The annular acceleration region is defined by the magnetic field lines that cross the null charge surface within the light cylinder. (2). If the potential drop in the annular region of a pulsar is high enough (normally the cases of young pulsars), charges in both the annular and the core regions could be accelerated and produce primary gamma-rays. Secondary pairs are generated in both regions and stream outwards to power the broadband radiations. (3). The potential drop in the annular region grows more rapidly than that in the core region. The annular acceleration process is a key point to produce wide emission beams as observed. (4). The advantages of both the polar cap and outer gap models are retained in this model. The geometric properties of the $\gamma$-ray emission from the annular flow is analogous to that presented in a previous work by Qiao et al., which match the observations well. (5). Since charges with different signs leave the pulsar through the annular and the core regions, respectively, the current closure problem can be partially solved.

 
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4 abstracts or titles contain neutron star, magnetar or pulsar


[6]  arXiv:0705.0014 [ps, pdf, other] :
Title: Galactic X-ray binary jets
Authors: Elena Gallo (UCSB)
Comments: Proceedings of the Fifth Stromlo Symposium: Disks, Winds & Jets - from Planets to Quasars

With their fast variability time-scales, Galactic X-ray binaries provide an excellent laboratory to explore the physics of accretion and related phenomena, most notably outflows, over different regimes. After comparing the phenomenology of jets in black hole X-ray binary systems to that of neutron stars, here I discuss the role of the jet at very low Eddington ratios, and present preliminary results obtained by fitting the broadband spectral energy distribution of a quiescent black hole binary with a `maximally jet-dominated' model.

 
[9]  arXiv:0705.0030 [ps, pdf, other] :
Title: High Frequency QPOs in Neutron Stars and Black Holes: Probing Dense Matter and Strong Gravitational Fields
Authors: Frederick K. Lamb
Comments: 30 pages, 8 figures, published in "From X-Ray Binaries to Gamma-ray Bursts", proceedings of a symposium held in memory of Jan van Paradijs 6-9 June 2001, eds. E.P.J. van den Heuvel, L. Kaper, E. Roi, & R.A.M.J. Wijers
Journal-ref: ASP Conference Series Vol. 308, 221-250 (2003)

Quasi-periodic oscillations (QPOs) have been discovered in the X-ray emission of many neutron stars and black holes. The QPOs with frequencies greater than about 300 Hz are thought to be produced near the surfaces of neutron stars and the event horizons of black holes. I first summarize some of the most important properties of the QPOs seen in neutron star and black hole systems. I then review some of the models that have been proposed and compare them with observational data. Finally, I describe how these QPOs can be used to determine the properties of dense matter and strong gravitational fields.

 
[15]  arXiv:0705.0065 [ps, pdf, other] :
Title: Discovery of the Putative Pulsar and Wind Nebula Associated with the TeV Gamma-ray Source HESS J1813-178
Authors: D. J. Helfand, E. V. Gotthelf, J. P. Halpern, F. Camilo, D. R. Semler (Columbia), R. H. Becker (UC Davis), R. L. White (STSI)
Comments: 7 pages, 6 figure, Latex, emulateapj style. To appear in the Astrophysical Journal

We present a Chandra X-ray observation of G12.82-0.02, a shell-like radio supernova remnant coincident with the TeV gamma-ray source HESS J1813-178. We resolve the X-ray emission from the co-located ASCA source into a point source surrounded by structured diffuse emission that fills the interior of the radio shell. The morphology of the diffuse emission strongly resembles that of a pulsar wind nebula. The spectrum of the compact source is well-characterized by a power-law with index Gamma approx 1.3, typical of young and energetic rotation-powered pulsars. For a distance of 4.5 kpc, consistent with the X-ray absorption and an association with the nearby star formation region W33, the 2-10 keV X-ray luminosities of the putative pulsar and nebula are L(PSR) = 3.2E33 ergs/s and L(PWN) = 1.4E34 ergs/s, respectively. Both the flux ratio of L(PWN)/L(PSR) = 4.3 and the total luminosity of this system predict a pulsar spin-down power of Edot > 1E37 ergs/s, placing it within the ten most energetic young pulsars in the Galaxy. A deep search for radio pulsations using the Parkes telescope sets an upper-limit of approx 0.07 mJy at 1.4 GHz for periods >~ 50 ms. We discuss the energetics of this source, and consider briefly the proximity of bright H2 regions to this and several other HESS sources, which may produce their TeV emission via inverse Compton scattering.

 
[21]  arXiv:0705.0119 [ps, pdf, other] :
Title: A search for X-ray counterparts of the millisecond pulsars in the globular cluster M28 (NGC 6626)
Authors: W. Becker, C.Y. Hui
Comments: Submitted for publication to Astronomy & Astrophysics Letter

A recent radio survey of globular clusters has increased the number of millisecond pulsars drastically. M28 is now the globular cluster with the third largest population of known pulsars, after Terzan 5 and 47 Tuc. This prompted us to revisit the archival Chandra data on M28 to evaluate whether the newly discovered millisecond pulsars find a counterpart among the various X-ray sources detected in M28 previously. The radio position of PSR J1824-2452H is found to be in agreement with the position of CXC 182431-245217 while some faint unresolved X-ray emission near to the center of M28 is found to be coincident with the millisecond pulsars PSR J1824-2452G, J1824-2452J, J1824-2452I and J1824-2452E.

 
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[18]  arXiv:0705.0285 [ps, pdf, other] :
Title: Rates and Characteristics of Intermediate-Mass-Ratio Inspirals Detectable by Advanced LIGO
Authors: Ilya Mandel, Duncan A. Brown, Jonathan R. Gair, M. Coleman Miller
Comments: Submitted to ApJ

Gravitational waves from the inspiral of a neutron star (NS) or stellar-mass black hole (BH) into a ~50 to ~350 solar-mass intermediate-mass black hole (IMBH) may be detectable by the planned advanced generation of ground-based gravitational-wave interferometers. Such intermediate mass ratio inspirals (IMRIs) are most likely to be found in globular clusters. We analyze four possible IMRI formation mechanisms: (i) hardening of a NS--IMBH or BH--IMBH binary via three body interactions, (ii) hardening via Kozai resonance in a hierarchical triple system, (iii) direct capture, and (iv) inspiral of a compact remnant from a tidally captured main-sequence star; we also discuss tidal effects when the inspiraling object is a neutron star. For each mechanism we predict the eccentricity distribution of the resulting IMRIs. We find that IMRIs will have largely circularized by the time they enter the sensitivity band of ground-based detectors. Hardening of a binary via three-body interactions, which is likely to be the dominant mechanism for IMRI formation, yields eccentricities under 10^{-4} when the gravitational wave (GW) frequency reaches 10 Hz. Even among IMRIs formed via direct captures, which can have the highest eccentricities, around 90 % will circularize to eccentricities under 0.1 before the GW frequency reaches 10 Hz. We estimate the rate of IMRI coalescences in globular clusters and the sensitivity of a network of three Advanced LIGO detectors to the resulting gravitational waves. We show that this detector network may see up to tens of IMRIs per year, though rates of one--few per year may be more plausible. We also estimate the loss in signal-to-noise ratio that will result from using circular IMRI templates for data analysis and find that, for the eccentricities we expect, this loss is negligible.

 

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2 abstracts or titles contain neutron star, magnetar or pulsar


[15]  arXiv:0705.0404 [ps, pdf, other] :
Title: Detection of Crab Giant Pulses Using the Mileura Widefield Array Low Frequency Demonstrator Field Prototype System
Authors: N. D. Ramesh Bhat, Randall B. Wayth, Haydon S. Knight, Judd D. Bowman, Divya Oberoi, David G. Barnes, Frank H. Briggs, Roger J. Cappallo, David Herne, Jonathon Kocz, Colin J. Lonsdale, Mervyn J. Lynch, Bruce Stansby, Jamie Stevens, Glen Torr, Rachel L. Webster, J. Stuart B. Wyithe
Comments: 10 pages, 6 figures, Accepted for publication in the Astrophysical Journal

We report on the detection of giant pulses from the Crab Nebula pulsar at a frequency of 200 MHz using the field deployment system designed for the Mileura Widefield Array's Low Frequency Demonstrator (MWA-LFD). Our observations are among the first high-quality detections at such low frequencies. The measured pulse shapes are deconvolved for interstellar pulse broadening, yielding a pulse-broadening time of 670$\pm$100 $\mu$s, and the implied strength of scattering (scattering measure) is the lowest that is estimated towards the Crab nebula from observations made so far. The sensitivity of the system is largely dictated by the sky background, and our simple equipment is capable of detecting pulses that are brighter than $\sim$9 kJy in amplitude. The brightest giant pulse detected in our data has a peak amplitude of $\sim$50 kJy, and the implied brightness temperature is $10^{31.6}$ K. We discuss the giant pulse detection prospects with the full MWA-LFD system. With a sensitivity over two orders of magnitude larger than the prototype equipment, the full system will be capable of detecting such bright giant pulses out to a wide range of Galactic distances; from $\sim$8 to $\sim$30 kpc depending on the frequency. The MWA-LFD will thus be a highly promising instrument for the studies of giant pulses and other fast radio transients at low frequencies.

 
[28]  arXiv:0705.0464 [ps, pdf, other] :
Title: Order in the chaos? The strange case of accreting millisecond pulsars
Authors: T. Di Salvo, L. Burderi, A. Riggio, A. Papitto, M. T. Menna
Comments: 10 Pages, 3 Figures. Invited talk at "The Multicoloured Landscape of Compact Objects and their Explosive Origins" (Cefalu, Sicily, 2006 June 11-24). Eds. L. Burderi et al. (New York: AIP)

We review recent results from the X-ray timing of accreting millisecond pulsars in Low Mass X-ray Binaries. This is the first time a timing analysis is performed on accreting millisecond pulsars, and for the first time we can obtain information on the behavior of a very fast pulsar subject to accretion torques. We find both spin-up and spin-down behaviors, from which, using available models for the accretion torques, we derive information on the mass accretion rate and magnetic field of the neutron star in these systems. We also find that the phase delays behavior as a function of time in these sources is sometimes quite complex and difficult to interpret, since phase shifts, most probably driven by variations of the X-ray flux, are sometimes present.

 

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2 abstracts or titles contain neutron star, magnetar or pulsar


[14]  arXiv:0705.0592 [ps, pdf, other] :
Title: A Natural Explanation for Magnetars
Authors: Dipankar Bhattacharya, Vikram Soni
Comments: 5 pages, 1 figure

We explore the possibility that a magnetar may owe its strong magnetic field to a magnetized core which, as indicated by certain equations of state, may form due to phase transitions at high density mediated by strong interaction within a sufficiently massive neutron star. We argue that the field derived from such a core could explain several inferred evolutionary behaviors of magnetars.

 
[29]  arXiv:0705.0685 [ps, pdf, other] :
Title: PSR J1453+1902 and the radio luminosities of solitary versus binary millisecond pulsars
Authors: D.R. Lorimer, M.A. McLaughlin, D.J. Champion, I.H. Stairs
Comments: 8 pages, 5 figures and 3 tables, accepted for publication by MNRAS

We present 3 yr of timing observations for PSR J1453+1902, a 5.79-ms pulsar discovered during a 430-MHz drift-scan survey with the Arecibo telescope. Our observations show that PSR J1453+1902 is solitary and has a proper motion of 8(2) mas/yr. At the nominal distance of 1.2 kpc estimated from the pulsar's dispersion measure, this corresponds to a transverse speed of 46(11) km/s, typical of the millisecond pulsar population. We analyse the current sample of 55 millisecond pulsars in the Galactic disk and revisit the question of whether the luminosities of isolated millisecond pulsars are different from their binary counterparts. We demonstrate that the apparent differences in the luminosity distributions seen in samples selected from 430-MHz surveys can be explained by small-number statistics and observational selection biases. An examination of the sample from 1400-MHz surveys shows no differences in the distributions. The simplest conclusion from the current data is that the spin, kinematic, spatial and luminosity distributions of isolated and binary millisecond pulsars are consistent with a single homogeneous population.

 

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[40]  arXiv:astro-ph/0609364 (replaced) [ps, pdf, other] :
Title: Magnetar oscillations pose challenges for strange stars
Authors: Anna L. Watts (MPA), Sanjay Reddy (LANL)
Comments: Parameter space expanded, 5 pages, 3 figures, MNRAS Letters in press
 
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[17]  arXiv:0705.0793 [ps, pdf, other] :
Title: RossiXTE monitoring of 4U 1636-53: I. Long-term evolution and kHz Quasi-Periodic Oscillations
Authors: Tomaso Belloni (INAF-OAB), Jeroen Homan (MIT), Sara Motta (INAF-OAB, Univ. Milano Bicocca), Eva Ratti (INAF-OAB, Univ. Milano Bicocca), Mariano Mendez (SRON Utrecht, Univ. Amsterdam, Univ. Utrecht)
Comments: 7 pages, 6 figures, accepted for publication on MNRAS

We have monitored the atoll-type neutron star low-mass X-ray binary 4U 1636-53 with the Rossi X-Ray Timing Explorer (RXTE) for more than 1.5 years. Our campaign consisted of short (~2 ks) pointings separated by two days, regularly monitoring the spectral and timing properties of the source. During the campaign we observed a clear long-term oscillation with a period of ~30-40 days, already seen in the light curves from the RXTE All-Sky Monitor, which corresponded to regular transitions between the hard (island) and soft (banana) states. We detected kHz QPOs in about a third of the observations, most of which were in the soft (banana) state. The distribution of the frequencies of the peak identified as the lower kHz QPO is found to be different from that previously observed in an independent data set. This suggests that the kHz QPOs in the system shows no intrinsically preferred frequency.

 

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[60]  arXiv:astro-ph/0702412 (replaced) [ps, pdf, other] :
Title: Experimental measurements of the O15(alpha,gamma)Ne19 reaction rate and the stability of thermonuclear burning on accreting neutron stars
Authors: Jacob Lund Fisker, Wanpeng Tan, Joachim Goerres, Michael Wiescher, Randall L. Cooper
Comments: Substantial revisions. 8 pages, 5 figures, accepted for publication in Astrophys. J
 
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3 abstracts or titles contain neutron star, magnetar or pulsar


[3]  arXiv:0705.0978 [ps, pdf, other] :
Title: X-ray Timing of PSR J1852+0040 in Kesteven 79: Evidence of Neutron Stars Weakly Magnetized at Birth
Authors: J. P. Halpern, E. V. Gotthelf, F. Camilo, F. D. Seward
Comments: 8 pages, 3 figures, to appear in The Astrophysical Journal

The 105-ms X-ray pulsar J1852+0040 is the central compact object (CCO) in SNR Kes 79. We report a sensitive upper limit on its radio flux density of 12 uJy at 2 GHz using the NRAO GBT. Timing using XMM and Chandra over a 2.4 yr span reveals no significant change in its spin period. The 2 sigma upper limit on the period derivative leads, in the dipole spin-down formalism, to an energy loss rate E-dot < 7e33 ergs/s, surface magnetic field strength B_p < 1.5e11 G, and characteristic age tau_c = P/2P-dot > 8 Myr. This tau_c exceeds the age of the SNR by 3 orders of magnitude, implying that the pulsar was born spinning at its current period. However, the X-ray luminosity of PSR J1852+0040, L(bol) ~ 3e33(d/7.1 kpc)^2 ergs/s is a large fraction of E-dot, which challenges the rotation-powered assumption. Instead, its high blackbody temperature, 0.46+/-0.04 keV, small blackbody radius ~ 0.8 km, and large pulsed fraction, ~ 80%, may be evidence of accretion onto a polar cap, possibly from a fallback disk made of supernova debris. If B_p < 1e10 G, an accretion disk can penetrate the light cylinder and interact with the magnetosphere while resulting torques on the neutron star remain within the observed limits. A weak B-field is also inferred in another CCO, the 424-ms pulsar 1E 1207.4-5209, from its steady spin and soft X-ray absorption lines. We propose this origin of radio-quiet CCOs: the B-field, derived from a turbulent dynamo, is weaker if the NS is formed spinning slowly, which enables it to accrete SN debris. Accretion excludes neutron stars born with both B_p < 1e11 G and P > 0.1 s from radio pulsar surveys, where B_p < 1e11 G is not encountered except among very old (tau_c > 40 Myr) or recycled pulsars. Finally, such a CCO, if born in SN 1987A, could explain the non-detection of a pulsar there.

 
[14]  arXiv:0705.1011 [ps, pdf, other] :
Title: Discovery of an Isolated Compact Object at High Galactic Latitude
Authors: R. E. Rutledge (McGill), D. B. Fox, A. H. Shevchuk (PSU)
Comments: 19 pages, 4 figures, ApJ, submitted

We report discovery of Calvera, a compact object at high Galactic latitude. We initially identified Calvera as a ROSAT All-Sky Survey Bright Source Catalog X-ray source, 1RXS J141256.0+792204, statistically likely to possess a high X-ray to optical flux ratio. Further observations using Swift, Gemini-North, and the Chandra X-ray Observatory refined the source position and confirmed the absence of any optical counterpart to an X-ray to optical flux ratio of F_X(0.1-2.4 keV)/F_V > 5100 (3 sigma). Interpretation of Calvera as a typical X-ray-dim isolated neutron star would place it at z~6.7 kpc above the Galactic disk -- in the Galactic halo -- implying that it either has an extreme space velocity (v_z > 6700 km s-1) or has failed to cool according to theoretical predictions. Interpretations as a persistent anomalous X-ray pulsar, or a ``compact central object'' present conflicts with these classes' typical properties. We conclude the properties of Calvera are most consistent with those of a nearby (150 to 560 pc) radio pulsar, similar to the radio millisecond pulsars of 47 Tuc, with further observations required to confirm this classification. If it is a millisecond pulsar, it would be among the X-ray brightest millisecond pulsars, and only the third northern hemisphere millisecond pulsar at such close distance, making it an interesting target for X-ray study, a radio pulsar timing array, and LIGO.

 
[26]  arXiv:0705.1108 [ps, pdf, other] :
Title: Shallow decay phase of GRB X-ray afterglows from relativistic wind bubbles
Authors: Yun-Wei Yu, Zi-Gao Dai
Comments: 5 pages, 4 figures, Accepted for Publication in A&A

The postburst object of a GRB is likely to be a highly magnetized, rapidly rotating compact object (e.g., a millisecond magnetar), which could produce an ultrarelativistic electron-positron-pair wind. The interaction of such a wind with an outwardly expanding fireball ejected during the burst leads to a relativistic wind bubble (RWB). We numerically calculate the dynamics and radiative properties of RWBs and use this model to explain the shallow decay phase of the early X-ray afterglows observed by Swift. We find that RWBs can fall into two types: forward-shock-dominated and reverse-shock-dominated bubbles. Their radiation during a period of $\sim 10^{2}-10^{5}$ seconds is dominated by the shocked medium and the shocked wind, respectively, based on different magnetic energy fractions of the shocked materials. For both types, the resulting light curves always have a shallow decay phase. In addition, we provide an example fit to the X-ray afterglows of GRB 060813 and GRB 060814 and show that they could be produced by forward-shock-dominated and reverse-shock-dominated bubbles, respectively. This implies that, for some early afterglows (e.g., GRB 060814), the long-lasting reverse shock emission is strong enough to explain their shallow decay phase.

 

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[14]  arXiv:0705.1249 [ps, pdf, other] :
Title: IGR J17254-3257, a new bursting neutron star
Authors: J. Chenevez, M. Falanga, E. Kuulkers, R. Walter, L. Bildsten, S. Brandt, N. Lund, T. Oosterbroek, J. Zurita Heras
Comments: 4 pages, 4 figures, 1 table; accepted for publication in A&A Letters. 1 reference (Cooper & Narayan, 2007) corrected

The study of the observational properties of uncommonly long bursts from low luminosity sources with extended decay times up to several tens of minutes is important when investigating the transition from a hydrogen-rich bursting regime to a pure helium regime and from helium burning to carbon burning as predicted by current burst theories. IGR J17254-3257 is a recently discovered X-ray burster of which only two bursts have been recorded: an ordinary short type I X-ray burst, and a 15 min long burst. An upper limit to its distance is estimated to about 14.5 kpc. The broad-band spectrum of the persistent emission in the 0.3-100 keV energy band obtained using contemporaneous INTEGRAL and XMM-Newton data indicates a bolometric flux of 1.1x10^-10 erg/cm2/s corresponding, at the canonical distance of 8 kpc, to a luminosity about 8.4x10^35 erg/s between 0.1-100 keV, which translates to a mean accretion rate of about 7x10^-11 solar masses per year. The low X-ray persistent luminosity of IGR J17254-3257 seems to indicate the source may be in a state of low accretion rate usually associated with a hard spectrum in the X-ray range. The nuclear burning regime may be intermediate between pure He and mixed H/He burning. The long burst is the result of the accumulation of a thick He layer, while the short one is a prematurate H-triggered He burning burst at a slightly lower accretion rate.

 

Cross-lists for Thu, 10 May 07

0 abstracts or titles contain neutron star, magnetar or pulsar


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0 abstracts or titles contain neutron star, magnetar or pulsar


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Submissions received from Wed 9 May 07 to Thu 10 May 07, announced Fri, 11 May 07

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1 abstracts or titles contain neutron star, magnetar or pulsar


[13]  arXiv:0705.1431 [ps, pdf, other] :
Title: The correlations between the spin frequencies and kHz QPOs of Neutron Stars in LMXBs
Authors: H.X. Yin, C.M. Zhang, Y.H. Zhao, Y.J. Lei, J.L. Qu, L.M. Song, F. Zhang
Comments: 4 pages, 2 figures, accepted for publication in A&A

We studied the correlations between spin frequencies and kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low mass X-ray binaries. The updated data of kHz QPOs and spin frequencies are statistically analyzed. We found that when two simultaneous kHz QPOs are present in the power spectrum, the minimum frequency of upper kHz QPO is at least 1.3 times larger than the spin frequency, i.e. \nu_{s}<\nu_{2min}/1.3. We also found that the average kHz QPO peak separation in 6 Atoll sources anti-correlates with the spin frequency in the form \lan\dn\ran = -(0.19\pm0.05)\ns+(389.40\pm21.67)Hz. If we shifted this correlation in the direction of the peak separation by a factor of 1.5, this correlation matches the data points of the two accretion powered millisecond X-ray pulsars, SAX J1808.4-3658 and XTE J1807-294.

 

Cross-lists for Fri, 11 May 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Fri, 11 May 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[41]  arXiv:0705.1249 (replaced) [ps, pdf, other] :
Title: IGR J17254-3257, a new bursting neutron star
Authors: J. Chenevez, M. Falanga, E. Kuulkers, R. Walter, L. Bildsten, S. Brandt, N. Lund, T. Oosterbroek, J. Zurita Heras
Comments: 4 pages, 4 figures, 1 table; accepted for publication in A&A Letters. 1 reference (Cooper & Narayan, 2007) corrected
 
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Submissions received from Thu 10 May 07 to Fri 11 May 07, announced Mon, 14 May 07

[ total of 47 entries: 1-47 ]
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3 abstracts or titles contain neutron star, magnetar or pulsar


[14]  arXiv:0705.1605 [ps, pdf, other] :
Title: Discovery of two candidate pulsar wind nebulae in very-high-energy gamma rays
Authors: H.E.S.S. Collaboration: F. Aharonian, et al
Comments: 10 pages, 3 figures, 2 tables, to appear in A&A

We present the discovery of two very-high-energy gamma-ray sources in an ongoing systematic search for emission above 100 GeV from pulsar wind nebulae in survey data from the H.E.S.S. telescope array. Imaging Atmospheric Cherenkov Telescopes are ideal tools for searching for extended emission from pulsar wind nebulae in the very-high-energy regime. H.E.S.S., with its large field of view of 5 degrees and high sensitivity, gives new prospects for the search for these objects. An ongoing systematic search for very-high-energy emission from energetic pulsars over the region of the Galactic plane between -60 degrees < l < 30 degrees, -2 degrees < b < 2 degrees is performed. For the resulting candidates, the standard H.E.S.S. analysis was applied and a search for multi-wavelength counterparts was performed. We present the discovery of two new candidate gamma-ray pulsar wind nebulae, HESS J1718-385 and HESS J1809-193. H.E.S.S. has proven to be a suitable instrument for pulsar wind nebula searches.

 
[16]  arXiv:0705.1621 [pdf] :
Title: The Spreading Layer of GX 9+9
Authors: Osmi Vilhu, Ada Paizis, Diana Hannikainen, Juho Schultz, Volker Beckmann
Comments: 4 pages (pdf), proceedings of the 6th INTEGRAL Workshop 'The Obscured Universe', July 2-8 2006, ESA SP-622

The spreading layer (SL) on neutron star surface of GX 9+9 during the upper banana state was studied using INTEGRAL and RXTE observations. The SL-area becomes larger with increasing accretion rate while the SL-temperature remains close to the critical Eddington value, confirming predictions by Inogamov and Sunyaev (1999) and Suleimanov and Poutanen (2006). However, at low accretion rate the observed temperature is higher and SL-belt shallower than those predicted, requiring confirmation and theoretical explananation.

 
[19]  arXiv:0705.1628 [ps, pdf, other] :
Title: The Plasma Emission Model of RX J1856.5-3754
Authors: N. Chkheidze, G. Machabeli
Comments: 5 pages, 4 figures

A spectral analysis of the nearby isolated neutron star RX J1856.5-3754 is presented. Applying the kinetic approach, the distribution functions of emitting electrons are derived and the entire spectra is fitted. It is found that waves excited by the cyclotron mechanism, come in the radio domain. We confirm that the cyclotron instability is quite efficient, since the estimations show that the time of wave-particle interaction is long enough for particles to acquire perpendicular momentum and generate observed radiation. The lack of rotational modulation is discussed and the pulsar spin period is estimated.

 

Cross-lists for Mon, 14 May 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Mon, 14 May 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[40]  arXiv:0705.1431 (replaced) [ps, pdf, other] :
Title: The correlations between the spin frequencies and kHz QPOs of Neutron Stars in LMXBs
Authors: H.X. Yin, C.M. Zhang, Y.H. Zhao, Y.J. Lei, J.L. Qu, L.M. Song, F. Zhang
Comments: 4 pages, 2 figures, accepted for publication in A&A
 
[45]  arXiv:astro-ph/0703062 (replaced) [ps, pdf, other] :
Title: Phase separation in the crust of accreting neutron stars
Authors: C. J. Horowitz, D. K. Berry, E. F. Brown
Comments: 8 pages, 6 figures, minor changes, Physical Review E in press
 
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Submissions received from Fri 11 May 07 to Mon 14 May 07, announced Tue, 15 May 07

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New submissions for Tue, 15 May 07

9 abstracts or titles contain neutron star, magnetar or pulsar


[6]  arXiv:0705.1730 [ps, pdf, other] :
Title: Astrophysics in 2006
Authors: Virginia Trimble, Markus J. Aschwanden, Carl J. Hansen
Comments: 244 pages, no figures

The fastest pulsar and the slowest nova; the oldest galaxies and the youngest stars; the weirdest life forms and the commonest dwarfs; the highest energy particles and the lowest energy photons. These were some of the extremes of Astrophysics 2006. We attempt also to bring you updates on things of which there is currently only one (habitable planets, the Sun, and the universe) and others of which there are always many, like meteors and molecules, black holes and binaries.

 
[8]  arXiv:0705.1742 [ps, pdf, other] :
Title: Magnetar Driven Bubbles and the Origin of Collimated Outflows in Gamma-ray Bursts
Authors: N. Bucciantini (1), E. Quataert (1), J. Arons (1), B.D. Metzger (1), Todd A. Thompson (2) ((1)Astronomy Department, UC Berkeley, (2)Department of Astrophysical Sciences, Princeton)
Comments: 14 pages, 8 figures, submitted to MNRAS

We model the interaction between the wind from a newly formed rapidly rotating magnetar and the surrounding supernova shock and host star. The dynamics is modeled using the two-dimensional, axisymmetric thin-shell equations. In the first ~10-100 seconds after core collapse the magnetar inflates a bubble of plasma and magnetic fields behind the supernova shock. The bubble expands asymmetrically because of the pinching effect of the toroidal magnetic field, just as in the analogous problem of the evolution of pulsar wind nebulae. The degree of asymmetry depends on E_mag/E_tot. The correct value of E_mag/E_tot is uncertain because of uncertainties in the conversion of magnetic energy into kinetic energy at large radii in relativistic winds; we argue, however, that bubbles inflated by newly formed magnetars are likely to be significantly more magnetized than their pulsar counterparts. We show that for a ratio of magnetic to total power supplied by the central magnetar L_mag/L_tot ~ 0.1 the bubble expands relatively spherically. For L_mag/L_tot ~ 0.3, however, most of the pressure in the bubble is exerted close to the rotation axis, driving a collimated outflow out through the host star. This can account for the collimation inferred from observations of long-duration gamma-ray bursts (GRBs). Outflows from magnetars become increasingly magnetically dominated at late times, due to the decrease in neutrino-driven mass loss as the young neutron star cools. We thus suggest that the magnetar-driven bubble initially expands relatively spherically, enhancing the energy of the associated supernova, while at late times it becomes progressively more collimated, producing the GRB.

 
[15]  arXiv:0705.1780 [ps, pdf, other] :
Title: Modelling magnetically deformed neutron stars
Authors: B. Haskell, L. Samuelsson, K. Glampedakis, N. Andersson

Rotating deformed neutron stars are important potential sources for groundbased gravitational-wave interferometers such as LIGO, GE0600 and VIRGO. One mechanism that may lead to significant non-asymmetries is the internal magnetic field. It is well known that a magnetic star will not be spherical and, if the magnetic axis is not aligned with the spin axis, the deformation will lead to the emission of gravitational waves. The aim of this paper is to develop a formalism that would allow us to model magnetically deformed stars, using both realistic equations of state and field configurations. As a first step, we consider a set of simplified model problems. Focusing on dipolar fields, we determine the internal magnetic field which is consistent with a given neutron star model. We then calculate the associated deformation. We conclude by discussing the relevance of our results for current gravitational-wave detectors and future prospects.

 
[23]  arXiv:0705.1826 [ps, pdf, other] :
Title: Dynamical non-axisymmetric instabilities in rotating relativistic stars
Authors: G. M. Manca, L. Baiotti, R. De Pietri, L. Rezzolla
Comments: To appear on CQG, NFNR special issue. 16 pages, 5 color figures, movies from this http URL

We present new results on dynamical instabilities in rapidly rotating neutron-stars. In particular, using numerical simulations in full General Relativity, we analyse the effects that the stellar compactness has on the threshold for the onset of the dynamical bar-mode instability, as well as on the appearance of other dynamical instabilities. By using an extrapolation technique developed and tested in our previous study [1], we explicitly determine the threshold for a wide range of compactnesses using four sequences of models of constant baryonic mass comprising a total of 59 stellar models. Our calculation of the threshold is in good agreement with the Newtonian prediction and improves the previous post-Newtonian estimates. In addition, we find that for stars with sufficiently large mass and compactness, the m=3 deformation is the fastest growing one. For all of the models considered, the non-axisymmetric instability is suppressed on a dynamical timescale with an m=1 deformation dominating the final stages of the instability. These results, together with those presented in [1], suggest that an m=1 deformation represents a general and late-time feature of non-axisymmetric dynamical instabilities both in full General Relativity and in Newtonian gravity.

 
[30]  arXiv:0705.1859 [ps, pdf, other] :
Title: X-ray emission from magnetic dissipation in the magnetar magnetosphere
Authors: Qinghuan Luo
Comments: 12 pages, 3 figures, Advances in Space Research, in press

Magnetic dissipation through decay of Alfven waves in the magnetar magnetosphere is discussed. Transport of magnetic fields in the star leads to dissipation of the magnetic energy through either direct internal heating or transferring of the energy in waves that decay in the magnetar magnetosphere. In the latter case, the Alfven waves are excited by crust dislocations or elastic waves underneath the star's surface. It is suggested that these Alfven waves can decay into ion sound waves which can be effectively damped leading to strong plasma heating. Hot plasmas expand producing transient X-rays.

 
[35]  arXiv:0705.1869 [pdf, other] :
Title: The Magnetic Field of the Solar Corona from Pulsar Observations
Authors: S. M. Ord, S. Johnston, J. Sarkissian
Comments: 16 pages, 4 figures (1 colour): Submitted to Solar Physics

We present a novel experiment with the capacity to independently measure both the electron density and the magnetic field of the solar corona. We achieve this through measurement of the excess Faraday rotation due to propagation of the polarised emission from a number of pulsars through the magnetic field of the solar corona. This method yields independent measures of the integrated electron density, via dispersion of the pulsed signal and the magnetic field, via the amount of Faraday rotation. In principle this allows the determination of the integrated magnetic field through the solar corona along many lines of sight without any assumptions regarding the electron density distribution. We present a detection of an increase in the rotation measure of the pulsar J1801$-$2304 of approximately 160 \rad at an elongation of 0.95$^\circ$ from the centre of the solar disk. This corresponds to a lower limit of the magnetic field strength along this line of sight of $> 393\mu\mathrm{G}$. The lack of precision in the integrated electron density measurement restricts this result to a limit, but application of coronal plasma models can further constrain this to approximately 20mG, along a path passing 2.5 solar radii from the solar limb. Which is consistent with predictions obtained using extensions to the Source Surface models published by Wilcox Solar Observatory

 
[40]  arXiv:0705.1901 [ps, pdf, other] :
Title: Hall drift of axisymmetric magnetic fields in solid neutron-star matter
Authors: Andreas Reisenegger, Rafael Benguria, Joaquin P. Prieto, Pablo A. Araya, Dong Lai
Comments: 8 pages, 5 figure panels; submitted to Astronomy & Astrophysics

Hall drift, i. e., transport of magnetic flux by the moving electrons giving rise to the electrical current, may be the dominant effect causing the evolution of the magnetic field in the solid crust of neutron stars. It is a nonlinear process that, despite a number of efforts, is still not fully understood. We use the Hall induction equation in axial symmetry to obtain some general properties of nonevolving fields, as well as analyzing the evolution of purely toroidal fields, their poloidal perturbations, and current-free, purely poloidal fields. We also analyze energy conservation in Hall instabilities and write down a variational principle for Hall equilibria. We show that the evolution of any toroidal magnetic field can be described by Burgers' equation, as previously found in plane-parallel geometry. It leads to sharp current sheets that dissipate on the Hall time scale, yielding a stationary field configuration that depends on a single, suitably defined coordinate. This field, however, is unstable to poloidal perturbations, which grow as their field lines are stretched by the background electron flow, as in instabilities earlier found numerically. On the other hand, current-free poloidal configurations are stable and could represent a long-lived crustal field supported by currents in the fluid stellar core.

 
[45]  arXiv:0705.1963 [ps, pdf, other] :
Title: Electron-muon heat conduction in neutron star cores via the exchange of transverse plasmons
Authors: P.S. Shternin, D.G. Yakovlev (Ioffe Institute)
Comments: 15 pages, 5 figures, to appear in Phys. Rev. D

We calculate the thermal conductivity of electrons and muons kappa_{e-mu} produced owing to electromagnetic interactions of charged particles in neutron star cores and show that these interactions are dominated by the exchange of transverse plasmons (via the Landau damping of these plasmons in nonsuperconducting matter and via a specific plasma screening in the presence of proton superconductivity). For normal protons, the Landau damping strongly reduces kappa_{e-mu} and makes it temperature independent. Proton superconductivity suppresses the reduction and restores the Fermi-liquid behavior kappa_{e-mu} ~ 1/T. Comparing with the thermal conductivity of neutrons kappa_n, we obtain kappa_{e-mu}> kappa_n for T>2 GK in normal matter and for any T in superconducting matter with proton critical temperatures T_c>3e9 K. The results are described by simple analytic formulae.

 
[48]  arXiv:0705.1973 [ps, pdf, other] :
Title: Years of RXTE Monitoring of Anomalous X-ray Pulsar 4U 0142+61: Long-Term Variability
Authors: R. Dib, V. M. Kaspi, F. P. Gavriil.
Comments: 28 pages, 8 figures, accepted by ApJ

We report on 10 years of monitoring of the 8.7-s Anomalous X-ray Pulsar 4U 0142+61 using the Rossi X-Ray Timing Explorer (RXTE). This pulsar exhibited stable rotation from 2000 March until 2006 February: the RMS phase residual for a spin-down model which includes nu, nudot, and nuddot is 2.3%. We report a possible phase-coherent timing solution valid over a 10-yr span extending back to March 1996. A glitch may have occured between 1998 and 2000, but is not required by the existing timing data. The pulse profile has been evolving since 2000. In particular, the dip of emission between its two peaks got shallower between 2002 and 2006, as if the profile were evolving back to its pre-2000 morphology, following an earlier event, which possibly also included the glitch suggested by the timing data. These profile variations are seen in the 2-4 keV band but not in 6-8 keV. We also detect a slow increase in the pulsed flux between 2002 May and 2004 December, such that it has risen by 36+/-3% over 2.6 years in the 2-10 keV band. The pulsed flux variability and the narrow-band pulse profile changes present interesting challenges to aspects of the magnetar model.

 

Cross-lists for Tue, 15 May 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[55]  arXiv:0705.1565 (cross-list from gr-qc) [ps, pdf, other] :
Title: Neutron stars in Einstein-aether theory
Authors: Christopher Eling, Ted Jacobson, M. Coleman Miller
Comments: 26 pages, 5 figures

As current and future experiments probe strong gravitational regimes around neutron stars and black holes, it is desirable to have theoretically sound alternatives to general relativity against which to test observations. Here we study the consequences of one such generalization, Einstein-aether theory, for the properties of non-rotating neutron stars. This theory has a parameter range that satisfies all current weak-field tests. We find that within this range it leads to lower maximum neutron star masses, as well as larger surface redshifts at a particular mass, for a given nuclear equation of state. For non-rotating black holes and neutron stars, the innermost stable circular orbit is only slightly modified in this theory, but the modification might well be greater for rapidly rotating objects.

 
[57]  arXiv:0705.1667 (cross-list from gr-qc) [ps, pdf, other] :
Title: How far from measuring the moment of inertia of the PSR J0737-3039A pulsar at 10% are we?
Authors: Lorenzo Iorio
Comments: LaTex2e, 6 pages, 1 table, no figures, 15 references. Caption of Table 1 improved

Here we consider the possibility-envisaged by many authors as feasible in the near future-of measuring at 10% the moment of inertia I of the PSR J0737-3039A pulsar via the Lense-Thirring periastron precession. Although the gravitomagnetic effect is expected to be of the order of 10^-4 deg yr^-1 and the present-day precision in phenomenologically determining the A's periastron rate is 6.8 10^-4 deg yr^-1, it turns out that the systematic uncertainty in the much larger gravitoelectric 1 PN precession, which should be subtracted from the measured one in order to pick up the gravitomagnetic rate, amounts to 0.10976 deg yr^-1. The major source of uncertainty is the relative semimajor axis a via the ratio of the pulsars' masses R, which involves the measurement of the B's projected semimajor axis x_B, and the Shapiro time delay s.

 

Replacements for Tue, 15 May 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[63]  arXiv:astro-ph/0611729 (replaced) [ps, pdf, other] :
Title: PSR B1828-11: a precession pulsar torqued by a quark planet?
Authors: K. Liu (PKU), Y. L. Yue (PKU), R. X. Xu (PKU)
Comments: 6 pages, 3 figures, accepted by MNRAS (Letters)
 
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Submissions received from Mon 14 May 07 to Tue 15 May 07, announced Wed, 16 May 07

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2 abstracts or titles contain neutron star, magnetar or pulsar


[10]  arXiv:0705.2054 [ps, pdf, other] :
Title: Periodic Bursts of Coherent Radio Emission from an Ultracool Dwarf
Authors: G. Hallinan, S. Bourke, C. Lane, A. Antonova, R. T. Zavala, W. F. Brisken, R.P. Boyle, F. J. Vrba, J.G. Doyle, A. Golden
Comments: 12 pages, 3 figures, accepted for publication in ApJ Letters

We report the detection of periodic (p = 1.96 hours) bursts of extremely bright, 100% circularly polarized, coherent radio emission from the M9 dwarf TVLM 513-46546. Simultaneous photometric monitoring observations have established this periodicity to be the rotation period of the dwarf. These bursts, which were not present in previous observations of this target, confirm that ultracool dwarfs can generate persistent levels of broadband, coherent radio emission, associated with the presence of kG magnetic fields in a large-scale, stable configuration. Compact sources located at the magnetic polar regions produce highly beamed emission generated by the electron cyclotron maser instability, the same mechanism known to generate planetary coherent radio emission in our solar system. The narrow beams of radiation pass our line of sight as the dwarf rotates, producing the associated periodic bursts. The resulting radio light curves are analogous to the periodic light curves associated with pulsar radio emission highlighting TVLM 513-46546 as the prototype of a new class of transient radio source.

 
[32]  arXiv:0705.2195 [ps, pdf, other] :
Title: Toroidal Magnetic Fields in Type II Superconducting Neutron Stars
Authors: Taner Akgun, Ira Wasserman (Cornell University)
Comments: 50 pages, 6 figures

We determine constraints on the form of axisymmetric toroidal magnetic fields dictated by hydrostatic balance in a type II superconducting neutron star with a barotropic equation of state. Using Lagrangian perturbation theory, we find the quadrupolar distortions due to such fields for various models of neutron stars with type II superconducting and normal regions. We find that the star becomes prolate and can be sufficiently distorted to display precession with a period of the order of years. We also study the stability of such fields using an energy principle, which allows us to extend the stability criteria established by R. J. Tayler for normal conductors to more general media with magnetic free energy that depends on density and magnetic induction, such as type II superconductors. We also derive the growth rate and instability conditions for a specific instability of type II superconductors, first discussed by P. Muzikar, C. J. Pethick and P. H. Roberts, using a local analysis based on perturbations around a uniform background.

 

Cross-lists for Wed, 16 May 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Wed, 16 May 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[44]  arXiv:0705.1667 (replaced) [ps, pdf, other] :
Title: How far from measuring the moment of inertia of the PSR J0737-3039A pulsar at 10% are we?
Authors: Lorenzo Iorio
Comments: LaTex2e, 6 pages, 1 table, no figures, 18 references. Terminology improved. References added. Discussion on the proposal of measuring the gravitomagnetic spin-orbit precession of the orbital angular momentum added
 
[45]  arXiv:0705.1869 (replaced) [pdf, other] :
Title: The Magnetic Field of the Solar Corona from Pulsar Observations
Authors: S. M. Ord, S. Johnston, J. Sarkissian
Comments: 16 pages, 4 figures (1 colour): Submitted to Solar Physics
 
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Submissions received from Tue 15 May 07 to Wed 16 May 07, announced Thu, 17 May 07

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2 abstracts or titles contain neutron star, magnetar or pulsar


[20]  arXiv:0705.2316 [ps, pdf, other] :
Title: On The Recently Discovered Pulsations From RX J1856.5-3754
Authors: N. Chkheidze, D. Lomiashvil
Comments: 7 pages, 2 figures

An explanation of the recently discovered 7 s pulsations from the isolated neutron star RX J1856.5-3754 is presented. It is assumed that the real spin period of this source is $\approx1$ s, whereas the observed spin-modulation is caused by the presence of a nearly transverse, very low frequency drift waves in the pulsar magnetosphere. It is supposed that the period of the drift wave is equal to a recently observed one. The simulated lightcurve is plotted, the angular parameters are defined and the value of the pulsed fraction of only $\sim 1.2%$ is explained.

 
[25]  arXiv:0705.2378 [ps, pdf, other] :
Title: X-ray emission from PSR J1809-1917 and its pulsar wind nebula, possibly associated with the TeV gamma-ray source HESS J1809-193
Authors: O. Kargaltsev, G. G. Pavlov
Comments: 13 pages, 10 figures and 3 tables, submitted to ApJ. Version with the high-resolution figures is available at this http URL

We detected X-ray emission from the 50-kyr-old pulsar J1809-1917 and resolved its pulsar wind nebula (PWN) with Chandra. The pulsar spectrum fits PL+BB model with the photon index of 1.2 and the BB temperature of 2 MK for n_{H}=0.7\times 10^{22} cm^{-2}. The luminosities are(4\pm 1)\times 10^{31} ergs s^{-1} for the PL component (in the 0.5-8 keV band) and ~1\times 10^{32} ergs s^{-1} for the BB component (bolometric) at a plausible distance of 3.5 kpc. The bright inner PWN component of a 3''\times12'' size is elongated in the north-south direction, with the pulsar close to its south end. This component is immersed in a larger (20''\times40''), similarly elongated outer PWN component of lower surface brightness. The elongated shape of the compact PWN can be explained by the ram pressure confinement of the pulsar wind due to the supersonic motion of the pulsar. The PWN spectrum fits a PL model with photon index of 1.4\pm0.1 and 0.5-8 keV luminosity of 4\times10^{32} ergs s^{-1}. The compact PWN appears to be inside a large-scale (~4'\times4') emission more extended to the south of the pulsar, i.e. in the direction of the alleged pulsar motion. To explain the extended X-ray emission ahead of the moving pulsar, one has to invoke strong intrinsic anisotropy of the pulsar wind or assume that this emission comes from a relic PWN swept by the asymmetrical reverse SNR shock. The pulsar and its PWN are located within the extent of the unidentified TeV source HESS J1809-193 whose brightest part is offset by ~8' to the south of the pulsar, i.e. in the same direction as the large-scale X-ray emission. Although the association between J1809-1917 and HESS J1809-193 is plausible, an alternative source of relativistic electrons powering HESS J1809-193 might be the serendipitously discovered X-ray source CXOU J180940.7-192544.

 

Cross-lists for Thu, 17 May 07

0 abstracts or titles contain neutron star, magnetar or pulsar


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0 abstracts or titles contain neutron star, magnetar or pulsar


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3 abstracts or titles contain neutron star, magnetar or pulsar


[7]  arXiv:0705.2456 [ps, pdf, other] :
Title: The role of GRB 031203 in clarifying the astrophysical GRB scenario
Authors: Remo Ruffini, Maria Grazia Bernardini, Carlo Luciano Bianco, Letizia Caito, Pascal Chardonnet, Maria Giovanna Dainotti, Federico Fraschetti, Roberto Guida, Gregory Vereshchagin, She-Sheng Xue
Comments: 8 pages, 11 figures, to appears in the proceedings of "The 6th INTEGRAL Workshop - The Obscured Universe", Moscow, 2006, ESA Special Publication, SP-622, in press

The luminosity and the spectral distribution of the afterglow of GRB 031203 have been presented within our theoretical framework, which envisages the GRB structure as composed by a proper-GRB, emitted at the transparency of an electron-positron plasma with suitable baryon loading, and an afterglow comprising the "prompt emission" as due to external shocks. In addition to the GRB emission, there appears to be a prolonged soft X-Ray emission lasting for 10^6-10^7 seconds followed by an exponential decay. This additional source has been called by us URCA-3. It is urgent to establish if this component is related to the GRB or to the Supernova (SN). In this second case, there are two possibilities: either the interaction of the SN ejecta with the interstellar medium or, possibly, the cooling of a young neutron star formed in the SN 2003lw process. The analogies and the differences between this triptych GRB 031203 / SN 2003lw / URCA-3 and the corresponding ones GRB 980425 / SN 1998bw / URCA-1 and GRB 030329 / SN 2003dh / URCA-2, as well as GRB 060218 / SN 2006aj are discussed.

 
[15]  arXiv:0705.2514 [ps, pdf, other] :
Title: The light curve of the companion to PSR B1957+20
Authors: Mark Reynolds, Paul Callanan, Andrew Fruchter, Manuel Torres, Martin Beer, Rachel Gibbons
Comments: 6 pages, 4 figures & 3tables. Accepted for publication in MNRAS

We present a new analysis of the light curve for the secondary star in the eclipsing binary millisecond pulsar system PSR B1957+20. Combining previous data and new data points at minimum from the Hubble Space Telescope, we have 100% coverage in the R-band. We also have a number of new K_s-band data points, which we use to constrain the infrared magnitude of the system. We model this with the Eclipsing Light Curve code (ELC). From the modelling with the ELC code we obtain colour information about the secondary at minimum light in BVRI and K. For our best fit model we are able to constrain the system inclination to 65 +/- 2 degrees for pulsar masses ranging from 1.3 -- 1.9 M_sun. The pulsar mass is unconstrained. We also find that the secondary star is not filling its Roche lobe. The temperature of the un-irradiated side of the companion is in agreement with previous estimates and we find that the observed temperature gradient across the secondary star is physically sustainable.

 
[18]  arXiv:0705.2530 [pdf, other] :
Title: On generation of Crab giant pulses
Authors: Maxim Lyutikov (Purdue University)
Comments: 16 pages

We propose that Crab giant pulses are generated on closed magnetic field lines near the light cylinder via anomalous cyclotron resonance on the ordinary mode. Waves are generated in a set of fine, unequally spaced, narrow emission bands at frequencies much lower than a local cyclotron frequency. Location of emission bands is fitted to spectral structures seen by Eilek & Hankins (2006). To reproduce the data, the required density of plasma on closed field lines is much higher, by a factor $\sim 3 \times 10^5$, than the minimal Goldreich-Julian density. Emission is generated by a population of highly energetic particles with radiation-limited Lorentz factors $\gamma \sim 7 \times 10^7$, produced during occasional reconnection close to the Y point, where the last closed field lines approach the light cylinder. The high over-density on closed field lines found here, modeling Crab giant pulses, matches the one inferred from modeling the eclipses of the binary pulsar PSR J0737-3039 (Lyutikov and Thompson 2005). It can be sustained through magnetic bottling due to an injection rate of approximately one Goldreich-Julian density per period, provided that particles on closed field lines have non-zero gyrational velocities. We suggest that presence of dense plasma on closed field lines is a generic property of pulsars.

 

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[3]  arXiv:0705.4095 [ps, pdf, other] :
Title: The variable radio-to-X-ray spectrum of the magnetar XTE J1810-197
Authors: F. Camilo (1), S. M. Ransom (2), J. Penalver (3), A. Karastergiou (3), M. van Kerkwijk (4), M. Durant (5), J. P. Halpern (1), J. Reynolds (6), C. Thum (3), D. J. Helfand (1), N. Zimmerman (1), I. Cognard (7) ((1) Columbia, (2) NRAO, (3) IRAM, (4) Toronto, (5) IAC, (6) ATNF, (7) CNRS)
Comments: Submitted to ApJ; 8 pages, 7 figures

We have observed the 5.54s anomalous X-ray pulsar XTE J1810-197 at radio, millimeter, and infrared (IR) wavelengths, with the aim of learning about its broad-band spectrum. At the IRAM 30m telescope, we have detected the magnetar at 88 and 144GHz, the highest radio-frequency emission ever seen from a pulsar. At 88GHz we detected numerous individual pulses, with typical widths ~2ms and peak flux densities up to 45Jy. Together with nearly contemporaneous observations with the Parkes, Nancay, and Green Bank telescopes, we find that in late 2006 July the spectral index of the pulsar was -0.5<alpha<0 over the range 1.4-144GHz. Nine dual-frequency Very Large Array and Australia Telescope Compact Array observations in 2006 May-September are consistent with this finding, while showing variability of alpha with time. We infer from the IRAM observations that XTE J1810-197 remains highly linearly polarized at millimeter wavelengths. Also, toward this pulsar, the transition frequency between strong and weak scattering in the interstellar medium may be near 50GHz. At Gemini, we detected the pulsar at 2.2um in 2006 September, at the faintest level yet observed, K_s=21.89+-0.15. We have also analyzed four archival IR Very Large Telescope observations (two unpublished), finding that the brightness fluctuated within a factor of 2-3 over a span of 3 years, unlike the monotonic decay of the X-ray flux. Thus, there is no correlation between IR and X-ray flux, and it remains uncertain whether there is any correlation between IR and radio flux.

 
[19]  arXiv:0705.4175 [ps, pdf, other] :
Title: Magnetic fields of our Galaxy on large and small scales
Authors: Jinlin Han (NAOC)
Comments: 9 pages. Invited Talk at IAU Symp.242, 'Astrophysical Masers and their Environments', Proceedings edited by J. M. Chapman & W. A. Baan

Magnetic fields have been observed on all scales in our Galaxy, from AU to kpc. With pulsar dispersion measures and rotation measures, we can directly measure the magnetic fields in a very large region of the Galactic disk. The results show that the large-scale magnetic fields are aligned with the spiral arms but reverse their directions many times from the inner-most arm (Norma) to the outer arm (Perseus). The Zeeman splitting measurements of masers in HII regions or star-formation regions not only show the structured fields inside clouds, but also have a clear pattern in the global Galactic distribution of all measured clouds which indicates the possible connection of the large-scale and small-scale magnetic fields.

 
[20]  arXiv:0705.4192 [ps, pdf, other] :
Title: Separated before birth: pulsars B2020+28 and B2021+51 as the remnants of runaway stars
Authors: V.V.Gvaramadze
Comments: 4 pages, 2 figures, accepted for publication in A&A Letters

Astrometric data on the pulsars B2020+28 and B2021+51 suggest that they originated within several parsecs of each other in the direction of the Cyg OB2 association. It was proposed that the pulsars share their origin in a common massive binary and were separated at the birth of the second pulsar following the asymmetric supernova explosion. We consider a different scenario for the origin of the pulsar pair based on a possibility that the pulsars were separated before their birth and that they are the remnants of runaway stars ejected (with velocities similar to those of the pulsars) from the core of Cyg OB2 due to strong three- or four-body dynamical encounters. Our scenario does not require any asymmetry in supernova explosions.

 
[24]  arXiv:0705.4223 [ps, pdf, other] :
Title: Predictions for Triple Stars and Pulsar Triples in Star Clusters
Authors: M. Trenti, S. Ransom, P. Hut, D. C. Heggie
Comments: 10 pages, 11 figures, MNRAS submitted

Though about 80 pulsar binaries have been detected in globular clusters so far, no pulsar has been found in a triple system in which all three objects are of comparable mass. Here we present predictions for the abundance of such triple systems, and for the most likely characteristics of these systems. Our predictions are based on an extensive set of more than 500 direct simulations of star clusters with primordial binaries, and a number of additional runs containing primordial triples. Our simulations employ a number N_{tot} of equal mass stars from N_{tot}=512 to N_{tot}=19661 and a primordial binary fraction from 0-50%. We find that typical triple abundances in the core of a dense cluster are two orders of magnitude lower than the binary abundances, which in itself already suggests that we don't have to wait too long for the first comparable-mass triple with a pulsar to be detected.

 

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[4]  arXiv:0705.4287 [ps, pdf, other] :
Title: Eccentric double white dwarfs as LISA sources in globular clusters
Authors: B. Willems (1), V. Kalogera (1), A. Vecchio (1,2), N. Ivanova (3), F.A. Rasio (1), J.M. Fregeau (1), K. Belczynski (4) ((1) Northwestern U., (2) U. of Birmingham, (3) U. of Toronto, (4) New Mexico State U.)
Comments: submitted to ApJ

We consider the formation of double white dwarfs (DWDs) through dynamical interactions in globular clusters. Such interactions can readily give rise to eccentric DWDs, in contrast to the exclusively circular population that is expected to form in the Galactic disk. We show that for a 5-year Laser Interferometer Space Antenna (LISA) mission and distances as far as the Large Magellanic Cloud, multiple harmonics from eccentric DWDs can be detected at a signal-to-noise ratio higher than 8 for at least a handful of eccentric DWDs, given their formation rate and typical merger lifetimes estimated from current cluster simulations. Consequently the association of eccentricity with stellar-mass LISA sources does not uniquely involve neutron stars, as is usually assumed. Due to the difficulty of detecting these systems with present and planned electromagnetic observatories, LISA could provide unique dynamical identifications of eccentric DWDs in globular clusters.

 
[13]  arXiv:0705.4350 [ps, pdf, other] :
Title: Numerical Study on Stellar Core Collapse and Neutrino Emission: Probe into the Spherically Symmetric Black Hole Progenitors with 3 - 30Msun Iron Cores
Authors: Ken'ichiro Nakazato, Kohsuke Sumiyoshi, Shoichi Yamada
Comments: 33 pages, 13 figures, accepted by ApJ

The existence of various anomalous stars, such as the first stars in the universe or stars produced by stellar mergers, has been recently proposed. Some of these stars will result in black hole formation. In this study, we investigate iron core collapse and black hole formation systematically for the iron-core mass range of 3 - 30Msun, which has not been studied well so far. Models used here are mostly isentropic iron cores that may be produced in merged stars in the present universe but we also employ a model that is meant for a Population III star and is obtained by evolutionary calculation. We solve numerically the general relativistic hydrodynamics and neutrino transfer equations simultaneously, treating neutrino reactions in detail under spherical symmetry. As a result, we find that massive iron cores with ~10Msun unexpectedly produce a bounce owing to the thermal pressure of nucleons before black hole formation. The features of neutrino signals emitted from such massive iron cores differ in time evolution and spectrum from those of ordinary supernovae. Firstly, the neutronization burst is less remarkable or disappears completely for more massive models because the density is lower at the bounce. Secondly, the spectra of neutrinos, except the electron type, are softer owing to the electron-positron pair creation before the bounce. We also study the effects of the initial density profile, finding that the larger the initial density gradient is, the more steeply the neutronization burst declines. Further more, we suggest a way to probe into the black hole progenitors from the neutrino emission and estimate the event number for the currently operating neutrino detectors.

 
[15]  arXiv:0705.4380 [ps, pdf, other] :
Title: Plasma Modes Along the Open Field Lines of a Neutron Star
Authors: U.A. Mofiz, B.J. Ahmedov
Journal-ref: Astrophys. J., 2000, 542, 484-492

We consider electrostatic plasma modes along the open field lines of a rotating neutron star. Goldreich-Julian charge density in general relativity is analyzed for the neutron star with zero inclination. It is found that the charge density is maximum at the polar cap and it remains almost same in certain extended region of the pole. For a steady state Goldreich-Julian charge density we found the usual plasma oscillation along the field lines; plasma frequency resembles to the gravitational redshift close to the Schwarzschild radius. We study the nonlinear plasma mode along the field lines. From the system of equations under general relativity, a second order differential equation is derived. The equation contains a term which describes the growing plasma modes near Schwarzschild radius in a black hole environment. The term vanishes with the distance far away from the gravitating object. For initially zero potential and field on the surface of a neutron star, Goldreich-Julian charge density is found to create the plasma mode, which is enhanced and propagates almost without damping along the open field lines. We briefly outline our plan to extend the work for studying soliton propagation along the open field lines of strongly gravitating objects.

 
[19]  arXiv:0705.4403 [ps, pdf, other] :
Title: Neutral Hydrogen Absorption Toward XTE J1810-197: the Distance to a Radio-Emitting Magnetar
Authors: Anthony H. Minter, Fernando Camilo, Scott M. Ransom, Jules P. Halpern, Neil Zimmerman
Comments: 35 pages, 11 figures, 5 Tables Submitted to ApJ

We have used the Green Bank Telescope to measure HI absorption against the anomalous X-ray pulsar XTE J1810-197. Assuming a flat rotation curve, we find that XTE J1810-197 is located at a distance of 3.4(+0.5,-0.7) kpc. For a rotation curve that incorporates a model of the Galactic bar, we obtain a distance of 4.0(+0.3,-0.8) kpc. Using a rotation curve that incorporates a model of the Galactic bar and the spiral arms of the Galaxy, the distance is 3.7(+/-0.6) kpc. These values are consistent with the distance to XTE J1810-197 of about 3.3 kpc derived from its dispersion measure, and estimates of 2-5 kpc obtained from fits to its X-ray spectra. Overall, we determine that XTE J1810-197 is located at a distance of 3.5(+/-0.5) kpc, possibly not far in front of the infrared dark cloud G10.74-0.13. We also used the GBT in an attempt to measure absorption in the OH 1612, 1665, 1667, and 1720 MHz lines against XTE J1810-197. We were unsuccessful in this, mainly because of its declining radio flux density. Analysis of HI 21 cm, OH, and CO(2-1) emission toward XTE J1810-197 allows us to place a lower limit of $N_{\rm H} \ga 4.6 \times 10^{21}$ cm$^{-2}$ on the non-ionized hydrogen column density to \magnetar, consistent with estimates obtained from fits to its X-ray spectra.

 

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[11]  arXiv:0705.4512 [pdf, other] :
Title: The r-process of stellar nucleosynthesis: Astrophysics and nuclear physics achievements and mysteries
Authors: M. Arnould, S. Goriely, K. Takahashi
Comments: 164 pages, 98 figures, accepted for publication in Phys. Rep. higher-quality version available at this http URL

The r-process, or the rapid neutron-capture process, of stellar nucleosynthesis is called for to explain the production of the stable (and some long-lived radioactive) neutron-rich nuclides heavier than iron that are observed in stars of various metallicities, as well as in the solar system.
A very large amount of nuclear information is necessary in order to model the r-process. This concerns the static characteristics of a large variety of light to heavy nuclei between the valley of stability and the vicinity of the neutron-drip line, as well as their beta-decay branches or their reactivity. The enormously challenging experimental and theoretical task imposed by all these requirements is reviewed, and the state-of-the-art development in the field is presented. Nuclear-physics-based and astrophysics-free r-process models of different levels of sophistication have been constructed over the years. We review their merits and their shortcomings. For long, the core collapse supernova of massive stars has been envisioned as the privileged r-process location. We present a brief summary of the one- or multidimensional spherical or non-spherical explosion simulations available to-date. Their predictions are confronted with the requirements imposed to obtain an r-process. The possibility of r-nuclide synthesis during the decompression of the matter of neutron stars following their merging is also discussed.

 
[13]  arXiv:0705.4543 [ps, pdf, other] :
Title: Constraining the Geometry of the Neutron Star RX J1856.5-3754
Authors: Wynn C. G. Ho (Harvard-Smithsonian CfA)
Comments: 7 pages, 6 figures; MNRAS, accepted

RX J1856.5-3754 is one of the brightest, nearby isolated neutron stars, and considerable observational resources have been devoted to its study. In previous work, we found that our latest models of a magnetic, hydrogen atmosphere matches well the entire spectrum, from X-rays to optical (with best-fitting neutron star radius R=14 km, gravitational redshift z_g~0.2, and magnetic field B~4x10^12 G). A remaining puzzle is the non-detection of rotational modulation of the X-ray emission, despite extensive searches. The situation changed recently with XMM-Newton observations that uncovered 7 s pulsations at the 1% level. By comparing the predictions of our model (which includes simple dipolar-like surface distributions of magnetic field and temperature) with the observed brightness variations, we are able to constrain the geometry of RX J1856.5-3754, with one angle < 6 deg and the other angle = 20-45 deg, though the solutions are not definitive given the observational and model uncertainties. These angles indicate a close alignment between the rotation and magnetic axes or between the rotation axis and the observer. We discuss our results in the context of RX J1856.5-3754 being a normal radio pulsar and a candidate for observation by future X-ray polarization missions such as Constellation-X or XEUS.

 
[17]  arXiv:0705.4574 [ps, pdf, other] :
Title: On the reconstruction of a magnetosphere of pulsars nearby the light cylinder surface
Authors: Z. Osmanov, G. Dalakishvili, G. Machabeli
Comments: 6 pages, 2 figures

A mechanism of generation of a toroidal component of large scale magnetic field, leading to the reconstruction of the pulsar magnetospheres is presented. In order to understand twisting of magnetic field lines, we investigate kinematics of a plasma stream rotating in the pulsar magnetosphere. Studying an exact set of equations describing the behavior of relativistic plasma flows, the increment of the curvature drift instability is derived, and estimated for $1s$ pulsars. It is shown that a new parametric mechanism is very efficient and can explain rotation energy pumping in the pulsar magnetospheres.

 
[20]  arXiv:0705.4594 [ps, pdf, other] :
Title: Two branches of neutron stars - reconciling a 2M_sun pulsar and SN1987A
Authors: P. Haensel, M. Bejger, J.L. Zdunik
Comments: 4 pages, 5 figures, submitted to A&A Letters

The analysis of SN1987A led Brown and Bethe (1995) to conclusion, that the maximum mass of cold neutron stars is low, M_max ~ 1.5M_sun. Such a low M_max, due to a kaon condensation in the stellar core, implies collapse of a too massive deleptonized protoneutron star into a black hole. This would naturally explain the lack of a neutron star in the SN1987A remnant. On the other hand, recent evaluation of mass of PSR J0751+1807 gives M_max > 2M_sun. This contradicts the original Bethe-Brown model, but can be reconciled within scenarios proposed in the present Letter. We consider two types of dense matter models with high-density softening, due to a transition from a non-strange N-phase of matter to a strangeness carrying phase S: kaon condensation and deconfinement of quarks. Two scenarios of neutron star formation in stellar core collapse are considered. In the first scenario, realized in sufficiently hot and dense supernova cores, nucleation of an S-phase is sufficiently rapid so as to form an S-phase core, and implying M_max = M^S_max =~ 1.5M_sun. In the second scenario, nucleation of the S-phase at neutron star birth is too slow to materialize, and the star becomes cold without forming an S-phase core. Then, stellar mass can increase via accretion, until central density \rho_crit is reached, and the S phase forms. This N branch of neutron stars ends at M=M_crit. We select several models of N-phase satifying the necessary condition M^N_max > 2M_sun and combine them with models of kaon condensation and quark deconfinement. For kaon condensation, we get M_crit =~ M^S_max =~ 1.5M_sun, which is ruled out by PSR J0751+1807. On the contrary, for the EOSs with quark deconfinement we get M_crit =~ M^N_max > 2M_sun, which reconciles SN1987A and PSR J0751+1807.

 

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[15]  arXiv:0706.0060 [pdf] :
Title: The physics of strong magnetic fields in neutron stars
Authors: Qiu-he Peng, Hao Tong
Journal-ref: Mon. Not. R. Astron. Soc. 378, 159 (2007)

In this paper we present a new result, namely that the primal magnetic field of the collapsed core during a supernova explosion will, as a result of the conservation of magnetic flux, receive a massive boost to more than 90 times its original value by the Pauli paramagnetization of the highly degenerate relativistic electron gas just after the formation of the neutron star. Thus, the observed super-strong magnetic field of neutron stars may originate from the induced Pauli paramagnetization of the highly degenerate relativistic electron gas in the interior of the neutron star. We therefore have an apparently natural explanation for the surface magnetic field of a neutron star.

 

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[47]  arXiv:gr-qc/0611120 (replaced) [ps, pdf, other] :
Title: Attempts to dynamically constrain the quadrupole mass moment of the millisecond pulsar PSR J1909-3744
Authors: Lorenzo Iorio
Comments: LaTex2e, 10 pages, no figures, 1 table, 21 references. Entirely rewritten version
 
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[38]  arXiv:0706.0500 [ps, pdf, other] :
Title: A deeper search for the progenitor of the Type Ic Supernova 2002ap
Authors: R. M. Crockett, S. J. Smartt, J. J. Eldridge, S. Mattila, D. R. Young, A. Pastorello, J. R. Maund, C. R. Benn, I. Skillen
Comments: 20 pages, 11 figures (resolution of images reduced), 6 tables, submitted for publication in MNRAS

(Abridged) We present a search for the progenitor star of the Type Ic Supernova 2002ap in deep, high quality pre-explosion observations taken with the Canada-France-Hawaii Telescope (CFHT). Aligning high-resolution Hubble Space Telescope (HST) observations of the supernova itself with the archival CFHT images allowed us to pinpoint the location of the progenitor site on the ground based observations. We find that a source visible in the B and R band pre-explosion images close to the position of the SN is (1) not coincident with the SN position within the uncertainties of our relative astrometry, and (2) is still visible ~ 4.7 yrs post-explosion in late-time observations taken with the William Herschel Telescope. We therefore conclude that it is not the progenitor of SN 2002ap. Comparing our luminosity limits with stellar models of single stars at appropriate metallicity (Z=0.008) we conclude that any single star progenitor must have experienced at least twice the standard mass loss rates during pre-Wolf-Rayet evolution, been initially 30-40M(Sun) and exploded as a Wolf-Rayet star of final mass 10-12M(Sun). Alternatively an initially 15-40M(Sun) progenitor may have evolved in an interacting binary system. We constrain any possible binary companion to a main sequence star of < 15M(Sun), a neutron star or a black hole. By combining the pre-explosion limits with the ejecta mass estimates and constraints from X-ray and radio observations we conclude that any binary interaction most likely occurred as Case B mass transfer, either with or without a subsequent common envelope evolution phase.

 

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[51]  arXiv:0705.1667 (replaced) [ps, pdf, other] :
Title: How far from measuring the moment of inertia of the PSR J0737-3039A pulsar at 10% are we?
Authors: Lorenzo Iorio
Comments: LaTex2e, 6 pages, 1 table, no figures, 18 references. Terminology improved. References added. Discussion on the proposal of measuring the gravitomagnetic spin-orbit precession of the orbital angular momentum added. Small notation improvements. Better referencing. Reference changed
 
[62]  arXiv:astro-ph/0701772 (replaced) [ps, pdf, other] :
Title: The quark core of protoneutron stars in the phase diagram of quark matter
Authors: F. Sandin, D. Blaschke
Comments: 18 pages, 25 figures, accepted for publication in Phys. Rev. D. Updated references and acknowledgements
 
[69]  arXiv:gr-qc/0611120 (replaced) [ps, pdf, other] :
Title: Attempts to dynamically constrain the quadrupole mass moment of the millisecond pulsar PSR J1909-3744
Authors: Lorenzo Iorio
Comments: LaTex2e, 10 pages, no figures, 1 table, 21 references. Entirely rewritten version
 
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[32]  arXiv:0706.0672 [ps, pdf, other] :
Title: Waves and instabilities in dissipative rotating superfluid neutron stars
Authors: T. Sidery, N. Andersson, G.L. Comer
Comments: 20 pages, MNRAS style, no figures

We discuss wave propagation in rotating superfluid neutron star cores, taking into account the vortex mediated mutual friction force. For models where the two fluids co-rotate in the unperturbed state, our analysis clarifies the role of chemical coupling and entrainment for sound and inertial waves. We also investigate the mutual friction damping, providing results that demonstrate the well-known fact that sound waves propagating along a vortex array are undamped. We show that the same is not true for inertial waves, which are damped by the mutual friction regardless of the propagation direction. We then include the vortex tension, which arises due to local vortex curvature. Focussing on purely transverse inertial waves, we derive the small correction that the tension induces in the wave frequency. Finally, we allow for a relative linear flow in the background (along the rotation axis). In this case we show how the mutual friction coupling may induce a dynamical instability in the inertial waves. We discuss the critical flow required for the instability to be present, its physical interpretation and the possible relevance it may have for neutron star physics.

 

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[21]  arXiv:0706.0828 [ps, pdf, other] :
Title: On the Magnetic Prandtl Number Behavior of Accretion Disks
Authors: Steven A. Balbus, Pierre Henri
Comments: 14 pages, Submitted to the Astrophysical Journal

We investigate the behavior of the magnetic Prandtl number (ratio of microscopic viscosity to resistivity) for accretion sources. Generally this number is very small in standard accretion disk models, but can become larger than unity within $\sim 50$ Schwarzschild radii of the central mass. Recent numerical investigations suggest a marked dependence of the level of MHD turbulence on the value of the Prandtl number. Hence, black hole and neutron star accretors, i.e. compact X-ray sources, are affected. The astrophysical consequences of this could be significant, including a possible route to understanding the mysterious state changes that have long characterized these sources.

 
[23]  arXiv:0706.0831 [ps, pdf, other] :
Title: Possible evolution of dim radio quiet neutron star 1E 1207.4-5209 based on a B-decay model
Authors: Askin Ankay, Arzu M. Ankay, E. Nihal Ercan
Comments: 13 pages, 1 figure
Journal-ref: International Journal of Modern Physics D 16, 619 (2007)

Dim radio-quiet neutron star (DRQNS) 1E 1207.4-5209 is one of the most heavily examined isolated neutron stars. Wide absorption lines were observed in its spectrum obtained by both XMM-Newton and Chandra X-ray satellites. These absorption lines can be interpreted as a principal frequency centered at 0.7 keV and its harmonics at 1.4, 2.1 and possibly 2.8 keV. The principal line can be formed by resonant proton cyclotron scattering leading to a magnetic field which is two orders of magnitude larger than the perpendicular component of the surface dipole magnetic field (B) found from the rotation period (P) and the time rate of change in the rotation period (\.{P}) of 1E 1207.4-5209. Besides, age of the supernova remnant (SNR) G296.5+10.0 which is physically connected to 1E 1207.4-5209 is two orders of magnitude smaller than the characteristic age ($\tau$=P/2\.{P}) of the neutron star. These huge differences between the magnetic field values and the ages can be explained based on a B-decay model. If the decay is assumed to be exponential, the characteristic decay time turns out to be several thousand years which is three orders of magnitude smaller than the characteristic decay time of radio pulsars represented in an earlier work. The lack of detection of radio emission from DRQNSs and the lack of point sources and pulsar wind nebulae in most of the observed SNRs can also be partly explained by such a very rapid exponential decay. The large difference between the characteristic decay times of DRQNSs and radio pulsars must be related to the differences in the magnetic fields, equation of states and masses of these isolated neutron stars.

 

Cross-lists for Thu, 7 Jun 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[40]  arXiv:0706.0288 (cross-list from hep-th) [ps, pdf, other] :
Title: Bumpy black holes from spontaneous Lorentz violation
Authors: Sergei Dubovsky, Peter Tinyakov, Matias Zaldarriaga
Comments: 40 pages, 4 figures

We consider black holes in Lorentz violating theories of massive gravity. We argue that in these theories black hole solutions are no longer universal and exhibit a large number of hairs. If they exist, these hairs probe the singularity inside the black hole providing a window into quantum gravity. The existence of these hairs can be tested by future gravitational wave observatories. We generically expect that the effects we discuss will be larger for the more massive black holes. In the simplest models the strength of the hairs is controlled by the same parameter that sets the mass of the graviton (tensor modes). Then the upper limit on this mass coming from the inferred gravitational radiation emitted by binary pulsars implies that hairs are likely to be suppressed for almost the entire mass range of the super-massive black holes in the centers of galaxies.

 

Replacements for Thu, 7 Jun 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[45]  arXiv:0704.2318 (replaced) [ps, pdf, other] :
Title: On a multi-resonant origin of high frequency quasiperiodic oscillations in the neutron-star X-ray binary 4U 1636-53
Authors: Zdenek Stuchlik, Gabriel Torok, Pavel Bakala
Comments: 7 pages, 3 figures, submitted to A&A
 
[48]  arXiv:0705.3063 (replaced) [ps, pdf, other] :
Title: The Evolution of Protoplanetary Disks Around Millisecond Pulsars: The PSR 1257 +12 System
Authors: Thayne Currie (Harvard-Smithsonian Center for Astrophysics, University of California-Los Angeles), Brad Hansen (University of California-Los Angeles)
Comments: 16 pages, 17 figures, Accepted for publication in The Astrophysical Journal (September 20, 2007 issue)
 
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Submissions received from Wed 6 Jun 07 to Thu 7 Jun 07, announced Fri, 8 Jun 07

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1 abstracts or titles contain neutron star, magnetar or pulsar


[28]  arXiv:0706.1054 [ps, pdf, other] :
Title: The Compact X-ray Source 1E 1547.0-5408 and the Radio Shell G327.24-0.13: A New Proposed Association between a Candidate Magnetar and a Candidate Supernova Remnant
Authors: Joseph D. Gelfand, B. M. Gaensler
Comments: 11 pages, 5 figures, ApJ accepted

We present X-ray, infrared and radio observations of the field centered on X-ray source 1E 1547.0-5408 in the Galactic Plane. A new Chandra observation of this source shows it is unresolved at arc-second resolution, and a new XMM observation shows that its X-ray spectrum is best described by an absorbed power-law and blackbody model. A comparison of the X-ray flux observed from this source between 1980 and 2006 reveals that its absorbed 0.5-10 keV X-ray flux decreased from ~2x10^-12 ergs cm-2 s-1 to ~3x10^-13 ergs cm-2 during this period. The most recent XMM observation allows us to put a 5 sigma confidence upper limit of 14% for the 0.5-10 keV peak-to-peak pulsed fraction. A near-infrared observation of this field shows a source with magnitude Ks = 15.9+/-0.2 near the position of 1E 1547.0-5408, but the implied X-ray to infrared flux ratio indicates the infrared emission is from an unrelated field source, allowing us to limit the IR magnitude of 1E 1547.0-5408 to >17.5. Archival radio observations reveal that 1E 1547.0-5408 sits at the center of a faint, small (4' diameter) radio shell, G327.24-0.13, which is possibly a previously unidentified supernova remnant. The X-ray properties of 1E 1547.0-5408 suggest that this source is a magnetar - a young neutron star whose X-ray emission is powered by the decay of its extremely strong magnetic field. The spatial coincidence between this source and G327.24-0.13 suggests that 1E 1547.0-5408 is associated with a young supernova remnant, supporting a neutron star interpretation. Additional observations are needed to confirm the nature of both 1E 1547.0-5408 and G327.24-0.13, and to determine if these sources are associated. If so, this pair will be an important addition to the small number of known associations between magnetars and supernova remnants.

 

Cross-lists for Fri, 8 Jun 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Fri, 8 Jun 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[34]  arXiv:0705.3717 (replaced) [ps, pdf, other] :
Title: Accurate X-ray position and multiwavelength observations of the isolated neutron star RBS 1774
Authors: N. Rea (SRON/U.Sydney), M.A.P. Torres (CfA), P.G. Jonker (SRON/Cfa), R. Mignani, S. Zane (MSSL), M. Burgay (INAF), D. Kaplan (MIT), R. Turolla (U.Padua), G.L. Israel (INAF), D. Steeghs (CfA)
Comments: 8 pages, 9 figures, accepted for publication on MNRAS
 
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Submissions received from Thu 7 Jun 07 to Fri 8 Jun 07, announced Mon, 11 Jun 07

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1 abstracts or titles contain neutron star, magnetar or pulsar


[5]  arXiv:0706.1074 [ps, pdf, other] :
Title: The Abundances of Light Neutron-Capture Elements in Planetary Nebulae II. s-process Enrichments and Interpretation
Authors: N. C. Sterling (1), Harriet L. Dinerstein (2) ((1) NASA Goddard Space Flight Center; (2) University of Texas at Austin)
Comments: 105 pages, including 19 tables and 9 figures. Accepted for publication in ApJS

We present the results of a large-scale survey of neutron(n)-capture elements in Galactic planetary nebulae (PNe), undertaken to study enrichments from s-process nucleosynthesis in their progenitor stars. From new K band observations of over 100 PNe supplemented by data from the literature, we have detected the emission lines [Kr III] 2.199 and/or [Se IV] 2.287 $\mu$m in 81 of 120 objects. We determine Se and Kr elemental abundances, employing ionization correction formulae derived in the first paper of this series. We find a significant range in Se and Kr abundances, from near solar (no enrichment) to enhanced by >1.0 dex relative to solar, which we interpret as self-enrichment due to in situ s-process nucleosynthesis. Kr tends to be more strongly enriched than Se; in 18 objects exhibiting both Se and Kr emission, we find that [Kr/Se] = 0.5$\pm$0.2.
Our survey has increased the number of PNe with n-capture element abundance determinations by a factor of ten, enabling us for the first time to search for correlations with other nebular properties. As expected, we find a positive correlation between s-process enrichments and the C/O ratio. Type I and bipolar PNe, which arise from intermediate-mass progenitors (>3-4 solar masses), exhibit little to no s-process enrichments. Finally, PNe with H-deficient Wolf-Rayet central stars do not exhibit systematically larger s-process enrichments than objects with H-rich nuclei. Overall, 44% of the PNe in our sample display significant s-process enrichments (>0.3 dex). Using an empirical PN luminosity function to correct for incompleteness, we estimate that the true fraction of s-process enriched Galactic PNe is at least 20%.

 

Cross-lists for Mon, 11 Jun 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Mon, 11 Jun 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[57]  arXiv:astro-ph/0609828 (replaced) [ps, pdf, other] :
Title: Heating in the Accreted Neutron Star Ocean: Implications for Superburst Ignition
Authors: Sanjib Gupta, Edward F. Brown, Hendrik Schatz, Peter Moeller, Karl-Ludwig Kratz
Comments: 10 pages, 11 figures, the Astrophysical Journal, in press (scheduled for v. 662). Revised from v1 in response to referee's comments
 
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Submissions received from Fri 8 Jun 07 to Mon 11 Jun 07, announced Tue, 12 Jun 07

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3 abstracts or titles contain neutron star, magnetar or pulsar


[22]  arXiv:0706.1320 [ps, pdf, other] :
Title: Accretion vs colliding wind models for the gamma-ray binary LS I +61 303: an assessment
Authors: G.E. Romero, A.T. Okazaki, M. Orellana, S.P. Owocki
Comments: Seven pages, 5 figures, submitted to A&A

LS I +61 303 is a puzzling Be/X-ray binary with variable gamma-ray emission at up TeV energies. The nature of the compact object and the origin of the high-energy emission are unclear. One family of models invokes particle acceleration in shocks from the collision between the B-star wind and a relativistic pulsar wind, while another centers on a relativistic jet powered by accretion. Recent high-resolution radio observations showing a putative "cometary tail" pointing away from the Be star near periastron have been cited as support for the pulsar-wind model. We wish here to carry out a quantitative assessment of these competing models for this extraordinary source. We apply a 3D SPH code for dynamical simulations of both the pulsar-wind-interaction and accretion-jet models. The former yields a description of the shape of the wind-wind interaction surface. The latter provides an estimation of the accretion rate. The results allow critical evaluation of how the two distinct models confront the data in various wavebands under a range of conditions. When one accounts for the 3D dynamical wind interaction under realistic constraints for the relative strength of the B-star and pulsar winds, the resulting form of the interaction front does not match the putative "cometary tail" claimed from radio observations. On the other hand, dynamical simulations of the accretion-jet model indicate that the orbital phase variation of accretion power includes a secondary broad peak well away from periastron, thus providing a plausible way to explain the observed TeV gamma ray emission toward apastron. We conclude that the colliding-wind model is not clearly established for LS I +61 303, while the accretion-jet model can reproduce many key characteristics of the observed TeV gamma-ray emission.

 
[49]  arXiv:0706.1511 [ps, pdf, other] :
Title: Pulsar Kicks With Modified URCA and Electrons in Landau Levels
Authors: Ernest M. Henley (Department of Physics, University of Washington), Mikkel B. Johnson (Los Alamos National Laboratory), Leonard S. Kisslinger (Department of Physics, Carnegie-Mellon University)
Comments: 10 pages, 6 figures

We derive the energy asymmetry given the proto-neutron star during the time when the neutrino sphere is near the surface of the proto-neutron star, using the modified URCA process. The electrons produced with the anti-neutrinos are in Landau levels due to the strong magnetic field, and this leads to asymmetry in the neutrino momentum, and a pulsar kick. Our main prediction is that the large pulsar kicks start at about 10 s and last for about 10 s, with the corresponding neutrinos correlated in the direction of the magnetic field. We predict a pulsar velocity of 2.57 $\times 10^{-4} (T/10^{10}K)^7$ km/s, which reaches 1000 km/s if T $\simeq 8.74 \times 10^{10}$ K.

 
[54]  arXiv:0706.1542 [ps, pdf, other] :
Title: Pulsar Physics and GLAST
Authors: Alice K. Harding
Comments: 5 pages, 2 figures, to appear in Proc. of First GLAST Symposium (Stanford, Feb. 5-8, 2007), eds. S.Ritz, P.F. Michelson, and C.Meegan, AIP Conf. Proc

Rotation-powered pulsars are excellent laboratories for study of particle acceleration as well as fundamental physics of strong gravity, strong magnetic fields, high densities and relativity. I will review the outstanding questions in pulsar physics and the prospects for finding answers with GLAST LAT observations. LAT observations should significantly increase the number of detected radio-loud and radio-quiet gamma-ray pulsars, including millisecond pulsars, giving much better statistics for elucidating population characteristics, will measure the high-energy spectrum and the shape of spectral cutoffs and determine pulse profiles for a variety of pulsars of different age. Further, measurement of phase-resolved spectra and energy dependent pulse profiles of the brighter pulsars should allow detailed tests of magnetospheric particle acceleration and radiation mechanisms, by comparing data with theoretical models that have been developed.

 

Cross-lists for Tue, 12 Jun 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Tue, 12 Jun 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[75]  arXiv:astro-ph/0612791 (replaced) [ps, pdf, other] :
Title: Constraints on Neutron Star Properties from X-ray Observations of Millisecond Pulsars
Authors: Slavko Bogdanov, George B. Rybicki, Jonathan E. Grindlay (Harvard/CfA)
Comments: 10 pages, 8 figures; accepted for publication in the Astrophysical Journal
 
[80]  arXiv:astro-ph/0703802 (replaced) [ps, pdf, other] :
Title: First X-ray observations of the young pulsar J1357-6429
Authors: Vyacheslav E. Zavlin
Comments: The timing analysis is based on the pulsar's spin parameters determined from contemporaneous radio observations taken at the Parkes radio telescope. The size of the paper has been modified to fit the ApJL format
 
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Submissions received from Mon 11 Jun 07 to Tue 12 Jun 07, announced Wed, 13 Jun 07

[ total of 66 entries: 1-66 ]
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2 abstracts or titles contain neutron star, magnetar or pulsar


[12]  arXiv:0706.1595 [ps, pdf, other] :
Title: Correlations between X-ray Spectral and Timing Characteristics in Cyg X-2
Authors: Lev Titarchuk (GMU/NRL/GSFC), Sergey Kuznetsov (UCR/IKI, Russia), Nikolai Shaposhnikov (USRA/GSFC)
Comments: 7 pages, 4 figures, accepted for publication in ApJ (October 1, 2007, v667n2 issue)

Correlations between the quasi-periodic oscillations (QPOs) and the spectral power-law index have been reported for a number of black hole candidate sources and for four neutron star (NS) sources, 4U 0614+09, 4U 1608-52, 4U 1728-34 and Sco X-1. An examination of QPO frequencies and index relationship in Cyg X-2 is reported herein. The RXTE spectrum of Cyg X-2 can be adequately represented by a simple two-component model of Compton up-scattering with a soft photon electron temperature of about 0.7 keV and an iron K-line. Inferred spectral power-law index shows correlation with the low QPO frequencies. We find that the Thomson optical depth of the Compton cloud (CC) tau, in framework of spherical geometry, is in the range of ~4-6, which is consistent with the neutron star's surface being obscured. The NS high frequency pulsations are presumably suppressed as a result of photon scattering off CC electrons because of such high values of tau. We also point out a number of similarities in terms timing (presence of low and high frequency QPOs) and spectral (high CC optical depth and low CC plasma temperature) appearances between Cyg X-2 and Sco X-1.

 
[23]  arXiv:0706.1656 [ps, pdf, other] :
Title: Millisecond pulsars around intermediate-mass black holes in globular clusters
Authors: B. Devecchi, M. Colpi, M. Mapelli, A. Possenti
Comments: 14 pages, 11 figures, 4 tables, to be published in MNRAS

We study the process of dynamical capture of a millisecond pulsar (MSP) by a single or binary IMBH, simulating various types of single-binary and binary-binary encounters. It is found that [IMBH,MSP] binaries form over cosmic time in a cluster, via encounters of wide--orbit binary MSPs off the single IMBH, and at a lower pace, via interactions of (binary or single) MSPs with the IMBH orbited by a typical cluster star. The formation of an [IMBH,MSP] system is strongly inhibited if the IMBH is orbited by a stellar mass black hole. The [IMBH,MSP] binaries that form are relatively short-lived, $\lsim 10^{8-9}$ yr, since their orbits decay via emission of gravitational waves. The detection of an [IMBH,MSP] system has a low probability of occurrence, when inferred from the current sample of MSPs in GCs. If next generation radio telescopes, like SKA, will detect an order of magnitude larger population of MSP in GCs, at least one [IMBH,MSP] is expected. Therefore, a complete search for low-luminosity MSPs in the GCs of the Milky Way with SKA will have the potential of testing the hypothesis that IMBHs of order $100 \msun$ are commonly hosted in GCs.

 

Cross-lists for Wed, 13 Jun 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Wed, 13 Jun 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[62]  arXiv:astro-ph/0701888 (replaced) [ps, pdf, other] :
Title: Pulsar's kicks and Gamma-ray bursts
Authors: X. H. Cui (PKU), H. G. Wang (GZU), R. X. Xu (PKU), G. J. Qiao (PKU)
Comments: 4 pages, 1 figure, accepeted by A&A
 
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Submissions received from Tue 12 Jun 07 to Wed 13 Jun 07, announced Thu, 14 Jun 07

[ total of 61 entries: 1-61 ]
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1 abstracts or titles contain neutron star, magnetar or pulsar


[26]  arXiv:0706.1909 [ps, pdf, other] :
Title: Observations of X-rays and Thermal Dust Emission from the Supernova Remnant Kes 75
Authors: T. D. Morton, P. Slane, K. J. Borkowski, S. P. Reynolds, D. J. Helfand, B. M. Gaensler, J. P. Hughes
Comments: 7 pages, 2 tables, 4 figures, uses emulateapj. Accepted for publication in ApJ

We present Spitzer Space Telescope and Chandra X-ray Observatory observations of the composite Galactic supernova remnant Kes 75 (G29.7-0.3). We use the detected flux at 24 microns and hot gas parameters from fitting spectra from new, deep X-ray observations to constrain models of dust emission, obtaining a dust-to-gas mass ratio M_dust/M_gas ~0.001. We find that a two-component thermal model, nominally representing shocked swept-up interstellar or circumstellar material and reverse-shocked ejecta, adequately fits the X-ray spectrum, albeit with somewhat high implied densities for both components. We surmise that this model implies a Wolf-Rayet progenitor for the remnant. We also present infrared flux upper limits for the central pulsar wind nebula.

 

Cross-lists for Thu, 14 Jun 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Thu, 14 Jun 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[48]  arXiv:0705.0464 (replaced) [ps, pdf, other] :
Title: Order in the chaos? The strange case of accreting millisecond pulsars
Authors: T. Di Salvo, L. Burderi, A. Riggio, A. Papitto, M. T. Menna
Comments: 10 Pages, 3 Figures. Final version to be published on AIP Conference Proceedings
 
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Submissions received from Wed 13 Jun 07 to Thu 14 Jun 07, announced Fri, 15 Jun 07

[ total of 60 entries: 1-60 ]
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1 abstracts or titles contain neutron star, magnetar or pulsar


[30]  arXiv:0706.2120 [ps, pdf, other] :
Title: IRAS08281-4850 and IRAS14325-6428: two A-type post-AGB stars with s-process enrichment
Authors: M. Reyniers, G.C. Van de Steene, P.A.M. van Hoof, H. Van Winckel
Comments: 8 pages, 6 figures, accepted by A&A

One of the puzzling findings in the study of the chemical evolution of (post-)AGB stars is why very similar stars (in terms of metallicity, spectral type, infrared properties, etc...) show a very different photospheric composition. We aim at extending the still limited sample of s-process enriched post-AGB stars, in order to obtain a statistically large enough sample that allows us to formulate conclusions concerning the 3rd dredge-up occurrence. We selected two post-AGB stars on the basis of IR colours indicative of a past history of heavy mass loss: IRAS08281-4850 and IRAS14325-6428. They are cool sources in the locus of the Planetary Nebulae (PNe) in the IRAS colour-colour diagram. Abundances of both objects were derived for the first time on the basis of high-quality UVES and EMMI spectra, using a critically compiled line list with accurate log(gf) values, together with the latest Kurucz model atmospheres. Both objects have very similar spectroscopically defined effective temperatures of 7750-8000K. They are strongly carbon and s-process enriched, with a C/O ratio of 1.9 and 1.6, and an [ls/Fe] of +1.7 and +1.2, for IRAS08281 and IRAS14325 resp. Moreover, the spectral energy distributions (SEDs) point to heavy mass-loss during the preceding AGB phase. IRAS08281 and IRAS14325 are prototypical post-AGB objects in the sense that they show strong post 3rd dredge-up chemical enrichments. The neutron irradiation has been extremely efficient, despite the only mild sub-solar metallicity. This is not conform with the recent chemical models. The existence of very similar post-AGB stars without any enrichment emphasizes our poor knowledge of the details of the AGB nucleosynthesis and dredge-up phenomena. We call for a very systematic chemical study of all cool sources in the PN region of the IRAS colour-colour diagram.

 

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0 abstracts or titles contain neutron star, magnetar or pulsar


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[7]  arXiv:0706.3243 [ps, pdf, other]
Title: Quark deconfinement in neutron star cores and the ground state of neutral matter Authors: Chang-Qun Ma, Chun-Yuan Gao Comments: 13 pages, 4 figures Subjects: Astrophysics (astro-ph)

Whether or not deconfined quark phase exists in neutron star cores and represents the ground state of neutral matter at moderate densities are open questions. We use two realistic effective quark models, the three-flavor Nambu-Jona-Lasinio model and the modified quark-meson coupling model, to describe the neutron star matter. After constructing possible hybrid equations of state (EOSes) with unpaired or color superconducting quark phase, we systematically discuss the observational constraints of neutron stars on the EOSes. It is found that the neutron star with pure quark matter core is unstable and the hadronic phase with hyperons is denied, while hybrid EOSes with two-flavor color superconducting phase or unpaired quark matter phase are both allowed by the tight and most reliable constraints from two stars Ter 5 I and EXO 0748-676. And the hybrid EOS with unpaired quark matter phase is allowed even compared with the tightest constraint from the most massive pulsar star PSR J0751+1807. Therefore, we conclude that the ground state of neutral matter at moderate densities is in deconfined quark phase likely.

Cross-lists for Mon, 25 Jun 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Mon, 25 Jun 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[43]  arXiv:0706.2255 (replaced) [ps, pdf, other]
Title: The magnetic field topology in the reconnecting pulsar magnetosphere Authors: Ioannis Contopoulos Comments: Accepted for publication in Astronomy and Astrophysics Subjects: Astrophysics (astro-ph)
[52]  arXiv:astro-ph/0702089 (replaced) [ps, pdf, other]
Title: Evaluating Spectral Models and the X-ray States of Neutron-Star X-ray Transients Authors: Dacheng Lin, Ronald A. Remillard, Jeroen Homan (MIT Kavli Institute for Astrophysics and Space Research) Comments: 15 pages, 15 figures, accepted for publication in the ApJ Subjects: Astrophysics (astro-ph)
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[3]  arXiv:0706.3421 [ps, pdf, other]
Title: The cold neutron star in the soft X-ray transient 1H 1905+000 Authors: Peter G. Jonker, Daniel Steeghs, Deepto Chakrabarty, Adrienne M. Juett Comments: 5 pages, 3 figures, accepted for publication in ApJ Letters Subjects: Astrophysics (astro-ph)

We report on our analysis of 300 ks of Chandra observations of the neutron star soft X-ray transient 1H1905+000 in quiescence. We do not detect the source down to a 95% confidence unabsorbed flux upper limit of 2E-16 erg cm-2 s-1 in the 0.5-10 keV energy range for an assumed Gamma=2 power law spectral model. A limit of 1.4E-16 erg cm-2 s-1 is derived if we assume that the spectrum of 1H1905+000 in quiescence is described well with a black body of temperature of 0.2 keV. For the upper limit to the source distance of 10 kpc this yields a 0.5-10 keV luminosity limit of 2.4E30 / 1.7E30 erg/s for the abovementioned power law or black body spectrum, respectively. This luminosity limit is lower than the luminosity of A0620-00, the weakest black hole soft X-ray transient in quiescence reported so far. Together with the uncertainties in relating the mass transfer and mass accretion rates we come to the conclusion that the claim that there is evidence for the presence of a black hole event horizon on the basis of a lower quiescent luminosity for black holes than for neutron stars is unproven. We also briefly discuss the implications of the low quiescent luminosity of 1H1905+000 for the neutron star equation of state. Using deep Magellan images of the field of 1H1905+000 obtained at excellent observing conditions we do not detect the quiescent counterpart at the position of the outburst optical counterpart down to a magnitude limit of i'>25.3. This can be converted to a limit on the absolute magnitude of the counterpart of I>9.6 which implies that the counterpart can only be a brown or a white dwarf.

[8]  arXiv:0706.3448 [ps, pdf, other]
Title: Daily Observations of Interstellar Scintillation in PSR B0329+54 Authors: Z. Yan, N. Wang, R. N. Manchester, H. X. Wang Subjects: Astrophysics (astro-ph)

The phenomena of diffractive interstellar scintillation (DISS) and refractive interstellar scintillation (RISS) are not yet well understood. In an observing session of about 20 days using the Nanashan 25-m telescope at 1.5 GHz, we focused on PSR B0329+54 to study the scintillation properties of the interstellar medium (ISM) along the line of sight to this pulsar and the refractive effects on diffractive parameters. We obtained scintillation parameters, including flux density, decorrelation bandwidth, diffractive time-scale and the drift rate of the dynamic spectra respectively. We calculate the modulation indices of flux density, decorrelation bandwidth and diffractive time-scale and derive the RISS time-scales using the structure functions of these parameters. Cross-correlations among flux density, decorrelation bandwidth and diffractive time-scale are weak and not in accord with theoretical predictions whereas the observed modulation indices are close to the predicted values. Refractive time-scales are much shorter than predictions based on a power-law spectrum of electron density fluctuations and the thin screen model.

[25]  arXiv:0706.3578 [ps, pdf, other]
Title: On the corona of magnetars Authors: Yury Lyubarsky, David Eichler Comments: 23 pages, 2 fig. Submitted to ApJ Subjects: Astrophysics (astro-ph)

Slow dissipation of non-potential magnetic fields in the magnetosphere of the magnetar is assumed to accelerate particles to hundreds MeV along the magnetic field lines. We consider interaction of fast particles with the surface of the magnetar. We argue that the collisionless dissipation does not work in the atmosphere of the neutron star because the two-stream instability is stabilized by the inhomogeneity of the atmosphere. Rather, the dominant dissipation mechanism is collisional Landau levelexcitations followed by pair production via the deexcitation gamma-rays ultimately leading to electrons with the energy below the Landau energy. We show that, because of the effects of the superstrong magnetic field, these electrons could emerge from the surface carrying most of the original energy so that a hot corona arises with the temperature of 1 - 2 MeV. This extended corona is better suited than a thin atmosphere to convert most of the primary beam energy to non-thermal radiation and, as we show, most of the coronal energy release is radiated away in the hard X-ray and the soft gamma-ray bands by Comptonization and bremsstrahlung. The radiation spectrum is a power-law with the photon index $1<\alpha<2$. The model may account for the persistent hard X-ray emission discovered recently from the soft gamma-ray repeaters and anomalous X-ray pulsars and predicts that the radiation spectrum is extended into the MeV band.

Cross-lists for Tue, 26 Jun 07

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0 abstracts or titles contain neutron star, magnetar or pulsar


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5 abstracts or titles contain neutron star, magnetar or pulsar


[1]  arXiv:0706.3698 [ps, pdf, other]
Title: On the nature of QPO in the tail of SGR giant flares Authors: A.N. Timokhin (1,2), D. Eichler (1), Yu. Lyubarsky (1) ((1) Ben-Gurion University of the Negev, Beer-Sheva, Israel; (2) Sternberg Astronomical Institute, Moscow, Russia) Comments: 7 pages, 4 figures, emulateapj style Subjects: Astrophysics (astro-ph)

A model is presented for the quasiperiodic component of magnetar emission during the tail phase of giant flares. The model invokes modulation of the particle number density in the magnetosphere. The magnetospheric currents are modulated by torsional motion of the surface and we calculate that the amplitude of neutron star surface oscillation should be ~1% of the NS radius in order to produce the observed features in the power spectrum. Using an axisymmetric analytical model for structure of the magnetosphere of an oscillating NS, we calculate the angular distribution of the optical depth to the resonant Compton scattering. The anisotropy of the optical depth may be why QPO are observed only at particular rotational phases.

[17]  arXiv:0706.3762 [ps, pdf, other]
Title: Dynamics and neutrino signal of black hole formation in non-rotating failed supernovae. I. EOS dependence Authors: K. Sumiyoshi (Numazu CT), S. Yamada (Waseda Univ.), H. Suzuki (Tokyo Univ. of Science) Comments: 32 pages, 33 figures, accepted for publication in ApJ Subjects: Astrophysics (astro-ph)

We study the black hole formation and the neutrino signal from the gravitational collapse of a non-rotating massive star of 40 Msun. Adopting two different sets of realistic equation of state (EOS) of dense matter, we perform the numerical simulations of general relativistic neutrino-radiation hydrodynamics under the spherical symmetry. We make comparisons of the core bounce, the shock propagation, the evolution of nascent proto-neutron star and the resulting re-collapse to black hole to reveal the influence of EOS. We also explore the influence of EOS on the neutrino emission during the evolution toward the black hole formation. We find that the speed of contraction of the nascent proto-neutron star, whose mass increases fast due to the intense accretion, is different depending on the EOS and the resulting profiles of density and temperature differ significantly. The black hole formation occurs at 0.6-1.3 sec after bounce when the proto-neutron star exceeds its maximum mass, which is crucially determined by the EOS. We find that the average energies of neutrinos increase after bounce because of rapid temperature increase, but at different speeds depending on the EOS. The duration of neutrino emission up to the black hole formation is found different according to the different timing of re-collapse. These characteristics of neutrino signatures are distinguishable from those for ordinary proto-neutron stars in successful core-collapse supernovae. We discuss that a future detection of neutrinos from black-hole-forming collapse will contribute to reveal the black hole formation and to constrain the EOS at high density and temperature.

[37]  arXiv:0706.3838 [ps, pdf, other]
Title: Eight powers of ten: similarities in black hole accretion on all mass scales Authors: Rob Fender (Southampton), Elmar Koerding, Tomaso Belloni, Phil Uttley, Ian McHardy, Tasso Tzioumis Comments: Invited Review at the VI Microquasar Workshop: Microquasars and beyond, Sept 18-22 2006, Como, Italy. To be published online by PoS Subjects: Astrophysics (astro-ph)

In this paper we discuss the recent advances in the quantitative comparison of accretion, and the accretion:jet coupling, in accreting black holes in both X-ray binaries (where M ~ 10Msun) and Active Galactic Nuclei (10^5Msun < M < 10^9Msun). These similarities include the radiative efficiency and jet power as a function of accretion rate, which are themselves probably the origin of the `fundamental plane of black hole activity'. A second `fundamental plane' which connects mass, accretion rate and timing properties provides us with a further physical diagnostic. Patterns of radio loudness (i.e. jet production) as a function of luminosity and accretion state are shown to be similar for X-ray binaries and AGN. Finally we discuss how neutron stars are a useful control sample, and what the future may hold for this field.

[38]  arXiv:0706.3839 [ps, pdf, other]
Title: The variable radio counterpart and possible large-scale jet of the new Z-source XTE J1701-462 Authors: R P Fender (Southampton), M Dahlem, J Homan, S Corbel, R Sault, T M Belloni Comments: Accepted for publication as a Letter in MNRAS Subjects: Astrophysics (astro-ph)

We report radio observations, made with the Australia Telescope Compact Array, of the X-ray transient XTE J1701-462. This system has been classified as a new `Z' source, displaying characteristic patterns of behaviour probably associated with accretion onto a low magnetic field neutron star at close to the Eddington limit. The radio counterpart is highly variable, and was detected in six of sixteen observations over the period 2006 January -- April. The coupling of radio emission to X-ray state, despite limited sampling, appears to be similar to that of other `Z' sources, in that there is no radio emission on the flaring branch. The mean radio and X-ray luminosities are consistent with the other Z sources for a distance of 5--15 kpc. The radio spectrum is unusually flat, or even inverted, in contrast to the related sources, Sco X-1 and Cir X-1, which usually display an optically thin radio spectrum. Deep wide-field observations indicate an extended structure three arcminutes to the south which is aligned with the X-ray binary. This seems to represent a significant overdensity of radio sources for the field and so, although a background source remains a strong possibility, we consider it plausible that this is a large-scale jet associated with XTE J1701-462.

[46]  arXiv:0706.3881 [ps, pdf, other]
Title: Evidence for a parsec scale X-ray jet from the accreting neutron star Circinus X-1 Authors: S. Heinz, N. S. Schulz, W. N. Brandt, D. K. Galloway Comments: 5 pages, 3 figures, accepted for publication in ApJ Letter Subjects: Astrophysics (astro-ph)

We analyzed the zero-order image of a 50 ks Chandra gratings observation of Circinus X-1, taken in 2005 during the source's low-flux state. Circinus X-1 is an accreting neutron star that exhibits ultra-relativistic arcsecond-scale radio jets and diffuse arcminute-scale radio jets and lobes. The image shows a clear excess along the general direction of the north-western counter-jet, coincident with the radio emission, suggesting that it originates either in the jet itself or in the shock the jet is driving into its environment. This makes Circinus X-1 the first neutron star for which an extended X-ray jet has been detected. The kinetic jet power we infer is significantly larger than the minimum power required for the jet to inflate the large scale radio nebula.

Cross-lists for Wed, 27 Jun 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Wed, 27 Jun 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[61]  arXiv:astro-ph/0609047 (replaced) [ps, pdf, other]
Title: Magnetar-Driven Magnetic Tower as a Model for Gamma-Ray Bursts and Asymmetric Supernovae Authors: Dmitri A. Uzdensky (Princeton University and CMSO), Andrew I. MacFadyen (IAS and NYU) Comments: 16 pages, 7 figures; accepted to ApJ Subjects: Astrophysics (astro-ph)
[62]  arXiv:astro-ph/0611100 (replaced) [ps, pdf, other]
Title: Spitzer Mid-infrared Upper Limits on Anomalous X-Ray Pulsars 1E 1048.1-5937, 1RXS J170849-400910, and XTE J1810-197 Authors: Z. Wang, V. M. Kaspi, S. J. U. Higdon Comments: 6 pages, 5 figures, ApJ, accepted Subjects: Astrophysics (astro-ph)
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[21]  arXiv:0706.3972 [ps, pdf, other]
Title: XMM-Newton observation of the persistent Be/neutron-star system X Persei at a high-luminosity level Authors: N. La Palombara, S. Mereghetti (INAF/IASF-Milano) Comments: 8 pages, 8 figures, 4 tables. Accepted for publication by Astronomy & Astrophysics Subjects: Astrophysics (astro-ph)

We report on the XMM-Newton observation of the HMXRB X Persei, the prototype of the persistent and low-luminosity Be/neutron star pulsars, which was performed on February 2003. The source was detected at a luminosity level of ~ 1.4x10^35 erg/s, which is the highest level of the latest three decades. The pulsation period has increased up to 839.3 s, thus confirming the overall spin-down of the NS detected in the previous observations. The folded light-curve has a complex structure, with features not observed at lower luminosities, and shows a significant energy dependence. The spectral analysis reveals the presence of a significant excess at low energies over the main power-law spectral component, which can be described by a black-body spectrum of high temperature (kT_BB ~ 1.5 keV) and small emitting region (R_BB ~ 340 m); its properties are consistent with a polar-cap origin. Phase-resolved spectroscopy shows that the emission spectrum varies along the pulse period, but it is not possible to prove whether the thermal component is pulsed or not.

Cross-lists for Thu, 28 Jun 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Thu, 28 Jun 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[65]  arXiv:gr-qc/0702039 (replaced) [ps, pdf, other]
Title: Upper limits on gravitational wave emission from 78 radio pulsars Authors: The LIGO Scientific Collaboration: B. Abbott, et al, M. Kramer, A. G. Lyne Comments: 21 pages, accepted for Phys. Rev. D Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)
[66]  arXiv:gr-qc/0703152 (replaced) [ps, pdf, other]
Title: Binary system delays and timing noise in searches for gravitational waves from known pulsars Authors: Matthew Pitkin, Graham Woan (University of Glasgow) Comments: 10 pages, 11 figures, accepted by Phys. Rev. D Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)
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5 abstracts or titles contain neutron star, magnetar or pulsar


[5]  arXiv:0706.4096 [ps, pdf, other]
Title: Formation and evolution of compact binaries in globular clusters: II. Binaries with neutron stars Authors: N. Ivanova, C. Heinke, F.A. Rasio, K. Belczynski, J. Fregeau Comments: 20 pages, 6 figures, 12 tables, MNRAS submitted Subjects: Astrophysics (astro-ph)

In this paper, the second of a series, we study the stellar dynamical and evolutionary processes leading to the formation of compact binaries containing neutron stars in dense globular clusters. For this study, 70 dense clusters were simulated independently, with a total stellar mass ~2x10^7Msun, well exceeding the mass of all dense globular clusters in our Galaxy. We find that, in order to reproduce the empirically derived formation rate of low-mass X-ray binaries (LMXBs), we must assume that NSs can be formed via electron-capture supernovae with typical natal kicks smaller than in core-collapse supernovae. Our results explain the observed dependence of the number of LMXBs on ``collision number'' as well as the large scatter observed between different globular clusters. We predict that the number of quiescent LMXBs should not have a strong metallicity dependence. For millisecond pulsars (MSPs), we distinguish high-magnetic-field (short-lived) and low-magnetic-field (long-lived) populations. With this distinction, we obtain good agreement of our models with the numbers and characteristics of observed MSPs in 47 Tuc and Terzan 5, as well as with the cumulative statistics for MSPs detected in globular clusters of different dynamical properties. We find that significant production of merging double neutron stars potentially detectable as short gamma-ray bursts occurs only in very dense, most likely core-collapse clusters.

[12]  arXiv:0706.4139 [ps, pdf, other]
Title: Short Gamma-Ray Bursts and Binary Mergers in Spiral and Elliptical Galaxies: Redshift Distribution and Hosts Authors: R. O'Shaughnessy (1), V. Kalogera (1), K. Belczynski (2) ((1) Northwestern University, (2) New Mexico State University) Comments: 14 figures, using bitmapped fonts (via eps2eps) to fit in archive space restrictions; better resolution figures are available from the author. Submitted to apj Subjects: Astrophysics (astro-ph)

To test whether the short GRB rates, redshift distribution and host galaxies are consistent with current theoretical predictions, we use avery large database of population synthesis calculations to examine BH-NS and NS-NS merger rates in the universe, factoring in (i) the star formation history of the universe, (ii) a heterogeneous population of star-forming galaxies, including spirals and ellipticals, and (iii) a simple flux-limited selection model for short GRB detection. When we require our models reproduce the known short GRB rates and redshift measurements (and, for NS-NS, the merger rates extrapolated from binary pulsars in the Galaxy), a small fraction of models reproduce all observations, both when we assume a NS-NS and a BH-NS origin for bursts. Most commonly models produce mergers preferentially in spiral galaxies if short GRBs arise from NS-NS mergers alone. Model universes where present-day binary mergers occur preferentially in elliptical galaxies necessarily include a significant fraction of binaries with long delay times between birth and merger (often $O(10{\rm Gyr})$). Though long delays occur, almost all of our models predict that a higher proportion of short GRBs should occur at moderate to high redshift (e.g., $z>1$) than has presently been observed, in agreement with recent observations which suggest a selection bias towards successful follow-up of low-redshift short GRBs. Finally, if only a fraction of BH-NS mergers have the right combination of masses and spins to make GRBs, then at best only a small fraction of BH-NS models could be consistent with all {\em current} available data. (Abridged)

[13]  arXiv:0706.4140 [ps, pdf, other]
Title: Improbability of DUrca process constraints EOS Authors: Hao Tong, Qiu-he Peng Comments: Accepted by ChJAA Subjects: Astrophysics (astro-ph)

According to recent observational and theoretical progresses, the DUrca process (direct Urca process) may be excluded from the category of neutron star cooling mechanisms. This result combined with the latest nuclear symmetry energy experiments, will provide us an independent way of testing the EOS (equation of state) for supranormal density. For example, soft EOSs such as FPS will probably be excluded.

[17]  arXiv:0706.4156 [ps, pdf, other]
Title: Glitches in Anomalous X-ray Pulsars Authors: Rim Dib, Victoria M. Kaspi, Fotis P. Gavriil Comments: 47 pages, 17 figures, 8 tables, submitted to ApJ Subjects: Astrophysics (astro-ph)

(Abridged). We report on 8.7 and 7.6yr of RXTE observations of the Anomalous X-ray Pulsars (AXPs) RXS J170849.0-400910 and 1E 1841-045, respectively. These observations, part of a larger RXTE AXP monitoring program, have allowed us to study the long-term timing, pulsed flux, and pulse profile evolution of these objects. We report on four new glitches, one from RXS J170849.0-400910 and three from 1E 1841-045. One of the glitches from 1E 1841-045 is among the largest ever seen in a neutron star, having fractional frequency jump (delta nu)/nu=1.6E-5. With nearly all known persistent AXPs now seen to glitch, such behavior is clearly generic to this source class. We compare AXP glitches with those in radio pulsars. We show that in terms of fractional frequency change, AXPs are among the most actively glitching neutron stars, with glitch amplitudes in general larger than in radio pulsars. However, in terms of absolute glitch amplitude, AXP glitches are unremarkable. We show that the largest observed AXP glitches show recoveries that are unusual among those of radio pulsar glitches, with the combination of glitch recovery time scale and fraction yielding changes in spin-down rates in the days following the glitch of the order of, or larger than, the long-term average. We also observed a large fractional increase in the magnitude of the spin-down rate of 1E 1841-045 following its largest glitch. These observations are challenging to interpret in standard glitch models, as is the frequent occurence of large glitches given AXPs' high measured temperatures. Furthermore, we show that AXP glitches appear to fall in two classes: radiatively loud and radiatively quiet. We also show that pulse profile changes and pulsed flux changes are very common among these AXPs, and are generally not correlated with any obvious timing behavior.

[25]  arXiv:0706.4241 [ps, pdf, other]
Title: The role of thermal pressure in jet launching Authors: Noam Soker (Technion, Israel) Comments: To appear in the proceedings of Star-disk interaction in young stars, Grenoble 2007, ed. J. Bouvier Subjects: Astrophysics (astro-ph)

I present and discuss a unified scheme for jet launching that is based on stochastic dissipation of the accretion disk kinetic energy, mainly via shock waves. In this scheme, termed thermally-launched jet model, the kinetic energy of the accreted mass is transferred to internal energy, e.g., heat or magnetic energy. The internal energy accelerates a small fraction of the accreted mass to high speeds and form jets. For example, thermal energy forms a pressure gradient that accelerates the gas. A second acceleration stage is possible wherein the primary outflow stretches magnetic field lines. The field lines then reconnect and accelerate small amount of mass to very high speeds. This double-stage acceleration process might form highly relativistic jets from black holes and neutron stars. The model predicts that detail analysis of accreting brown dwarfs that launch jets will show the mass accretion rate to be larger than 10^{-9}-10^{-8} Mo/year, which is higher than present claims in the literature.

Cross-lists for Fri, 29 Jun 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Fri, 29 Jun 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[41]  arXiv:0705.0155 (replaced) [ps, pdf, other]
Title: Accreting Neutron Stars in Low-Mass X-Ray Binary Systems Authors: Frederick K. Lamb, Stratos Boutloukos Comments: 22 pages, 7 figures, updated list of sources and references, to appear in "Short-period Binary Stars: Observation, Analyses, and Results", eds. E.F. Milone, D.A. Leahy, and D. Hobill (Dordrecht: Springer, this http URL) Subjects: Astrophysics (astro-ph)
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[11]  arXiv:0706.4360 [ps, pdf, other]
Title: Cold r-Process in Neutrino-Driven Winds Authors: Shinya Wanajo Comments: 5 pages, 3 figures, submitted to ApJL Subjects: Astrophysics (astro-ph)

The r-process in a low temperature environment is explored, in which the neutron emission by photodisintegration does not play a role (cold r-process). A semi-analytic neutrino-driven wind model is utilized for this purpose. The temperature in a supersonically expanding outflow can quickly drop to a few 10^8 K, where the (n, gamma)-(gamma, n) equilibrium is never achieved during the heavy r-nuclei synthesis. In addition, the neutron capture competes with the beta-decay owing to the low matter density. Despite such non-standard physical conditions for the cold r-process, a solar-like r-process abundance curve can be reproduced. The cold r-process predicts, however, the low lead production compared to that expected in the traditional r-process conditions, which can be a possible explanation for the low lead abundances found in a couple of r-process-rich Galactic halo stars.

Cross-lists for Mon, 2 Jul 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[36]  arXiv:0706.4108 (cross-list from stat.ME) [pdf, other]
Title: Event Weighted Tests for Detecting Periodicity in Photon Arrival Times Authors: Peter Bickel, Bas Kleijn, John Rice Subjects: Methodology (stat.ME); Astrophysics (astro-ph); Applications (stat.AP)

This paper treats the problem of detecting periodicity in a sequence of photon arrival times, which occurs, for example, in attempting to detect gamma-ray pulsars. A particular focus is on how auxiliary information, typically source intensity, background intensity, and incidence angles and energies associated with each photon arrival should be used to maximize the detection power. We construct a class of likelihood-based tests, score tests, which give rise to event weighting in a principled and natural way, and derive expressions quantifying the power of the tests. These results can be used to compare the efficacies of different weight functions, including cuts in energy and incidence angle. The test is targeted toward a template for the periodic lightcurve, and we quantify how deviation from that template affects the power of detection.

Replacements for Mon, 2 Jul 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[43]  arXiv:0706.3881 (replaced) [ps, pdf, other]
Title: Evidence for a parsec scale X-ray jet from the accreting neutron star Circinus X-1 Authors: S. Heinz, N. S. Schulz, W. N. Brandt, D. K. Galloway Comments: Added journal reference, corrected on reference and typo in labels for Fig. 1; 5 pages, 3 figures, ApJ Letter, in press Subjects: Astrophysics (astro-ph)
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[27]  arXiv:0707.0264 [ps, pdf, other]
Title: Magnetar-energized supernova explosions and GRB-jets Authors: S. S. Komissarov, M. V. Brakov Comments: submitted to MNRAS Subjects: Astrophysics (astro-ph)

In this paper we report on the early evolution of core-collapse supernova explosion following the birth of a magnetar with the dipolar magnetic field of B=10^{15}G and the rotational period of 2ms, which was studied by means of axisymmetric general relativistic MHD simulations. The numerical models exhibit highly collimated magnetically-driven jets very early on. The jets are super-Alfvenic but remain sub-fast until the end of the simulations (t=0.2s). The power released in the jets is about 3x10^{50}erg/s which implies the spin-down time of ~37s. The total rotational energy of the magnetar, E~10^{52}erg, is sufficient to drive hypernova but it is not clear as to how large a fraction of this energy can be transfered to the stellar envelope. Given the observed propagation speed of the jets, v_p~0.17c, they are expected to traverse the progenitor in few seconds and after this most of the released rotational energy would be simply carried away by these jets into the surrounding space. Our results provide the first more or less self-consistent numerical model of a central engine capable of producing, in the supernova setting and on a long-term basis, collimated jets with sufficient power to explain long duration GRBs and their afterglows. Although the flow speed of our jets is relatively low, v_j~0.5c$, the rapid cooling of proto-neutron star will eventually result in much higher magnetization of its magnetospheres and ultra-relativistic asymptotic speeds of the jets. Given the relatively long cooling time-scale we still expect the jets to be only weakly relativistic by the time of break out. This leads to a model of GRB jets with systematic longitudinal variation of Lorentz factor which may have specific observational signatures both in the prompt and the afterglow emission.

Cross-lists for Tue, 3 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Tue, 3 Jul 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[43]  arXiv:0705.1901 (replaced) [ps, pdf, other]
Title: Hall drift of axisymmetric magnetic fields in solid neutron-star matter Authors: Andreas Reisenegger, Rafael Benguria, Joaquin P. Prieto, Pablo A. Araya, Dong Lai Comments: 8 pages, 5 figure panels; new version with very small correction; accepted by Astronomy & Astrophysics Subjects: Astrophysics (astro-ph); Mathematical Physics (math-ph); Exactly Solvable and Integrable Systems (nlin.SI); Plasma Physics (physics.plasm-ph)
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[27]  arXiv:0707.0485 [ps, pdf, other]
Title: Linking the X-ray timing and spectral properties of the glitching AXP 1RXS J170849-400910 Authors: G.L. Israel (1), D. Gotz (2), S. Zane (3), S. Dall'osso (1), N. Rea (4), L. Stella (1) ((1) Inaf Oa Roma, (2) Cea Saclay, (3) MSSL, (4) Sron) Comments: Submitted to A&A, 4 pages; results presented at the INT meeting "The Neutron Star Crust and Surface: Observations and Models" on June 27 Subjects: Astrophysics (astro-ph)

Previous studies of the X-ray flux and spectral properties of 1RXS J170849-400910 showed hints of a possible correlation with the spin glitches that occurred in 1999 and 2001. However, due to the sparseness of spectral measurements and the paucity of detected glitches no firm conclusion could be drawn. We retrieved and analysed 204 archival XTE pointings of 1RXS J170849-400910 covering the time interval between January 2003 and June 2006 and carried out a detailed timing analysis by means of phase fitting techniques. We detected two relatively large glitches Delta nu / nu of 1.2 and 2.1 10^-6 occurred in January and June 2005. Interestingly, the occurrence times of these glitches fit well with those we predicted in previous studies and based on the flux and spectral parameters evolution. This finding clearly confirm a deep connection between the flux, spectral and timing properties of 1RXS J170849-400910.

Cross-lists for Wed, 4 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Wed, 4 Jul 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[43]  arXiv:astro-ph/0701851 (replaced) [ps, pdf, other]
Title: On the validity of the Wigner-Seitz approximation in neutron star crust Authors: N. Chamel (IAA), S. Naimi (IPNO), E. Khan (IPNO), J. Margueron (IPNO) Comments: 7 pages, with figures - PTH, version 2 Subjects: Astrophysics (astro-ph); Nuclear Theory (nucl-th)
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4 abstracts or titles contain neutron star, magnetar or pulsar


[9]  arXiv:0707.0516 [pdf, other]
Title: Deep VLT infrared observations of X-ray Dim Isolated Neutron Stars Authors: G. Lo Curto, R.P. Mignani, R. Perna, G.L. Israel Comments: 6 pages, 2 figures, accepted by A&A on 26-06-2007 Subjects: Astrophysics (astro-ph)

X-ray observations have unveiled the existence of a family of radio-quiet Isolated Neutron Stars whose X-ray emission is purely thermal, hence dubbed X-ray Dim Isolated Neutron Stars (XDINSs). While optical observations have allowed to relate the thermal emission to the neutron star cooling and to build the neutron star surface thermal map, IR observations are critical to pinpoint a spectral turnover produced by a so far unseen magnetospheric component, or by the presence of a fallback disk. The detection of such a turnover can provide further evidence of a link between this class of isolated neutron stars and the magnetars, which show a distinctive spectral flattening in the IR.
Here we present the deepest IR observations ever of five XDINSs, which we use to constrain a spectral turnover in the IR and the presence of a fallback disk. The data are obtained using the ISAAC instrument at the VLT.
For none of our targets it was possible to identify the IR counterpart down to limiting magnitudes H = 21.5 - 22.9. Although these limits are the deepest ever obtained for neutron stars of this class, they are not deep enough to rule out the existence and the nature of a possible spectral flattening in the IR. We also derive, by using disk models, the upper limits on the mass inflow rate in a fallback disk. We find the existence of a putative fallback disk consistent (although not confirmed) with our observations.

[25]  arXiv:0707.0576 [ps, pdf, other]
Title: Magnetically-dominated jets inside collapsing stars as a model for gamma-ray bursts and supernova explosions Authors: Dmitri A. Uzdensky (Princeton University), Andrew I. MacFadyen (IAS and NYU) Comments: Invited paper in the "Physics of Plasmas" (May 2007 special issue), based on an invited talk at the 48th Annual Meeting of the APS Division of Plasma Physics (Oct. 30 - Nov. 3, 2006, Philadelphia, PA); 24 pages, 7 figures Journal-ref: Physics of Plasmas, vol. 14, 056506 (2007) Subjects: Astrophysics (astro-ph)

It has been suggested that magnetic fields play a dynamically-important role in core-collapse explosions of massive stars. In particular, they may be important in the collapsar scenario for gamma-ray bursts (GRB), where the central engine is a hyper-accreting black hole or a millisecond magnetar. The present paper is focussed on the magnetar scenario, with a specific emphasis on the interaction of the magnetar magnetosphere with the infalling stellar envelope. First, the ``Pulsar-in-a-Cavity'' problem is introduced as a paradigm for a magnetar inside a collapsing star. The basic set-up of this fundamental plasma-physics problem is described, outlining its main features, and simple estimates are derived for the evolution of the magnetic field. In the context of a collapsing star, it is proposed that, at first, the ram pressure of the infalling plasma acts to confine the magnetosphere, enabling a gradual build-up of the magnetic pressure. At some point, the growing magnetic pressure overtakes the (decreasing) ram pressure of the gas, resulting in a magnetically-driven explosion. The explosion should be highly anisotropic, as the hoop-stress of the toroidal field, confined by the surrounding stellar matter, collimates the magnetically-dominated outflow into two beamed magnetic-tower jets. This creates a clean narrow channel for the escape of energy from the central engine through the star, as required for GRBs. In addition, the delayed onset of the collimated-explosion phase can explain the production of large quantities of Nickel-56, as suggested by the GRB-Supernova connection. Finally, the prospects for numerical simulations of this scenario are discussed.

[26]  arXiv:0707.0577 [ps, pdf, other]
Title: Pulsar kicks by anisotropic neutrino emission from quark matter Authors: I. Sagert, J. Schaffner-Bielich Comments: 6 pages, 3 figures, poster contribution at the conference "Nuclear Physics in Astrophysics III",Dresden,March 26-31,2007 Subjects: Astrophysics (astro-ph)

We discuss an acceleration mechanism for pulsars out of their supernova remnants based on asymmetric neutrino emission from quark matter in the presence of a strong magnetic field. The polarized electron spin fixes the neutrino emission from the direct quark Urca process in one direction along the magnetic field. We calculate the magnetic field strength which is required to polarize the electron spin as well as the required initial proto-neutron star temperature for a successfull acceleration mechanism. In addition we discuss the neutrino mean free paths in quark as well as in neutron matter which turn out to be very small. Consequently, the high neutrino interaction rates will wash out the asymmetry in neutrino emission. As a possible solution to this problem we take into account effects from colour superconductivity.

[35]  arXiv:0707.0624 [ps, pdf, other]
Title: Kinematical Studies of the Low Mass X-Ray Binary GR Mus (XB1254-690) Authors: A. D. Barnes, J. Casares, R. Cornelisse, P. A. Charles, D. Steeghs, R. I. Hynes, K. O'Brien Comments: 10 pages, 14 figures, accepted for publication in MNRAS Subjects: Astrophysics (astro-ph)

We present simultaneous high-resolution optical spectroscopy and X-ray data of the X-ray binary system GR Mus (XB1254-690), obtained over a full range of orbital phases. The X-ray observations are used to re-establish the orbital ephemeris for this source. The optical data includes the first spectroscopic detection of the donor star in this system, through the use of the Doppler Tomography technique on the Bowen fluorescence blend (~4630-4650 A). In combination with an estimate for the orbital parameters of the compact object using the wings of the He II 4686 emission line, dynamical mass constraints of 1.20 < M_X/M_{sun} < 2.64 for the neutron star and 0.45 < M_2/M_{sun} < 0.85 for the companion are derived.

Cross-lists for Thu, 5 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Thu, 5 Jul 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[54]  arXiv:0707.0485 (replaced) [ps, pdf, other]
Title: Linking the X-ray timing and spectral properties of the glitching AXP 1RXS J170849-400910 Authors: G.L. Israel (1), D. Gotz (2), S. Zane (3), S. Dall'osso (1), N. Rea (4), L. Stella (1) ((1) Inaf Oa Roma, (2) Cea Saclay, (3) MSSL, (4) Sron) Comments: Submitted to A&A, 4 pages; results presented at the INT meeting "The Neutron Star Crust and Surface: Observations and Models" on June 27 Subjects: Astrophysics (astro-ph)
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[7]  arXiv:0707.0711 [ps, pdf, other]
Title: Spin distribution following minor mergers and the effect of spin on the detection range for low-mass-ratio inspirals Authors: Ilya Mandel Comments: 18 pages, 5 figures Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc)

We compute the probability distribution for the spin of a black hole following a series of minor mergers with isotropically distributed, non-spinning, inspiraling compact objects. By solving the Fokker-Planck equation governing this stochastic process, we obtain accurate analytical fits for the evolution of the mean and standard deviation of the spin distribution in several parameter regimes. We complement these analytical fits with numerical Monte-Carlo simulations in situations when the Fokker-Planck analysis is not applicable. We find that a ~150 solar-mass intermediate-mass black hole that gained half of its mass through minor mergers with neutron stars will have dimensionless spin parameter chi=a/M~0.2 \pm 0.08. We estimate the effect of the spin of the central black hole on the detection range for intermediate-mass-ratio inspiral (IMRI) detections by Advanced LIGO and extreme-mass-ratio inspiral(EMRI) detections by LISA. We find that for realistic black hole spins, the inclination-averaged Advanced-LIGO IMRI detection range may be increased by up to 10% relative to the range for IMRIs into non-spinning intermediate-mass black holes. For LISA, we find that the detection range for EMRIs into 10^5 solar-mass massive black holes (MBHs) is not significantly affected by MBH spin, the range for EMRIs into 10^6 solar-mass MBHs is affected at the ~ 10% level, and EMRIs into maximally spinning 10^7 solar-mass MBHs are detectable to a distance ~25 times greater than EMRIs into non-spinning black holes. The resulting bias in favor of detecting EMRIs into rapidly spinning MBHs will play a role when extracting the MBH spin distribution from EMRI statistics.

[17]  arXiv:0707.0800 [ps, pdf, other]
Title: Resolving the bow-shock nebula around the old pulsar PSR B1929+10 with multi-epoch Chandra observations Authors: C. Y. Hui, W. Becker (MPE) Comments: Submitted to A&A, 7 pages, 6 figures and 3 tables Subjects: Astrophysics (astro-ph)

We have studied the nearby old pulsar PSR B1929+10 and its surrounding medium utilizing the sub-arcsecond angular resolution of Chandra. The Chandra data are found to be fully consistent with the results obtained from deep XMM-Newton observations as far as the pulsar is concerned. The non-thermal emission nature of the pulsar's X-radiation is confirmed. In addition to the X-ray trail seen already in previous observations by ROSAT and XMM-Newton an arc-like nebula intimately surrounding the pulsar is discovered at a signal-to-noise ratio of ~ 5. Using two Chandra observations separated by about six months morphological variability of this arc-like nebula is indicated.

[23]  arXiv:0707.0832 [ps, pdf, other]
Title: HESS J1616-508: likely powered by PSR J1617-5055 Authors: R. Landi, A. De Rosa, A.J. Dean, L. Bassani, P. Ubertini, A.J. Bird Comments: 7 pages, including 5 figures and 1 table. Accepted for publication in MNRAS Subjects: Astrophysics (astro-ph)

HESS J1616-508 is one of the brightest emitters in the TeV sky. Recent observations with the IBIS/ISGRI telescope on board the INTEGRAL spacecraft have revealed that a young, nearby and energetic pulsar, PSR J1617-5055, is a powerful emitter of soft gamma-rays in the 20-100 keV domain. In this paper we present an analysis of all available data from the INTEGRAL, Swift, BeppoSAX and XMM-Newton telescopes with a view to assessing the most likely counterpart to the HESS source. We find that the energy source that fuels the X/gamma-ray emissions is derived from the pulsar, both on the basis of the positional morphology, the timing evidence and the energetics of the system. Likewise, the 1.2% of the pulsar's spin down energy loss needed to power the 0.1-10 TeV emission is also fully consistent with other HESS sources known to be associated with pulsars. The relative sizes of the X/gamma-ray and VHE sources are consistent with the expected lifetimes against synchrotron and Compton losses for a single source of parent electrons emitted from the pulsar. We find that no other known object in the vicinity could be reasonably considered as a plausible counterpart to the HESS source. We conclude that there is good evidence to assume that the HESS J1616-508 source is driven by PSR J1617-5055 in which a combination of synchrotron and inverse Compton processes combine to create the observed morphology of a broad-band emitter from keV to TeV energies.

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[18]  arXiv:0707.0937 [ps, pdf, other]
Title: VLT observations of the Central Compact Object in the Vela Jr. supernova remnant Authors: R. P. Mignani (UCL-MSSL), A. De Luca (INAF-Iasf), S. Zaggia (INAF-Oap), D. Sester, A. Pellizzoni, S. Mereghetti, P. A. Caraveo (IASF-Inaf) Comments: 8 pages, 4 figures, A&Aaccepted Subjects: Astrophysics (astro-ph)

X-ray observations have unveiled the existence of enigmatic point-like sources at the center of young (a few kyrs) supernova remnants. These sources, known as Central Compact Objects (CCOs), are thought to be neutron stars produced by the supernova explosion, although their X-ray phenomenology makes them markedly different from all the other young neutron stars discovered so far.The aim of this work is to search for the optical/IR counterpart of the Vela Junior CCO and to understand the nature of the associated Halpha nebula discovered by Pellizzoni et al. (2002).}{We have used deep optical (R band) and IR (J,H,Ks bands) observations recently performed by our group with the ESO VLT to obtain the first deep, high resolution images of the field with the goal of resolving the nebula structure and pinpointing a point-like source possibly associated with the neutron star.Our R-band image shows that both the nebula's flux and its structure are very similar to the Halpha ones, suggesting that the nebula spectrum is dominated by pure Halpha line emission. However, the nebula is not detected in our IR observations, whick makes it impossible to to constrain its spectrum. A faint point-like object (J>22.6, H~21.6, Ks ~ 21.4) compatible with the neutron star's Chandra X-ray position is detected in our IR images (H and Ks) but not in the optical one (R > 25.6), where it is buried by the nebula background. The nebula is most likely a bow-shock produced by the neutron star motion through the ISM or, alternatively, a photo-ionization nebula powered by UV radiation from a hot neutron star.

[28]  arXiv:0707.0995 [ps, pdf, other]
Title: An XMM-Newton observation of the neutron star X-ray transient 2S 1803-245 in quiescence Authors: R. Cornelisse, R. Wijnands, J. Homan Comments: 5 pages, 3 figures, accepted for publication in MNRAS Subjects: Astrophysics (astro-ph)

We observed the neutron star X-ray transient 2S 1803-245 in quiescence with the X-ray satellite XMM-Newton, but did not detect it. An analysis of the X-ray bursts observed during the 1998 outburst of 2S 1803-245 gives an upper-limit to the distance of <7.3 kpc, leading to an upper-limit on the quiescent 0.5-10 keV X-ray luminosity of <2.8x10^32 erg/s (3sigma). Since the expected orbital period of 2S 1803-245 is several hrs, this limit is not much higher than those observed for the quiescent black hole transients with similar orbital periods.

Cross-lists for Mon, 9 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Mon, 9 Jul 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[44]  arXiv:0707.0264 (replaced) [pdf, other]
Title: Magnetar-energized supernova explosions and GRB-jets Authors: S. S. Komissarov, M. V. Barkov Comments: submitted to MNRAS, few typos corrected, better images Subjects: Astrophysics (astro-ph)
[52]  arXiv:astro-ph/0703802 (replaced) [ps, pdf, other]
Title: First X-ray observations of the young pulsar J1357-6429 Authors: Vyacheslav E. Zavlin Comments: Minor changes, including the reference to Esposito et al. (2007 A&A, 467, L45). Accepted by ApJ Letters Subjects: Astrophysics (astro-ph)
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[8]  arXiv:0707.1091 [pdf]
Title: Smashnova Model Authors: C Sivaram (1) ((1) Indian Institute of Astrophysics) Subjects: Astrophysics (astro-ph)

An alternate model for gamma ray bursts is suggested. For a white dwarf (WD) and neutron star (NS) very close binary system, the WD (close to Mch) can detonate due to tidal heating, leading to a SN. Material falling on to the NS at relativistic velocities can cause its collapse to a magnetar or quark star or black hole leading to a GRB. As the material smashes on to the NS, it is dubbed the Smashnova model. Here the SN is followed by a GRB. NS impacting a RG (or RSG) (like in Thorne-Zytkow objects) can also cause a SN outburst followed by a GRB. Other variations are explored.

Cross-lists for Tue, 10 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Tue, 10 Jul 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[39]  arXiv:0705.3451 (replaced) [ps, pdf, other]
Title: On the Possibility of Observing the Shapiro Effect for Pulsars in Globular Clusters Authors: T.I.Larchenkova (1), A.A.Lutovinov (2), ((1) Astro Space Center, Lebedev Physical Institute, Russian Academy of Sciences, (2) Space Research Institute, Russian Academy of Sciences) Comments: 26 pages, 9 figures Journal-ref: Astronomy Letters, 2007, V.33, pp.455-467 Subjects: Astrophysics (astro-ph)
[41]  arXiv:0705.4095 (replaced) [ps, pdf, other]
Title: The variable radio-to-X-ray spectrum of the magnetar XTE J1810-197 Authors: F. Camilo (1), S. M. Ransom (2), J. Penalver (3), A. Karastergiou (3), M. H. van Kerkwijk (4), M. Durant (5), J. P. Halpern (1), J. Reynolds (6), C. Thum (3), D. J. Helfand (1), N. Zimmerman (1), I. Cognard (7) ((1) Columbia, (2) NRAO, (3) IRAM, (4) Toronto, (5) IAC, (6) ATNF, (7) CNRS) Comments: Accepted for publication in ApJ; contains improved discussion of infrared uncertainties Subjects: Astrophysics (astro-ph)
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[6]  arXiv:0707.1547 [ps, pdf, other]
Title: The Next Geminga: Search for Radio and X-ray Pulsations from the Neutron Star Identified with 3EG J1835+5918 Authors: J.P. Halpern, F. Camilo, E.V. Gotthelf Comments: 4 pages, 1 figure, to appear in The Astrophysical Journal Subjects: Astrophysics (astro-ph)

We report unsuccessful searches for pulsations from the neutron star RX J1836.2+5925 identified with the EGRET source 3EG J1835+5918. A 24 hr observation with the NRAO Green Bank Telescope at 820 MHz placed an upper limit on flux density of 17 uJy for P > 10 ms, and gradually increasing limits for 1 < P < 10 ms. The equivalent luminosity is lower than that of any known pulsar with the possible exception of the radio-quiet gamma-ray pulsar Geminga. A set of observations with the Chandra X-ray Observatory HRC totaling 118 ks revealed no pulsar with 1 ms < P < 10 s. The upper limit on its pulsed fraction is 35% assuming a sinusoidal pulse shape. The position of RX J1836.2+5925 in Chandra observations separated by 3 years is unchanged within errors, leading to an upper limit on its proper motion of <0.14"/yr, or v < 530 km/s at d = 800 pc, a maximum distance estimated from its thermal X-ray spectrum. With these null results, the properties of 3EG J1835+5918 and its X-ray counterpart RX J1836.2+5925 are consistent with a more distant or older version of Geminga, or perhaps a recycled pulsar. Having nearly exhausted the capabilities of current instrumentation at all wavelengths, it will likely fall to the Gamma-ray Large Area Space Telescope to discover pulsations from 3EG J1835+5918.

[14]  arXiv:0707.1602 [ps, pdf, other]
Title: A 1.4-GHz Arecibo Survey for Pulsars in Globular Clusters Authors: J.W.T. Hessels (Univ. of Amsterdam/McGill), S.M. Ransom (NRAO), I.H. Stairs (UBC), V.M. Kaspi (McGill), P.C.C. Freire (NAIC) Comments: 27 pages, 6 tables, 5 figures Submitted to ApJ, includes referee comments Subjects: Astrophysics (astro-ph)

We have surveyed all 22 known Galactic globular clusters observable with the Arecibo radio telescope and within 70kpc of the Sun for radio pulsations at ~1.4GHz. Data were taken with the Wideband Arecibo Pulsar Processor, which provided the large bandwidth and high time and frequency resolution needed to detect fast-spinning, faint pulsars. We have also employed advanced search techniques to maintain sensitivity to short orbital period binaries. These searches have discovered 11 new millisecond pulsars and 2 promising candidates in 5 clusters, almost doubling the population of pulsars in the Arecibo-visible globular clusters. Ten of these new pulsars are in binary systems, and 3 are eclipsing. This survey has discovered significantly more very fast-spinning pulsars (P_spin <~ 4ms) and short orbital period systems (P_orb <~ 6hr) than previous surveys of the same clusters. We discuss some properties of these systems, as well as some characteristics of the globular cluster pulsar population in general, particularly its luminosity distribution.

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[13]  arXiv:0707.1727 [ps, pdf, other]
Title: Generalised Inverse-Cowling Approximation for Polar $w$-mode Oscillations of Neutron Stars Authors: J. Wu, P.T. Leung Comments: 11 pages, 4 figures, accepted for publication in MNRAS Subjects: Astrophysics (astro-ph)

Adopting the Lindblom-Detweiler formalism for polar oscillations of neutron stars, we study the $w$-mode oscillation and find that the Lagrangian change in pressure, measured by the physical quantity $X$, is negligibly small. Based on this observation, we develop the generalised inverse-Cowling approximation (GICA) with the approximation $X=X'=0$, where $X'$ is the derivative of $X$ with respect to the circumferential radius, for $w$-mode oscillations of neutron stars. Under GICA, $w$-mode oscillations are described by a second-order differential system, which can yield accurate frequencies and damping rates of quasi-normal modes.

[20]  arXiv:0707.1759 [ps, pdf, other]
Title: Torsional shear oscillations in the neutron star crust driven by restoring force of elastic stresses Authors: S. I. Bastrukov, H.-K. Chang, J. Takata, G.-T. Chen, I. V. Molodtsova Comments: 18 pages, 6 figures, Submitted to MNRAS Subjects: Astrophysics (astro-ph)

We present several examples of exact solution of the eigenfrequency problem for elastic torsional vibrations in the homogeneous and non-homogeneous models of the neutron star crust. Particular attention is given to the large lengthscale regime of nodeless axisymmetric differentially rotational vibrations, presumably about magnetic axis of the star. Highlighted is the distinction between analytic forms and numerical estimates for the frequency, computed as a function of multipole degree of nodeless torsional oscillations and fractional depth of peripheral seismogenic layer, caused by different boundary conditions imposed on the toroidal field of material displacements being the general solution to equation of Newtonian elastodynamics in the spherical polar coordinates. The relevance of considered models to quasiperiodic oscillations recently detected during the flare of SGR 1806-20 and SGR 1900+14 is discussed.

[22]  arXiv:0707.1782 [ps, pdf, other]
Title: Magnetic reconnection at the termination shock in a striped pulsar wind Authors: Jerome Petri, Yuri Lyubarsky Comments: Accepted by A&A Subjects: Astrophysics (astro-ph)

Most of the rotational luminosity of a pulsar is carried away by a relativistic magnetised wind in which the matter energy flux is negligible compared to the Poynting flux. Near the equatorial plane of an obliquely rotating pulsar magnetosphere, the magnetic field reverses polarity with the pulsar period, forming a wind with oppositely directed field lines. This structure is called a striped wind; dissipation of alternating fields in the striped wind is the object of our study.
The aim of this paper is to study the conditions required for magnetic energy release at the termination shock of the striped pulsar wind. Magnetic reconnection is considered via analytical methods and 1D relativistic PIC simulations.
An analytical condition on the upstream parameters for partial and full magnetic reconnection is derived from the conservation laws of energy, momentum and particle number density across the relativistic shock. Furthermore, by using a 1D relativistic PIC code, we study in detail the reconnection process at the termination shock.
We found a very simple criterion for dissipation of alternating fields at the termination shock, depending on the upstream parameters of the flow. 1D relativistic PIC simulations are in agreement with our criterion.
Thus, alternating magnetic fields annihilate easily at relativistic highly magnetised shocks.

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[12]  arXiv:0707.1907 [ps, pdf, other]
Title: A Catalog of Diffuse X-ray-Emitting Features within 20 pc of Sgr A*: Twenty Pulsar Wind Nebulae? Authors: M. P. Muno (Caltech), F. K. Baganoff (MIT), W. N. Brandt (Penn State), M. R. Morris (UCLA), J.-L. Starck (CEA Saclay) Comments: 14 pages, 8 figures, 5 in color. Submitted to ApJ Subjects: Astrophysics (astro-ph)

We present a catalog of 34 diffuse features identified in X-ray images of the Galactic center taken with the Chandra X-ray Observatory. Several of the features have been discussed in the literature previously, including 7 that are associated with a complex of molecular clouds that exhibits fluorescent line emission, 4 that are superimposed on the supernova remnant Sgr A East, 2 that are coincident with radio features that are thought to be the shell of another supernova remnant, and one that is thought to be a pulsar wind nebula only a few arcseconds in projection from Sgr A*. However, this leaves 20 features that have not been reported previously. Based on the weakness of iron emission in their spectra, we propose that most of them are non-thermal. One long, narrow feature points toward Sgr A*, and so we propose that this feature is a jet of synchrotron-emitting particles ejected from the supermassive black hole. For the others, we show that their sizes (0.1-2 pc in length for D=8 kpc), X-ray luminosities (between 10^32 and 10^34 erg/s, 2-8 keV), and spectra (power laws with Gamma=1-3) are consistent with those of pulsar wind nebulae. Based on the star formation rate at the Galactic center, we expect that ~20 pulsars have formed in the last 300 kyr, and could be producing pulsar wind nebulae. Only one of the 19 candidate pulsar wind nebulae is securely detected in an archival radio image of the Galactic center; the remainder have upper limits corresponding to L_R<la10^31 erg/s. These radio limits do not strongly constrain their natures, which underscores the need for further multi- wavelength studies of this unprecedented sample of Galactic X-ray emitting structures.

[32]  arXiv:0707.2036 [ps, pdf, other]
Title: The Optical Spectrum of the Vela Pulsar Authors: R.P. Mignani (UCL, MSSL), S. Zharikov (UNAM), P. A. Caraveo (IASF, INAF) Comments: 7 pages, 8 figures, accepted for publication in A&A Subjects: Astrophysics (astro-ph)

Our knowledge of the optical spectra of Isolated Neutron Stars (INSs) is limited by their intrinsic faintness. Among the fourteen optically identified INSs, medium resolution spectra have been obtained only for a handful of objects. No spectrum has been published yet for the Vela pulsar (PSR B0833-45), the third brightest (V=23.6) INS with an optical counterpart. Optical multi-band photometry underlines a flat continuum.In this work we present the first optical spectroscopy observations of the Vela pulsar, performed in the 4000-11000 A spectral range.Our observations have been performed at the ESO VLT using the FORS2 instrument. The spectrum of the Vela pulsar is characterized by a flat power-law (alpha = -0.04 +/- 0.04), which compares well with the values obtained from broad-band photometry. This confirms, once more, that the optical emission of Vela is entirely of magnetospheric origin. The comparison between the optical spectral indeces of rotation-powered INSs does not show evidence for a spectral evolution suggesting that, as in the X-rays, the INS aging does not affect the spectral properties of the magnetospheric emission. At the same time, the optical spectral indeces are found to be nearly always flatter then the X-rays ones, clearly suggesting a general spectral turnover at lower energies.

[39]  arXiv:0707.2067 [ps, pdf, other]
Title: On the mass of the neutron star in V395 Car/2S 0921-630 Authors: D.Steeghs (Warwick/CfA), P.G.Jonker (SRON/CfA) Comments: 4 pages, 3 figures, submitted to ApJ Letters Subjects: Astrophysics (astro-ph)

We report high-resolution optical spectroscopy of the low-mass X-ray binary V395 Car/2S 0921-630 obtained with the MIKE echelle spectrograph on the Magellan-Clay telescope. Our spectra are obtained near superior conjunction of the mass donor star and we exploit the absorption lines originating from the back-side of the K-type object to accurately derive its rotational velocity. Using K0-K1 III templates, we find vsini=32.9 +/- 0.8 km/s. We show that the choice of template star and the assumed limb darkening coefficient has little impact on the derived rotational velocity. This value is a significant revision downwards compared to previously published values. We derive new system parameter constraints in the light of our much lower rotational velocity. We find M_1=1.44 +/- 0.10 Msun, M_2=0.35 +/- 0.03 Msun, and q=0.24 +/- 0.02 where the errors have been estimated through a Monte-Carlo simulation. A possible remaining systematic effect is the fact that we may be over-estimating the orbital velocity of the mass donor due to irradiation effects. However, any correction for this effect will only reduce the compact object mass further, down to a minimum mass of M_1=1.05 +/- 0.08 Msun. There is thus strong evidence that the compact object in this binary is a neutron star of rather typical mass and that the previously reported mass values of 2-4Msun were too high due to an over-estimate of the rotational broadening.

Cross-lists for Mon, 16 Jul 07

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Replacements for Mon, 16 Jul 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[55]  arXiv:0707.1759 (replaced) [ps, pdf, other]
Title: Torsional shear oscillations in the neutron star crust driven by restoring force of elastic stresses Authors: S. I. Bastrukov, H.-K. Chang, J. Takata, G.-T. Chen, I. V. Molodtsova Comments: 18 pages, 6 figures, Submitted to MNRAS; corrected typos Subjects: Astrophysics (astro-ph)
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7 abstracts or titles contain neutron star, magnetar or pulsar


[3]  arXiv:0707.2093 [ps, pdf, other]
Title: X-ray and Near-IR Variability of the Anomalous X-ray Pulsar 1E 1048.1-5937: From Quiescence Back to Activity Authors: Cindy R. Tam (1), Fotis P. Gavriil (2), Rim Dib (1), Victoria M. Kaspi (1), Peter M. Woods (3), Cees Bassa (1) ((1) McGill University, (2) NASA GSFC, (3) Dynetics, Inc.; NSSTC) Comments: 13 pages (5 figures) in emulateapj style. Submitted to ApJ Subjects: Astrophysics (astro-ph)

(Abridged) Monitoring of the anomalous X-ray pulsar 1E 1048.1-5937 in 2005-2006 with the RXTE, CXO, and HST has revealed that the source entered a phase of X-ray and near-IR radiative quiescence, simultaneous with timing stability. During its ~2001-2004 active period, the source exhibited two large, long-term X-ray pulsed-flux flares as well as short bursts, and large (>10x) torque changes. A series of four simultaneous observations with CXO and HST approximately equispaced in 2006 showed that its X-ray flux and spectrum and near-IR flux, both variable prior to 2005, stabilized. The near-IR flux (m_{F110W} > 24.8 mag, m_{F160W} ~ 22.70 mag) is considerably fainter in 2006 than previously measured. Recently, in 2007 March, this newfound quiescence was interrupted by a sudden flux enhancement, spectral changes and a pulse morphology change, simultaneous with a large spin-up glitch and near-IR enhancement. Specifically, our RXTE observations revealed a sudden pulsed flux increase by a factor of ~3 in the 2-10 keV band. In Target of Opportunity observations with CXO and Swift, we found that the total X-ray flux increased much more than the pulsed flux, reaching a peak value of >7 times the quiescent value (2-10 keV). The total and pulsed flux are slowly decaying with time but the source continues, in 2007 July, to be much brighter than in quiescence. With these recent data, we find a strong anti-correlation between X-ray flux and pulsed fraction. In addition, we find a correlation between X-ray spectral hardness and flux. Simultaneously with the radiative and timing changes, we observed a significant X-ray pulse morphology change such that the profile went from nearly sinusoidal to having multiple peaks.

[7]  arXiv:0707.2100 [ps, pdf, other]
Title: Relativistic Jets and Long-Duration Gamma-ray Bursts from the Birth of Magnetars Authors: N. Bucciantini (1), E. Quataert (1), J. Arons (1), B.D. Metzger (1), Todd A. Thompson (2) ((1)Astronomy Department, UC Berkeley, (2)Department of Astrophysical Sciences, Princeton) Comments: 5 pages, 3 figures, submitted to MNRAS letter, presented at the conference "Astrophysics of Compact Objects", 1-7 July, Huangshan, China Subjects: Astrophysics (astro-ph)

We present time-dependent axisymmetric magnetohydrodynamic simulations of the interaction of a relativistic magnetized wind produced by a proto-magnetar with a surrounding stellar envelope, in the first ~10 seconds after core collapse. We inject a super-magnetosonic wind with \dot E = 10^{51} ergs/s into a cavity created by an outgoing supernova shock. A strong toroidal magnetic field builds up in the bubble of plasma and magnetic field that is at first inertially confined by the progenitor star. This drives a jet out along thepolar axis of the star, even though the star and the magnetar wind are each spherically symmetric. The jet has the properties needed to produce a long-duration gamma-ray burst (GRB). At ~5 s after core bounce, the jet has escaped the host star and the Lorentz factor of the material in the jet at large radii ~10^{11} cm is similar to that in the magnetar wind near the source. Most of the spindown power of the central magnetar escapes via the relativistic jet. There are fluctuations in the Lorentz factor and energy flux in the jet on ~ 0.01-0.1 second timescale. These may contribute to variability in GRB emission (e.g., via internal shocks).

[9]  arXiv:0707.2105 [ps, pdf, other]
Title: A model for cyclotron resonance scattering features Authors: G. Schönherr (1,2,3), J. Wilms (2), P. Kretschmar (3), I. Kreykenbohm (1,4), A. Santangelo (1), R. E. Rothschild (5), W. Coburn (6), R. Staubert (1) ((1) IAA Tübingen, (2) Remeis-Observatory Bamberg, (3) ESA-ESAC, Madrid, (4) ISDC, (5) CASS UC San Diego, (6) SSL UC Berkeley) Comments: 16 pages, 15 figures, Astron. Astrophys. (in press) Subjects: Astrophysics (astro-ph)

(abbreviated version of the abstract) We study the physics of cyclotron line formation in the high-energy spectra of accreting X-ray pulsars using Monte Carlo methods, assuming that the line-forming region is a low-density electron plasma in a sub-critical magnetic field. We investigate the dependence of the shape of the fundamental line on angle, geometry, optical depth and temperature. We also discuss variations of the line ratios for non-uniform magnetic fields. These numerical predictions for the line profiles are linked to results from observational data analysis using an XSPEC model based on the Monte Carlo simulations. We apply this model to observational data from RXTE and INTEGRAL. The predicted strong emission wings of the fundamental cyclotron feature are not found in observational data, hinting at a bottom illuminated slab geometry for line formation.

[23]  arXiv:0707.2219 [ps, pdf, other]
Title: Hypernovae and their Gamma-Ray Bursts Connection Authors: Ken'ichi Nomoto, Masaomi Tanaka, Nozomu Tominaga, Keiichi Maeda, Paolo A. Mazzali Comments: 23 pages, 12 figures. To appear in New Astronomy Reviews, Proceedings of the Conference ``A LIFE WITH STARS'' Subjects: Astrophysics (astro-ph)

The connection between long Gamma Ray Bursts (GRBs) and Supernovae (SNe), have been established through the well observed cases of GRB980425/SN 1998bw, GRB030329/SN 2003dh and GRB031203/SN 2003lw. These events can be explained as the prompt collapse to a black hole (BH) of the core of a massive star (M ~ 40 Msun) that had lost its outer hydrogen and helium envelopes. All these SNe exhibited strong oxygen lines, and their energies were much larger than those of typical SNe, thus these SNe are called Hypernovae (HNe). The case of SN 2006aj/GRB060218 appears different: the GRB was weak and soft (an X-Ray Flash, XRF); the SN is dimmer and has very weak oxygen lines. The explosion energy of SN 2006aj was smaller, as was the ejected mass. In our model, the progenitor star had a smaller mass than other GRB/SNe (M ~ 20 Msun), suggesting that a neutron star (NS) rather than a black hole was formed. If the nascent neutron star was strongly magnetized (a so-called magnetar) and rapidly spinning, it may launch a weak GRB or an XRF. The final fate of 20-30 Msun stars show interesting variety, as seen in the very peculiar Type Ib/c SN 2005bf. This mass range corresponds to the NS to BH transition. We also compare the nucleosynthesis feature of HNe with the metal-poor stars and suggest the Hypernova-First Star connection.

[31]  arXiv:0707.2255 [ps, pdf, other]
Title: The r-Process in Supersonic Neutrino-Driven Winds: The Roll of Wind Termination Shock Authors: Takami Kuroda, Shinya Wanajo, Ken'ichi Nomoto Comments: 11 pages, 7 figures, submitted to ApJ Subjects: Astrophysics (astro-ph)

Recent hydrodynamic studies of core-collapse supernovae imply that the neutrino-heated ejecta from a nascent neutron star develops to supersonic outflows. These supersonic winds are influenced by the reverse shock from the preceding supernova ejecta, forming the wind termination shock. We investigate the effects of the termination shock in neutrino-driven winds and its roll on the r-process. Supersonic outflows are calculated with a semi-analytic neutrino-driven wind model. Subsequent termination-shocked, subsonic outflows are obtained by applying the Rankine-Hugoniot relations. We find a couple of effects that can be relevant for the r-process. First is the sudden slowdown of the temperature decrease by the wind termination. Second is the entropy jump by termination-shock heating, up to several 100NAk. Nucleosynthesis calculations in the obtained winds are performed to examine these effects on the r-process. We find that 1) the slowdown of the temperature decrease plays a decisive roll to determine the r-process abundance curves. This is due to the strong dependences of the nucleosynthetic path on the temperature during the r-process freezeout phase. Our results suggest that only the termination-shocked winds with relatively small shock radii (~500km) are relevant for the bulk of the solar r-process abundances (A~100-180). The heaviest part in the solar r-process curve (A~180-200), however, can be reproduced both in shocked and unshocked winds. These results may help to constrain the mass range of supernova progenitors relevant for the r-process. We find, on the other hand, 2) negligible roles of the entropy jump on the r-process. This is a consequence that the sizable entropy increase takes place only at a large shock radius (~10,000km) where the r-process has already ceased.

[36]  arXiv:0707.2288 [ps, pdf, other]
Title: Stellar population synthesis of post-AGB stars: the s-process in MACHO47.2496.8 Authors: A. Bonacic Marinovic, M. Lugaro, M. Reyniers, H. Van Winckel Comments: accepted for publication on Astronomy & Astrophysics Letters Subjects: Astrophysics (astro-ph)

The low-metallicity RV Tauri star MACHO47.2496.8, recently discovered in the Large Magellanic Cloud, is highly enriched in carbon and heavy elements produced by the slow neutron capture process (s-process), and is most probably a genuine post-C(N-type) asymptotic giant branch (AGB) star. We use the analysis of the abundances of MACHO47.2496.8 to constrain free parameters in AGB models. We test which values of the free parameters describing uncertain physical mechanisms in AGB stars, namely the third dredge-up and the features of the 13C neutron source, produce models that better match the abundances observed in MACHO47.2496.8. We carry out stellar population synthesis coupled with s-process nucleosynthesis using a synthetic stellar evolution code. The s-process ratios observed in MACHO47.2496.8 can be matched by the same models that explain the s-process ratios of Galactic AGB and post-AGB stars of metallicity > Z_sun/10, except for the choice of the effectiveness of 13C as a neutron source, which has to be lower by roughly a factor of 3 to 6. The less effective neutron source for lower metallicities is also required when comparing population synthesis results to observations of Galactic halo $s$-enhanced stars, such as Pb stars. The 12C/13C ratio in MACHO47.2496.8 cannot be matched simultaneously and requires the occurrence of extra-mixing processes. The confirmed trend of the decreased efficiency of the 13C neutron source with metallicity requires an explanation from AGB s-process models. The present work is to date the first comparison between theoretical models and the detailed abundances of an extragalactic post-AGB star.

[37]  arXiv:0707.2292 [ps, pdf, other]
Title: Relativistic stars with a linear equation of state: analogy with classical isothermal spheres and black holes Authors: Pierre-Henri Chavanis Subjects: Astrophysics (astro-ph)

We complete our previous investigation concerning the structure and the stability of ``isothermal'' spheres in general relativity. This concerns objects that are described by a linear equation of state $P=q\epsilon$ so that the pressure is proportional to the energy density. In the Newtonian limit $q\to 0$, this returns the classical isothermal equation of state. We consider specifically a self-gravitating radiation (q=1/3), the core of neutron stars (q=1/3) and a gas of baryons interacting through a vector meson field (q=1). We study how the thermodynamical parameters scale with the size of the object and find unusual behaviours due to the non-extensivity of the system. We compare these scaling laws with the area scaling of the black hole entropy. We also determine the domain of validity of these scaling laws by calculating the critical radius above which relativistic stars described by a linear equation of state become dynamically unstable. For photon stars, we show that the criteria of dynamical and thermodynamical stability coincide. Considering finite spheres, we find that the mass and entropy as a function of the central density present damped oscillations. We give the critical value of the central density, corresponding to the first mass peak, above which the series of equilibria becomes unstable. Finally, we extend our results to $d$-dimensional spheres. We show that the oscillations of mass versus central density disappear above a critical dimension $d_{crit}(q)$. For Newtonian isothermal stars (q=0) we recover the critical dimension $d_{crit}=10$. For the stiffest stars (q=1) we find $d_{crit}=4+\sqrt{13}=7.6055513...$ and for a self-gravitating radiation (q=1/d) we find $d_{crit}=9.9072909...$ very close to 10. Finally, we give analytical solutions of relativistic isothermal spheres in 2D gravity.

Cross-lists for Tue, 17 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Tue, 17 Jul 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[57]  arXiv:0704.1732 (replaced) [ps, pdf, other]
Title: Spheroidal and torsional modes of quasistatic shear oscillations in the solid globe models of nuclear physics and pulsar astrophysics Authors: S. Bastrukov, H-K. Chang, S. Misicu, I. Molodtsova, D. Podgainy Comments: 34 pages; 6 figures Subjects: Astrophysics (astro-ph)
[69]  arXiv:0707.1759 (replaced) [ps, pdf, other]
Title: Torsional shear oscillations in the neutron star crust driven by restoring force of elastic stresses Authors: S. I. Bastrukov, H.-K. Chang, J. Takata, G.-T. Chen, I. V. Molodtsova Comments: 18 pages, 6 figures, Submitted to MNRAS; corrected typos Subjects: Astrophysics (astro-ph)
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[29]  arXiv:0707.2547 [ps, pdf, other]
Title: An empirical model for the beams of radio pulsars Authors: A. Karastergiou, S. Johnston Comments: Accepted for publication in MNRAS Subjects: Astrophysics (astro-ph)

Motivated by recent results on the location of the radio emission in pulsar magnetospheres, we have developed a model which can account for the large diversity found in the average profile shapes of pulsars. At the centre of our model lies the idea that radio emission at a particular frequency arises from a wide range of altitudes above the surface of the star and that it is confined to a region close to the last open field lines. We assert that the radial height range over which emission occurs is responsible for the complex average pulse shapes rather than the transverse (longitudinal) range proposed in most current models. By implementing an abrupt change in the height range to discriminate between young, short-period, highly-energetic pulsars and their older counterparts, we obtain the observed transition between the simple and complex average pulse profiles observed in each group respectively. Monte Carlo simulations are used to demonstrate the match of our model to real observations.

Cross-lists for Wed, 18 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


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[46]  arXiv:0707.2740 [ps, pdf, other]
Title: Mass, radius, and composition of the outer crust of nonaccreting cold neutron stars Authors: Matthias Hempel, Jurgen Schaffner-Bielich Comments: 5 pages, 2 figures, submitted to J. Phys. G, part of the proceedings of the Nuclear Physics in Astrophysics III conference in Dresden Subjects: Astrophysics (astro-ph)

The properties and composition of the outer crust of nonaccreting cold neutron stars are studied by applying the model of Baym, Pethick, and Sutherland, which was extended by including higher order corrections of the atomic binding, screening, exchange and zero-point energy. The most recent experimental nuclear data from the atomic mass table of Audi, Wapstra, and Thibault from 2003 is used. Extrapolation to the drip line is utilized by various state-of-the-art theoretical nuclear models (finite range droplet, relativistic nuclear field and non-relativistic Skyrme Hartree-Fock parameterizations). The different nuclear models are compared with respect to the mass and radius of the outer crust for different neutron star configurations and the nuclear compositions of the outer crust.

Cross-lists for Thu, 19 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Thu, 19 Jul 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[72]  arXiv:astro-ph/0703116 (replaced) [ps, pdf, other]
Title: The theory of pulsar winds and nebulae Authors: J. G. Kirk, Y. Lyubarsky, J. Petri Comments: 33 pages, to appear in Springer Lecture Notes on "Neutron stars and pulsars, 40 years after the discovery", ed W.Becker Subjects: Astrophysics (astro-ph)
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[3]  arXiv:0707.2802 [ps, pdf, other]
Title: Determination of the mass of the neutron star in SMC X-1, LMC X-4 and Cen X-3 with VLT/UVES Authors: A. van der Meer, L. Kaper, M. H. van Kerkwijk, M. H. M. Heemskerk, E.P.J. van den Heuvel Comments: Accepted for publication in Astronomy and Astrophysics Subjects: Astrophysics (astro-ph)

We present the results of a spectroscopic monitoring campaign of the OB-star companions to the eclipsing X-ray pulsars SMC X-1, LMC X-4 and Cen X-3. High-resolution optical spectra obtained with UVES on the ESO Very Large Telescope are used to determine the radial-velocity orbit of the OB (super)giants with high precision. The excellent quality of the spectra provides the opportunity to measure the radial-velocity curve based on individual lines, and to study the effect of possible distortions of the line profiles due to e.g. X-ray heating on the derived radial-velocity amplitude. Several spectral lines show intrinsic variations with orbital phase. The magnitude of these variations depends on line strength, and thus provides a criterion to select lines that do not suffer from distortions. The undistorted lines show a larger radial-velocity amplitude than the distorted lines, consistent with model predictions. Application of our line-selection criteria results in a mean radial-velocity amplitude K(Opt) of 20.2 +/- 1.1, 35.1 +/- 1.5, and 27.5 +/- 2.3 km/s (1 sigma errors), for the OB companion to SMC X-1, LMC X-4 and Cen X-3, respectively. Adding information on the projected rotational velocity of the OB companion (derived from our spectra), the duration of X-ray eclipse and orbital parameters of the X-ray pulsar (obtained from literature), we arrive at a neutron star mass of 1.06^{+0.11}_{-0.10}, 1.25^{+0.11}_{-0.10} and 1.34^{+0.16}_{-0.14} M{sun} for SMC X-1, LMC X-4 and Cen X-3, respectively. The mass of SMC X-1 is near the minimum mass (~1 M{sun}) expected for a neutron star produced in a supernova. We discuss the implications of the measured mass distribution on the neutron-star formation mechanism, in relation to the evolutionary history of the massive binaries.

[28]  arXiv:0707.2935 [ps, pdf, other]
Title: X-ray Observations and Infrared Identification of the Transient 7.8 s X-ray Binary Pulsar XTE J1829-098 Authors: J. P. Halpern, E. V. Gotthelf Comments: 6 pages, 7 figures. To appear in The Astrophysical Journal Subjects: Astrophysics (astro-ph)

XMM-Newton and Chandra observations of the transient 7.8 s pulsar XTE J1829-098 are used to characterize its pulse shape and spectrum, and to facilitate a search for an optical or infrared counterpart. In outburst, the absorbed, hard X-ray spectrum with Gamma = 0.76+/-0.13 and N_H = (6.0+/-0.6) x 10^{22} cm^{-2} is typical of X-ray binary pulsars. The precise Chandra localization in a faint state leads to the identification of a probable infrared counterpart at R.A. = 18h29m43.98s, decl. = -09o51'23.0" (J2000.0) with magnitudes K=12.7, H=13.9, I>21.9, and R>23.2. If this is a highly reddened O or B star, we estimate a distance of 10 kpc, at which the maximum observed X-ray luminosity is 2x10^{36} ergs s^{-1}, typical of Be X-ray transients or wind-fed systems. The minimum observed luminosity is 3x10^{32}(d/10 kpc)^2 ergs s^{-1}. We cannot rule out the possibility that the companion is a red giant. The two known X-ray outbursts of XTE J1829-098 are separated by ~1.3 yr, which may be the orbital period or a multiple of it, with the neutron star in an eccentric orbit. We also studied a late M-giant long-period variable that we found only 9" from the X-ray position. It has a pulsation period of ~1.5 yr, but is not the companion of the X-ray source.

Cross-lists for Fri, 20 Jul 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[39]  arXiv:0707.2681 (cross-list from nucl-th) [ps, pdf, other]
Title: Shear viscosity of neutron matter from realistic nucleon-nucleon interactions Authors: Omar Benhar, Marco Valli Comments: 4 pages, 4 figures Subjects: Nuclear Theory (nucl-th); Astrophysics (astro-ph)

The calculation of transport properties of Fermi liquids, based on the formalism developed by Abrikosov and Khalatnikov, requires the knowledge of the probability of collisions between quasiparticles in the vicinity of the Fermi surface. We have carried out a numerical study of the shear viscosity of pure neutron matter, whose value plays a pivotal role in determining the stability of rotating neutron stars, in which these processes are described using a state-of-the-art nucleon-nucleon potential model. Within our approach medium modifications of the scattering cross section are consistently taken into account, through an effective interaction obtained from the matrix elements of the bare interaction between correlated states. Inclusion of medium effects lead to a large increase of the viscosity at densities larger than $\sim 0.1$ fm^{-3}.

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0 abstracts or titles contain neutron star, magnetar or pulsar


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[15]  arXiv:0707.3037 [ps, pdf, other]
Title: The optical counterpart of IGR J00291+5934 in quiescence Authors: P. D'Avanzo, S. Campana, S. Covino, G. L. Israel, L. Stella, G. Andreuzzi Comments: 6 pages, 5 figures. Accepted for publication in Astronomy and Astrophysics Subjects: Astrophysics (astro-ph)

The recent (December 2004) discovery of the sixth accretion-powered millisecond X-ray pulsar IGR J00291+5934 provides a very good chance to deepen our knowledge of such systems. Although these systems are well studied at high energies, poor informations are available for their optical/NIR counterparts during quiescence. Up to now, only for SAX J1808.4-3658, the first discovered system of this type, we have a secure multiband detection of its optical counterpart in quiescence. Among the seven known system IGR J00291+5934 is the one that resembles SAX J1808.4-3658 more closely. With the Italian 3.6 m TNG telescope, we have performed deep optical and NIR photometry of the field of IGR J00291+5934 during quiescence in order to look for the presence of a variable counterpart. We present here the first multiband ($VRIJH$) detection of the optical and NIR counterpart of IGR J00291+5934 in quiescence as well as a deep upper limit in the $K-$band. We obtain an optical light curve that shows variability consistent with a sinusoidal modulation at the known 2.46 hr orbital period and present evidence for a strongly irradiated companion.

Cross-lists for Mon, 23 Jul 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[28]  arXiv:0707.2768 (cross-list from gr-qc) [ps, pdf, other]
Title: Incompressible fluid inside an astrophysical black hole? Authors: Fabrizio Canfora Comments: 32 pages, 2 figures Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph); Mesoscopic Systems and Quantum Hall Effect (cond-mat.mes-hall); High Energy Physics - Theory (hep-th)

It is argued that under natural hypothesis the Fermions inside a black hole formed after the collapse of a neutron star could form a non compressible fluid (well before reaching the Planck scale) leading to some features of integer Quantum Hall Effect. The relations with black hole entropy are analyzed. Insights coming from Quantum Hall Effect are used to analyze the coupling with Einstein equations. Connections with some cosmological scenarios and with higher dimensional Quantum Hall Effect are shortly pointed out.

Replacements for Mon, 23 Jul 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[36]  arXiv:0705.1742 (replaced) [ps, pdf, other]
Title: Magnetar Driven Bubbles and the Origin of Collimated Outflows in Gamma-ray Bursts Authors: N. Bucciantini (1), E. Quataert (1), J. Arons (1), B.D. Metzger (1), Todd A. Thompson (2) ((1)Astronomy Department, UC Berkeley, (2)Department of Astrophysical Sciences, Princeton) Comments: 14 pages, 8 figures, accepted for publication in MNRAS Subjects: Astrophysics (astro-ph)
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[29]  arXiv:0707.3301 [ps, pdf, other]
Title: Pulse Profiles, Spectra and Polarization Characteristics of Non-Thermal Emissions from the Crab-Like Pulsars Authors: J.Takata, H.-K.Chang Comments: 39 pages, 11 figures, Accepted for publication in ApJ Subjects: Astrophysics (astro-ph)

We discuss non-thermal emission mechanism of the Crab-like pulsars with both a two-dimensional electrodynamical study and a three-dimensional model. We investigate the emission process in the outer gap accelerator. In the two-dimensional electrodynamical study, we solve the Poisson equation of the accelerating electric field in the outer gap and the equation of motion of the primary particles with the synchrotron and the curvature radiation process and the pair-creation process. We show a solved gap structure which produces a consistent gamma-ray spectrum with EGRET observation. Based on the two-dimensional model, we conduct a three-dimensional emission model to calculate the synchrotron and the inverse-Compton processes of the secondary pairs produced outside the outer gap. We calculate the pulse profiles, the phase-resolved spectra and the polarization characteristics in optical to $\gamma$-ray bands to compare the observation of the Crab pulsar and PSR B0540-69. For the Crab pulsar, we find that the outer gap geometry extending from near the stellar surface to near the light cylinder produces a complex morphology change of the pulse profiles as a function of the photon energy. This predicted morphology change is quite similar with that of the observations. The calculated phase-resolved spectra are consistent with the data through optical to the $\gamma$-ray bands. We demonstrate that the 10$\sim$20 % of the polarization degree in the optical emissions from the Crab pulsar and the Vela pulsar are explained by the synchrotron emissions with the particle gyration motion.

[38]  arXiv:0707.3363 [ps, pdf, other]
Title: Very deep X-ray observations of the Anomalous X-ray Pulsar 4U 0142+614 Authors: N. Rea, E. Nichelli, G.L. Israel, R. Perna, T. Oosterbroek, A.N. Parmar, R. Turolla, S. Campana, L. Stella, S. Zane, L. Angelini Comments: 9 pages, 5 figures; accepted for publication on MNRAS Subjects: Astrophysics (astro-ph)

We report on two new XMM-Newton observations of the Anomalous X-ray Pulsar (AXP) 4U 0142+614 performed in March and July 2004, collecting the most accurate spectrum for this source to date. Furthermore, we analyse two short archival observations performed in February 2002 and January 2003 (the latter already reported by G\"ohler et al. 2005) in order to study the long term behaviour of this AXP. 4U 0142+614 appears to be relatively steady in flux between 2002 and 2004, and the phase-averaged spectrum does not show any significant variability between the four epochs. We derive the deepest upper limits to date on the presence of lines in the 4U 0142+614 spectrum as a function of energy: equivalent width in the 1-3 keV energy range < 4 eV and < 8 eV for narrow and broad lines, respectively. A remarkable energy dependence in both the pulse profile and the pulsed fraction is detected, and consequently pulse-phase spectroscopy shows spectral variability as a function of phase. By making use of XMM-Newton and INTEGRAL data, we successfully model the 1-250 keV spectrum of 4U 0142+614 with three models presented in Rea et al. (2007a), namely the canonical absorbed blackbody plus two power-laws, a resonant cyclotron scattering model plus one power-law and two log-parabolic functions.

Cross-lists for Tue, 24 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Tue, 24 Jul 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[79]  arXiv:0706.0060 (replaced) [pdf]
Title: The physics of strong magnetic fields in neutron stars Authors: Qiu-he Peng, Hao Tong Comments: With erratum in this version Journal-ref: Mon. Not. R. Astron. Soc. 378, 159 (2007) Subjects: Astrophysics (astro-ph)
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[7]  arXiv:0707.3475 [ps, pdf, other]
Title: Electric field of a point-like charge in a strong magnetic field and ground state of a hydrogen-like atom Authors: A. E. Shabad, V. V. Usov Comments: 40 pages, 6 figures, submitted to Phys. Rev. D Subjects: Astrophysics (astro-ph)

In an external constant magnetic field, so strong that the electron Larmour length is much shorter than its Compton length, we consider the modification of the Coulomb potential of a point charge owing to the vacuum polarization. We establish a short-range component of the static interaction in the Larmour scale, expressed as a Yukawa-like law, and reveal the corresponding "photon mass" parameter. The electrostatic force regains its long-range character in the Compton scale: the tail of the potential follows an anisotropic Coulomb law, decreasing away from the charge slower along the magnetic field and faster across. In the infinite-magnetic-field limit the potential is confined to an infinitely thin string passing though the charge parallel to the external field. This is the first evidence for dimensional reduction in the photon sector of quantum electrodynamics. The one-dimensional form of the potential on the string is derived that includes a delta-function centered in the charge. The nonrelativistic ground state energy of a hydrogen-like atom is found with its use and shown not to be infinite in the infinite-field limit. These results may be useful for studying properties of matter at the surface of extremely magnetized neutron stars.

[23]  arXiv:0707.3529 [ps, pdf, other]
Title: Chandra Observation of PSR B1823-13 and its Pulsar Wind Nebula Authors: G. G. Pavlov, O. Kargaltsev, W. F. Brisken Comments: 13 pages, 8 figures and 3 tables; submitted to ApJ Subjects: Astrophysics (astro-ph)

We report on an observation of the Vela-like pulsar B1823-13 and its synchrotron nebula with Chandra.The pulsar's spectrum fits a power-law model with a photon index Gamma_PSR=2.4 for the plausible hydrogen column density n_H=10^{22} cm^{-2}, corresponding to the luminosity L_PSR=8*10^{31} ergs s^{-1} in the 0.5-8 keV band, at a distance of 4 kpc. The pulsar radiation likely includes magnetospheric and thermal components, but they cannot be reliably separated because of the small number of counts detected and strong interstellar absorption. The pulsar is surrounded by a compact, 25''x 10'', pulsar wind nebula (PWN) elongated in the east-west direction, which includes a brighter inner component, 7''x 3'', elongated in the northeast-southwest direction. The slope of the compact PWN spectrum is Gamma_comp=1.3, and the 0.5-8 keV luminosity is L_comp~3*10^{32} ergs s^{-1}. The compact PWN is surrounded by asymmetric diffuse emission (extended PWN) seen up to at least 2.4' south of the pulsar, with a softer spectrum (Gamma_ext=1.9), and the 0.5-8 keV luminosity L_ext~10^{33}-10^{34} ergs s^{-1}. We also measured the pulsar's proper motion using archival VLA data: \mu_\alpha=23.0+/-2.5 mas yr^{-1},
\mu_\delta=-3.9+/-3.3 mas yr^{-1}, which corresponds to the transverse velocity v_perp=440 km s^{-1}. The direction of the proper motion is approximately parallel to the elongation of the compact PWN, but it is nearly perpendicular to that of the extended PWN and to the direction towards the center of the bright VHE gamma-ray source HESS J1825-137, which is likely powered by PSR B1823-13.

Cross-lists for Wed, 25 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Wed, 25 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


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[12]  arXiv:0707.3691 [ps, pdf, other]
Title: Strong first-order phase transition in a rotating neutron star core and the associated energy release Authors: J. L. Zdunik, M. Bejger, P. Haensel, E. Gourgoulhon Comments: 9 pages, 12 figures, submitted to A&A Subjects: Astrophysics (astro-ph)

We calculate the energy release associated with a strong first-order phase transition, from normal phase N to an "exotic" superdense phase S, in a rotating neutron star. Such a phase transition, accompanied by a density jump rho_N --> rho_S, is characterized by rho_S/rho_N > 3/2(1+P_0/rho_N c^2), where P_0 is the pressure, at which phase transition occurs. Configurations with small S-phase cores are then unstable and collapse into stars with large S-phase cores. The energy release is equal to the difference in mass-energies between the initial (normal) configuration and the final configuration containing an S-phase core, total stellar baryon mass and angular momentum being kept constant. The calculations of the energy release are based on precise numerical 2-D calculations. Polytropic equations of state (EOSs) as well as realistic EOS with strong first-order phase transition due to kaon condensation are used. For polytropic EOSs, a large parameter space is studied. For a fixed "overpressure", dP, defined as the relative excess of central pressure of collapsing metastable star over the pressure of equilibrium first-order phase transition, the energy release E_rel does not depend on the stellar angular momentum. It coincides with that for nonrotating stars with the same dP. Therefore, results of 1-D calculations of E_rel(dP) for non-rotating stars can be used to predict, with very high precision, the outcome of much harder to perform 2-D calculations for rotating stars with the same dP. This result holds also for dP_min < dP < 0, corresponding to phase transitions with climbing over the energy barrier separating metastable N-phase configurations from those with an S-phase core. Such phase transitions could be realized in the cores of newly born, hot, pulsating neutron stars.

Cross-lists for Thu, 26 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Thu, 26 Jul 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[50]  arXiv:0707.1759 (replaced) [ps, pdf, other]
Title: Torsional shear oscillations in the neutron star crust driven by restoring force of elastic stresses Authors: S. I. Bastrukov, H.-K. Chang, J. Takata, G.-T. Chen, I. V. Molodtsova Comments: 18 pages, 6 figures, Submitted to MNRAS; corrected typos Subjects: Astrophysics (astro-ph)
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Cross-lists for Fri, 27 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Fri, 27 Jul 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[27]  arXiv:gr-qc/0702039 (replaced) [ps, pdf, other]
Title: Upper limits on gravitational wave emission from 78 radio pulsars Authors: The LIGO Scientific Collaboration: B. Abbott, et al, M. Kramer, A. G. Lyne Comments: 21 pages, accepted for Phys. Rev. D, fixed typo in eq. 6.5 Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)
[ total of 38 entries: 1-38 ]
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1 abstracts or titles contain neutron star, magnetar or pulsar


[17]  arXiv:0707.4105 [ps, pdf, other]
Title: Semiclassical theory of charged pion radiation by nucleons in a strong homogeneous magnetic field Authors: T. Herpay, A. Patkos Comments: 10 pages, 2 figures Subjects: Astrophysics (astro-ph)

Charged pions produced in very high energy hadronic interactions might be the dominant source of cosmic neutrinos in the GeV--TeV range. Spectral energy power of \pi^+ radiation by high energy protons moving in strong magnetic fields typical for magnetars is determined with a semiclassical treatment of the effective pion-nucleon model. The main characteristics emerging from a saddle point approximation to the summation over the allowed range of Landau levels is a sharp lower cut: E_\pi>0.25 E_p. The magnitude of the spectral power agrees in this region with the synchrotron radiation spectra of neutral pions.

Cross-lists for Mon, 30 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Mon, 30 Jul 07

0 abstracts or titles contain neutron star, magnetar or pulsar


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Astrophysics authors/titles "new"

4 abstracts or titles contain neutron star, magnetar or pulsar


[7]  arXiv:0707.4199 [ps, pdf, other]
Title: On the Possibility of the Detection of Extinct Radio Pulsars Authors: V. S. Beskin, S. A. Eliseeva Comments: 5 pages, 1 figure corrected version of the paper that was published in Astronomy Letters Journal-ref: Astron.Lett. 29 (2003) 20-25 Subjects: Astrophysics (astro-ph)

We explore the possibilities for detecting pulsars that have ceased to radiate in the radio band. We consider two models: the model with hindered particle escape from the pulsar surface (first suggested by Ruderman and Sutherland 1975) and the model with free particle escape (Arons 1981; Mestel 1999). In the model with hindered particle escape, the number of particles that leave the pulsar magnetosphere is small and their radiation cannot be detected with currently available instruments. At the same time, for the free particle escape model, both the number of particles and the radiation intensity are high enough for such pulsars to be detectable with the presently available receivers such as GLAST and AGILE spacecrafts. It is also possible that extinct radio pulsars can be among the unidentified EGRET sources.

[17]  arXiv:0707.4279 [ps, pdf, other]
Title: Non-Thermal X-ray Properties of Rotation Powered Pulsars and Their Wind Nebulae Authors: Xiang-Hua Li, Fang-Jun Lu, Zhuo Li Comments: 14 pages, 8 figures, 3 Tables, and ApJ submitted Subjects: Astrophysics (astro-ph)

We present a statistical study of the non-thermal X-ray emission of 29 young rotation powered pulsars (RPPs) and 22 pulsar wind nebulae (PWNe) by using {\sl Chandra} and {\sl XMM-Newton} observations, which with the high spatial resolutions enable us to spatially resolve pulsars from their surrounding PWNe. We obtain the X-ray luminosities and spectra separately for RPPs and PWNe, and then we investigate their distribution and relation to each other and also relations with other rotational parameters. In the pair-correlation analysis we find that: (1) the nonthermal pulsar X-ray luminosity $L_{\rm x,psr}$ is strongly correlated with the pulsar period $P$, period derivative $\dot{P}$, characteristic age $\tau$, and spin-down power $\dot{E}$, $L_{\rm x,psr}=10^{-3.7}\dot{E}^{1.0\pm0.1}$; (2) the pulsar photon spectral index $\Gamma_{\rm psr}$ is negatively correlated with $\dot{P}$ and $\dot{E}$ but positively correlated with $\tau$; (3) the PWN X-ray luminosity $L_{\rm x,pwn}$ shows weak correlation with $\dot{P}$ and strong correlation with $\tau$ and $\dot{E}$, $L_{\rm x,pwn}=10^{-19.0}\dot{E}^{1.4\pm0.2}$; (4) the PWN photon spectral index $\Gamma_{\rm pwn}$ is positively correlated with $L_{\rm x,pwn}$ and $L_{\rm x,pwn}/\dot{E}$. The statistic study of PWN spectral properties supports the particle wind model in which the X-ray emitting electrons are accelerated by the termination shock of the wind.

[21]  arXiv:0707.4293 [ps, pdf, other]
Title: Modeling Dense Stellar Systems Authors: Piet Hut, Shin Mineshige, Douglas C. Heggie, Junichiro Makino Comments: 23 pages, to appear in Prog. Theor. Phys Subjects: Astrophysics (astro-ph)

Black holes and neutron stars present extreme forms of matter that cannot be created as such in a laboratory on Earth. Instead, we have to observe and analyze the experiments that are ongoing in the Universe. The most telling observations of black holes and neutron stars come from dense stellar systems, where stars are crowded close enough to each other to undergo frequent interactions. It is the interplay between black holes, neutron stars and other objects in a dense environment that allows us to use observations to draw firm conclusions about the properties of these extreme forms of matter, through comparisons with simulations. The art of modeling dense stellar systems through computer simulations forms the main topic of this review.

[27]  arXiv:0707.4345 [ps, pdf, other]
Title: Alfven Wave-Driven Supernova Explosion Authors: T.K.Suzuki (U.Tokyo), K.Sumiyoshi (Numazu CT), S. Yamada (Waseda U.) Comments: 4 pages, 3 figures embedded, submitted to ApJL Subjects: Astrophysics (astro-ph)

We investigate the role of Alfven waves in the core-collapse supernova (SN) explosion. We assume that Alfven waves are generated by convections inside a proto-neutron star (PNS) and emitted from its surface. Then these waves propagate outwards and dissipate via nonlinear processes and heat up matter around a stalled prompt shock. To quantitatively assess the importance of this process for revival of the stalled shock, we perform 1D time-dependent hydrodynamical simulations, taking into account the heating via the dissipation of Alfven waves. We show that the shock revival occurs if the surface field strength is larger than ~2x10^{15}G and if the amplitude of velocity fluctuation at the PNS surface is larger than ~ 20% of the local sound speed. Interestingly, the Alfven wave mechanism is self-regulating in the sense that the explosion energy is not very sensitive to the surface field strength and initial amplitude of Alfven waves as long as they are larger than the threshold values given above. It should be emphasized that Alfven waves can produce SN explosions even without rotation if a PNS has strong magnetic fields of the magnetar scale.

Cross-lists for Tue, 31 Jul 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[52]  arXiv:0707.4067 (cross-list from nucl-th) [ps, pdf, other]
Title: The Equation of State of Dense Matter : from Nuclear Collisions to Neutron Stars Authors: Fiorella Burgio (INFN Sezione di Catania, Italy) Comments: 8 pages, 5 figures, invited talk given at NPA3, Dresden, March 2007 Subjects: Nuclear Theory (nucl-th); Astrophysics (astro-ph); High Energy Physics - Phenomenology (hep-ph)

The Equation of State (EoS) of dense matter represents a central issue in the study of compact astrophysical objects and heavy ion reactions at intermediate and relativistic energies. We have derived a nuclear EoS with nucleons and hyperons within the Brueckner-Hartree-Fock approach, and joined it with quark matter EoS. For that, we have employed the MIT bag model, as well as the Nambu--Jona-Lasinio (NJL) and the Color Dielectric (CD) models, and found that the NS maximum masses are not larger than 1.7 solar masses. A comparison with available data supports the idea that dense matter EoS should be soft at low density and quite stiff at high density.

Replacements for Tue, 31 Jul 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[54]  arXiv:astro-ph/0508409 (replaced) [ps, pdf, other]
Title: Statistics of Extinct Radio Pulsars Authors: V. S. Beskin, S. A. Eliseeva Comments: 7 pages, 8 figures. Corrected Introduction and figures 1 and 8 Journal-ref: Astron.Lett. 31 (2005) 263-270 Subjects: Astrophysics (astro-ph)
[70]  arXiv:0707.3363 (replaced) [ps, pdf, other]
Title: Very deep X-ray observations of the Anomalous X-ray Pulsar 4U 0142+614 Authors: N. Rea, E. Nichelli, G.L. Israel, R. Perna, T. Oosterbroek, A.N. Parmar, R. Turolla, S. Campana, L. Stella, S. Zane, L. Angelini Comments: 9 pages, 5 figures; accepted for publication on MNRAS (typos corrected and few references added) Subjects: Astrophysics (astro-ph)
[ total of 71 entries: 1-71 ]
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2 abstracts or titles contain neutron star, magnetar or pulsar


[9]  arXiv:0707.4498 [ps, pdf, other]
Title: Fission Cycling in a Supernova r-process Authors: J. Beun, G. C. McLaughlin, R. Surman, W. R. Hix Comments: 9 pages, 8 figures Subjects: Astrophysics (astro-ph)

Recent halo star abundance observations exhibit an important feature of consequence to the r-process: the presence of a main r-process between the second and third peaks which is consistent among halo stars. We explore fission cycling and steady-beta flow as the driving mechanisms behind this feature. The presence of fission cycling during the r-process can account for nucleosynthesis yields between the second and third peaks, whereas the presence of steady-beta flow can account for consistent r-process patterns, robust under small variations in astrophysical conditions. We employ the neutrino-driven wind of the core-collapse supernova to examine fission cycling and steady-beta flow in the r-process. As the traditional neutrino-driven wind model does not produce the required very neutron-rich conditions for these mechanisms, we examine changes to the neutrino physics necessary for fission cycling to occur in the neutrino-driven wind environment, and we explore under what conditions steady-beta flow is obtained.

[26]  arXiv:0707.4614 [ps, pdf, other]
Title: Thermal conductivity of ions in a neutron star envelope Authors: A.I. Chugunov (1), P. Haensel ((1) Ioffe Physico-Technical Instititute, St.Petersburg; (2) N.Copernicus Astronomical Center, Warsaw) Comments: 12 pages, 5 figures; to appear in MNRAS Subjects: Astrophysics (astro-ph)

We analyze the thermal conductivity of ions (equivalent to the conductivity of phonons in crystalline matter) in a neutron star envelope.
We calculate the ion/phonon thermal conductivity in a crystal of atomic nuclei using variational formalism and performing momentum-space integration by Monte Carlo method. We take into account phonon-phonon and phonon-electron scattering mechanisms and show that phonon-electron scattering dominates at not too low densities. We extract the ion thermal conductivity in ion liquid or gas from literature.
Numerical values of the ion/phonon conductivity are approximated by analytical expressions, valid for T>10^5 K and 10^5 g cm^-3 < \rho < 10^14 g cm^-3. Typical magnetic fields B~10^12 G in neutron star envelopes do not affect this conductivity although they strongly reduce the electron thermal conductivity across the magnetic field. The ion thermal conductivity remains much smaller than the electron conductivity along the magnetic field. However, in the outer neutron star envelope it can be larger than the electron conductivity across the field, that is important for heat transport across magnetic field lines in cooling neutron stars. The ion conductivity can greatly reduce the anisotropy of heat conduction in outer envelopes of magnetized neutron stars.

Cross-lists for Wed, 1 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[54]  arXiv:0707.4327 (cross-list from gr-qc) [pdf, other]
Title: Stochastic background from extra-galactic double neutron stars Authors: T. Regimbau, B. Chauvineau Comments: 13 pages, 7 figures - proceeding of a talk given at the 11th GWDAW, to appear in CQG Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)

We present Monte Carlo simulations of the extra galactic population of inspiralling double neutron stars, and estimate its contribution to the astrophysical gravitational wave background, in the frequency range of ground based interferometers, corresponding to the last thousand seconds before the last stable orbit when more than 96 percent of the signal is released. We show that sources at redshift z>0.5 contribute to a truly continuous background which may be detected by correlating third generation interferometers.

Replacements for Wed, 1 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[62]  arXiv:astro-ph/0608205 (replaced) [ps, pdf, other]
Title: Direct Measurement of Neutron-Star Recoil in the Oxygen-Rich Supernova Remnant Puppis A Authors: P. Frank Winkler, Robert Petre Subjects: Astrophysics (astro-ph)
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Astrophysics authors/titles "new"

8 abstracts or titles contain neutron star, magnetar or pulsar


[2]  arXiv:0708.0002 [ps, pdf, other]
Title: 1E 1547.0-5408: a radio-emitting magnetar with a rotation period of 2 seconds Authors: F. Camilo (Columbia), S. M. Ransom (NRAO), J. P. Halpern (Columbia), J. Reynolds (ATNF) Comments: Accepted for publication in ApJ Letters Subjects: Astrophysics (astro-ph)

The variable X-ray source 1E 1547.0-5408 was identified by Gelfand & Gaensler (2007) as a likely magnetar in G327.24-0.13, an apparent supernova remnant. No X-ray pulsations have been detected from it. Using the Parkes radio telescope, we discovered pulsations with period P = 2.069 s. Using the Australia Telescope Compact Array, we localized these to 1E 1547.0-5408. We measure dP/dt = (2.318+-0.005)e-11, which for a magnetic dipole rotating in vacuo gives a surface field strength of 2.2e14 G, a characteristic age of 1.4 kyr, and a spin-down luminosity of 1.0e35 ergs/s. Together with its X-ray characteristics, these rotational parameters of 1E 1547.0-5408 prove that it is a magnetar, only the second known to emit radio waves. The distance is ~9 kpc, derived from the dispersion measure of 830 pc/cc. The pulse profile at a frequency of 1.4 GHz is extremely broad and asymmetric due to multipath propagation in the ISM, as a result of which only approximately 75% of the total flux at 1.4 GHz is pulsed. At higher frequencies the profile is more symmetric and has FWHM = 0.12P. Unlike in normal radio pulsars, but in common with the other known radio-emitting magnetar, XTE J1810-197, the spectrum over 1.4-6.6 GHz is flat or rising, and we observe large, sudden changes in the pulse shape. In a contemporaneous Swift X-ray observation, 1E 1547.0-5408 was detected with record high flux, f_X(1-8 keV) ~ 5e-12 ergs/cm^2/s, 16 times the historic minimum. The pulsar was undetected in archival radio observations from 1998, implying a flux < 0.2 times the present level. Together with the transient behavior of XTE J1810-197, these results suggest that radio emission is triggered by X-ray outbursts of usually quiescent magnetars.

[8]  arXiv:0708.0015 [ps, pdf, other]
Title: Is there a link between the neutron-star spin and the frequency of the kilohertz quasi-periodic oscillations? Authors: Mariano Mendez (SRON - Netherlands Institute for Space Research), Tomaso Belloni (INAF - Osservatorio Astronomico di Brera) Comments: Accepted for publication in MNRAS. 8 pages + 4 figures. Uses mn2e.cls Subjects: Astrophysics (astro-ph)

There is a general consensus that the frequencies of the kilohertz Quasi-Periodic Oscillations (kHz QPOs) in neutron-star low-mass X-ray binaries are directly linked to the spin of the neutron star. The root of this idea is the apparent clustering of the ratio of the frequency difference of the kHz QPOs and the neutron-star spin frequency, $\Delta\nu/\nu_s$, at around 0.5 and 1 in ten systems for which these two quantities have been measured. Here we reexamine all available data of sources for which there exist measurements of two simultaneous kHz QPOs and spin frequencies, and we advance the possibility that $\Delta\nu$ and $\nu_s$ are not related to each other. We discuss ways in which this possibility could be tested with current and future observations.

[17]  arXiv:0708.0060 [ps, pdf, other]
Title: The Nature of the Compact X-ray Source in Supernova Remnant RCW 103 Authors: Xiang-Dong Li Comments: 12 pages, 1 figure, accepted to ApJL Subjects: Astrophysics (astro-ph)

The discovery of the 6.67 hr periodicity in the X-ray source 1E 161348-5055 associated with the supernova remnant RCW 103 has raised interesting suggestions about the nature of the X-ray source. Here we argue that in either accreting neutron star or magnetar model, a supernova fallback disk may be a critical ingredient in theoretical interpretations of 1E 161348-5055. We further emphasize the effect of fallback disks on the evolution of young compact objects in various ways, and suggest that even SS 433 could also be powered by fallback disk accretion process.

[23]  arXiv:0708.0086 [ps, pdf, other]
Title: Neutron star cooling after deep crustal heating in the X-ray transient KS 1731-260 Authors: P. S. Shternin (1), D. G. Yakovlev (1), P. Haensel (2), A. Y. Potekhin (1) ((1) Ioffe Phys.-Tech. Inst., St.-Petersburg; (2) N. Copernicus Astron. Center, Warsaw) Comments: 5 pages, 2 figures, submitted to MNRAS Subjects: Astrophysics (astro-ph)

We simulate the cooling of the neutron star in the X-ray transient KS 1731-260 after the source returned to quiescence in 2001 from a long (>~ 12.5 yr) outburst state. We show that the cooling can be explained assuming that the crust underwent deep heating during the outburst stage. In our best theoretical scenario the neutron star has no enhanced neutrino emission in the core, and its crust is thin, superfluid, and has the normal thermal conductivity. The thermal afterburst crust-core relaxation in the star may be not over.

[32]  arXiv:0708.0131 [ps, pdf, other]
Title: On the Density Dependent Nuclear Matter Compressibility Authors: V.A. Dexheimer, C.A.Z. Vasconcellos, B.E.J. Bodmann Subjects: Astrophysics (astro-ph)

In the present work we apply a quantum hadrodynamic effective model in the mean-field approximation to the description of neutron stars. We consider an adjustable derivative-coupling model and study the parameter influence on the dynamics of the system by analyzing the full range of values they can take. We establish a set of parameters which define a specific model that is able to describe phenomenological properties such as the effective nucleon mass at saturation as well as global static properties of neutron stars (mass and radius). If one uses observational data to fix the maximum mass for neutron stars by a specific model, we are able to predict the compression modulus of nuclear matter K = 257,2MeV.

[37]  arXiv:0708.0148 [ps, pdf, other]
Title: Modelling the behaviour of accretion flows in X-ray binaries Authors: Chris Done, Marek Gierlinski, Aya Kubota Comments: 76 pages, accepted for publication in Astronomy and Astrophysics Reviews Subjects: Astrophysics (astro-ph)

(abridged) We review how the recent increase in X-ray and radio data from black hole and neutron star binaries can be merged together with theoretical advances to give a coherent picture of the physics of the accretion flow in strong gravity. Both long term X-ray light curves, X-ray spectra, the rapid X-ray variability and the radio jet behaviour are consistent with a model where a standard outer accretion disc is truncated at low luminosities, being replaced by a hot, inner flow which also acts as the launching site of the jet. Decreasing the disc truncation radius leads to softer spectra, as well as higher frequencies (including QPO's) in the power spectra, and a faster jet. The collapse of the hot flow when the disc reaches the last stable orbit triggers the dramatic decrease in radio flux, as well as giving a qualitative (and often quantitative) explanation for the major hard--soft spectral transition seen in black holes and neutron stars.
After collapse of the hot inner flow, the spectrum in black hole systems can be dominated by the disc emission. Its behaviour is consistent with the existence of a last stable orbit, and such data can be used to estimate the black hole spin. These systems can also show very different spectra at these high luminosities, in which the disc spectrum is strongly distorted by Comptonization. The structure of the accretion flow becomes increasingly uncertain as the luminosity approaches (and exceeds) the Eddington luminosity, though there is growing evidence that winds play an important role. We stress that these high Eddington fraction flows are key to understanding many disparate and currently very active fields such as ULX, Narrow Line Seyfert 1's, and the growth of the first black holes in the Early Universe.

[41]  arXiv:0708.0189 [ps, pdf, other]
Title: Pulsar model of the high energy phenomenology of LS 5039 Authors: Agnieszka Sierpowska-Bartosik, Diego F. Torres Subjects: Astrophysics (astro-ph)

Under the assumption that LS 5039 is a system composed by a pulsar rotating around an O6.5V star in a ~3.9 day orbit, we present the results of a theoretical modeling of the high energy phenomenology observed by the High Energy Stereoscopy Array (H.E.S.S.). This model (including detailed account of the system geometry, Klein-Nishina inverse Compton, gamma-gamma absorption, and cascading) is able to describe well the rich observed phenomenology found in the system at all timescales, both flux and spectrum-wise.

[48]  arXiv:0708.0211 [ps, pdf, other]
Title: The long-term evolution of the spin, pulse shape, and orbit of the accretion-powered millisecond pulsar SAX J1808.4-3658 Authors: Jacob M. Hartman (1), Alessandro Patruno (2), Deepto Chakrabarty (1), David L. Kaplan (1), Craig B. Markwardt (3), Edward H. Morgan (1), Paul S. Ray (4), Michiel van der Klis (2), Rudy Wijnands (2) ((1) MIT, (2) Univ. Amsterdam, (3) Univ. Maryland and GSFC, (4) Naval Research Lab) Comments: 21 pages, 9 figures; submitted to ApJ Subjects: Astrophysics (astro-ph)

We present a 7 yr timing study of the 2.5 ms X-ray pulsar SAX J1808.4-3658, an X-ray transient with a recurrence time of ~2 yr, using data from the Rossi X-ray Timing Explorer covering 4 transient outbursts (1998-2005). We verify that the 401 Hz pulsation traces the spin frequency fundamental and not a harmonic. Substantial pulse shape variability, both stochastic and systematic, was observed during each outburst. Analysis of the systematic pulse shape changes suggests that, as an outburst dims, the X-ray "hot spot" on the pulsar surface drifts longitudinally and a second hot spot may appear. The overall pulse shape variability limits the ability to measure spin frequency evolution within a given X-ray outburst (and calls previous nudot measurements of this source into question), with typical upper limits of |nudot| < 2.5x10^{-14} Hz/s (2 sigma). However, combining data from all the outbursts shows with high (6 sigma) significance that the pulsar is undergoing long-term spin down at a rate nudot = (-5.6+/-2.0)x10^{-16} Hz/s, with most of the spin evolution occurring during X-ray quiescence. We discuss the possible contributions of magnetic propeller torques, magnetic dipole radiation, and gravitational radiation to the measured spin down, setting an upper limit of B < 1.5x10^8 G for the pulsar's surface dipole magnetic field and Q < 4.4x10^{36} g cm^2 for the mass quadrupole moment. We also measured an orbital period derivative of Pdot = (3.5+/-0.2)x10^{-12} s/s. In an appendix we derive an improved (0.15 arcsec) source position from optical data.

Cross-lists for Thu, 2 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[55]  arXiv:0707.4544 (cross-list from math-ph) [ps, pdf, other]
Title: Orbital period derivative of a binary system using an exact orbital energy equation Authors: Vikram H. Zaveri Comments: 4 pages Subjects: Mathematical Physics (math-ph); Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc)

It is proposed that the equations of motion that yielded two major predictions of general relativity without utilizing Riemannian geometry and geodesic trajectories are exact in nature and can be applied to pulsars and inspiralling compact binaries for analyzing orbital period derivative and two polarization gravitational wave forms. Exactness of these equations eliminates the need for higher order xPN corrections to the orbital energy part of the balance equation.

Replacements for Thu, 2 Aug 07

0 abstracts or titles contain neutron star, magnetar or pulsar


[ total of 64 entries: 1-64 ]
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1 abstracts or titles contain neutron star, magnetar or pulsar


[18]  arXiv:0708.0290 [ps, pdf, other]
Title: HST multi-epoch imaging of the PSR B0540-69 system unveils a highly dynamic synchrotron nebula Authors: A. De Luca, R.P. Mignani, P.A. Caraveo, G.F. Bignami Comments: 11 pages, 3 figures. Accepted for publication in ApJ Letters Subjects: Astrophysics (astro-ph)

PSR B0540-69 is the Crab twin in the Large Magellanic Cloud. Age, energetic and overall behaviour of the two pulsars are very similar. The same is true for the general appearance of their pulsar wind nebulae (PWNe). Analysis of Hubble Space Telescope images spanning 10 years unveiled significant variability in the PWN surrounding PSR B0540-69, with a hot spot moving at ~0.04c. Such behaviour, reminiscent of the variability observed in the Crab nebula along the counter-jet direction, may suggest an alternative scenario for the geometry of the system. The same data were used to assess the pulsar proper motion. The null displacement recorded over 10 y allowed us to set a 3sigma upper limit of 290 km/s to the pulsar velocity.

Cross-lists for Fri, 3 Aug 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[36]  arXiv:0707.4620 (cross-list from nucl-th) [ps, pdf, other]
Title: Nuclear equation of state at high baryonic density and compact star constraints Authors: D.N. Basu, P. Roy Chowdhury, C. Samanta Comments: 24 pages including 2 tables and 6 figures Subjects: Nuclear Theory (nucl-th); Astrophysics (astro-ph)

A mean field calculation is carried out to obtain the equation of state (EoS) of nuclear matter from a density dependent M3Y interaction (DDM3Y). The energy per nucleon is minimized to obtain ground state of the symmetric nuclear matter (SNM). The constants of density dependence of the effective interaction are obtained by reproducing the saturation energy per nucleon and the saturation density of SNM. The energy variation of the exchange potential is treated properly in the negative energy domain of nuclear matter. The EoS of SNM, thus obtained, is not only free from the superluminosity problem but also provides excellent estimate of nuclear incompressibility. The EoS of asymmetric nuclear matter is calculated by adding to the isoscalar part, the isovector component of M3Y interaction. The SNM and pure neutron matter EoS are used to calculate the nuclear symmetry energy which is found to be consistent with that extracted from the isospin diffusion in heavy-ion collisions at intermediate energies. The $\beta$ equilibrium proton fraction calculated from the symmetry energy and related theoretical findings are consistent with the constraints derived from the observations on compact stars.

[38]  arXiv:0708.0020 (cross-list from physics.plasm-ph) [ps, pdf, other]
Title: Spin solitons in magnetized pair plasmas Authors: G. Brodin, M. Marklund Comments: 7 pages Subjects: Plasma Physics (physics.plasm-ph); Astrophysics (astro-ph)

A set of fluid equations, taking into account the spin properties of the electrons and positrons in a magnetoplasma, are derived. The magnetohydrodynamic limit of the pair plasma is investigated. It is shown that the microscopic spin properties of the electrons and positrons can lead to interesting macroscopic and collective effects in strongly magnetized plasmas. In particular, it is found that new Alfvenic solitary structures, governed by a modified Korteweg-de Vries equation, are allowed in such plasmas. These solitary structures vanish if the quantum spin effects are neglected. Our results should be of relevance for astrophysical plasmas, e.g. in pulsar magnetospheres.

Replacements for Fri, 3 Aug 07

0 abstracts or titles contain neutron star, magnetar or pulsar


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Astrophysics authors/titles "new"

6 abstracts or titles contain neutron star, magnetar or pulsar


[2]  arXiv:0708.0406 [ps, pdf, other]
Title: Robust Models for Phase Shifts in Accreting Binary Stars Authors: Andrew G. Cantrell, Charles D. Bailyn Comments: 38 pages, 3 figures, to be published in ApJ Subjects: Astrophysics (astro-ph)

Radial velocity studies of accreting binary stars commonly use accretion disk emission lines to determine the radial velocity of the primary star and therefore the mass ratio. These emission line radial velocity curves are often shifted in phase from the expected motion of the primary. These phase shifts cast doubt on the use of disk emission lines in the determination of mass ratios. We present a systematic study of phase shifts, using data from the literature to distinguish between possible explanations of the phase shift. We find that one widely adopted class of models is contradicted by observations (section 2). We present a generalized form of another class of models, which we call "measurement offset models." We show that these models are quantitatively consistent with existing data (figures 2 and 3, and the discussion in section 4.4). We consider the implications of adopting measurement offset models, for both disk structure and determination of binary parameters. Specifically, we describe in section 6 how measurement offset models may be used improve determinations of the mass ratio based on disk emission lines. This could be a valuable new tool in determining masses of important astrophysical objects such as accreting neutron stars and black holes.

[5]  arXiv:0708.0413 [ps, pdf, other]
Title: Non-Detection of Gravitationally Redshifted Absorption Lines in the X-ray Burst Spectra of GS 1826-24 Authors: Albert K.H. Kong, Jon M. Miller, Mariano Mendez, Jean Cottam, Walter H.G. Lewin, Frederik Paerels, Erik Kuulkers, Rudy Wijnands Comments: 4 pages, 4 figures; submitted to ApJL Subjects: Astrophysics (astro-ph)

During a 200 ks observation with the XMM-Newton Reflection Grating Spectrometer, we detected 16 type-I X-ray bursts from GS 1826-24. We combined the burst spectra in an attempt to measure the gravitational redshifts from the surface of the neutron star. We divided the composite GS 1826-24 burst spectrum into three groups based on the blackbody temperature during the bursts. The spectra do not show any obvious discrete absorption lines. We compare our observations with those of EXO 0748-676.

[15]  arXiv:0708.0473 [ps, pdf, other]
Title: Cygnus X-3 transition from the ultrasoft to the hard state Authors: V. Beckmann, S. Soldi, G. Belanger, S. Brandt, M. D. Caballero-Garcia, G. De Cesare, N. Gehrels, S. Grebenev, O. Vilhu, A. von Kienlin, T.J.-L. Courvoisier Comments: 4 pages, 3 figures, accepted for publication as A&A Research Note Subjects: Astrophysics (astro-ph)

Aims: The nature of Cygnus X-3 is still not understood well. This binary system might host a black hole or a neutron star. Recent observations by INTEGRAL have shown that Cygnus X-3 was again in an extremely ultrasoft state. Here we present our analysis of the transition from the ultrasoft state, dominated by blackbody radiation at soft X-rays plus non-thermal emission in the hard X-rays, to the low hard state.
Methods: INTEGRAL observed Cyg X-3 six times during three weeks in late May and early June 2007. Data from IBIS/ISGRI and JEM-X1 were analysed to show the spectral transition.
Results: During the ultrasoft state, the soft X-ray spectrum is well-described by an absorbed (NH = 1.5E22 1/cm**2) black body model, whereas the X-ray spectrum above 20 keV appears to be extremely low and hard (Gamma = 1.7). During the transition, the radio flux rises to a level of >1 Jy, and the soft X-ray emission drops by a factor of 3, while the hard X-ray emission rises by a factor of 14 and becomes steeper (up to Gamma = 4).
Conclusions: The ultrasoft state apparently precedes the emission of a jet, which is apparent in the radio and hard X-ray domain.

[16]  arXiv:0708.0498 [ps, pdf, other]
Title: Orbital Evolution of an Accreting Millisecond Pulsar: Witnessing the Banquet of a Hidden Black Widow Authors: T. Di Salvo, L. Burderi, A. Riggio, A. Papitto, M.T. Menna Comments: 10 pages, including 3 figures. Submitted to MNRAS on 2007 July 23 Subjects: Astrophysics (astro-ph)

We have performed a timing analysis of all the four X-ray outbursts from the accreting millisecond pulsar SAX J1808.4-3658 observed so far by RXTE. For each of the outbursts we have found the local best orbital solution, keeping fixed to their best fit values the orbital period and the a sin i amplitude, and fitting for the time of ascending node passage. Plotting the best-fit values obtained in this way versus time, we find a highly statistically significant parabolic trend, which gives an orbital period of 7249.156499(9) s and an orbital period derivative of (3.40 \pm 0.09) x 10^{-12} s/s. This derivative is positive, suggesting a degenerate or fully convective companion star, and is more than one order of magnitude higher than what is expected from angular momentum losses caused by gravitational radiation under the hypothesis of conservative mass transfer. We find that the only way to explain this puzzling result is that during X-ray quiescence the source is ejecting matter (and angular momentum) from the inner Lagrangian point. We propose a possible orbital evolution of the system and demonstrate that this kind of sources are capable to efficiently ablate the companion star, and therefore are hidden black widows visible in X-rays during transient mass transfer episodes.

[18]  arXiv:0708.0502 [ps, pdf, other]
Title: Neutron Stars in a Chiral Model with Finite Temperature Authors: V. Dexheimer, S. Schramm, H. Stoecker Comments: Proceeding to the conference Nuclear Physics in Astrophysics III Accepted for publication in Journal of Physics G: Nuclear and Particle Physics Subjects: Astrophysics (astro-ph)

Neutron star matter is investigated in a hadronic chiral model approach using the lowest flavor-SU(3) multiplets for baryons and mesons. The parameters are determined to yield consistent results for saturated nuclear matter as well as for finite nuclei. The influence of baryonic resonances is discussed. The global properties of a neutron star such as its mass and radius are determined. Proto-neutron star properties are studied by taking into account trapped neutrinos, temperature and entropy effects.

[22]  arXiv:0708.0534 [ps, pdf, other]
Title: Precise determination of orbital parameters in system with slowly drifting phases: application to the case of XTE J1807-294 Authors: A. Riggio, T. Di Salvo, L. Burderi, R. Iaria, A. Papitto, T. Menna, G. Lavagetto Comments: 14 pages, including 6 figures. Submitted to MNRAS Subjects: Astrophysics (astro-ph)

We describe a timing technique that allows to obtain precise orbital parameters of an accreting millisecond pulsar in those cases in which intrinsic variations of the phase delays (caused e.g. by proper variation of the spin frequency) with characteristic timescale longer than the orbital period do not allow to fit the orbital parameters over a long observation (tens of days). We show under which conditions this method can be applied and show the results obtained applying this method to the 2003 outburst observed by RXTE of the accreting millisecond pulsar XTE J1807-294 which shows in its phase delays a non-negligible erratic behavior. We refined the orbital parameters of XTE J1807-294 using all the 90 days in which the pulsation is strongly detected and the method applicable. In this way we obtain the orbital parameters of the source with a precision more than one order of magnitude better than the previous available orbital solution, a precision obtained to date, on accreting millisecond pulsars, only for XTE J1807-294 analyzing several outbursts spanning over seven years and with a much better statistics.

Cross-lists for Mon, 6 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[28]  arXiv:0708.0307 (cross-list from hep-ph) [ps, pdf, other]
Title: Color-flavor locked superconductor in a magnetic field Authors: Jorge L. Noronha, Igor A. Shovkovy Comments: 11 pages, 3 figures. The scale on the horizontal axis in Fig.1 is corrected. In addition, numerical results for a smaller gap are added. Other minor corrections are made in the text. Conclusions are unchanged Subjects: High Energy Physics - Phenomenology (hep-ph); Astrophysics (astro-ph); High Energy Physics - Theory (hep-th)

We study the effects of moderately strong magnetic fields on the properties of color-flavor locked color superconducting quark matter in the framework of the Nambu-Jona-Lasinio model. We find that the energy gaps, which describe the color superconducting pairing as well as the magnetization, are oscillating functions of the magnetic field. Also, we observe that the oscillations of the magnetization can be so strong that homogeneous quark matter becomes metastable for a range of parameters. We suggest that this points to the possibility of magnetic domains or other types of magnetic inhomogeneities in the quark cores of magnetars.

Replacements for Mon, 6 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[44]  arXiv:0705.3713 (replaced) [ps, pdf, other]
Title: The Magnetar Nature and the Outburst Mechanism of a Transient Anomalous X-ray Pulsar Authors: Tolga Guver, Feryal Ozel, Ersin Gogus, Chryssa Kouveliotou Comments: Accepted by ApJ Letters with minor changes Subjects: Astrophysics (astro-ph)
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Astrophysics authors/titles "new"

2 abstracts or titles contain neutron star, magnetar or pulsar


[16]  arXiv:0708.0696 [ps, pdf, other]
Title: Thermal Timescale Mass Transfer Rates in Intermediate-Mass X-ray Binaries Authors: Xiao-Jie Xu, Xiang-Dong Li Comments: 13 pages, 4 figures, and 2 tables, accepted for publication in A&A Subjects: Astrophysics (astro-ph)

Thermal timescale mass transfer generally occurs in close binaries where the donor star is more massive than the accreting star. The mass transfer rates are usually estimated in terms of the Kelvin-Helmholtz timescale of the donor star. But recent investigations indicate that this method may overestimate the real mass transfer rates in accreting white dwarf or neutron star binary systems. We have systematically investigated the thermal-timescale mass transfer processes in intermediate-mass X-ray binaries, by calculating binary evolution sequences with various initial donor masses and orbital periods. From the calculated results we find that on average the mass transfer rates are lower than traditional estimates by a factor of $\sim 4$.

[30]  arXiv:0708.0791 [ps, pdf, other]
Title: An unexpected outburst from A0535+262 Authors: A. B. Hill, A. J. Bird, A. J. Dean, V. A. McBride, V. Sguera, D. J. Clark, M. Molina, S. Scaringi, S. E. Shaw Comments: 5 pages, 4 figures, 1 table. Accepted for publication in MNRAS Subjects: Astrophysics (astro-ph)

A0535+262 is a transient Be/X-ray binary system which was in a quiescent phase from 1994-2005. In this paper we report on the timing and spectral properties of the INTEGRAL detection of the source in October 2003. The source is detected for ~6000 seconds in the 18-100 keV energy band at a luminosity of ~3.8 x 10^{35} erg s^{-1}; this is compatible with the high end of the range of luminosities expected for quiescent emission. The system is observed to be outside of the centrifugal inhibition regime and pulsations are detected with periodicity, P=103.7 +/- 0.1 seconds. An examination of the pulse history of the source shows that it had been in a constant state of spin-down since it entered the quiescent phase in 1994. The rate of spin-down implies the consistent presence of an accretion disk supplying torques to the pulsar. The observations show that the system is still active and highly variable even in the absence of recent Type I or Type II X-ray outbursts.

Cross-lists for Tue, 7 Aug 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Tue, 7 Aug 07

0 abstracts or titles contain neutron star, magnetar or pulsar


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Astrophysics authors/titles "new"

5 abstracts or titles contain neutron star, magnetar or pulsar


[4]  arXiv:0708.0829 [ps, pdf, other]
Title: Discovery of 442-Hz Pulsations from an X-ray Source in the Globular Cluster NGC 6440 Authors: Fotis P. Gavriil (1,2), Tod E. Strohmayer (2), Jean H. Swank (2), Craig B. Markwardt (2,4) Comments: 4 pages, 3 figures, submitted to ApJ Letters Subjects: Astrophysics (astro-ph)

We report on the serendipitous discovery of a 442-Hz pulsar during a Rossi X-ray Timing Explorer (RXTE) observation of the globular cluster NGC 6440. The oscillation is detected following a burst-like event which was decaying at the beginning of the observation. The time scale of the decay suggests we may have seen the tail-end of a long-duration burst. Low-mass X-ray binaries (LMXBs) are known to emit thermonuclear X-ray bursts that are sometimes modulated by the spin frequency of the star, the so called burst oscillations. The pulsations reported here are peculiar if interpreted as canonical burst oscillations. In particular, the pulse train lasted for ~500 s, much longer than in standard burst oscillations. The signal was highly coherent and drifted down by ~2x10^-3 Hz, much smaller than the ~Hz drifts typically observed during normal bursts. The pulsations are reminiscent of those observed during the much more energetic ``superbursts'', however, the temporal profile and the energetics of the burst suggest that it was not the tail end nor the precursor feature of a superburst. It is possible that we caught the tail end of an outburst from a new `intermittent'' accreting X-ray millisecond pulsar, a phenomenon which until now has only been seen in HETE J1900.1$-$2455 (Galloway et al. 2007). We note that (Kaaret et al. 2003) reported the discovery of a 409.7 Hz burst oscillation from SAX J1748.9-2021, also located in NGC 6440. However, Chandra X-ray
Observatory imaging indicates it contains several point-like X-ray sources, thus the 442 Hz object is likely a different source.

[26]  arXiv:0708.0900 [ps, pdf, other]
Title: Spin-down of compact stars and energy release of a first-order phase transition Authors: Kang Miao, Zheng Xiao-Ping, Pan Na-Na Comments: 13 pages, 7 figures Subjects: Astrophysics (astro-ph)

The deconfinement phase transition from hadronic matter to quark matter can continuously occur during spins down of neutron stars. It will lead to the release of latent heat if the transition is the first-order one. We have investigated the energy release of such deconfinement phase transition for rotating hybrid stars model which include mixed phase of hadronic matter and quark matter. The release of latent heat per baryon is calculated through studying a randomly process of infinitesimal compressing. Finally, we can self-consistently get the heating luminosity of deconfinement phase transition by imputing the EOS of mixed phase, and based on the equation of rotation structure of stars.

[34]  arXiv:0708.0953 [ps, pdf, other]
Title: Chandra View of DA 530: A Sub-Energetic Supernova Remnant with a Pulsar Wind Nebula? Authors: Bing Jiang, Yang Chen, Q. Daniel Wang Comments: 23 pages, 7 figures, accepted for publication in ApJ Subjects: Astrophysics (astro-ph)

Based on a Chandra ACIS observation, we report the detection of an extended X-ray feature close to the center of the remnant DA 530 with 5.3 sigma above the background within a circle of 20'' radius. This feature, characterized by a power-law with the photon index gamma=1.6+-0.8 and spatially coinciding with a nonthermal radiosource, most likely represents a pulsar wind nebula. We have further examined the spectrum of the diffuse X-ray emission from the remnant interior with a background-subtracted count rate of ~0.06 counts s^-1 in 0.3-3.5 keV. The spectrum of the emission can be described by a thermal plasma with a temperature of ~0.3-0.6 keV and a Si over-abundance of >~7 solar. These spectral characteristics, together with the extremely low X-ray luminosity, suggest that the remnant arises from a supernova with an anomalously low mechanical energy (<10^50 ergs). The centrally-filled thermal X-ray emission of the remnant may indicate an early thermalization of the SN ejecta by the circum-stellar medium. Our results suggest that the remnant is likely the product of a core-collapsed SN with a progenitor mass of 8-12 Msun. Similar remnants are probably common in the Galaxy, but have rarely been studied.

[42]  arXiv:0708.0993 [ps, pdf, other]
Title: A Simple Model for Pulse Profiles from Precessing Pulsars, with Special Application to Relativistic Binary PSR B1913+16 Authors: Timothy Clifton, Joel M. Weisberg Comments: 34 pages and 8 figures. Submitted to ApJ Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc)

We study the observable pulse profiles that can be generated from precessing pulsars. A novel coordinate system is defined to aid visualization of the observing geometry. Using this system we explore the different families of profiles that can be generated by simple, circularly symmetric beam shapes. An attempt is then made to fit our model to the observations of relativistic binary PSR B1913+16. It is found that while qualitatively similar pulse profiles can be produced, this minimal model is insufficient for an accurate match to the observational data. Consequently, we confirm that the emission beam of PSR B1913+16 must deviate from circular symmetry, as first reported by Weisberg and Taylor (2002). We also comment on the applicability of our analysis technique to other precessing pulsars, both binary and isolated.

[43]  arXiv:0708.1000 [pdf, other]
Title: Particle Acceleration and Magnetic Dissipation in Relativistic Current Sheet of Pair Plasmas Authors: S. Zenitani, M. Hoshino Comments: 60 pages, 27 figures. Accepted for publication in ApJ Subjects: Astrophysics (astro-ph)

We study linear and non-linear development of relativistic and ultra-relativistic current sheets of pair plasmas with anti-parallel magnetic fields. Two types of two-dimensional problems are investigated by particle-in-cell (PIC) simulations. First, we present the development of relativistic magnetic reconnection, whose outflow speed is an order of the light speed c. It is demonstrated that particles are strongly accelerated in and around the reconnection region, and that most of magnetic energy is converted into "non-thermal" part of plasma kinetic energy. Second, we present another two-dimensional problem of a current sheet in a cross-field plane. In this case, the relativistic drift kink instability (RDKI) occurs. Particle acceleration also takes place, but the RDKI fast dissipates the magnetic energy into plasma heat. We discuss the mechanism of particle acceleration and the theory of the RDKI in detail. It is important that properties of these two processes are similar in the relativistic regime of T > mc^2, as long as we consider the kinetics. Comparison of the two processes indicates that magnetic dissipation by the RDKI is more favorable process in the relativistic current sheet. Therefore the striped pulsar wind scenario should be reconsidered by the RDKI.

Cross-lists for Wed, 8 Aug 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Wed, 8 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[48]  arXiv:0704.0799 (replaced) [ps, pdf, other]
Title: Spin Evolution of Accreting Neutron Stars: Nonlinear Development of the R-mode Instability Authors: Ruxandra Bondarescu, Saul A. Teukolsky, Ira Wasserman (Cornell University) Comments: 18 pages, 9 figures. Error Corrected. Includes referee input Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc)
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4 abstracts or titles contain neutron star, magnetar or pulsar


[3]  arXiv:0708.1024 [pdf, other]
Title: Neutron star magnetospheres: the binary pulsar, Crab and magnetars Authors: Maxim Lyutikov (Purdue University) Comments: Proceedings, Huangshan meeting "Astrophysics of Compact Objects" Subjects: Astrophysics (astro-ph)

A number of disparate observational and theoretical pieces of evidence indicate that, contrary to the conventional wisdom, neutron stars' closed field lines are populated by dense, hot plasma and may be responsible for producing some radio and high energy emission. This conclusion is based on eclipse modeling of the binary pulsar system PSR J0737-3039A/B (Lyutikov & Thompson 2005), a quantitative theory of Crab giant pulses (Lyutikov 2007) and a number of theoretical works related to production of non-thermal spectra in magnetars through resonant scattering. In magnetars, dense pair plasma is produced by twisting magnetic field lines and associated electric fields required to lift the particles from the surface. In long period pulsars, hot particles on closed field lines can be efficiently trapped by magnetic mirroring, so that relatively low supply rate, e.g. due to a drift from open field lines, may result in high density. In short period pulsars, magnetic mirroring does not work; large densities may still be expected at the magnetic equator near the Y-point.

[11]  arXiv:0708.1050 [ps, pdf, other]
Title: Pulsars: Progress, Problems and Prospects Authors: Jonathan Arons Comments: 55 pages, 21 figures. To appear in Springer Lecture Notes on "Neutron Stars and Pulsars, 40 years after the discovery", ed. W.Becker, 2008 Subjects: Astrophysics (astro-ph)

I survey recent successes in the application of relativistic MHD and force-free electrodynamics to the modeling of the pulsars' rotational energy loss mechanism as well as to the structure and emission characteristics of Pulsar Wind Nebulae. I suggest that unsteady reconnection in the current sheet separating the closed from the open zones of the magnetosphere is responsible for the torque fluctuations observed in some pulsars, as well as for departures of the braking index from the canonical value of 3. I emphasize the significance of the boundary layer between the closed and open zones as the active site in the outer magnetopshere. I elaborate on the conflict between the models currently in use to interpret the gamma ray and X-ray pulses from these systems with the electric current flows found in the spin down models. Because the polar cap ``gap'' is the essential component in the supply of plasma to pulsar magnetospheres and to pulsar wind nebulae, I emphasize the importance of high sensitivity gamma ray observations of pulsars with core components of radio emission and high magnetospheric voltage, since these observations will look directly into the polar plasma production region. I also discuss the shock conversion of flow energy into the spectra of the synchrotron emitting particles in the Nebulae. I comment on the prospects for future developments and improvements in all these areas.

[20]  arXiv:0708.1110 [ps, pdf, other]
Title: Discovery of coherent millisecond X-ray pulsations in Aql X-1 Authors: P. Casella, D. Altamirano, R. Wijnands, M. van der Klis (University of Amsterdam) Comments: 4 pages, 3 figures, submitted to ApJ Letters. Uses emulateapj.cls Subjects: Astrophysics (astro-ph)

We report the discovery of an episode of coherent millisecond X-ray pulsation in the neutron star low-mass X-ray binary Aql X-1. The episode lasts for slightly more than 150 seconds, during which the pulse frequency is consistent with being constant. No X-ray burst or other evidence of thermonuclear burning activity is seen in correspondence with the pulsation, which can thus be identified as occurring in the persistent emission. The pulsation frequency is 550.27 Hz, very close (0.5 Hz higher) to the maximum reported frequency from burst oscillations in this source. Hence we identify this frequency with the neutron star spin frequency. The pulsed fraction is strongly energy dependent, ranging from <1% (3-5 keV) to >10% (16-30 keV). We discuss possible physical interpretations and their consequences for our understanding of the lack of pulsation in most neutron star low-mass X-ray binaries. If interpreted as accretion-powered pulsation, Aql X-1 might play a key role in understanding the differences between pulsating and non-pulsating sources.

[29]  arXiv:0708.1149 [ps, pdf, other]
Title: Discovery of Pulsations and a Possible Spectral Feature in the X-ray Emission from Rotating Radio Transient J1819-1458 Authors: M. A. McLaughlin, N. Rea, B. M. Gaensler, S. Chatterjee, F. Camilo, M. Kramer, D. R. Lorimer, A. G. Lyne, G. L. Israel, A. Possenti Comments: 5 figures, accepted by ApJ Subjects: Astrophysics (astro-ph)

PSR J1819-1458 is a rotating radio transient (RRAT) source with an inferred surface dipole magnetic field strength of 5e13 G and a 4.26-s spin period. We present XMM-Newton observations of the X-ray counterpart of this source, CXOU J181939.1-145804, in which we identify pulsations and a possible spectral feature. The X-ray pulsations are at the period predicted by the radio ephemeris, providing an unambiguous identification with the radio source and confirmation of its neutron star nature. The X-ray pulse has a 0.3-5 keV pulsed fraction of 34% and is aligned with the expected phase of the radio pulse. The X-ray spectrum is fit well by an absorbed blackbody with kT = 0.14 keV with the addition of an absorption feature at 1 keV, with total absorbed flux of 1.5e-13 ergs/cm^2/s (0.3-5 keV). This absorption feature is well modeled by a Gaussian or resonant cyclotron scattering model, but its significance is dependent on the choice of continuum model. We find no evidence for any X-ray bursts or aperiodic variability on timescales of 6 ms to the duration of the observation and can place the most stringent limit to date of < 3e-9 ergs/cm^2/s on the absorbed 0.3-5 keV flux of any bursts.

Cross-lists for Thu, 9 Aug 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Thu, 9 Aug 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[38]  arXiv:astro-ph/0702228 (replaced) [ps, pdf, other]
Title: Gravitational waves from relativistic neutron star mergers with nonzero-temperature equations of state Authors: R. Oechslin, H.-T. Janka (MPI for Astrophysics, Garching, Germany) Comments: 5 pages, 4 figures, revised version accepted for publication in PRL Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc)
[48]  arXiv:0708.0953 (replaced) [ps, pdf, other]
Title: Chandra View of DA 530: A Sub-Energetic Supernova Remnant with a Pulsar Wind Nebula? Authors: Bing Jiang, Yang Chen, Q. Daniel Wang Comments: 23 pages, 7 figures, accepted for publication in ApJ; complete the abstract on astro-ph and correct some typos Subjects: Astrophysics (astro-ph)
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2 abstracts or titles contain neutron star, magnetar or pulsar


[40]  arXiv:0708.1316 [ps, pdf, other]
Title: Intermittent millisecond X-ray pulsations from the neutron-star X-ray transient SAX J1748.9-2021 in the globular cluster NGC 6440 Authors: D. Altamirano, P. Casella, A. Patruno, R. Wijnands, M. van der Klis Comments: 5 pages, 4 figures, Submitted to ApJL. Uses emulateapj.cls Subjects: Astrophysics (astro-ph)

We report on the detection of intermittent X-ray pulsations with a frequency of 442 Hz from the neutron-star X-ray binary SAX J1748.9--2021 in the globular cluster NGC 6440. The pulsations were seen during the 2001 and 2005 outburst of the source, albeit only intermittently, appearing and disappearing on timescales of hundreds of seconds. We found a suggestive relationship between the occurrence of type-I X-ray bursts and the appearance of the pulsations but the current data does not allow to determine if this is a strict relationship. The behavior of pulsations is very similar to the X-ray pulsations seen in the intermittent accreting millisecond X-ray pulsar HETE J1900.1--2455, strongly suggesting that SAX J1748.9--2021 is also an accretion driven millisecond X-ray pulsar. The reason for the intermittence of the pulsations in this source and in HETE J1900.1--2455 remains unclear. By studying the Doppler shift on the pulsation frequency due to orbital motion, we could determine an orbital period of 8.7 hrs. The companion star is likely a main sequence or a slightly evolved star with a mass of $\sim$1 $M_\odot$. This would make SAX J1748.9--2021 the accreting millisecond X-ray pulsar with the longest orbital period and the most massive companion star.

[41]  arXiv:0708.1323 [ps, pdf, other]
Title: A Large-Scale Survey of Neutron-Capture Element Abundances in Planetary Nebulae Authors: N. C. Sterling (1), Harriet L. Dinerstein (2), T. R. Kallman (1) ((1) NASA Goddard Space Flight Center; (2) University of Texas at Austin) Comments: 8 pages, 2 figures. To appear in "Asymmetrical Planetary Nebulae IV," eds. R. L. M. Corradi, A. Manchado & N. Soker Subjects: Astrophysics (astro-ph)

We present results from the first large-scale survey of neutron(n)-capture element abundances in planetary nebulae (PNe). This survey was motivated by the fact that a PN may be enriched in n-capture elements if its progenitor star experienced s-process nucleosynthesis during the asymptotic giant branch (AGB) phase. [Kr III] 2.199 and/or [Se IV] 2.287 $\mu$m were detected in 81 PNe out of 120 PNe, for a detection rate of nearly 70%. We derive Se and Kr abundances or upper limits using ionization correction factors derived from photoionization models. A significant range is found in the Se and Kr abundances, from near solar (no enrichment), to enriched by a factor of ten. Our survey has increased the number of PNe with known n-capture element abundances by an order of magnitude, enabling us to explore correlations between s-process enrichments and other nebular and central star properties. In particular, the Se and Kr enrichments display a positive correlation with nebular C/O ratios, as theoretically expected. Peimbert Type I PNe and bipolar PNe, whose progenitors are believed to be intermediate-mass stars (>3-4 M_sun), exhibit little or no s-process enrichment. Interestingly, PNe with H-deficient [WC] central stars do not exhibit systematically larger s-process enrichments than other PNe, despite the fact that their central stars are enriched in C and probably n-capture elements. Finally, the few PNe in our sample with known or probable binary central star systems exhibit little s-process enrichment, which may be explained if binary interactions truncated their AGB phases. We also briefly discuss a new observational program to detect optical emission lines of n-capture elements, and new atomic data calculations that will greatly improve the accuracy of n-capture element abundance determinations in PNe.

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Cross-lists for Mon, 13 Aug 07

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[40]  arXiv:0708.1281 (cross-list from hep-ph) [ps, pdf, other]
Title: Anomaly mediated neutrino-photon interactions at finite baryon density Authors: Jeffrey A. Harvey, Christopher T. Hill, Richard J. Hill Comments: 4 pages, 2 figures Subjects: High Energy Physics - Phenomenology (hep-ph); Astrophysics (astro-ph); High Energy Physics - Theory (hep-th); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)

We propose new physical processes based on the axial vector anomaly and described by the Wess-Zumino-Witten term that couples the photon, Z-boson, and the omega-meson. The interaction takes the form of a pseudo-Chern-Simons term, $\sim \epsilon_{\mu\nu\rho\sigma}\omega^\mu Z^\nu F^{\rho\sigma}$. This term induces neutrino-photon interactions at finite baryon density via the coupling of the Z-boson to neutrinos. These interactions may be detectable in various laboratory and astrophysical arenas. The new interactions may account for the MiniBooNE excess. They also produce a competitive contribution to neutron star cooling at temperatures >10^9 K. These processes and related axion--photon interactions at finite baryon density appear to be relevant in many astrophysical regimes.

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[23]  arXiv:0708.1618 [ps, pdf, other]
Title: Gluon Vortices and Induced Magnetic Field in Compact Stars Authors: Efrain J. Ferrer Comments: To appear in the Proceedings of the VII Latin American Symposium on Nuclear Physics and Applications. Cusco (Peru) June 2007 Subjects: Astrophysics (astro-ph)

The natural candidates for the realization of color superconductivity are the extremely dense cores of compact stars, many of which have very large magnetic fields, especially the so-called magnetars. In this paper we discuss how a color superconducting core can serve to generate and enhance the stellar magnetic field without appealing to a magnetohydrodynamic dynamo mechanism.

[24]  arXiv:0708.1629 [pdf, other]
Title: Fast spectroscopy and imaging with the FORS2 HIT mode Authors: Kieran O'Brien Comments: 19 pages, 7 figures, to appear in "High Time Resolution Astrophysics, Galway 2006" Subjects: Astrophysics (astro-ph)

The HIgh-Time resolution (HIT) mode of FORS2 has 3 sub-modes that allow for imaging and spectroscopy over a range of timescales from milliseconds up to seconds. It is the only high time resolution spectroscopy mode available on an 8m class telescope. In imaging mode, it can be used to measure the pulse of pulsars and spinning white dwarfs in a variety of high throughput broad- and narrow-band filters. In spectroscopy mode it can take up to 10 spectra per second using a novel ''shift-and-wait'' clocking pattern for the CCD. It takes advantage of the user-designed masks which can be inserted into FORS2 to allow any two targets within the 6.8' x 6.8' field of view of FORS2 to be selected. A number of integration, or more precisely 'wait', times are available, which together with the high throughput GRISMs can observe the entire optical spectrum on a range of timescales.

Cross-lists for Tue, 14 Aug 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Tue, 14 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[56]  arXiv:0706.3062 (replaced) [ps, pdf, other]
Title: Carbon Detonation and Shock-Triggered Helium Burning in Neutron Star Superbursts Authors: Nevin N. Weinberg (UC Berkeley), Lars Bildsten (KITP, UCSB) Comments: 11 pages, 11 figures, accepted to ApJ; discussion about onset of detonation discussed in new detail, including a new figure Subjects: Astrophysics (astro-ph)
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[3]  arXiv:0708.1767 [pdf, other]
Title: Where, oh where has the r-process gone? Authors: Y.-Z. Qian, G. J. Wasserburg Comments: 52 pages including figures Journal-ref: Physics Reports 442 (2007) 237 Subjects: Astrophysics (astro-ph)

We present a review of the possible sources for r-process nuclei. It is known that there is as yet no self-consistent mechanism to provide abundant neutrons for a robust r-process in the neutrino-driven winds from nascent neutron stars. We consider that the heavy r-nuclei with mass numbers A>130 (Ba and above) cannot be produced in the neutrino-driven winds. Nonetheless, the r-process and the neutrino-driven winds may be directly or indirectly related by some unknown additional mechanism, which, for example, could provide ejecta with very short dynamic timescales of <0.004 s. This undetermined mechanism must supply a neutron source within the same general stellar sites that undergo core collapse to produce the neutron star. Observational data on low-metallicity stars in the Galactic halo show that sites producing the heavy r-nuclei do not produce Fe or any other elements between N and Ge. Insofar as a forming neutron star is key to producing the heavy r-nuclei, then the only possible sources are supernovae resulting from collapse of O-Ne-Mg cores or accretion-induced collapse of white dwarfs, neither of which produce the elements of the Fe group or those of intermediate mass (above C and N). Using a template star with high enrichments of heavy r-nuclei and another with low enrichments we develop a two-component model based on the abundances of Eu (from sources for heavy r-nuclei) and Fe (from Fe core-collapse supernovae). This model gives very good quantitative predictions for the abundances of all the other elements in those metal-poor stars with [Fe/H]<-1.5 for which the Eu and Fe abundances are known. (Abridged)

[7]  arXiv:0708.1787 [ps, pdf, other]
Title: Supernova SN2006gy as a first ever Quark Nova? Authors: Denis Leahy, Rachid Ouyed (University of Calgary, Calgary, Alberta, Canada) Comments: 4 journal pages and 1 figure Subjects: Astrophysics (astro-ph)

The most luminous Supernova SN2006gy (more than a 100 times brighter than a typical supernova) has been a challenge to explain by standard models. For example, pair instability supernovae which are luminous enough seem to have too slow a rise, and core collapse supernovae do not seem to be luminous enough. We present an alternative scenario involving the quark-nova phenomenon (an explosive transition of the newly born neutron star to a quark star) in which a second explosion (delayed) occurs inside the ejecta of a normal supernova. The reheated supernova ejecta can radiate at higher levels for longer periods of time primarily due to reduced adiabatic expansion losses, unlike the standard supernova case. We find an encouraging match between the resulting lightcurve and that observed in the case of SN2006gy suggesting that we might have at hand the first ever signature of a quark-nova.

[9]  arXiv:0708.1792 [ps, pdf, other]
Title: Radiative Column and Light Curve of X-Ray Binary Pulsars Authors: S. Karino Comments: 13 pages, 7 figures, accepted for publication in PASJ Subjects: Astrophysics (astro-ph)

We examine the published light curves (LCs) of 117 X-ray binary pulsars, focusing on the dependence of their light curves on the observed energy bands. It is found that the energy dependence of the LCs appears only when the X-ray luminosity is larger than ~ 5 x 10^36 erg/s. Assuming that the behavior of light curve is related to the radiative accretion column on the neutron star surface, this energy threshold can be considered as the observational proof of the accretion column formation proposed by Basko and Sunyaev. Once we can grasp the existence of radiative column, we can also obtain several useful informations on the neutron star properties. As an instance, we perform the statistical analysis of the orientation angle of the magnetic axis, and we find that the inclination angle of magnetic axis should be small in order to explain the observed statistics.

Cross-lists for Wed, 15 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[41]  arXiv:0708.1619 (cross-list from nucl-th) [ps, pdf, other]
Title: Magnetic Phases in Dense Quark Matter Authors: Vivian de la Incera Comments: Presented at VII Latin American Symposium on Nuclear Physics and Applications, El Cusco, Peru, June 2007 Subjects: Nuclear Theory (nucl-th); Astrophysics (astro-ph); High Energy Physics - Phenomenology (hep-ph)

In this paper I discuss the magnetic phases of the three-flavor color superconductor. These phases can take place at different field strengths in a highly dense quark system. Given that the best natural candidates for the realization of color superconductivity are the extremely dense cores of neutron stars, which typically have very large magnetic fields, the magnetic phases here discussed could have implications for the physics of these compact objects.

Replacements for Wed, 15 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[50]  arXiv:0705.1565 (replaced) [ps, pdf, other]
Title: Neutron stars in Einstein-aether theory Authors: Christopher Eling, Ted Jacobson, M. Coleman Miller Comments: 25 pages, 4 figures; v2: removed comment about rotating objects in abstract, simplified the discussion of aether-matter couplings, removed one extraneous mass vs. pressure plot, added brief discussion of ae-theory effects in Ozel's mass determination method, corrected typos Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph); High Energy Physics - Theory (hep-th)
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[15]  arXiv:0708.2063 [ps, pdf, other]
Title: Pulsar Radio Emission Cutoffs Authors: Ericsson D. Lopez Comments: 8 pages, no figures Journal-ref: Published in: CP784, Magnetic Fields in the Universe: From Laboratory and Stars to Primordial Structures, edited by E.M. de Gouveia Dal ino, G. Lugones and A. Lazarian, (2005), 697 Subjects: Astrophysics (astro-ph)

The propagation of radio emission in pulsar magnetospheres is discussed. We follow a kinematics model in order to derive dispersion relations for electromagnetic oscillations and transversal waves, propagating in a cold moving plasma. We have included relativistic corrections on the dispersion properties, involved with the relativistic motion of the emitting plasma. The occurrence of plasma instabilities is analyzed beside the conditions which should be fulfilled in order to permit the wave propagation and conversion in regions close to the cutoffs of the system. The existence of various frequencies of resonance has been predicted and we are working out these results in order to explain the low-frequency cutoffs observed in radio pulsar spectra.

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Replacements for Thu, 16 Aug 07

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[34]  arXiv:0704.1732 (replaced) [ps, pdf, other]
Title: Spheroidal and torsional modes of quasistatic shear oscillations in the solid globe models of nuclear physics and pulsar astrophysics Authors: S. Bastrukov, H-K. Chang, S. Misicu, I. Molodtsova, D. Podgainy Comments: 34 pages; 6 figures; Int.J.Mod.Phys.A.2007.Vol.22.N19.pp3261-3291 Subjects: Astrophysics (astro-ph)
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[23]  arXiv:0708.2263 [ps, pdf, other]
Title: The SN 1987A Link to Others and Gamma-Ray Bursts Authors: John Middleditch Comments: 13 pages, 2 figures, submitted to ApJ Letters Subjects: Astrophysics (astro-ph)

Early measurements of SN 1987A can be interpreted in light of the beam/jet (BJ) which had to hit polar ejecta (PE) to produce the "Mystery Spot" (MS), some 22 light-days distant. Other details of SN 1987A strongly suggest that it resulted from a merger of two stellar cores of a common envelope (CE) binary, i.e. a "double degenerate" (DD)-initiated SN. Without having to blast through the CE of Sk -69 202, it is likely that the BJ would have caused a full, long-soft gamma-ray burst (lGRB) upon hitting the PE, thus DD can produce lGRBs (and, of course, MSPs). Because DD must be the overwhelmingly dominant merger/SN mechanism in elliptical galaxies, where only short, hard GRBs (sGRBs) have been observed, DD without CE or PE must also produce sGRBs, and thus the pre-CE/PE impact photon spectrum of 99% of all GRBs is known, and neutron star (NS)-NS mergers may not make GRBs as we know them, and/or be as common as previously thought. The many details of Ia's strongly suggest that these are also DD formed, and the single degenerate total thermonuclear disruption paradigm is now in serious doubt as well. This is a cause for concern in Ia Cosmology, because Type Ia SNe will appear to be Ic's when viewed from their DD merger poles, given sufficient matter above that lost to core-collapse. As a DD-initiated SN, 1987A appears to be the Rosetta Stone for 99% of SNe, GRBs and MSPs, including all recent nearby SNe except SN 1986J, and the more distant SN 2006gy. There is no for exotica, such as "collapsars," to account for GRBs.

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[3]  arXiv:0708.2279 [ps, pdf, other]
Title: Relating gravitational wave constraints from primordial nucleosynthesis, pulsar timing, laser interferometers, and the CMB: implications for the early universe Authors: Latham A. Boyle (CITA/Princeton), Alessandra Buonanno (Maryland) Comments: v1: 12 + 6 pages (main text + appendices), 7 figures; v2: fonts fixed in figures Subjects: Astrophysics (astro-ph)

We derive a general master equation relating the gravitational-wave observables r and Omega_gw(f). Here r is the tensor-to-scalar ratio, constrained by cosmic-microwave-background (CMB) experiments; and Omega_gw(f) is the energy spectrum of primordial gravitational-waves, constrained e.g. by pulsar-timing measurements, laser-interferometer experiments, and Big Bang Nucleosynthesis (BBN). Differentiating the master equation yields a new expression for the tilt d(ln Omega_gw(f))/d(ln f). The relationship between r and Omega_gw(f) depends sensitively on the uncertain physics of the early universe, and we show that this uncertainty may be encapsulated (in a model-independent way) by two quantities: w_hat(f) and nt_hat(f), where nt_hat(f) is a certain logarithmic average over nt(k) (the primordial tensor spectral index); and w_hat(f) is a certain logarithmic average over w_tilde(a) (the effective equation-of-state in the early universe, after horizon re-entry). Here the effective equation-of-state parameter w_tilde(a) is a combination of the ordinary equation-of-state parameter w(a) and the bulk viscosity zeta(a). Thus, by comparing constraints on r and Omega_gw(f), one can obtain (remarkably tight) constraints in the [w_hat(f), nt_hat(f)] plane. In particular, this is the best way to constrain (or detect) the presence of a ``stiff'' energy component (with w > 1/3) in the early universe, prior to BBN. Finally, although most of our analysis does not assume inflation, we point out that if CMB experiments detect a non-zero value for r, then we will immediately obtain (as a free by-product) a new upper bound w_hat < 0.55 on the logarithmically averaged effective equation-of-state parameter during the ``primordial dark age'' between the end of inflation and the start of BBN.

[6]  arXiv:0708.2296 [ps, pdf, other]
Title: Linking Jet Emission, X-ray States and Hard X-ray Tails in the Neutron Star X-ray Binary GX 17+2 Authors: S. Migliari (CASS/UCSD), J. C. A. Miller-Jones (Amsterdam), R. P. Fender (Southampton), J. Homan (MIT), T. Di Salvo (Palermo), R. E. Rothschild (CASS/UCSD), M. P. Rupen (NRAO), J. A. Tomsick (SSL/UCB), R. Wijnands (Amsterdam), M. van der Klis (Amsterdam) Comments: Accepted by ApJ Subjects: Astrophysics (astro-ph)

We present the results from simultaneous radio (Very Large Array) and X-ray (Rossi-X-ray Timing Explorer) observations of the Z-type neutron star X-ray binary GX~17+2. The aim is to assess the coupling between X-ray and radio properties throughout its three rapidly variable X-ray states and during the time-resolved transitions. These observations allow us, for the first time, to investigate quantitatively the possible relations between the radio emission and the presence of the hard X-ray tails and the X-ray state of the source. The observations show: 1) a coupling between the radio jet emission and the X-ray state of the source, i.e. the position in the X-ray hardness-intensity diagram (HID); 2) a coupling between the presence of a hard X-ray tail and the position in the HID, qualitatively similar to that found for the radio emission; 3) an indication for a quantitative positive correlation between the radio flux density and the X-ray flux in the hard-tail power law component; 4) evidence for the formation of a radio jet associated with the Flaring Branch-to-Normal Branch X-ray state transition; 5) that the radio flux density of the newly-formed jet stabilizes when also the normal-branch oscillation (NBO) in the X-ray power spectrum stabilizes its characteristic frequency, suggesting a possible relation between X-ray variability associated to the NBO and the jet formation. We discuss our results in the context of jet models.

[8]  arXiv:0708.2337 [ps, pdf, other]
Title: Evolution of the bursting-layer wave during a Type 1 X-ray burst Authors: R. G. Berkhout (Leiden Observatory), Yuri Levin (Leiden Observatory and Lorentz Institute) Comments: 8 pages, submitted to MNRAS Subjects: Astrophysics (astro-ph)

In a popular scenario due to Heyl, quasi periodic oscillations (QPOs) which are seen during type 1 X-ray bursts are produced by giant travelling waves in neutron-star oceans. Piro and Bildsten have proposed that during the burst cooling the wave in the bursting layer may convert into a deep crustal interface wave, which would cut off the visible QPOs. This cut-off would help explain the magnitude of the QPO frequency drift, which is otherwise overpredicted by a factor of several in Heyl's scenario. In this paper, we study the coupling between the bursting layer and the deep ocean. The coupling turns out to be weak and only a small fraction of the surface-wave energy gets transferred to that of the crustal-interface wave during the burst. Thus the crustal-interface wave plays no dynamical role during the burst, and no early QPO cut-off should occur.

[12]  arXiv:0708.2352 [ps, pdf, other]
Title: Pulsar kicks by anisotropic neutrino emission from quark matter in strong magnetic fields Authors: I. Sagert, J. Schaffner-Bielich Comments: 14 pages, 10 figures Subjects: Astrophysics (astro-ph)

We discuss a pulsar acceleration mechanism based on asymmetric neutrino emission from the direct quark Urca process in the interior of proto neutron stars. The anisotropy is caused by a strong magnetic field which polarises the spin of the electrons opposite to the field direction. Due to parity violation the neutrinos and anti-neutrinos leave the star in one direction accelerating the pulsar. We calculate for varying quark chemical potentials the kick velocity in dependence of the quark phase temperature and its radius. Ignoring neutrino quark scattering we find that within a quark phase radius of 10 km and temperatures larger than 5 MeV kick velocities of 1000km s$^{-1}$ can be reached very easily. On the other hand taking into account the small neutrino mean free paths it seems impossible to reach velocities higher than 100km s$^{-1}$ even when including effects from colour superconductivity where the neutrino quark interactions are suppressed.

[13]  arXiv:0708.2362 [ps, pdf, other]
Title: WIMP Annihilation and Cooling of Neutron Stars Authors: Chris Kouvaris Comments: 20 pages, 2 figures Subjects: Astrophysics (astro-ph)

We study the effect of WIMP annihilation on the temperature of a neutron star. We shall argue that the released energy due to WIMP annihilation inside the neutron stars, might affect the temperature of stars older than 10 million years, flattening out the temperature at $\sim 10^4$ K for a typical neutron star.

[16]  arXiv:0708.2372 [ps, pdf, other]
Title: Searching for a Pulsar in SN1987A Authors: R. N. Manchester Comments: 10 pages, 3 figures. To appear in "Supernova 1987A: Twenty Years After: Supernovae and Gamma-Ray Bursters", edited by S. Immler, K. W. Weiler and R. McCray, American Institute of Physics, New York, 2007, in press Subjects: Astrophysics (astro-ph)

SN 1987A offered a unique opportunity to detect a pulsar at the very beginning of its life and to study its early evolution. Despite many searches at radio and optical wavelengths, no pulsar has yet been detected. Details of a recent search using the Parkes radio telescope are given. Limits on the X-ray, optical and radio luminosity of a point source at the centre of SN 1987A place limits on the properties of a central neutron star. However, neither these nor the pulsar limits preclude the presence of a relatively slowly rotating neutron star (P >~ 100 ms) with a moderate surface dipole magnetic field in SN 1987A. Galactic studies suggest that a significant fraction of pulsars are born with parameters in this range. In view of this, continued searches for a pulsar in SN 1987A are certainly justified.

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[9]  arXiv:0708.2482 [ps, pdf, other]
Title: Pulsar slow glitches in a solid quark star model Authors: C. Peng (PKU), R. X. Xu (PKU) Comments: 5 pages, 5 figures Subjects: Astrophysics (astro-ph)

A series of five unusual slow glitches of the radio pulsar B1822-09 (PSR J1825-0935) were observed over the 1995-2005 interval. This phenomenon is understood in a solid quark star model, where the reasonable parameters for slow glitches are presented in the paper. It is proposed that, because of increasing shear stress as a pulsar spins down, a slow glitch may occur, beginning with a collapse of a superficial layer of the quark star. This layer of material turns equivalently to viscous fluid at first, the viscosity of which helps deplete the energy released from both the accumulated elastic energy and the gravitation potential. This performs then a process of slow glitch. Numerical calculations show that the observed slow glitches could be reproduced if the effective coefficient of viscosity is ~10^2 cm$^2/s and the initial velocity of the superficial layer is order of 10^{-10} cm/s in the coordinate rotating frame of the star.

[13]  arXiv:0708.2505 [ps, pdf, other]
Title: Radio Emission Signatures in the Crab Pulsar Authors: T. H. Hankins, J. A. Eilek Comments: 26 pages, 10 figures, to appear in ApJ Subjects: Astrophysics (astro-ph)

Our high time resolution observations of individual pulses from the Crab pulsar show that both the time and frequency signatures of the interpulse are distinctly different from those of the main pulse. Main pulses can occasionally be resolved into short-lived, relatively narrow-band nanoshots. We believe these nanoshots are produced by soliton collapse in strong plasma turbulence. Interpulses at centimeter wavelengths are very different. Their dynamic spectrum contains regular, microsecond-long emission bands. We have detected these bands, proportionately spaced in frequency, from 4.5 to 10.5 GHz. The bands cannot easily be explained by any current theory of pulsar radio emission; we speculate on possible new models.

[37]  arXiv:0708.2693 [ps, pdf, other]
Title: On the stability of precessing superfluid neutron stars Authors: K. Glampedakis, N. Andersson, D. I. Jones Comments: 4 pages, Revtex, 1 eps figure Subjects: Astrophysics (astro-ph)

We discuss a new superfluid instability occuring in the interior of mature neutron stars with implications for freely precessing neutron stars. This short-wavelength instability is similar to the instability which is responsible for the formation of turbulence in superfluid Helium. Its existence raises serious questions about our understanding of neutron star precession and complicates attempts to constrain neutron star interiors using such observations.

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[16]  arXiv:0708.2756 [ps, pdf, other]
Title: Long-term X-ray changes in the emission from the anomalous X-ray pulsar 4U 0142+61 Authors: M. E. Gonzalez (1), R. Dib (1), V. M. Kaspi (1), P. M. Woods (2), C. R. Tam (1), F. P. Gavriil (3) ((1) McGill University, (2) Dynetics, Inc.; NSSTC, (3) NASA GSFC) Comments: 10 pages, 9 figures, in emulateapj style. Submitted to ApJ Subjects: Astrophysics (astro-ph)

We present results obtained from X-ray observations of the anomalous X-ray pulsar (AXP) 4U 0142+61 taken between 2000-2007 using XMM-Newton, Chandra and Swift. In observations taken before 2006, the pulse profile is observed to become more sinusoidal and the pulsed fraction increased with time. These results confirm those derived using the Rossi X-ray Timing Explorer and expand the observed evolution to energies below 2 keV. The XMM-Newton total flux in the 0.5-10 keV band is observed to be nearly constant in observations taken before 2006, while an increase of ~10% is seen afterwards and coincides with the burst activity detected from the source in 2006-2007. After these bursts, the evolution towards more sinusoidal pulse profiles ceased while the pulsed fraction showed a further increase. No evidence for large-scale, long-term changes in the emission as a result of the bursts is seen. The data also suggest a correlation between the flux and hardness of the spectrum, with brighter observations on average having a harder spectrum. As pointed out by other authors, we find that the standard blackbody plus power-law model does not provide the best spectral fit to the emission from 4U 0142+61. We also report on observations taken with the Gemini telescope after two bursts. These observations show source magnitudes consistent with previous measurements. Our results demonstrate the wide range of X-ray variability characteristics seen in AXPs and we discuss them in light of current emission models for these sources.

[27]  arXiv:0708.2810 [ps, pdf, other]
Title: Is a soft nuclear equation of state extracted from heavy-ion data incompatible with pulsar data? Authors: Irina Sagert, Mirjam Wietoska, Jurgen Schaffner-Bielich, Christian Sturm Comments: 8 pages, 1 figure, contribution to the proceedings of the international conference on 'Nuclear Physics in Astrophysics III', Dresden, Germany, March 26-31, 2007 Subjects: Astrophysics (astro-ph)

We discuss the recent constraints on the nuclear equation of state from pulsar mass measurements and from subthreshold production of kaons in heavy-ion collisions. While recent pulsar data points towards a hard equation of state, the analysis of the heavy-ion data allows only for soft equations of state. We resolve the apparent contradiction by considering the different density regimes probed. We argue that future measurements of global properties of low-mass pulsars can serve as an excellent cross-check to heavy-ion data.

[33]  arXiv:0708.2831 [ps, pdf, other]
Title: The rotational broadening of V395 Car - implications on compact object's mass Authors: T. Shahbaz (IAC), C.A. Watson (Univ. Sheffield) Comments: 5 pages, 7 figures, accpeted by AA Subjects: Astrophysics (astro-ph)

CONTEXT: The masses previously obtained for the X-ray binary 2S0921-630 inferred a compact object that was either a high-mass neutron star or low-mass black-hole, but used a previously published value for the rotational broadening (vsini) with large uncertainties. AIMS: We aim to determine an accurate mass for the compact object through an improved measurement of the secondary star's projected equatorial rotational velocity. METHODS: We have used UVES echelle spectroscopy to determine the vsini of the secondary star (V395 Car) in the low-mass X-ray binary 2S0921-630 by comparison to an artificially broadened spectral-type template star. In addition, we have also measured vsini from a single high signal-to-noise ratio absorption line profile calculated using the method of Least-Squares Deconvolution (LSD). RESULTS: We determine vsini to lie between 31.3+/-0.5km/s to 34.7+/-0.5km/s (assuming zero and continuum limb darkening, respectively) in disagreement with revious results based on intermediate resolution spectroscopy obtained with the 3.6m NTT. Using our revised vsini value in combination with the secondary star's radial velocity gives a binary mass ratio of 0.281+/-0.034. Furthermore, assuming a binary inclination angle of 75 degrees gives a compact object mass of 1.37+/-0.13Mo. CONCLUSIONS: We find that using relatively low-resolution spectroscopy can result in systemic uncertainties in the measured vsini values obtained using standard methods. We suggest the use of LSD as a secondary, reliable check of the results as LSD allows one to directly discern the shape of the absorption line profile. In the light of the new vsini measurement, we have revised down the compact object's mass, such that it is now compatible with a canonical neutron star mass.

[42]  arXiv:0708.2876 [ps, pdf, other]
Title: Tkachenko modes as sources of quasiperiodic pulsar spin variations Authors: Jorge Noronha (Frankfurt U., FIAS), Armen Sedrakian (Frankfurt U.) Comments: 5 pages, 3 figures, uses RevTex Subjects: Astrophysics (astro-ph); Nuclear Theory (nucl-th)

We study the long wavelength shear modes (Tkachenko waves) of triangular lattices of singly quantized vortices in neutron star interiors taking into account the mutual friction between the superfluid and the normal fluid and the shear viscosity of the normal fluid. The set of Tkachenko modes that propagate in the plane orthogonal to the spin vector are weakly damped if the coupling between the superfluid and normal fluid is small. In strong coupling, their oscillation frequencies are lower and are undamped for small and moderate shear viscosities. The periods of these modes are consistent with the observed ~100-1000 day variations in spin of PSR 1828-11.

Cross-lists for Wed, 22 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[52]  arXiv:0708.2436 (cross-list from gr-qc) [ps, pdf, other]
Title: Relativistic hydrodynamics in the presence of puncture black holes Authors: Joshua A. Faber, Thomas W. Baumgarte, Zachariah B. Etienne, Stuart L. Shapiro, Keisuke Taniguchi Comments: 21 pages, 21 figures, RevTex, submitted to PRD Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)

Many of the recent numerical simulations of binary black holes in vacuum adopt the moving puncture approach. This successful approach avoids the need to impose numerical excision of the black hole interior and is easy to implement. Here we wish to explore how well the same approach can be applied to moving black hole punctures in the presence of relativistic hydrodynamic matter. First, we evolve single black hole punctures in vacuum to calibrate our BSSN implementation and to confirm that the numerical solution for the exterior spacetime is invariant to any ``junk'' (i.e., constraint-violating) initial data employed in the black hole interior. Then we focus on relativistic Bondi accretion onto a moving puncture Schwarzschild black hole as a numerical testbed for our HRSC relativistic hydrodynamics scheme. We find that the hydrodynamical equations can be evolved successfully in the interior without imposing numerical excision. These results help motivate the adoption of the moving puncture approach to treat the binary black hole-neutron star problem using conformal thin-sandwich initial data.

Replacements for Wed, 22 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[59]  arXiv:astro-ph/0701095 (replaced) [ps, pdf, other]
Title: Observations of the 599 Hz Accreting X-ray Pulsar IGR J00291+5934 during the 2004 Outburst and in Quiescence Authors: M. A. P. Torres, P. G. Jonker, D. Steeghs, G. H. A. Roelofs, J. S. Bloom, J. Casares, E. E. Falco, M. R. Garcia, T. R. Marsh, M. Mendez, J. M. Miller, G. Nelemans, P. Rodriguez-Gil Comments: 10 pages, 7 figures, 3 tables. Revision both in text and figures to match the accepted manuscript to appear in ApJ Subjects: Astrophysics (astro-ph)
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[9]  arXiv:0708.2934 [ps, pdf, other]
Title: Observation of Galactic Sources of Very High Energy Gamma-Rays with the MAGIC Telescope Authors: H. Bartko Comments: Brief Review, to be pulished in: Mod. Phys. Lett. A Journal-ref: Mod. Phys. Lett. A, Vol. 22, No. 29 (2007) pp. 2167-2174 Subjects: Astrophysics (astro-ph)

The MAGIC telescope with its 17m diameter mirror is today the largest operating single-dish Imaging Air Cherenkov Telescope (IACT). It is located on the Canary Island La Palma, at an altitude of 2200m above sea level, as part of the Roque de los Muchachos European Northern Observatory. The MAGIC telescope detects celestial very high energy gamma-radiation in the energy band between about 50 GeV and 10 TeV. Since the autumn of 2004 MAGIC has been taking data routinely, observing various objects, like supernova remnants (SNRs), gamma-ray binaries, Pulsars, Active Galactic Nuclei (AGN) and Gamma-ray Bursts (GRB). We briefly describe the observational strategy, the procedure implemented for the data analysis, and discuss the results of observations of Galactic Sources.

[17]  arXiv:0708.2965 [ps, pdf, other]
Title: Constraining Crystalline Color Superconducting Quark Matter with Gravitational-Wave Data Authors: Lap-Ming Lin Comments: 5 pages. Accepted for publication in PRD (Rapid Communication) Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)

We estimate the maximum equatorial ellipticity sustainable by solid compact stars composed of crystalline color superconducting quark matter. For the theoretically allowed range of the gap parameter $\Delta$, the maximum ellipticity could be as large as 10^{-2}, which is about four orders of magnitude larger than the tightest upper limit obtained by the recent third and fourth science runs of the LIGO and GEO 600 gravitational wave detectors based on the data from 78 radio pulsars. We point out that the current gravitational-wave strain upper limit already has some implications for the gap parameter $\Delta$ in the crystalline color superconducting phase. In particular, the upper limit for the Crab pulsar implies that $\Delta$ is less than O(20) MeV for a range of quark chemical potential accessible in compact stars, assuming that the pulsar has a mass $1.4 M_{\odot}$, radius 10 km, breaking strain 10^{-3}, and that it has the maximum quadrupole deformation it can sustain without fracturing.

Cross-lists for Thu, 23 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[38]  arXiv:0708.2720 (cross-list from gr-qc) [ps, pdf, other]
Title: Simulating binary neutron stars: dynamics and gravitational waves Authors: Matthew Anderson, Eric W. Hirschmann, Luis Lehner, Steven L. Liebling, Patrick M. Motl, David Neilsen, Carlos Palenzuela, Joel E. Tohline Comments: 14 pages, 15 figures Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)

We model two mergers of orbiting binary neutron stars, the first forming a black hole and the second a differentially rotating neutron star. We extract gravitational waveforms in the wave zone. Comparisons to a post-Newtonian analysis allow us to compute the orbital kinematics, including trajectories and orbital eccentricities. We verify our code by evolving single stars and extracting radial perturbative modes, which compare very well to results from perturbation theory. The Einstein equations are solved in a first order reduction of the generalized harmonic formulation, and the fluid equations are solved using a modified Convex Essentially Non-Oscillatory method. All calculations are done in three spatial dimensions without symmetry assumptions. We use the \had computational infrastructure for distributed adaptive mesh refinement.

Replacements for Thu, 23 Aug 07

0 abstracts or titles contain neutron star, magnetar or pulsar


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2 abstracts or titles contain neutron star, magnetar or pulsar


[18]  arXiv:0708.3197 [ps, pdf, other]
Title: From Microscales to Macroscales in 3D: Selfconsistent Equation of State for Supernova and Neutron Star Models Authors: W. G. Newton, J. R. Stone, A. Mezzacappa Comments: 6 pages, 11 figures. Published in conference proceedings Journal of Physics: Conference Series 46 (2006) 408. Extended version to be submitted to Phys. Rev. C Journal-ref: Journal of Physics: Conference Series 46 (2006) 408 Subjects: Astrophysics (astro-ph)

First results from a fully self-consistent, temperature-dependent equation of state that spans the whole density range of neutron stars and supernova cores are presented. The equation of state (EoS) is calculated using a mean-field Hartree-Fock method in three dimensions (3D). The nuclear interaction is represented by the phenomenological Skyrme model in this work, but the EoS can be obtained in our framework for any suitable form of the nucleon-nucleon effective interaction. The scheme we employ naturally allows effects such as (i) neutron drip, which results in an external neutron gas, (ii) the variety of exotic nuclear shapes expected for extremely neutron heavy nuclei, and (iii) the subsequent dissolution of these nuclei into nuclear matter. In this way, the equation of state is calculated across phase transitions without recourse to interpolation techniques between density regimes described by different physical models. EoS tables are calculated in the wide range of densities, temperature and proton/neutron ratios on the ORNL NCCS XT3, using up to 2000 processors simultaneously.

[20]  arXiv:0708.3212 [ps, pdf, other]
Title: A New Study of the Transition to Uniform Nuclear Matter in Neutron Stars and Supernovae Authors: W. G. Newton Comments: 4 pages, 2 figures. Participant Contribution at the ``Dense Matter in Heavy Ion Collisions and Astrophysics" Summer School, JINR, Dubna, Aug. 21 - Sept. 1, 2006. To be published in PEPAN letters Subjects: Astrophysics (astro-ph)

A comprehensive microscopic study of the properties of bulk matter at densities just below nuclear saturation $\rho_s = 2.5 \sim 10^{14}$ g cm$^{-3}$, zero and finite temperature and high neutron fraction, is outlined, and preliminary results presented. Such matter is expected to exist in the inner crust of neutron stars and during the core collapse of massive stars with $M \gtrsim 8M_{\odot}

Cross-lists for Fri, 24 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[30]  arXiv:0708.2984 (cross-list from gr-qc) [ps, pdf, other]
Title: Is LIGO already constraining the parameters of QCD? Authors: B. Haskell, N. Andersson, D. I. Jones, L. Samuelsson Comments: 4 pagers, RevTeX, 3 eps figures Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)

We estimate the maximal deformation that can be sustained by a rotating neutron star with a crystalline colour superconducting quark core. Our results suggest that current gravitational-wave data from LIGO may already be constraining the relevant QCD parameters. We discuss the uncertainties associated with our simple model and how it can be improved in the future.

Replacements for Fri, 24 Aug 07

0 abstracts or titles contain neutron star, magnetar or pulsar


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4 abstracts or titles contain neutron star, magnetar or pulsar


[7]  arXiv:0708.3275 [ps, pdf, other]
Title: $XMM$ observation of 1RXS J180431.1-273932: a new M-type X-ray binary with a 494 s-pulse period neutron star? Authors: A. A. Nucita, S. Carpano, M. Guainazzi Comments: in press on A&A Subjects: Astrophysics (astro-ph)

Low-mass X-ray binaries are binary systems composed of a compact object and a low-mass star. Recently, a new class of these systems, known as symbiotic $X$-ray binaries (with a neutron star with a M-type giant companion), has been discovered. Here, we present long-duration ${\it XMM}$ observations of the source 1RXS J180431.1-273932. Temporal and spectral analysis of the source was performed along with a search for an optical counterpart. We used a Lomb-Scargle periodogram analysis for the period search and evaluated the confidence level using Monte-Carlo simulations. The source is characterized by regular pulses so that it is most likely a neutron star. A modulation of $494.1\pm0.2$ s (3$\sigma$ error) was found with a confidence level of $>$99%. Evidence of variability is also present, since the data show a rate of change in the signal of $\sim -7.7\times 10^{-4}$ counts s$^{-1}$ hr$^{-1}$. A longer observation will be necessary in order to determine if the source shows any periodic behavior. The spectrum can be described by a power law with photon index $\Gamma\sim 1$ and a Gaussian line at 6.6 keV. The X-ray flux in the 0.2--10 keV energy band is $5.4\times 10^{-12}$ erg s$^{-1}$ cm$^{-2}$. The identification of an optical counterpart (possibly an M6III red-giant star with an apparent visual magnitude of $\simeq 17.6$) allows a conservative distance of $\sim 10$ kpc to be estimated. Other possibilities are also discussed. Once the distance was estimated, we got an $X$-ray luminosity of $L_X\ut<6\times 10^{34}$ erg s$^{-1}$, which is consistent with the typical $X$-ray luminosity of a symbiotic LMXB system.

[12]  arXiv:0708.3330 [ps, pdf, other]
Title: Swift/XRT monitoring of five orbital cycles of LSI +61 303 Authors: P. Esposito, P. A. Caraveo, A. Pellizzoni, A. De Luca, N. Gehrels, M. A. Marelli Comments: Accepted for publication in Astronomy and Astrophysics Subjects: Astrophysics (astro-ph)

LSI +61 303 is one of the most interesting high-mass X-ray binaries owing to its spatially resolved radio emission and its TeV emission, generally attributed to non-thermal particles in an accretion-powered relativistic jet or in the termination shock of the relativistic wind of a young pulsar. Also, the nature of the compact object is still debated. Only LS 5039 and PSR B1259-63 (which hosts a non-accreting millisecond pulsar) have similar characteristics. We study the X-ray emission from LSI +61 303 covering both short-term and orbital variability. We also investigate the source spectral properties in the soft X-ray (0.3-10 keV) energy range. 25 snapshot observations of LSI +61 303 have been collected in 2006 with the XRT instrument on-board the Swift satellite over a period of four months, corresponding to about five orbital cycles. Since individual data sets have too few counts for a meaningful spectral analysis, we extracted a cumulative spectrum. The count rate folded at the orbital phase shows a clear modulation pattern at the 26.5 days period and suggests that the X-ray peak occurs around phase 0.65. Moreover, the X-ray emission appears to be variable on a timescale of ~1 ks. The cumulative spectrum is well described by an absorbed power-law model, with hydrogen column density Nh=(5.7+/-0.3)E+21 cm^-2 and photon index 1.78+/-0.05. No accretion disk signatures, such as an iron line, are found in the spectrum.

[14]  arXiv:0708.3343 [pdf]
Title: Thermal gravitational waves Authors: C. Sivaram (1), Kenath Arun (2) ((1) Indian Institute of astrophysics; (2) Christ Junior College) Comments: 20 pages, 57 equations Subjects: Astrophysics (astro-ph)

There is a lot of current interest in sources of gravitational waves and active ongoing projects to detect such radiation, such as the LIGO project. These are long wavelength, low frequency gravitational waves. LISA would be sensitive to much longer wavelengths and lower fluxes. However compact stellar objects can generate high frequency thermal gravitational radiation, which in the case of hot neutron stars can be high. Also white dwarfs and main-sequence stars can generate such radiation from plasma-Coulomb collisions. Again gamma ray bursts and relativistic jets could also be sources of such radiation. Terminal stages of evaporating black holes could also generate high frequency gravitational radiation. A comparative study is made of the thermal gravitational wave emission from all of the above sources, and the background flux is estimated. The earliest phases of the universe close to the Planck scale would also leave remnant thermal gravitational waves. The integrated thermal gravitational flux as the universe expands is also estimated and compared with that from all the discrete sources discussed above. Possible schemes to detect such sources of high frequency thermal gravitational radiation are discussed and the physical principles involved are elaborated.

[18]  arXiv:0708.3372 [ps, pdf, other]
Title: Delayed neutrino-driven supernova explosions aided by the standing accretion-shock instability Authors: A. Marek, H.-Th. Janka (MPI for Astrophysics, Garching) Comments: 22 pages, 13 figures, 39 eps files; submitted to ApJ; high-resolution images can be obtained upon request Subjects: Astrophysics (astro-ph)

We present results of 2D hydrodynamic simulations of stellar core collapse, which confirm that the neutrino-heating mechanism remains viable for the explosion of a wider mass range of supernova progenitors. We used an energy-dependent treatment of the neutrino transport based on the ray-by-ray plus approximation, in which the number, energy, and momentum equations are closed with a variable Eddington factor obtained by iteratively solving a model Boltzmann equation. We focus here on the evolution of a 15 Msun progenitor and show that shock revival and most likely an explosion are initiated at about 600 ms post bounce, powered by neutrino energy deposition. Similar to previous findings for an 11.2 Msun star, but significantly later, the onset of the explosion is fostered by the standing accretion shock instability (SASI). This instability exhibits highest growth rates for the dipole and quadrupole modes, which lead to large-amplitude bipolar shock oscillations and push the shock to larger radii, thus increasing the time accreted matter is exposed to neutrino heating in the gain layer. Therefore also convective overturn behind the shock is strengthened. A soft nuclear equation of state that causes a rapid contraction and a smaller radius of the forming neutron star and thus a fast release of gravitational binding energy, seems to be more favorable for an explosion. Rotation has the opposite effect because it leads to a more extended and cooler neutron star and thus lower neutrino luminosities and mean energies and less neutrino heating. Neutron star g-mode oscillations and the acoustic mechanism play no important role in our simulations. (abridged)

Cross-lists for Mon, 27 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[25]  arXiv:0708.3137 (cross-list from hep-ph) [ps, pdf, other]
Title: Recent Developments on Kaon Condensation and Its Astrophysical Implications Authors: Gerald E. Brown, Chang-Hwan Lee, Mannque Rho Comments: 39 pages, latex Subjects: High Energy Physics - Phenomenology (hep-ph); Astrophysics (astro-ph); Nuclear Theory (nucl-th)

We discuss three different ways to arrive at kaon condensation at $n_c\simeq 3 n_0$ where $n_0$ is nuclear matter density: (1) Fluctuating around the $n=0$ vacuum in chiral perturbation theory, (2) fluctuating around $n_{VM}$ near the chiral restoration density $n_\chi$ where the vector manifestation of hidden local symmetry is reached and (3) fluctuating around the Fermi liquid fixed point at $\sim n_0$. We argue that when the critical density $n_c < n_\chi$ is reached in a neutron star, the electrons turn into $K^-$ mesons, which go into an S-wave Bose condensate. This reduces the pressure substantially and the neutron star goes into a black hole. Next we develop the argument that the collapse of a neutron star into a black hole takes place for a star of $M \simeq 1.5\msun$. This means that Supernova 1987A had a black hole as result. We also show that two neutron stars in a binary have to be within 4% of each other in mass, for neutron stars sufficiently massive that they escape helium shell burning. For those that are so light that they do have helium shell burning, after a small correction for this they must be within 4% of each other in mass. Observations support the proximity in mass inside of a neutron star binary. The result of strangeness condensation is that there are $\sim 5$ times more low-mass black-hole, neutron-star binaries than double neutron-star binaries although the former are difficult to observe.

Replacements for Mon, 27 Aug 07

3 abstracts or titles contain neutron star, magnetar or pulsar


[31]  arXiv:astro-ph/0703181 (replaced) [ps, pdf, other]
Title: Pulsed X-ray Emission from Pulsar A in the Double Pulsar System J0737-3039 Authors: S. Chatterjee, B. M. Gaensler, A. Melatos, W. F. Brisken, B. W. Stappers Comments: Accepted by ApJ; 7 pages, 3 figures, emulateapj; small revisions in response to comments Subjects: Astrophysics (astro-ph)
[37]  arXiv:0706.3041 (replaced) [ps, pdf, other]
Title: Population synthesis of radio and gamma-ray millisecond pulsars from the Galactic disk Authors: Sarah A. Story, Peter L. Gonthier, Alice K. Harding Comments: 38 pages, 10 figures, accepted in ApJ - new version Subjects: Astrophysics (astro-ph)
[39]  arXiv:0708.0086 (replaced) [ps, pdf, other]
Title: Neutron star cooling after deep crustal heating in the X-ray transient KS 1731-260 Authors: P. S. Shternin (1), D. G. Yakovlev (1), P. Haensel (2), A. Y. Potekhin (1) ((1) Ioffe Phys.-Tech. Inst., St.-Petersburg; (2) N. Copernicus Astron. Center, Warsaw) Comments: 5 pages, 2 figures, accepted by MNRAS. In v.2, two references added and typos corrected Subjects: Astrophysics (astro-ph)
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Astrophysics authors/titles "new"

8 abstracts or titles contain neutron star, magnetar or pulsar


[2]  arXiv:0708.3395 [ps, pdf, other]
Title: On the Conditions for Neutron-Rich Gamma-Ray Burst Outflows Authors: Brian D. Metzger, Todd A. Thompson, Eliot Quataert Comments: 24 pages, 7 figures, submitted to ApJ Subjects: Astrophysics (astro-ph)

We calculate the structure and neutron content of neutrino-heated MHD winds driven from the surface of newly-formed magnetars (``proto-magnetars'') and from the midplane of hyper-accreting disks, two of the possible central engines for gamma-ray bursts (GRBs) and hyper-energetic supernovae (SNe). Both the surface of proto-magnetars and the midplane of neutrino-cooled accretion flows (NDAFs) are electron degenerate and neutron-rich (neutron-to-proton ratio n/p >> 1). If this substantial free neutron excess is preserved to large radii in ultra-relativistic outflows, several important observational consequences may result. Weak interaction processes, however, can drive n/p to ~1 in the nondegenerate regions that obtain just above the surfaces of NDAFs and proto-magnetars. Our calculations show that mildly relativistic neutron-rich outflows from NDAFs are possible in the presence of a strong poloidal magnetic field. However, we find that neutron-rich winds possess a minimum mass-loss rate that likely precludes simultaneously neutron-rich and ultra-relativistic (Lorentz factor > 100) NDAF winds accompanying a substantial accretion power. In contrast, proto-magnetars are capable of producing neutron-rich long-duration GRB outflows ~10-30 seconds following core bounce for sub-millisecond rotation periods; such outflows would, however, accompany only extremely energetic events, in which the GRB + SN energy budget exceeds ~ 4e52 ergs. Neutron-rich highly relativistic outflows may also be produced during some short-duration GRBs by geometrically thick accretion disks formed from compact object mergers. The implications for r-process nucleosynthesis, optical transients due to non-relativistic neutron-rich winds, and Nickel production in proto-magnetar and NDAF winds are also briefly discussed.

[12]  arXiv:0708.3462 [ps, pdf, other]
Title: Search for pulsed multi-TeV gamma rays from the Crab pulsar using the Tibet-III air shower array Authors: The Tibet AS Gamma Collaboration: M. Amenomori, et al Comments: 4 pages, 3 figures, proceedings of 30th ICRC, International Cosmic Ray Conference 2007, Merida, Yucatan, Mexico, 3-11 July 2007 Subjects: Astrophysics (astro-ph)

We searched for pulsed gamma-ray emissions from the Crab pulsar using data of the Tibet-III air shower array from November 1999 through November 2005. No evidence for the pulsed emissions was found in our analysis. Upper limits at different energies were calculated for a $3 \sigma$ confidence level in the energy range of multi-TeV to several hundred TeV.

[20]  arXiv:0708.3536 [ps, pdf, other]
Title: Suzaku Observations of Hercules X-1 : Measurements of the Two Cyclotron Harmonics Authors: Teruaki Enoto (1), Kazuo Makishima (1 and 2), Yukikatsu Terada (2), Tatehiro Mihara (2), Kazuhiro Nakazawa (1), Tsuyoshi Ueda (1), Tadayasu Dotani (3), Motohide Kokubun (3), Fumiaki Nagase (3), Sachindra Naik (3), Motoko Suzuki (3), Motoki Nakajima (4), Hiromitsu Takahashi (5) ((1) Department of Physics, The University of Tokyo, (2) Cosmic Radiationn Laboratory, The Institute of Physics and Chemical Research (RIKEN), (3) Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), (4) Department of Physics, College of Science and Technology, Nihon University, (5) Department of Physical Science, Hiroshima University) Comments: 22 pages, 10 figures, accepted for publication in PASJ Subjects: Astrophysics (astro-ph)

The accretion-powered pulsar Her X-1 was observed with Suzaku twice in its main-on state, on 2005 October 5-6 and 2006 March 29-30, for a net exposure of 30.5 ks and 34.4 ks, respectively. In the 2005 and 2006 observations, the source was detected at an average 10-30 keV intensity of 290 mCrab and 230 mCrab, respectively. The intrinsic pulse period was measured on both occasions at 1.23776 s by HXD-PIN, after barycentric and binary corrections. The pulse phase-averaged spectra in the energy range above 10 keV are well fitted by ``Negative and Positive power-law times EXponential (NPEX)'' model, multiplied by a fundamental cyclotron resonance scattering feature at ~36 keV which appears very significantly in the HXD-PIN data. The resonance profiles were reproduced successfully by the Lorentzian type scattering cross section, rather than by a Gaussian type alternative. The pulse phase-averaged HXD-GSO data, covering 50-120 keV, are featureless. However, in a differential spectrum between the pulse-decay phase and off-pulse phase, the second harmonic cyclotron resonance was detected in the GSO data at ~73 keV, with a depth of 1.6_-0.7^+0.9. This makes Her X-1 a 6th pulsar with established second harmonic resonance. Implications of these results are briefly discussed.

[26]  arXiv:0708.3566 [ps, pdf, other]
Title: Does Sub-millisecond Pulsar XTE J1739-285 Contain a Low Magnetic Neutron Star or Quark Star ? Authors: C. M. Zhang, H.X. Yin, Y.H. Zhao, Y.C. Wei, X.D. Li Comments: 10 pages, 2 figures, accepted by PASP 2007 Subjects: Astrophysics (astro-ph)

With the possible detection of the fastest spinning nuclear-powered pulsar XTE J1739-285 of frequency 1122 Hz (0.8913 ms), it arouses us to constrain the mass and radius of its central compact object and to imply the stellar matter compositions: neutrons or quarks. Spun-up by the accreting materials to such a high rotating speed, the compact star should have either a small radius or short innermost stable circular orbit. By the empirical relation between the upper kHz quasi-periodic oscillation frequency and star spin frequency, a strong constraint on mass and radius is obtained as 1.51 solar masses and 10.9 km, which excludes most equations of states (EOSs) of normal neutrons and strongly hints the star promisingly to be a strange quark star. Furthermore, the star magnetic field is estimated to be about $4\times10^{7} (G) < B < 10^{9} (G) $, which reconciles with those of millisecond radio pulsars, revealing the clues of the evolution linkage of two types of astrophysical objects.

[30]  arXiv:0708.3597 [ps, pdf, other]
Title: Equilibrium Configurations of Strongly Magnetized Neutron Stars with Realistic Equations of State Authors: Kenta Kiuchi, Kei Kotake Comments: submitted to MNRAS Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc)

We investigate equilibrium sequences of magnetized rotating stars with four kinds of realistic equations of state (EOSs) of SLy (Douchin et al.), FPS (Pandharipande et al.), Shen (Shen et al.), and LS (Lattimer & Swesty). Employing the Tomimura-Eriguchi scheme to construct the equilibrium configurations. we study the basic physical properties of the sequences in the framework of Newton gravity. In addition we newly take into account a general relativistic effect to the magnetized rotating configurations. With these computations, we find that the properties of the Newtonian magnetized stars, e.g., structure of magnetic field, highly depends on the EOSs.
The toroidal magnetic fields concentrate rather near the surface for Shen and LS EOSs than those for SLy and FPS EOSs. The poloidal fields are also affected by the toroidal configurations. Paying attention to the stiffness of the EOSs, we analyze this tendency in detail. In the general relativistic stars, we find that the difference due to the EOSs becomes small because all the employed EOSs become sufficiently stiff for the large maximum density, typically greater than $10^{15}\rm{g} \rm{cm}^{-3}$. The maximum baryon mass of the magnetized stars with axis ratio $q\sim 0.7$ increases about up to twenty percents for that of spherical stars. We furthermore compute equilibrium sequences at finite temperature, which should serve as an initial condition for the hydrodynamic study of newly-born magnetars. Our results suggest that we may obtain information about the EOSs from the observation of the masses of magnetars.

[33]  arXiv:0708.3615 [ps, pdf, other]
Title: Relativistic iron emission lines in neutron star low-mass X-ray binaries as probes of neutron star radii Authors: Edward M. Cackett, Jon M. Miller (Michigan), Sudip Bhattacharyya (NASA/GSFC), Jonathan E. Grindlay (CfA), Jeroen Homan (MIT), Michiel van der Klis (Amsterdam), Tod E. Strohmayer (NASA/GSFC), Rudy Wijnands (Amsterdam) Comments: 5 pages, 3 figures, 3 tables, submitted to ApJL Subjects: Astrophysics (astro-ph)

Using Suzaku observations of three neutron star low-mass X-ray binaries (Ser X-1, 4U 1820-30 and GX 349+2) we have found broad, asymmetric, relativistic Fe K emission lines in all three objects. These Fe K lines can be well fit by a model for lines from a relativistic accretion disk ('diskline'), allowing a measurement of the inner radius of the accretion disk, and hence an upper limit on the neutron star radius. These upper limits correspond to 14.5 - 16.5 km for a 1.4 M(solar) neutron star. The inner disk radii we measure with Fe K lines are in good agreement with the inner disk radii implied by kHz QPOs observed in both 4U 1820-30 and GX 349+2, supporting the inner disk nature of kHz QPOs. Additionally, the Fe K lines observed in these neutron stars are narrower than those in the black holes that are thought to be close to maximally spinning, as one would expect if inferences for spin are robust.

[38]  arXiv:0708.3648 [ps, pdf, other]
Title: Evidence of a Broad Relativistic Iron Line from the Neutron Star Low-Mass X-ray Binary Serpens X-1 Authors: Sudip Bhattacharyya (NASA/GSFC, UMCP), Tod E. Strohmayer (NASA/GSFC) Comments: 13 pages, 2 tables, 2 figures, published in ApJ Letters Journal-ref: Astrophys.J. 664 (2007) L103-L106 Subjects: Astrophysics (astro-ph)

We report on an analysis of XMM-Newton data from the neutron star low mass X-ray binary (LMXB) Serpens X-1 (Ser X-1). Spectral analysis of EPIC PN data indicates that the previously known broad iron K$\alpha$ emission line from this source has a significantly skewed structure with a moderately extended red wing. The asymmetric shape of the line is well described with the laor and diskline models in XSPEC and strongly supports an inner accretion disk origin of the line. To our knowledge this is the first strong evidence of a relativistic line in a neutron star LMXB. This finding suggests that the broad lines seen in other neutron star LMXBs likely originate from the inner disk as well. Detailed study of such lines opens up a new way to probe neutron star parameters and their strong gravitational fields. The red wing of the iron line from Ser X-1 is not as broad as that observed from some black hole systems. This is not unreasonable for a neutron star system, as the accretion disk has to terminate at or before the hard stellar surface. Finally, the inferred source inclination angle in the approximate range 40 degree to 60 degree is consistent with the lack of dips and eclipses from Ser X-1.

[39]  arXiv:0708.3653 [ps, pdf, other]
Title: Thermonuclear Flame Spreading on Rapidly Spinning Neutron Stars: Indications of the Coriolis Force? Authors: Sudip Bhattacharyya (NASA/GSFC, UMCP), Tod E. Strohmayer (NASA/GSFC) Comments: 8 pages, 4 figures, accepted for publication in ApJ Letters Subjects: Astrophysics (astro-ph)

Millisecond period brightness oscillations during the intensity rise of thermonuclear X-ray bursts are likely caused by an azimuthally asymmetric, expanding burning region on the stellar surface. The time evolution of the oscillation amplitude during the intensity rise encodes information on how the thermonuclear flames spread across the stellar surface. This process depends on properties of the accreted burning layer, surface fluid motions, and the surface magnetic field structure, and thus can provide insight into these stellar properties. We present two examples of bursts from different sources that show a decrease in oscillation amplitude during the intensity rise. Using theoretical modeling, we demonstrate that the observed amplitude evolution of these bursts is not well described by a uniformly expanding circular burning region. We further show that by including in our model the salient aspects of the Coriolis force (as described by Spitkovsky, Levin, and Ushomirsky) we can qualitatively reproduce the observed evolution curves. Our modeling shows that the evolutionary structure of burst oscillation amplitude is sensitive to the nature of flame spreading, while the actual amplitude values can be very useful to constrain some source parameters.

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[25]  arXiv:0708.3816 [ps, pdf, other]
Title: Constraining the equation of state of supra-nuclear dense matter from XMM-Newton observations of neutron stars in globular clusters Authors: N. A. Webb, D. Barret Comments: 10 pages, 8 figures, accepted to be published in The Astrophysical Journal Subjects: Astrophysics (astro-ph)

We report on the detailed modelling of the X-ray spectra of three likely neutron stars. The neutron stars, observed with XMM-Newton are found in three quiescent X-ray binaries in the globular clusters: omega Cen, M 13 and NGC 2808. Whether they are accreting at very low rates or radiating energy from an accretion heated core, their X-ray spectra are expected to be those of a hydrogen atmosphere. We use and compare publicly available hydrogen atmosphere models, with constant and varying surface gravities to constrain the masses and radii of the neutron stars. Thanks to the high XMM-Newton throughput, and the accurate distances available for these clusters, using the latest science analysis software release and calibration of the XMM-Newton EPIC cameras, we derive the most stringent constraints on the masses and radii of the neutron stars obtained to date from these systems. A comparison of the models indicate that previously used hydrogen atmosphere models (assuming constant surface gravity) tend to underestimate the mass and overestimate the radius of neutron stars. Our data constrain the allowed equations of state to those which concern normal nucleonic matter and one possible strange quark matter model, thus constraining radii to be from 8 km and masses up to 2.4 M$_\odot$.

Cross-lists for Wed, 29 Aug 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Wed, 29 Aug 07

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[45]  arXiv:0706.1511 (replaced) [ps, pdf, other]
Title: Pulsar Kicks With Modified URCA and Electrons in Landau Levels Authors: Ernest M. Henley (Department of Physics, University of Washington), Mikkel B. Johnson (Los Alamos National Laboratory), Leonard S. Kisslinger (Department of Physics, Carnegie-Mellon University) Comments: 10 pages, 6 figures Subjects: Astrophysics (astro-ph)
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[1]  arXiv:0708.3848 [ps, pdf, other]
Title: The Second Stars Authors: Falk Herwig Comments: Biermann award 2004 lecture, AG meeting, Prague Journal-ref: 2005RvMA...18...21 Subjects: Astrophysics (astro-ph)

The ejecta of the first probably very massive stars polluted the Big Bang primordial element mix with the first heavier elements. The resulting ultra metal-poor abundance distribution provided the initial conditions for the second stars of a wide range of initial masses reaching down to intermediate and low masses. The importance of these second stars for understanding the origin of the elements in the early universe are manifold. While the massive first stars have long vanished the second stars are still around and currently observed. They are the carriers of the information about the first stars, but they are also capable of nuclear production themselves. For example, in order to use ultra or extremely metal-poor stars as a probe for the r-process in the early universe a reliable model of the s-process in the second stars is needed. Eventually, the second stars may provide us with important clues on questions ranging from structure formation to how the stars actually make the elements, not only in the early but also in the present universe. In particular the C-rich extremely metal-poor stars, most of which show the s-process signature, are thought to be associated with chemical yields from the evolved giant phase of intermediate mass stars. Models of such AGB stars at extremely low metallicity now exist, and comparison with observation show important discrepancies, for example with regard to the synthesis of nitrogen. This may hint at burning and mixing aspects of extremely metal-poor evolved stars that are not yet included in the standard picture of evolution, as for example the hydrogen-ingestion flash. The second stars of intermediate mass may have also played an important role in the formation of heavy elements that form through slow neutron capture reaction chains (s-process). Comparison of models with observations reveal which aspects of the physics input and assumptions need to be improved. The s-process is a particularly useful diagnostic tool for probing the physical processes that are responsible for the creation of elements in stars, like for example rotation. As new observational techniques and strategies continue to penetrate the field, for example the multi-object spectroscopy, or the future spectroscopic surveys, the extremely metal-poor stars will play an increasingly important role to address some of the most fundamental and challenging, current questions of astronomy.

[9]  arXiv:0708.3863 [ps, pdf, other]
Title: Condensed Surfaces of Magnetic Neutron Stars, Thermal Surface Emission, and Particle Acceleration Above Pulsar Polar Caps Authors: Zach Medin, Dong Lai Comments: 25 pages, 11 figures, submitted to MNRAS Subjects: Astrophysics (astro-ph)

For sufficiently strong magnetic fields and/or low temperatures, the neutron star surface may be in a condensed state with little gas or plasma above it. Such surface condensation can significantly affect the thermal emission from isolated neutron stars, and may lead to the formation of a charge-depleted acceleration zone ("vacuum gap") in the magnetosphere above the stellar polar cap. Using the latest results on the cohesive property of magnetic condensed matter, we quantitatively determine the conditions for surface condensation and vacuum gap formation in magnetic neutron stars. We find that condensation can occur if the thermal energy kT of the neutron star surface is less than about 8% of its cohesive energy Q_s, and that a vacuum gap can form if the neutron star's rotation axis and magnetic moment point in opposite directions and kT is less than about 4% of Q_s. Thus, vacuum gap accelerators may exist for some neutron stars. Motivated by this result, we also study the physics of pair cascades in the vacuum gap model for photon emission by accelerating electrons and positrons due to both curvature radiation and resonant/nonresonant inverse Compton scattering. Our calculations of the condition of cascade-induced vacuum breakdown and the related pulsar death line/boundary generalize previous works to the superstrong field regime. We find that inverse Compton scatterings do not produce a sufficient number of high energy photons in the gap and thus do not lead to pair cascades for most neutron star parameters. We discuss the implications of our results for the recent observations of neutron star thermal radiation as well as for the detection/non-detection of radio emission from high-B pulsars and magnetars.

[30]  arXiv:0708.3996 [ps, pdf, other]
Title: Models of crustal heating in accreting neutron stars Authors: P. Haensel, J.L. Zdunik Comments: 8 pages, 5 figures, Submitted to A&A Subjects: Astrophysics (astro-ph)

Heating associated with non-equilibrium nuclear reactions in accreting neutron-star crusts is reconsidered, taking into account suppression of neutrino losses demonstrated recently by Gupta et al. Two initial compositions of the nuclear burning ashes, A=56 and A=106, are considered. Dependence of the integrated crustal heating on uncertainties plaguing pycnonuclear reaction models is studied.
One-component plasma approximation is used, with compressible liquid-drop model of Mackie and Baym to describe nuclei. Evolution of a crust shell is followed from 10^8 g/cm^3 to 10^(13.6) g/cm^3
The integrated heating in the outer crust agrees nicely with results of self-considtent multicomponent plasma simulations of Gupta et al.; their results fall between our curves obtained for A=56 and A=106. Total crustal heat per one accreted nucleon ranges between 1.5 MeV to 1.9 MeV for A=106 and A=56, respectively. The value of total crustal heat per nucleon depends weakly on the presence of pycnonuclear reactions at densities 10^(12)-10^(13) g/cm^3. Remarkable insensitivity of the total crustal heat on the details of the distribution of nuclear processes in accreted crust is explained.

Cross-lists for Thu, 30 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[33]  arXiv:0708.3818 (cross-list from gr-qc) [pdf, other]
Title: All-sky search for periodic gravitational waves in LIGO S4 data Authors: LIGO Scientific Collaboration: B. Abbott, et al Comments: 39 pages, 41 figures Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)

We report on an all-sky search with the LIGO detectors for periodic gravitational waves in the frequency range 50-1000 Hz and with the frequency's time derivative in the range -1.0E-8 Hz/s to zero. Data from the fourth LIGO science run (S4) have been used in this search. Three different semi-coherent methods of transforming and summing strain power from Short Fourier Transforms (SFTs) of the calibrated data have been used. The first, known as "StackSlide", averages normalized power from each SFT. A "weighted Hough" scheme is also developed and used, and which also allows for a multi-interferometer search. The third method, known as "PowerFlux", is a variant of the StackSlide method in which the power is weighted before summing. In both the weighted Hough and PowerFlux methods, the weights are chosen according to the noise and detector antenna-pattern to maximize the signal-to-noise ratio. The respective advantages and disadvantages of these methods are discussed. Observing no evidence of periodic gravitational radiation, we report upper limits; we interpret these as limits on this radiation from isolated rotating neutron stars. The best population-based upper limit with 95% confidence on the gravitational-wave strain amplitude, found for simulated sources distributed isotropically across the sky and with isotropically distributed spin-axes, is 4.28E-24 (near 140 Hz). Strict upper limits are also obtained for small patches on the sky for best-case and worst-case inclinations of the spin axes.

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[19]  arXiv:0708.4128 [ps, pdf, other]
Title: On radio emission of the Geminga pulsar and RBS 1223 at the frequency of 111 MHz Authors: Alexander A. Ershov (Pushchino Radio Astronomy Observatory, ASC, LPI) Comments: 4 pages, 3 figures Subjects: Astrophysics (astro-ph)

I have searched for pulsed radio emission from the Geminga pulsar and for the nearby isolated neutron star 1RX J1308.6+2127 (RBS 1223) at the frequency of 111 MHz. No pulsed signals were detected from these sources. Upper limits for mean flux density are 0.4 - 4 mJy for the Geminga pulsar and 1.5 - 15 mJy for RBS 1223 depending on assumed duty cycle (.05 - .5) of the pulsars.

[26]  arXiv:0708.4163 [ps, pdf, other]
Title: Chemical evolution of neutron capture elements in our Galaxy and in the dwarf spheroidal galaxies of the Local Group Authors: Gabriele Cescutti (Astronomy Department, Trieste University) Comments: 182 pages, 74 figures, PhD Thesis. Supervisor: Francesca Matteucci. High quality figures upon request Subjects: Astrophysics (astro-ph)

By adopting a chemical evolution model for the Milky Way already reproducing the evolution of several chemical elements, we compare our theoretical results with accurate and new stellar data of neutron capture elements and we are able to impose strong constraints on the nucleosynthesis of the studied elements. We can suggest the stellar sites of production for each element. In particular, the r-process component of each element (if any) is produced in the mass range from 10 to 30 Msun, whereas the s-process component arises from stars in the range from 1 to 3 Msun. Using the same chemical evolution model, extended to different galactocentric distances, we obtain results on the radial gradients of the Milky Way. We compare the results of the model not only for the neutron capture elements but also for alpha-elements and iron peak elements with new data of Cepheids stars. We give a possible explanation to the considerable scatter of neutron capture elements observed in low metallicity stars in the solar vicinity, compared to the small star to star scatter observed for the alpha-elements. In fact, we have developed a stochastic chemical evolution model, in which the main assumption is a random formation of new stars, subject to the condition that the cumulative mass distribution follows a given initial mass function. With our model we are able to reproduce the different features of neutron capture elements and alpha-elements. Finally, we test the prescriptions for neutron capture elements also for the dwarf spheroidal galaxies of the Local Group. We predict that the chemical evolution of these elements in dwarf spheroidal galaxies is different from the evolution in the solar vicinity and indicates that dwarf spheroidal galaxies (we see nowadays) cannot be the building blocks of our Galaxy.

Cross-lists for Fri, 31 Aug 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[37]  arXiv:0708.3436 (cross-list from nucl-th) [ps, pdf, other]
Title: High-density Skyrmion matter and Neutron Stars Authors: Prashanth Jaikumar (IMSc, Chennai), Manjari Bagchi (TIFR, Mumbai), Rachid Ouyed (U. Calgary) Comments: 9 pages, 5 figures Subjects: Nuclear Theory (nucl-th); Astrophysics (astro-ph)

We examine neutron star properties based on a model of dense matter composed of B=1 skyrmions immersed in a mesonic mean field background. The model realizes spontaneous chiral symmetry breaking non-linearly and incorporates scale-breaking of QCD through a dilaton VEV that also affects the mean fields. Quartic self-interactions among the vector mesons are introduced on grounds of naturalness in the corresponding effective field theory. Within a plausible range of the quartic couplings, the model generates neutron star masses and radii that are consistent with a preponderance of observational constraints, including recent ones that point to the existence of relatively massive neutron stars with M~2.0 Msun with radii R~12-14 km. If the existence of neutron stars with such dimensions is confirmed, matter at supra-nuclear density is stiffer than extrapolations of most microscopic models suggest.

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[6]  arXiv:0708.4251 [ps, pdf, other]
Title: Evidence for alignment of the rotation and velocity vectors in pulsars. II. Further data and emission heights Authors: Simon Johnston, M. Kramer, A. Karastergiou, G. Hobbs, S. Ord, J. Wallman Comments: Accepted by MNRAS. 14 pages Subjects: Astrophysics (astro-ph)

We have conducted observations of 22 pulsars at frequencies of 0.7, 1.4 and 3.1 GHz and present their polarization profiles. The observations were carried out for two main purposes. First we compare the orientation of the spin and velocity vectors to verify the proposed alignment of these vectors by Johnston et al. (2005). We find, for the 14 pulsars for which we were able to determine both vectors, that 7 are plausibly aligned, a fraction which is lower than, but consistent with, earlier measurements. Secondly, we use profiles obtained simultaneously at widely spaced frequencies to compute the radio emission heights. We find, similar to other workers in the field, that radiation from the centre of the profile originates from lower in the magnetosphere than the radiation from the outer parts of the profile.

[24]  arXiv:0708.4345 [ps, pdf, other]
Title: Boiling of nuclear liquid in core-collapse supernova explosions Authors: Peter Fomin, Dmytro Iakubovskyi, Yuri Shtanov Comments: 13 pages, section V is revised Subjects: Astrophysics (astro-ph)

We investigate the possibility of boiling instability of nuclear liquid in the inner core of the proto-neutron star formed in the core collapse of a type II supernova. We derive a simple criterion for boiling to occur. Using this criterion for one of best described equations of state of supernova matter, we find that boiling is quite possible under the conditions realized inside the proto-neutron star. We discuss consequences of this process such as the increase of heat transfer rate and pressure in the boiling region. We expect that taking this effect into account in the conventional neutrino-driven delayed-shock mechanism of type II supernova explosions can increase the explosion energy and reduce the mass of the neutron-star remnant.

Cross-lists for Mon, 3 Sep 07

0 abstracts or titles contain neutron star, magnetar or pulsar


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[10]  arXiv:0709.0061 [ps, pdf, other]
Title: GRB060602B = Swift J1749.4-2807: an unusual transiently accreting neutron-star X-ray binary Authors: Rudy Wijnands, Evert Rol, Ed M. Cackett, Rhaana L.C. Starling, Ron A. Remillard Comments: Submitted to MNRAS Subjects: Astrophysics (astro-ph)

We present an analysis of the Swift BAT and XRT data of GRB060602B, which is most likely an accreting neutron star in a binary system and not a gamma-ray burst. Our analysis shows that the BAT burst spectrum is consistent with a thermonuclear flash (type-I X-ray burst) from the surface of an accreting neutron star in a binary system. The X-ray binary nature is further confirmed by the report of a detection of a faint point source at the position of the XRT counterpart of the burst in archival XMM-Newton data approximately 6 years before the burst and in more recent XMM-Newton data obtained at the end of September 2006 (nearly 4 months after the burst). Since the source is very likely not a gamma-ray burst, we rename the source Swift J1749.4-2807, based on the Swift/BAT discovery coordinates. Using the BAT data of the type-I X-ray burst we determined that the source is at most at a distance of 6.7+-1.3 kpc. For a transiently accreting X-ray binary its soft X-ray behaviour is atypical: its 2-10 keV X-ray luminosity (as measured using the Swift/XRT data) decreased by nearly 3 orders of magnitude in about 1 day, much faster than what is usually seen for X-ray transients. If the earlier phases of the outburst also evolved this rapidly, then many similar systems might remain undiscovered because the X-rays are difficult to detect and the type-I X-ray bursts might be missed by all sky surveying instruments. This source might be part of a class of very-fast transient low-mass X-ray binary systems of which there may be a significant population in our Galaxy.

[24]  arXiv:0709.0135 [ps, pdf, other]
Title: An improved solar wind electron-density model for pulsar timing Authors: X. P. You, G. B. Hobbs, W. A. Coles, R. N. Manchester, J. L. Han Comments: Accepted by ApJ, 13 pages, 4 figures Subjects: Astrophysics (astro-ph)

Variations in the solar wind density introduce variable delays into pulsar timing observations. Current pulsar timing analysis programs only implement simple models of the solar wind, which not only limit the timing accuracy, but can also affect measurements of pulsar rotational, astrometric and orbital parameters. We describe a new model of the solar wind electron density content which uses observations from the Wilcox Solar Observatory of the solar magnetic field. We have implemented this model into the tempo2 pulsar timing package. We show that this model is more accurate than previous models and that these corrections are necessary for high precision pulsar timing applications.

[30]  arXiv:0709.0168 [ps, pdf, other]
Title: Gravitational waves from 3D MHD core collapse simulations Authors: S.Scheidegger, T.Fischer, M.Liebendoerfer Comments: 9 pages, 6 figures, submitted to A&A Subjects: Astrophysics (astro-ph)

We present the gravitational wave analysis from rotating (model s15g) and nearly non-rotating (model s15h) 3D MHD core collapse supernova simulations at bounce and the first couple of ten milliseconds afterwards. The simulations are launched from realistic progenitor stars and include the most important general relativistic effects. The input physics uses the Lattimer-Swesty equation of state for hot, dense matter and a neutrino parametrisation scheme that is accurate until the first few ms after bounce. The 3D simulations allow us to study features already known from 2D simulations as well as non-axisymmetric effects. We find the generic type I signals at bounce with maximum amplitudes of 566 cm (s15g) and 11 cm (s15h). The corresponding narrow-band spectra peak around 921 Hz (s15g) and 911 Hz (s15h), respectively. Additionally, 'burst-with-memory' signals, caused by convective instabilities in the protoneutron star are present in later stages of the simulation. Beside these results we found that rotation plays an important role in the damping of the equatorial signal in the convective phase. Both core collapse simulations indicate that corresponding events in our Galaxy would be detectable by the LIGO detector.

[43]  arXiv:0709.0214 [ps, pdf, other]
Title: Thermal Evolution of Strange Stars Authors: Zhou Xia, Wang Lingzhi, Zhou Aizhi Comments: 13 pages, 2 figures Subjects: Astrophysics (astro-ph)

We investigated the thermal evolution of rotating strange stars with the deconfinement heating due to magnetic braking. We consider the stars consisting of either normal quark matter or color-flavor-locked phase. Combining deconfinement heating with magnetic field decay, we find that the thermal evolution curves are identical to pulsar data.

[45]  arXiv:0709.0227 [ps, pdf, other]
Title: Importance of constraining dense matter equation of state in pulsar astrophysics Authors: Manjari Bagchi Comments: 8 pages, 2 figures, 1 table Subjects: Astrophysics (astro-ph)

Radio pulsars are believed to be neutron stars or strange stars. There are a number of Equations of State for neutron matter and strange quark matter. The surface magnetic field of a pulsar, estimated by equating the spin down luminosity with the dipole radiation power depends on the choice of the Equation of State and differ significantly from the canonical value.

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[24]  arXiv:0709.0403 [ps, pdf, other]
Title: Unstable g-modes in Proto-Neutron Stars Authors: V. Ferrari, L. Gualtieri, J. A. Pons Comments: 10 pages, 3 figures, to appear on Class. Quant. Grav Subjects: Astrophysics (astro-ph)

In this article we study the possibility that, due to non-linear couplings, unstable g-modes associated to convective motions excite stable oscillating g-modes. This problem is of particular interest, since gravitational waves emitted by a newly born proto-neutron star pulsating in its stable g-modes would be in the bandwidth of VIRGO and LIGO. Our results indicate that nonlinear saturation of unstable modes occurs at relatively low amplitudes, and therefore, even if there exists a coupling between stable and unstable modes, it does not seem to be sufficiently effective to explain, alone, the excitation of the oscillating g-modes found in hydrodynamical simulations.

[27]  arXiv:0709.0417 [ps, pdf, other]
Title: Nucleosynthesis in the Early Galaxy Authors: F. Montes, T. C. Beers, J. Cowan, T. Elliot, K. Farouqi, R. Gallino, M. Heil, K.-L. Kratz, B. Pfeiffer, M. Pignatari, H. Schatz Comments: 28 pages, 7 Postscript figures. To be published in The Astrophysical Journal Subjects: Astrophysics (astro-ph)

Recent observations of r-process-enriched metal-poor star abundances reveal a non-uniform abundance pattern for elements $Z\leq47$. Based on non-correlation trends between elemental abundances as a function of Eu-richness in a large sample of metal-poor stars, it is shown that the mixing of a consistent and robust light element primary process (LEPP) and the r-process pattern found in r-II metal-poor stars explains such apparent non-uniformity. Furthermore, we derive the abundance pattern of the LEPP from observation and show that it is consistent with a missing component in the solar abundances when using a recent s-process model. As the astrophysical site of the LEPP is not known, we explore the possibility of a neutron capture process within a site-independent approach. It is suggested that scenarios with neutron densities $n_{n}\leq10^{13}$ $cm^{-3}$ or in the range $n_{n}\geq10^{24}$ $cm^{-3}$ best explain the observations.

[47]  arXiv:0709.0501 [ps, pdf, other]
Title: Neutrino-Induced Gamma-Ray Emission from Supernovae Authors: Yu Lu, Yong-Zhong Qian Comments: 28 pages, 9 figures, submitted to Physical Review D Subjects: Astrophysics (astro-ph)

During a core-collapse supernova, absorption of anti-nu_e emitted from the proto-neutron star by protons in the hydrogen envelope produces neutrons and positrons. Neutron capture on protons and positron annihilation then produce gamma rays of 2.22 and 0.511 MeV, respectively. We calculate the fluxes of these gamma rays expected from a supernova with an 11 M_sun progenitor. The flux from neutron capture on protons exponentially decays on a timescale of 564 s, which is determined by neutron decay and capture on protons and 3He nuclei. The peak flux is 2.38x10^{-7}/cm^2/s for a supernova at a distance of 1 kpc. In contrast, the gamma-ray flux from positron annihilation follows the time evolution of the anti-nu_e luminosity and lasts for ~10 s. The peak flux in this case is 6.8x10^{-5}/cm^2/s for a supernova at a distance of 1 kpc. Detection of the above gamma-ray fluxes is beyond the capability of current instruments, and perhaps even those planned for the near future. However, if such fluxes can be detected, they not only constitute a new kind of signals that occur during the gap of several hours between the neutrino signals and the optical display of a supernova, but may also provide a useful probe of the conditions in the surface layers of the supernova progenitor.

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Replacements for Wed, 5 Sep 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[57]  arXiv:astro-ph/0611014 (replaced) [ps, pdf, other]
Title: Heat blanketing envelopes and thermal radiation of strongly magnetized neutron stars Authors: A. Y. Potekhin (1), G. Chabrier (2), D. G. Yakovlev (1) ((1) Ioffe Institute, St. Petersburg; (2) CRAL, ENS-Lyon) Comments: 9 pages, 7 figures. Proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface" (April 24-28, 2006, London, UK). In v3, misprints concerning relativistic corrections in Eqs.(2), (4), (5), and boundary conditions are corrected Journal-ref: Astrophys. Space Sci. 308 (2007) 353-361 Subjects: Astrophysics (astro-ph)
[65]  arXiv:0707.1759 (replaced) [ps, pdf, other]
Title: Torsional shear oscillations in the neutron star crust driven by restoring force of elastic stresses Authors: S. I. Bastrukov, H.-K. Chang, J. Takata, G.-T. Chen, I. V. Molodtsova Comments: 18 pages, 7 figures, MNRAS, accepted Subjects: Astrophysics (astro-ph)
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[11]  arXiv:0709.0543 [ps, pdf, other]
Title: Stellar Wind Accretion in GX301-2: Evidence for a High-density Stream Authors: D.A. Leahy, M.Kostka Comments: 19 pages, 6 figures Subjects: Astrophysics (astro-ph)

The X-ray binary system GX301-2 consists of a neutron star in an eccentric orbit accreting from the massive early-type star WRAY 977. It has previously been shown that the X-ray orbital light curve is consistent with existence of a gas stream flowing out from Wray 977 in addition to its strong stellar wind. Here, X-ray monitoring observations by the Rossi X-ray Timing Explorer (RXTE)/ All-Sky-Monitor (ASM) and pointed observations by the RXTE/ Proportional Counter Array (PCA) over the past decade are analyzed. We analyze both the flux and column density dependence on orbital phase. The wind and stream dynamics are calculated for various system inclinations, companion rotation rates and wind velocities, as well as parametrized by the stream width and density. These calculations are used as inputs to determine both the expected accretion luminosity and the column density along the line-of-sight to the neutron star. The model luminosity and column density are compared to observed flux and column density vs. orbital phase, to constrain the properties of the stellar wind and the gas stream. We find that the change between bright and medium intensity levels is primarily due to decreased mass loss in the stellar wind, but the change between medium and dim intensity levels is primarily due to decreased stream density. The mass-loss rate in the stream exceeds that in the stellar wind by a factor of 2.5. The quality of the model fits is significantly better for lower inclinations, favoring a mass for WRAY 977 of 53 to 62 Msun.

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Cross-lists for Fri, 7 Sep 07

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[24]  arXiv:0709.1043 [ps, pdf, other]
Title: Signals of the QCD Phase Transition in the Heavens Authors: J. Schaffner-Bielich Comments: 13 pages, three figures, invited talk given at 4th international workshop on the 'Critical Point and Onset of Deconfinement' (CPOD2007), GSI Darmstadt, Germany, July 9-13, 2007 GSI Darmstadt,Germany Subjects: Astrophysics (astro-ph)

The modern phase diagram of strongly interacting matter reveals a rich structure at high-densities due to phase transitions related to the chiral symmetry of quantum chromodynamics (QCD) and the phenomenon of color superconductivity. These exotic phases have significant impacts on high-density astrophysics as the properties of neutron stars and the evolution of astrophysical systems as proto-neutron stars, core-collapse supernovae and neutron star mergers. Most recent pulsar mass measurements and constraints on neutron star radii are critically discussed. Astrophysical signals for exotic matter and phase transitions in high-density matter proposed recently in the literature are outlined. A strong first order phase transition leads to the emergence of a third family of compact stars besides white dwarfs and neutron stars. The different microphysics of quark matter results in an enhanced r-mode stability window for rotating compact stars compared to normal neutron stars. Future telescope and satellite data will allow to extract signals from phase transitions in dense matter in the heavens and will reveal properties of the phases of dense QCD. Spectral line profiles out of x-ray bursts will determine the mass-radius ratio of compact stars. Gravitational wave patterns from collapsing neutron stars or neutron star mergers will even be able to constrain the stiffness of the quark matter equation of state. Future astrophysical data can therefore provide a crucial cross-check to the exploration of the QCD phase diagram with the heavy-ion program of the CBM detector at the FAIR facility.

Cross-lists for Mon, 10 Sep 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Mon, 10 Sep 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[57]  arXiv:astro-ph/0703346 (replaced) [pdf, other]
Title: The Birthrate of Magnetars Authors: Ramandeep Gill, Jeremy Heyl (University of British Columbia) Comments: 8 pages, 3 figures, changes to reflect version accepted by Monthly Notices of the Royal Astronomical Society Subjects: Astrophysics (astro-ph)
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[20]  arXiv:0709.1224 [ps, pdf, other]
Title: Magnetized strange quark matter and magnetized strange quark stars Authors: R. Gonzalez Felipe, A. Perez Martinez, H. Perez Rojas, M. Orsaria Comments: 9 pages, 9 figures Subjects: Astrophysics (astro-ph)

Strange quark matter could be found in the core of neutron stars or forming strange quark stars. As is well known, these astrophysical objects are endowed with strong magnetic fields which affect the microscopic properties of matter and modify the macroscopic properties of the system. In this paper we study the role of a strong magnetic field in the thermodynamical properties of a magnetized degenerate strange quark gas, taking into account beta-equilibrium and charge neutrality. Quarks and electrons interact with the magnetic field via their electric charges and anomalous magnetic moments. In contrast to the magnetic field value of 10^19 G, obtained when anomalous magnetic moments are not taken into account, we find the upper bound B < 8.6 x 10^17 G, for the stability of the system. A phase transition could be hidden for fields greater than this value.

[30]  arXiv:0709.1283 [ps, pdf, other]
Title: The fundamental role of the retarded potential in the electrodynamics of superluminal sources Authors: Houshang Ardavan, Arzhang Ardavan, John Singleton, Joseph Fasel, Andrea Schmidt Subjects: Astrophysics (astro-ph)

We calculate the gradient of the radiation field generated by a polarization current with a superluminally rotating distribution pattern and show that the absolute value of this gradient increases as R^(7/2) with distance R within the sharply focused subbeams constituting the overall radiation beam. This result not only supports the earlier finding that the azimuthal and polar widths of these subbeams narrow with distance (as R^(-3) and R^(-1), respectively), but also implies that the boundary contribution to the solution of the wave equation governing the radiation field does not always vanish in the limit where the boundary tends to infinity. There is a fundamental difference between the classical expressions for the retarded potential and field: while the boundary contribution for the potential can always be made zero via a gauge transformation preserving the Lorenz condition, that for the field may be neglected only if it diminishes with distance faster than the contribution of the source density in the far zone. In the case of a rotating superluminal source, however, the boundary term in the retarded solution for the field is by a factor of order R^(1/2) larger than the source term of this solution in the limit, which explains why an argument based on the solution of the wave equation governing the field that neglects the boundary term (such as that presented by J. H. Hannay) misses the nonspherical decay of the field. Given that the distribution of the radiation field of an accelerated superluminal source in the far zone is not known a priori, the only way to calculate the free-space radiation field of such sources is via the retarded solution for the potential. Finally, we apply these findings to pulsar observational data: the more distant a pulsar, the narrower and brighter its giant pulses should be.

[32]  arXiv:0709.1305 [ps, pdf, other]
Title: Possible evidence that pulsars are quark stars Authors: Renxin Xu (PKU) Comments: 6 pages, 2 figures; a talk at the international conference "Astrophysics of Compact Objects" (July 1-7, 2007; Huangshan, China); this http URL A mistake in Fig.1 is corrected Subjects: Astrophysics (astro-ph); High Energy Physics - Phenomenology (hep-ph)

It is a pity that the real state of matter in pulsar-like stars is still not determined confidently because of the uncertainty about cold matter at supranuclear density, even 40 years after the discovery of pulsar. Nuclear matter (related to neutron stars) is one of the speculations for the inner constitution of pulsars even from the Landau's time more than 70 years ago, but quark matter (related to quark stars) is an alternative due to the fact of asymptotic freedom of interaction between quarks as the standard model of particle physics develops since 1960s. Therefore, one has to focus on astrophysical observations in order to answer what the nature of pulsars is. In this presentation, I would like to summarize possible observational evidence/hints that pulsar-like stars could be quark stars, and to address achievable clear evidence for quark stars in the future experiments.

[33]  arXiv:0709.1320 [ps, pdf, other]
Title: CANGAROO-III Search for Gamma Rays from SN 1987A and the Surrounding Field Authors: R. Enomoto, et al (CANGAROO-III collaboration) Comments: 5 pages, 5 figures, Accepted for publication in ApJ Subjects: Astrophysics (astro-ph)

Optical images of SN 1987A show a triple ring structure. The inner (dust) ring has recently increased in brightness and in the number of hot spots suggesting that the supernova shock wave has collided with the dense pre-existing circumstellar medium, a scenario supported by radio and X-ray observations. Such a shocked environment is widely expected to result in the acceleration of charged particles, and the accompanying emission of very high energy gamma-rays. Here, we report the results of observations made in 2004 and 2006 which yield upper limits on the TeV gamma-ray flux, which are compared with a theoretical prediction. In addition, we set upper limits on the TeV flux for four high energy objects which are located within the same field of view of the observation: the super-bubble 30 Dor C, the Crab-like pulsar PSR B0540$-$69, the X-ray binary LMC X-1, and the supernova remnant N157B.

Cross-lists for Tue, 11 Sep 07

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[9]  arXiv:0709.1484 [ps, pdf, other]
Title: Ascertaining the Core Collapse Supernova Mechanism: An Emerging Picture? Authors: A. Mezzacappa, S.W. Bruenn, J.M. Blondin, W.R. Hix, O.E.B. Messer Comments: 9 pages, 3 figures Journal-ref: The Multicolored Landscape of Compact Objects and Their Explosive Origins, AIP Conference Proceedings, Volume 924, pp. 234-242 (Proceedings of Cefalu 2006, Cefalu, Sicily, June 11-24, 2006) Subjects: Astrophysics (astro-ph)

Here we present the results from two sets of simulations, in two and three spatial dimensions. In two dimensions, the simulations include multifrequency flux-limited diffusion neutrino transport in the "ray-by-ray-plus" approximation, two-dimensional self gravity in the Newtonian limit, and nuclear burning through a 14-isotope alpha network. The three-dimensional simulations are model simulations constructed to reflect the post stellar core bounce conditions during neutrino shock reheating at the onset of explosion. They are hydrodynamics-only models that focus on critical aspects of the shock stability and dynamics and their impact on the supernova mechanism and explosion. In two dimensions, we obtain explosions (although in one case weak) for two progenitors (11 and 15 Solar mass models). Moreover, in both cases the explosion is initiated when the inner edge of the oxygen layer accretes through the shock. Thus, the shock is not revived while in the iron core, as previously discussed in the literature. The three-dimensional studies of the development of the stationary accretion shock instability (SASI) demonstrate the fundamentally new dynamics allowed when simulations are performed in three spatial dimensions. The predominant l=1 SASI mode gives way to a stable m=1 mode, which in turn has significant ramifications for the distribution of angular momentum in the region between the shock and proto-neutron star and, ultimately, for the spin of the remnant neutron star. Moreover, the three-dimensional simulations make clear, given the increased number of degrees of freedom, that two-dimensional models are severely limited by artificially imposed symmetries.

[10]  arXiv:0709.1485 [ps, pdf, other]
Title: Compact Stars as Dark Matter Probes Authors: Gianfranco Bertone (IAP), Malcolm Fairbairn (CERN) Comments: 9 pages, 5 figures, revtex Subjects: Astrophysics (astro-ph)

We discuss the consequences of the accretion of dark matter (DM) particles on compact stars such as white dwarfs and neutron stars. We show that in large regions of the DM parameter space, these objects are sensitive probes of the presence of DM and can be used to set constraints both on the DM density and on the physical properties of DM particles.

[13]  arXiv:0709.1492 [ps, pdf, other]
Title: SGRs and AXPs proposed as ancestors of the Magnificent seven Authors: Brian Niebergal, Rachid Ouyed, Denis Leahy Comments: submitted to A&A letters to the editor Subjects: Astrophysics (astro-ph)

The recently suggested correlation between the surface temperature and the magnetic field in isolated neutron stars does not seem to work well for SGRs, AXPs and X-ray dim isolated neutron stars (XDINs; specifically the Magnificent Seven or M7). Instead by appealing to a Color-Flavor Locked Quark Star (CFLQS) we find a more natural explanation. In this picture, the heating is provided by magnetic flux expulsion from a crust-less superconducting quark star. Combined with our previous studies concerning the possibility of SGRs, AXPs, and XDINs as CFLQSs, this provides another piece of evidence that these objects are all related. Specifically, we propose that XDINs are the descendants of SGRs and AXPs.

[48]  arXiv:0709.1693 [ps, pdf, other]
Title: Discovery of the accretion-powered millisecond pulsar SWIFT J1756.9-2508 with a low-mass companion Authors: H. A. Krimm, C. B. Markwardt, C. J. Deloye, P. Romano, D. Chakrabarty, S. Campana, J. R. Cummings, D. K. Galloway, N. Gehrels, J. M. Hartman, P. Kaaret, E. H. Morgan, J. Tueller Comments: 13 pages, 2 figures, accepted by Astrophysical Journal Letters Subjects: Astrophysics (astro-ph)

We report on the discovery by the Swift Gamma-Ray Burst Explorer of the eighth known transient accretion-powered millisecond pulsar, SWIFT J1756.9-2508, as part of routine observations with the Swift Burst Alert Telescope hard X-ray transient monitor. The pulsar was subsequently observed by both the X-Ray Telescope on Swift and the Rossi X-Ray Timing Explorer Proportional Counter Array. It has a spin frequency of 182 Hz (5.5 ms) and an orbital period of 54.7 minutes. The minimum companion mass is between 0.0067 and 0.0086 solar masses, depending on the mass of the neutron star, and the upper limit on the mass is 0.030 solar masses (95% confidence level). Such a low mass is inconsistent with brown dwarf models, and comparison with white dwarf models suggests that the companion is a He-dominated donor whose thermal cooling has been at least modestly slowed by irradiation from the accretion flux. No X-ray bursts, dips, eclipses or quasi-periodic oscillations were detected. The current outburst lasted approximately 13 days and no earlier outbursts were found in archival data.

Cross-lists for Wed, 12 Sep 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Wed, 12 Sep 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[69]  arXiv:0708.3566 (replaced) [ps, pdf, other]
Title: Does Sub-millisecond Pulsar XTE J1739-285 Contain a Low Magnetic Neutron Star or Quark Star ? Authors: C. M. Zhang, H.X. Yin, Y.H. Zhao, Y.C. Wei, X.D. Li Comments: 10 pages, 2 figures, accepted by PASP 2007 Subjects: Astrophysics (astro-ph)
[73]  arXiv:0709.1305 (replaced) [ps, pdf, other]
Title: Possible evidence that pulsars are quark stars Authors: Renxin Xu (PKU) Comments: 6 pages, 2 figures; a talk at the international conference "Astrophysics of Compact Objects" (July 1-7, 2007; Huangshan, China); this http URL A mistake in Fig.1 is corrected Subjects: Astrophysics (astro-ph); High Energy Physics - Phenomenology (hep-ph)
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5 abstracts or titles contain neutron star, magnetar or pulsar


[10]  arXiv:0709.1766 [ps, pdf, other]
Title: Magnetohydrodynamics of Neutrino-Cooled Accretion Tori around a Rotating Black Hole in General Relativity Authors: M. Shibata, Y. Sekiguchi, R. Takahashi Comments: Shibata, M., Sekiguchi, Y., Takahashi, R., Progress of Theoretical Physics, 118, 257 (2007) Journal-ref: Shibata, M., Sekiguchi, Y., Takahashi, R., Progress of Theoretical Physics, 118, 257 (2007) Subjects: Astrophysics (astro-ph)

We present our first numerical results of axisymmetric magnetohydrodynamic simulations for neutrino-cooled accretion tori around rotating black holes in general relativity. We consider tori of mass $\sim 0.1$--0.4$M_{\odot}$ around a black hole of mass $M=4M_{\odot}$ and spin $a=0$--$0.9M$; such systems are candidates for the central engines of gamma-ray bursts (GRBs) formed after the collapse of massive rotating stellar cores and the merger of a black hole and a neutron star. In this paper, we consider the short-term evolution of a torus for a duration of $\approx 60$ ms, focusing on short-hard GRBs. Simulations were performed with a plausible microphysical equation of state that takes into account neutronization, the nuclear statistical equilibrium of a gas of free nucleons and $\alpha$-particles, black body radiation, and a relativistic Fermi gas (neutrinos, electrons, and positrons). Neutrino-emission processes, such as $e^{\pm}$ capture onto free nucleons, $e^{\pm}$ pair annihilation, plasmon decay, and nucleon-nucleon bremsstrahlung are taken into account as cooling processes. Magnetic braking and the magnetorotational instability in the accretion tori play a role in angular momentum redistribution, which causes turbulent motion, resultant shock heating, and mass accretion onto the black hole. The mass accretion rate is found to be $\dot M_* \sim 1$--$10 M_{\odot}$/s, and the shock heating increases the temperature to $\sim 10^{11}$ K. This results in a maximum neutrino emission rate of $L_{\nu}=$ several $\times 10^{53}$ ergs/s and a conversion efficiency $L_{\nu}/\dot M_* c^2$ on the order of a few percent for tori with mass $M_{\rm t} \approx 0.1$--0.4$M_{\odot}$ and for moderately high black hole spins.

[12]  arXiv:0709.1781 [ps, pdf, other]
Title: On scattering of Giant Pulses from the Crab Pulsar: a Scattering Function Authors: Alexander A. Ershov (Pushchino Radio Astronomy Observatory, ASC, LPI) Comments: 3 pages, 3 figures Subjects: Astrophysics (astro-ph)

Simultaneous dual-frequency observations of giant pulses from the Crab pulsar were performed at the frequencies of 61 and 111 MHz. It is shown that scattering of giant pulses from the Crab pulsar occurs at thick, and not at thin screen.

[16]  arXiv:0709.1795 [ps, pdf, other]
Title: Numerical Simulations of Equatorially-Asymmetric Magnetized Supernovae: Formation of Magnetars and Their Kicks Authors: Hidetomo Sawai, Kei Kotake, Shoichi Yamada Comments: 36 pages, 9 figures, accepted by the Astrophysical Journal Subjects: Astrophysics (astro-ph)

A series of numerical simulations on magnetorotational core-collapse supernovae are carried out. Dipole-like configurations which are offset northward are assumed for the initially strong magnetic fields together with rapid differential rotations. Aims of our study are to investigate effects of the offset magnetic field on magnetar kicks and on supernova dynamics. Note that we study a regime where the proto-neutron star formed after collapse has a large magnetic field strength approaching that of a ``magnetar'', a highly magnetized slowly rotating neutron star. As a result, equatorially-asymmetric explosions occur with a formation of the bipolar jets. Resultant magnetar's kick velocities are $\sim 300-1000$ km s$^{-1}$. We find that the acceleration is mainly due to the magnetic pressure while the somewhat weaker magnetic tension works toward the opposite direction, which is due to stronger magnetic field in the northern hemisphere. Noted that observations of magnetar's proper motions are very scarce, our results supply a prediction for future observations. Namely, magnetars possibly have large kick velocities, several hundred km s$^{-1}$, as ordinary neutron stars do, and in an extreme case they could have those up to 1000 km s$^{-1}$.

[29]  arXiv:0709.1855 [ps, pdf, other]
Title: GRB 060218: The nature of the optical-UV component Authors: C.-I. Björnsson (Stockholm Observatory) Comments: 16 pages, 1 figure, accepted to ApJ Subjects: Astrophysics (astro-ph)

The optical-UV component in GRB 060218 is assumed to be due to optically thick cyclotron emission. The key aspect of this model is the high temperature of the absorbing electrons. The heat input derives from nuclei accelerated in semi-relativistic internal shocks, like in ordinary gamma-ray bursts. Coulomb collisions transfer part of that energy to electrons. Inverse Compton cooling on the X-ray photons leads to electron temperatures around 100 keV. Such a high brightness temperature for the optical-UV emission implies an emitting area roughly equal to that of the thermal X-ray component. This suggests a model in which the radio, optical-UV and thermal X-ray emission are closely related: Although the optical-UV and thermal X-ray emission are two separate spectral components, it is argued that they both come from the photosphere of a quasi-spherical, continuous outflow, whose interaction with the circumstellar medium gives rise to the radio emission. The properties of GRB 060218, as measured in the co-moving frame, are similar to those of ordinary gamma-ray burst; i.e., the main difference is the much lower value of the bulk Lorentz factor in GRB 060218. The cyclotron absorption implies a magnetic field in rough equipartition with the matter energy density in the outflow. Hence, the magnetic field could have a dynamically important role, possibly with a magnetar as the central engine.

[38]  arXiv:0709.1915 [ps, pdf, other]
Title: Constraining neutron star tidal Love numbers with gravitational wave detectors Authors: Eanna E. Flanagan, Tanja Hinderer Comments: 4 pages, 2 figures Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc)

We quantify the ability of ground-based gravitational wave detectors to constrain the nuclear equation of state using the early, low frequency portion of the signal of detected neutron star - neutron star (NS-NS) inspirals. In this early adiabatic regime, the influence of a NS's internal structure on the phase of the waveform depends only on a single parameter lambda of the star related to its tidal Love number, namely the ratio of the induced quadrupole moment to the perturbing tidal gravitational field. We restrict attention to gravitational wave frequencies smaller than a cutoff frequency of 400 Hz. In this domain, f-mode frequency dependent corrections to the internal-structure signal are less than 3%, and higher order multipole corrections are less than 5%, for NS models with f-mode frequencies greater than 1 kHz. For an inspiral of two non-spinning 1.4 solar mass NSs at a signal-to-noise ratio of 20, LIGO I (LIGO II) detectors will be able to constrain lambda to lambda < 1.3 (3.3) 10^(37) g cm^2 s^2 with 90% confidence. Fully relativistic NS models show that the corresponding constraint on radius for LIGO I would be R < 12.5 km (14.1 km) for a n=0.5 (n=1.0) polytrope, for 1.4 solar mass NSs.

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[19]  arXiv:0709.2019 [ps, pdf, other]
Title: Drift Wave Model of Rotating Radio Transients Authors: D. Lomiashvili, G. Machabeli, I. Malov Comments: 9 pages, 3 figures Subjects: Astrophysics (astro-ph)

During the last few years there were discovered and deeply examined several transient neutron stars (Rotating Radio Transients). It is already well accepted that these objects are rotating neutron stars. But their extraordinary features (burst-like behavior) made necessary revision of well accepted models of pulsar interior structure. Nowadays most popular model for RRATs is precessing pulsar model, which is the subject of big discussion. We assume that these objects are pulsars with specific spin parameters. An important feature of our model, naturally explaining most of the properties of these neutron stars, is presence of very low frequency, nearly transverse drift waves propagating across the magnetic field and encircling the open field lines region of the pulsar magnetosphere.

Cross-lists for Fri, 14 Sep 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Fri, 14 Sep 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[58]  arXiv:0708.2810 (replaced) [ps, pdf, other]
Title: Is a soft nuclear equation of state extracted from heavy-ion data incompatible with pulsar data? Authors: Irina Sagert, Mirjam Wietoska, Jurgen Schaffner-Bielich, Christian Sturm Comments: 8 pages, 1 figure, contribution to the proceedings of the international conference on 'Nuclear Physics in Astrophysics III', Dresden, Germany, March 26-31, 2007, minor corrections to match published version, JPG in press Subjects: Astrophysics (astro-ph); Nuclear Theory (nucl-th)
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[37]  arXiv:0709.2361 [ps, pdf, other]
Title: Magnetically Torqued Thin Accretion Disks Authors: W. Kluzniak, S. Rappaport Comments: 9 figs (also in GIF format) Subjects: Astrophysics (astro-ph)

We compute the properties of a geometrically thin, steady accretion disk surrounding a central rotating, magnetized star. The magnetosphere is assumed to entrain the disk over a wide range of radii. The model is simplified in that we adopt two (alternate) ad hoc, but plausible, expressions for the azimuthal component of the magnetic field as a function of radial distance. We find a solution for the angular velocity profile tending to corotation close to the central star, and smoothly matching a Keplerian curve at a radius where the viscous stress vanishes. The value of this ''transition'' radius is nearly the same for both of our adopted B-field models. We then solve analytically for the torques on the central star and for the disk luminosity due to gravity and magnetic torques. When expressed in a dimensionless form, the resulting quantities depend on one parameter alone, the ratio of the transition radius to the corotation radius. For rapid rotators, the accretion disk may be powered mostly by spin-down of the central star. These results are independent of the viscosity prescription in the disk. We also solve for the disk structure for the special case of an optically thick alpha disk. Our results are applicable to a range of astrophysical systems including accreting neutron stars, intermediate polar cataclysmic variables, and T Tauri systems.

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[15]  arXiv:0709.2432 [pdf, other]
Title: Morphological Studies of the PWN Candidate HESS J1809-193 Authors: Nu. Komin, S. Carrigan, A. Djannati-Ataï, Y.A. Gallant, K. Kosack, G. Puehlhofer, S. Schwemmer, for the H.E.S.S. Collaboration Comments: proceedings of the 30th ICRC, Merida, Mexico Subjects: Astrophysics (astro-ph)

The source HESS J1809-193 was discovered in 2006 in data of the Galactic Plane survey, followed by several re-observations. It shows a hard gamma-ray spectrum and the emission is clearly extended. Its vicinity to PSR J1809-1917, a high spin-down luminosity pulsar powerful enough to drive the observed gamma-ray emission, makes it a plausible candidate for a TeV Pulsar Wind Nebula (PWN). On the other hand, in this region of the sky a number of faint, radio-emitting supernova remnants can be found, making a firm conclusion on the source type difficult.
Here we present a detailed morphological study of recent H.E.S.S. data and compare the result with X-ray measurements taken with Chandra and radio data. The association with a PWN is likely, but contributions from supernova remnants cannot be ruled out.

[33]  arXiv:0709.2549 [ps, pdf, other]
Title: Evidence of longterm cyclic evolution of radio pulsar periods Authors: Anton Biryukov, Gregory Beskin, Sergey Karpov, Lisa Chmyreva Comments: 8 pages, 8 figures. To appear in Advances in Space Research in the proceedings of the 36th COSPAR Scientific Assembly, Beijing, July 2006 Subjects: Astrophysics (astro-ph)

The measurements of pulsar frequency second derivatives have shown that they are 1e2...1e6 times larger than expected for standard pulsar spin-down law. Moreover, the second derivatives as well as braking indices are even negative for about half the pulsars. We explain these paradoxical results on the basis of the statistical analysis of the rotational parameters f0, f1 and f2 of the subset of 295 pulsars taken mostly from the ATNF database. We have found a strong correlation between f2 and f1 for both f2 > 0 (correlation coefficient r ~ 0.9) and f2 < 0 (r ~ 0.85), as well as between f0 and f1 (r ~ 0.6...0.7). We interpret these dependencies as evolutionary ones due to f1 being nearly proportional to the pulsars' age.
The derived statistical relations as well as "anomalous" values of f2 are well described by assuming the existence of long-time variations of the spin-down rate. The pulsar frequency evolution, therefore, consists of secular change of f0_{ev}(t), f1_{ev}(t) and f2_{ev}(t) according to the power law with n ~ 5, the irregularities, observed within the timespan as timing noise, and the non-monotonous variations on the timescale of several tens of years, which is larger than that of the timespan. It is possible that the nature of long-term variations is similar to that of short-term ones. The idea of non-constant secular pulsars' braking index n is also analysed.

[44]  arXiv:0709.2580 [ps, pdf, other]
Title: Pulse variation of the optical emission of Crab pulsar Authors: S. Karpov, G. Beskin, A. Biryukov, V. Plokhotnichenko, V. Debur, A. Shearer Comments: 9 pages, 14 figures. To appear in the Proceedings of 36th COSPAR Scientific Assembly, held 16 - 23 July 2006, in Beijing, China Subjects: Astrophysics (astro-ph)

The stability of the optical pulse of the Crab pulsar is analyzed based on the 1 $\mu$s resolution observations with the Russian 6-meter and William Hershel telescopes equipped with different photon-counting detectors. The search for the variations of the pulse shape along with its arrival time stability is performed. Upper limits on the possible short time scale free precession of the pulsar are placed. The evidence of pulse time of arrival (TOA) variations on 1.5-2 hours time scale is presented, along with evidence of small light curve (shape and separation of main and secondary peaks) changes between data sets, on time scale of years. Also, the fine structure of the main pulse is studied.

[60]  arXiv:0709.2676 [ps, pdf, other]
Title: The first polarimetric signatures of infrared jets in X-ray binaries Authors: T. Shahbaz (1), R.P. Fender (2), C.A. Watson (3), K. O'Brien (3) ((1) IAC, (2) U of Southampton, (3) U of Sheffield, (4) ESO) Comments: 5 pages, 4 figures, accepted by ApJ Subjects: Astrophysics (astro-ph)

We present near-infrared linear spectropolarimetry of a sample of persistent X-ray binaries, Sco X-1, Cyg X-2 and GRS1915+105. The slopes of the spectra are shallower than what is expected from a standard steady-state accretion disc, and can be explained if the near-infrared flux contains a contribution from an optically thin jet. For the neutron star systems, Sco X-1 and Cyg X-2, the polarization levels at 2.4um are 1.3+/-0.10% and 5.4+/-0.7% respectively which is greater than the polarization level at 1.65um. This cannot be explained by interstellar polarization or electron scattering in the anisotropic environment of the accretion flow. We propose that the most likely explanation is that this is the polarimetric signature of synchrotron emission arising from close to the base of the jets in these systems. In the black hole system GRS1915+105 the observed polarization, although high (5.0+/-1.2% at 2.4um), may be consistent with interstellar polarization. For Sco X-1 the position angle of the radio jet on the sky is approximately perpendicular to the near-infrared position angle (electric vector), suggesting that the magnetic field is aligned with the jet. These observations may be a first step towards probing the ordering, alignment and variability of the outflow magnetic field in a region closer to the central accreting object than is observed in the radio band.

Cross-lists for Tue, 18 Sep 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Tue, 18 Sep 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[73]  arXiv:astro-ph/0703287 (replaced) [ps, pdf, other]
Title: Limits on Mass and Radius for the ms-Period X-ray Pulsar SAX J1808.4-3658 Authors: Denis A. Leahy, Sharon M. Morsink, Coire Cadeau Comments: 10 pages, 4 figures. Accepted by ApJ. Analysis in v2 only uses data from the 1998 outburst. More details of the analysis included in v2 Subjects: Astrophysics (astro-ph)
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[20]  arXiv:0709.2807 [ps, pdf, other]
Title: Observations of VHE gamma-Ray Sources with the MAGIC Telescope Authors: Hendrik Bartko, for the MAGIC Collaboration Comments: ChJAA in press; Proceedings of the Frascati Workshop 2007 Vulcano (Italy), May 28 - June 2 "Multifrequency Behaviour Of High Energy Cosmic Sources" Subjects: Astrophysics (astro-ph)

The MAGIC telescope with its 17m diameter mirror is today the largest operating single-dish Imaging Air Cherenkov Telescope (IACT). It is located on the Canary Island La Palma, at an altitude of 2200m above sea level, as part of the Roque de los Muchachos European Northern Observatory. The MAGIC telescope detects celestial very high energy gamma-radiation in the energy band between about 50 GeV and 10 TeV. Since Autumn of 2004 MAGIC has been taking data routinely, observing various objects like supernova remnants (SNRs), gamma-ray binaries, Pulsars, Active Galactic Nuclei (AGN) and Gamma-ray Bursts (GRB). We briefly describe the observational strategy, the procedure implemented for the data analysis, and discuss the results for individual sources. An outlook to the construction of the second MAGIC telescope is given.

Cross-lists for Wed, 19 Sep 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[43]  arXiv:0709.2589 (cross-list from gr-qc) [ps, pdf, other]
Title: A post-Newtonian diagnosis of quasiequilibrium configurations of neutron star-neutron star and neutron star-black hole binaries Authors: Emanuele Berti, Sai Iyer, Clifford M. Will Comments: 17 pages, 6 tables, 8 figures Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)

We use a post-Newtonian diagnostic tool to examine numerically generated quasiequilibrium initial data sets for non-spinning double neutron star and neutron star-black hole binary systems. The PN equations include the effects of tidal interactions, parametrized by the compactness of the neutron stars and by suitable values of ``apsidal'' constants, which measure the degree of distortion of stars subjected to tidal forces. We find that the post-Newtonian diagnostic agrees well with the double neutron star initial data, typically to better than half a percent except where tidal distortions are becoming extreme. We show that the differences could be interpreted as representing small residual eccentricity in the initial orbits. In comparing the diagnostic with preliminary numerical data on neutron star-black hole binaries, we find less agreement.

Replacements for Wed, 19 Sep 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[65]  arXiv:0709.1305 (replaced) [ps, pdf, other]
Title: Possible evidence that pulsars are quark stars Authors: Renxin Xu (PKU) Comments: 6 pages, 2 figures; a talk at the international conference "Astrophysics of Compact Objects" (July 1-7, 2007; Huangshan, China); this http URL A mistake in Fig.1 is corrected; Correction of typos Subjects: Astrophysics (astro-ph); High Energy Physics - Phenomenology (hep-ph)
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[13]  arXiv:0709.2957 [ps, pdf, other]
Title: Radio and gamma-ray emissions from pulsars: possible observational tests Authors: G.J. Qiao, K.J. Lee, H.G. Wang, R.X. Xu, B. Zhang Comments: 6 pages, 5 figures, Proceedings of "Astrophysics of Compact Objects", 1th-7th, July, 2007 Subjects: Astrophysics (astro-ph)

Many models for the pulsar radio and $\gamma$-ray emissions have been developed. The tests for these models using observational data are very important. Tests for the pulsar radio emission models using frequency-altitude relation are presented in this paper. In the radio band, the mean pulse profiles evolve with observing frequencies. There are various styles of pulsar profile - frequency evolutions (which we call as "beam evolution" figure), e.g. some pulsars show that mean pulse profiles are wider and core emission is higher at higher frequencies than that at lower frequencies, but some other pulsars show completely the contrary results. We show that all these "beam evolution" figures can be understood by the Inverse Compton Scattering(ICS) model (see Qiao at al.2001 also). An important observing test is that, for a certain observing frequency different emission components are radiated from the different heights. For the $\gamma$-ray pulsars, the geometrical method (Wang et al. 2006) can be used to diagnose the radiation location for the $\gamma$-ray radiation. As an example, Wang et al. (2006) constrain the $\gamma$-ray radiation location of PSR B1055-52 to be the place near the null charge surface. Here we show that Wang's result matches the proposed radiation locations by the annular gap model as well as the outer gap models.

[23]  arXiv:0709.3025 [ps, pdf, other]
Title: Hard X-ray colours of Neutron Star and Black Hole Low Mass X-ray Binaries with INTEGRAL Authors: Simon E. Shaw, Ada Paizis, Nami Mowlavi, Stephane Paltani, Thierry J.-L. Courvoisier, Arvind Parmar Comments: Paper from poster presentation at COSPAR meeting, Beijing, 2006. in press: Advances in Space Research, Editor: Wynn Ho Subjects: Astrophysics (astro-ph)

The X-ray spectra of Low Mass X-ray Binaries (LMXB) can change on short time-scales, making it difficult to follow their spectral characteristics in detail through model fitting. Colour-colour (C-C) diagrams are therefore often used as alternative, model independent, tools to study the spectral variability of these sources. The INTEGRAL mission, with its high sensitivity, large field of view and good angular resolution, is well suited to study the hard X-ray properties of LMXBs. In particular the ISGRI imager on board of INTEGRAL allows the regular monitoring of the sources in the less frequently studied domain above 20 keV. In this proceeding, C-C diagrams have been made with data from the INTEGRAL public archive; a search is made for systematic differences in the C-C diagrams between black hole candidates (BH) and neutron stars (NS) in LMXBs using a moments analysis method.

[36]  arXiv:0709.3086 [ps, pdf, other]
Title: Wave Excitation in Discs Around Rotating Magnetic Stars Authors: Dong Lai (Cornell) Comments: 13 pages, 3 figures, MNRAS submitted Subjects: Astrophysics (astro-ph)

The accretion disc around a rotating magnetic star (neutron star, white dwarf or T Tauri star) is subjected to periodic vertical magnetic forces from the star, with the forcing frequency equal to the stellar spin frequency or twice the spin frequency. This gives rise bending waves in the disc that may influence the variabilities of the system. We study the excitation, propagation and dissipation of these waves using a hydrodynamical model coupled with a generic model description of the magnetic forces. The $m=1$ bending waves are excited at the Lindblad/vertical resonance, and propagate either to larger radii or inward toward the corotation resonance where dissipation takes place. While the resonant torque is negligible compared to the accretion torque, the wave nevertheless may reach appreciable amplitude and can cause or modulate flux variabilities from the system. We discuss applications of our result to the observed quasi-periodic oscillations from various systems, in particular neutron star low-mass X-ray binaries.

Cross-lists for Thu, 20 Sep 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Thu, 20 Sep 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[45]  arXiv:astro-ph/0512585 (replaced) [ps, pdf, other]
Title: Birth and Evolution of Isolated Radio Pulsars Authors: C.-A. Faucher-Giguere (1, 2), V. M. Kaspi (1) ((1) McGill University, (2) Harvard University) Comments: 27 pages, including 15 figures, accepted by ApJ Journal-ref: Astrophys.J. 643 (2006) 332-355 Subjects: Astrophysics (astro-ph)
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[11]  arXiv:0709.3125 [ps, pdf, other]
Title: Energy Dependent Morphology in the PWN candidate HESS J1825-137 Authors: The H.E.S.S Collaboration: S. Funk, J. A. Hinton, O. C. deJager Comments: Proceedings of the International Cosmic Ray Conference 2007, Merida Yucatan, Mexico Subjects: Astrophysics (astro-ph)

Observations with H.E.S.S. revealed a new source of very high-energy (VHE) gamma-rays above 100 GeV - HESS J1825-137 - extending mainly to the south of the energetic pulsar PSR B1823-13. A detailed spectral and morphological analysis of HESS J1825-137 reveals for the first time in VHE gamma-ray astronomy a steepening of the energy spectrum with increasing distance from the pulsar. This behaviour can be understood by invoking radiative cooling of the IC-Compton gamma-ray emitting electrons during their propagation. In this scenario the vastly different sizes between the VHE gamma-ray emitting region and the X-ray PWN associated with PSR B1823-13 can be naturally explained by different cooling timescales for the radiating electron populations. If this scenario is correct, HESS J1825-137 can serve as a prototype for a whole class of asymmetric PWN in which the X-rays are extended over a much smaller angular scales than the gamma-rays and can help understanding recent detections of X-ray PWN in systems such as HESS J1640-465 and HESS J1813-178. The future GLAST satellite will probe lower electron energies shedding further light on cooling and diffusion processes in this source.

[12]  arXiv:0709.3127 [ps, pdf, other]
Title: Future GLAST observations of Supernova remnants and Pulsar Wind Nebulae Authors: GLAST Collaboration: S. Funk Comments: Proceedings of the International Cosmic Ray Conference 2007 Merida Yucatan, Mexico Subjects: Astrophysics (astro-ph)

Shell-type Supernova remnants (SNRs) have long been known to harbour a population of ultra-relativistic particles, accelerated in the Supernova shock wave by the mechanism of diffusive shock acceleration. Experimental evidence for the existence of electrons up to energies of ~100 TeV was first provided by the detection of hard X-ray synchrotron emission as e.g. in the shell of the young SNR SN1006. Furthermore using theoretical arguments shell-type Supernova remnants have long been considered as the main accelerator of protons - Cosmic rays - in the Galaxy; definite proof of this process is however still missing. Pulsar Wind Nebulae (PWN) - diffuse structures surrounding young pulsars - are another class of objects known to be a site of particle acceleration in the Galaxy, again through the detection of hard synchrotron X-rays such as in the Crab Nebula. Gamma-rays above 100 MeV provide a direct access to acceleration processes. The GLAST Large Area telescope (LAT) will be operating in the energy range between 30 MeV and 300 GeV and will provide excellent sensitivity, angular and energy resolution in a previously rather poorly explored energy band. We will describe prospects for the investigation of these Galactic particle accelerators with GLAST.

[15]  arXiv:0709.3173 [ps, pdf, other]
Title: Physics of Interpulse Emission in Radio Pulsars Authors: S. A. Petrova Comments: 28 pages, 2 figures. Accepted for publication in ApJ Subjects: Astrophysics (astro-ph)

The magnetized induced Compton scattering off the particles of the ultrarelativistic electron-positron plasma of pulsar is considered. The main attention is paid to the transverse regime of the scattering, which holds in a moderately strong magnetic field. We specifically examine the problem on induced transverse scattering of the radio beam into the background, which takes place in the open field line tube of a pulsar. In this case, the radiation is predominantly scattered backwards and the scattered component may grow considerably. Based on this effect, we for the first time suggest a physical explanation of the interpulse emission observed in the profiles of some pulsars. Our model can naturally account for the peculiar spectral and polarization properties of the interpulses. Furthermore, it implies a specific connection of the interpulse to the main pulse, which may reveal itself in the consistent intensity fluctuations of the components at different timescales. Diverse observational manifestations of this connection, including the moding behavior of PSR B1822-09, the peculiar temporal and frequency structure of the giant interpulses in the Crab pulsar, and the intrinsic phase correspondence of the subpulse patterns in the main pulse and the interpulse of PSR B1702-19, are discussed in detail. It is also argued that the pulse-to-pulse fluctuations of the scattering efficiency may lead to strong variability of the interpulse, which is yet to be studied observationally. In particular, some pulsars may exhibit transient interpulses, i.e. the scattered component may be detectable only occasionally.

Cross-lists for Fri, 21 Sep 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Fri, 21 Sep 07

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[20]  arXiv:0709.3372 [ps, pdf, other]
Title: Two-dimensional Radiation-hydrodynamic Model for Supercritical Disk Accretion Flows onto Neutron Stars Authors: Ken Ohsuga Comments: 9 pages, 6 figures, accepted for publication in PASJ Subjects: Astrophysics (astro-ph)

We performed two-dimensional radiation hydrodynamic simulations of supercritical accretion flows around neutron stars (NSs). In contrast with the accretion flows onto black holes (BHs), we find that the shell-shaped high-density regions form around the NSs, since the radiation force is enhanced in the innermost regions. The enhanced radiation force drives strong outflows above and below the disk. The mass-accretion rate onto the NS exceeds the critical rate, $L_{\rm E}/c^2$, with $L_{\rm E}$ being the Eddington luminosity. However it is about $20-30%$ of that onto the BH, under the condition that we employ the same mass-input rate, $\dot{M}_{\rm input}$, which is mass injected from the outer disk boundary per unit time. The mass-outflow rate is a few-times larger in flows around NSs than in flows around BHs. The supercritical NS accretion flows mainly release the accretion energy as the kinetic energy of the outflows, though the disk luminosity is predominant over the kinetic energy output rate in the BH accretion flows. The resulting velocity and mass-outflow rate of the outflows are $0.2-0.3c$ and $150-700L_{\rm E}/c^2$, respectively, for the mass-input rate of $3\times 10^2\lsim \dot{M}_{\rm input}/(L_{\rm E}/c^2)\lsim 3\times 10^3$. This implies that the SS433 jets can be roughly explained by the supercritical accretion onto a NS. However, the collimation angle of the outflows in our simulations ($\sim 20^\circ$) is larger than that of the SS433 jets (a few degrees).

[36]  arXiv:0709.3454 [ps, pdf, other]
Title: First Stars VIII -- Enrichment of the neutron-capture elements in the early Galaxy Authors: P. Francois, E. Depagne, V. Hill, M. Spite, F. Spite, B. Plez, T. C. Beers, J. Andersen, G. James, B. Barbuy, R. Cayrel, P. Bonifacio, P. Molaro, B. Nordström, F. Primas Comments: 19 pages, 16 figures, A&A accepted Subjects: Astrophysics (astro-ph)

Our aim is to measure accurate, homogeneous neutron-capture element abundances for the sample of 32 EMP giant stars studied earlier in this series, including 22 stars with [Fe/H] $< -$3.0. Based on high-resolution, high S/N spectra from the ESO VLT/UVES, 1D, LTE model atmospheres, and synthetic spectrum fits, we determine abundances or upper limits for the 16 elements Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Yb in all stars. As found earlier, [Sr/Fe], [Y/Fe], [Zr/Fe] and [Ba/Fe] are below Solar in the EMP stars, with very large scatter. However, we find a tight anti-correlation of [Sr/Ba], [Y/Ba], and [Zr/Ba] with [Ba/H] for $-4.5 <$ [Ba/H] $< -2.5$, also when subtracting the contribution of the main $r$-process as measured by [Ba/H]. The huge, well-characterised scatter of the [n-capture/Fe] ratios in our EMP stars is in stark contrast to the negligible dispersion in the [$\alpha$/Fe] and [Fe-peak/Fe] ratios for the same stars found in Paper V. These results demonstrate that a second (``weak'' or LEPP) $r$-process dominates the production of the lighter neutron-capture elements for [Ba/H] $< -2.5$. The combination of very consistent [$\alpha$/Fe] and erratic [n-capture/Fe] ratios indicates that inhomogeneous models for the early evolution of the halo are needed. Our accurate data provide strong constraints on future models of the production and mixing of the heavy elements in the early Galaxy.

Cross-lists for Mon, 24 Sep 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Mon, 24 Sep 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[61]  arXiv:0704.0799 (replaced) [ps, pdf, other]
Title: Spin Evolution of Accreting Neutron Stars: Nonlinear Development of the R-mode Instability Authors: Ruxandra Bondarescu, Saul A. Teukolsky, Ira Wasserman (Cornell University) Comments: 18 pages, 9 figures. Error Corrected. Includes referee input. Corrected References Journal-ref: Phys. Rev. D 76, 064019 (2007) Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc)
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6 abstracts or titles contain neutron star, magnetar or pulsar


[10]  arXiv:0709.3614 [ps, pdf, other]
Title: Search for Pulsar Wind Nebula Associations of Unidentified TeV Gamma-Ray Sources Authors: Chulhoon Chang, Alexander Konopelko, Wei Cui (Purdue University) Comments: 20 pages, 4 figures, 4 tables, submitted to ApJ Subjects: Astrophysics (astro-ph)

Many of the recently discovered galactic very high-energy gamma-ray sources are associated with pulsar wind nebulae, which represent the most populous galactic source class at TeV energies. In addition, H.E.S.S. detector discovered in the galactic plane survey a representative population of unidentified TeV gamma-ray sources. For a number of these sources a pulsar is an evident association, which is often located within an extended region of the TeV gamma-ray emission. These particular H.E.S.S. sources are promising candidates for yet not resolved pulsar wind nebulae. Here we have undertaken a systematic search for X-ray counterparts, using the archival Chandra data, within the extension bounds of the unidentified H.E.S.S. sources, in particular those associated with young, energetic pulsars. A number of X-ray sources have been detected in corresponding Chandra fields. Two of them, CXOU J161729.3-505512 and CXOU J170252.4-412848, are of a special interest because of their exact positional coincidence with the pulsars PSR J1617-5055 and PSR J1702-4128, respectively. All of the detected sources are consistent with being point sources of X-ray emission. The analysis of the archival Chandra data for another young energetic pulsar PSR J1913+1011, associated with the newly discovered TeV gamma-ray source HESS J1912+101, does not reveal any statistically significant excess around the pulsar position. No evident X-ray emission can be seen at the center of gravity of HESS J1912+101 either. The corresponding flux upper limits are given. We discuss the implications of these results.

[11]  arXiv:0709.3621 [ps, pdf, other]
Title: Constraining properties of rapidly rotating neutron stars using data from heavy-ion collisions Authors: Plamen G. Krastev, Bao-An Li, Aaron Worley Comments: 7 pages, 9 figures and 2 tables. Submitted to Astronomy and Astrophysics Subjects: Astrophysics (astro-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)

Aims.- Properties, structure, and thermal evolution of neutron stars are determined by the equation of state of stellar matter. Recent data on isospin-diffusion in heavy-ion collisions at intermediate energies and the size of neutron skin in $^{208}Pb$ have constrained considerably the density dependence of the nuclear symmetry energy and, in turn, the equation of state of neutron-rich nucleonic matter. These constraints could provide useful information about the global properties of rapidly rotating neutron stars. Methods.- Models of rapidly rotating neutron stars are constructed applying several nucleonic equations of state. Particular emphasis is placed on configurations rotating rigidly at 716 and 1122Hz. The range of allowed hydrostatic equilibrium solutions is determined and tested for stability. The effect of rotation on the internal composition and thermal properties of neutron stars is also examined. Results.- At a given rotational frequency, each equation of state yields a range of possible neutron stars configurations restricted by the Keplerian (mass-shedding) limit, corresponding to the maximal circumferential radius, and the limit due to the onset of instabilities with respect to axial-symmetric perturbations, corresponding to the minimal equatorial radius of a stable neutron star model. We show that the mass of a neutron star rotating uniformly at $1122Hz$ is between 1.7 and $2.1M_{\sun}$. Central stellar density and proton fraction decrease with increasing rotational frequency with respect to static models and, depending on the exact stellar mass and angular velocity, can drop below the Direct Urca threshold thus closing the fast cooling channel.

[30]  arXiv:0709.3712 [ps, pdf, other]
Title: Long term hard X-ray variability of the anomalous X-ray pulsar 1RXS J170849.0-400910 discovered with INTEGRAL Authors: D. Gotz, N. Rea, G.L. Israel, S. Zane, P. Esposito, E.V. Gotthelf, S. Mereghetti, A. Tiengo, R. Turolla Comments: 5 pages, 2 figures, accepted for publication in Astronomy & Astrophysics main journal Subjects: Astrophysics (astro-ph)

We report on a multi-band high-energy observing campaign aimed at studying the long term spectral variability of the Anomalous X-ray Pulsar (AXP) 1RXS J170849.0-400910, one of the magnetar candidates. We observed 1RXS J170849.0-400910 in Fall 2006 and Spring 2007 simultaneously with Swift/XRT, in the 0.1-10 keV energy range, and with INTEGRAL/IBIS, in the 20-200 keV energy range. Furthermore, we also reanalyzed, using the latest calibration and software, all the publicly available INTEGRAL data since 2002, and the soft X-ray data starting from 1999 taken using BeppoSAX, Chandra, XMM, and Swift/XRT, in order to study the soft and hard X-ray spectral variability of 1RXS J170849.0-400910. We find a long-term variability of the hard X-ray flux, extending the hardness-intensity correlation proposed for this source over 2 orders of magnitude in energy.

[36]  arXiv:0709.3730 [ps, pdf, other]
Title: Interaction and ablation of fall-back disks in isolated neutron stars Authors: P B Jones Comments: 9 pages; to be published in Monthly Notices of the Royal Astronomical Society Subjects: Astrophysics (astro-ph)

An analysis of ablation processes is made for a fall-back disk with inner and outer radii external to the neutron-star light cylinder. The calculated ablation rate leads, with certain other assumptions, to a simple expression relating the inner radius and mean mass per unit area of any long-lived fall-back disk. Expressions for the torque components generated by interaction with the pulsar wind are obtained. It is not impossible that these could be responsible for small observable variations in pulse shape and spin-down rate but they are unlikely to be the source of the periodic changes seen in several pulsars.

[52]  arXiv:0709.3773 [ps, pdf, other]
Title: Transient neutron star X-ray binaries with Simbol-X Authors: S. Campana (Osservatorio astronomico di Brera) Comments: Invited talk at the conference "Simbol-X: the Hard X-ray Universe in focus" held in Bologna, 14-16 May 2007 (5 pages, 7 figures) Subjects: Astrophysics (astro-ph)

We present a brief overview of test-bed observations on accreting neutron star binaries for the Simbol-X mission. We show that Simbol-X will provide unique observations able to disclose the physical mechanisms responsible for their high energy emission.

[59]  arXiv:0709.3798 [ps, pdf, other]
Title: Neutron star crust beyond the Wigner-Seitz approximation Authors: N. Chamel Comments: 8 pages, 2 figures. Proceedings of the International Symposium on Exotic States of Nuclear Matter, Catania (Italy), June 11-15, 2007 Subjects: Astrophysics (astro-ph)

For more than three decades, the inner crust of neutron stars, formed of a solid lattice of nuclear clusters coexisting with a gas of electrons and neutrons, has been traditionally studied in the Wigner-Seitz approximation. The validity of this approximation is discussed in the general framework of the band theory of solids, which has been recently applied to the nuclear context. Using this novel approach, it is shown that the unbound neutrons move in the crust as if their mass was increased.

Cross-lists for Tue, 25 Sep 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Tue, 25 Sep 07

2 abstracts or titles contain neutron star, magnetar or pulsar


[82]  arXiv:0707.0264 (replaced) [pdf, other]
Title: Magnetar-energized supernova explosions and GRB-jets Authors: S. S. Komissarov, M. V. Barkov Comments: accepted by MNRAS, additional simulations, expanded discussion Subjects: Astrophysics (astro-ph)
[85]  arXiv:0707.2067 (replaced) [ps, pdf, other]
Title: On the mass of the neutron star in V395 Car/2S 0921-630 Authors: D.Steeghs (Warwick/CfA), P.G.Jonker (SRON/CfA) Comments: 4 pages, 3 figures, accepted for publication in ApJ Letters Subjects: Astrophysics (astro-ph)
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[3]  arXiv:0709.3836 [ps, pdf, other]
Title: Flares from spiral waves by lensing and time-delay amplification? Authors: V. Karas, M. Dovciak, A. Eckart, L. Meyer Comments: Proceedings of the Workshop on the Black Holes and Neutron Stars, eds. S. Hledik and Z. Stuchlik, 19-21 September 2007 (Silesian University, Opava), in preparation Subjects: Astrophysics (astro-ph)

Episodically accreting black holes are thought to produce flares when a chunk of particles is accelerated to high velocity near the black hole horizon. This also seems to be the case of Sagittarius A* in the Galactic Center, where the broad-band radiation is produced, likely via the synchrotron self-Compton mechanism. It has been proposed that strong-field gravitational lensing magnifies the flares. The effect of lensing is generally weak and requires a fine-tuned geometrical arrangement, which occurs with only a low probability. However, there are several aspects that make Sagittarius A* a promising target to reveal strong gravity effects. Unlike type II (obscured) active galaxies, chances are that a flare is detected at high inclination, which would be favourable for lensing. Time delays can then significantly influence the observed flare duration and the form of light-curve profiles. Here we discuss an idea that the impact of lensing amplification should be considerably enhanced when the shape of the flaring clump is appropriately elongated in the form of a spiral wave or a narrow filament, rather than a simple (circular) spot which we employed previously within the phenomenological `orbiting spot model'. By parameterizing the emission region in terms of the spiral shape and contrast, we are able to extend the spot model to more complicated sources. In the case of spirals, we notice a possibility that more photons reach a distant observer at the same moment because of interplay between lensing and light-travel time. The effect is not symmetrical with respect to leading versus trailing spirals, so in principle the source geometry can be constrained. In spite of this, the spot model seems to provide entirely adequate framework to study the currently available data.

[8]  arXiv:0709.3854 [ps, pdf, other]
Title: Arecibo HI Absorption Measurements of Pulsars and the Electron Density at Intermediate Longitudes in the First Galactic Quadrant Authors: J. M. Weisberg, S. Stanimirovic, K. Xilouris, A. Hedden, A. de la Fuente, S. B. Anderson, F. A. Jenet Comments: Accepted by Astrophysical Journal September 2007 Subjects: Astrophysics (astro-ph)

We have used the Arecibo telescope to measure the HI absorption spectra of eight pulsars. We show how kinematic distance measurements depend upon the values of the galactic constants R_o and Theta_o, and we select our preferred current values from the literature. We then derive kinematic distances for the low-latitude pulsars in our sample and electron densities along their lines of sight. We combine these measurements with all others in the inner galactic plane visible from Arecibo to study the electron density in this region. The electron density in the interarm range 48 degrees < l < 70 degrees is [0.017 (-0.007,+0.012) (68% c.l.)] cm^(-3). This is 0.75 (-0.22,+0.49) (68% c.l.) of the value calculated by the Cordes & Lazio (2002) galactic electron density model. The model agrees more closely with electron density measurements toward Arecibo pulsars lying closer to the galactic center, at 30 degrees<l<48 degrees. Our analysis leads to the best current estimate of the distance of the relativistic binary pulsar B1913+16: d=(9.0 +/- 3) kpc.
We use the high-latitude pulsars to search for small-scale structure in the interstellar hydrogen observed in absorption over multiple epochs. PSR B0301+19 exhibited significant changes in its absorption spectrum over 22 yr, indicating HI structure on a ~500 AU scale.

[9]  arXiv:0709.3868 [ps, pdf, other]
Title: Observations of the Crab Nebula and Pulsar with VERITAS Authors: O. Celik, for the VERITAS Collaboration Comments: 4 pages; contribution to the 30th International Cosmic Ray Conference, Merida, Mexico, July 2007 Subjects: Astrophysics (astro-ph)

Observations of the Crab Nebula have proven to be the best tool to calibrate and to characterize the performance of a Cherenkov telescope. Scientifically, it is interesting to measure the energy spectrum of the Crab Nebula close to the inverse-Compton peak where a deviation is expected from the power law seen at energies above 300 GeV. Additionally, it is important to search for pulsed emission from the Crab Pulsar at energies beyond the 10 GeV upper limit of the EGRET pulsar detection. Since current models predict a cut-off in pulsed emission between 10 and 100 GeV, measurements at energies close to this range may help to discriminate between them. We observed the Crab extensively in the 2006-2007 season during the VERITAS 2- and 3-telescope commissioning phases. Using this data set we reconstructed a preliminary energy spectrum of the signal from the Crab Nebula. We also measured the optical pulsed signal to validate our GPS time-stamping and barycentering techniques and obtained an upper limit for the pulsed emission at gamma-ray energies.

[22]  arXiv:0709.3957 [ps, pdf, other]
Title: A note on the cyclic evolution of the pulsar magnetosphere Authors: Ioannis Contopoulos Comments: Accepted for publication in Astronomy & Astrophysics Subjects: Astrophysics (astro-ph)

Positive and negative pulsar breaking indices suggest that some fraction of the pulsar spindown torque undergoes a cyclic evolution. The observed strong correlation of `anomalous' breaking indices with pulsar age implies that the characteristic periodicity timescale is in the range 100 to 10,000 years depending on the fraction of the spindown torque that undergoes cyclic evolution, 1 to 100% respectively. We argue that the longest variability timescale is consistent with a neutron star magnetic cycle similar to the solar cycle.

[29]  arXiv:0709.3975 [ps, pdf, other]
Title: Observations of Pulsar Wind Nebulae with the VERITAS Array of Imaging Atmospheric Cherenkov Telescopes Authors: A. Konopelko, for the VERITAS collaboration Comments: 4 pages; contribution to the 30th International Cosmic Ray Conference, Merida, Mexico, July 2007 Subjects: Astrophysics (astro-ph)

Many of the recently discovered galactic very high-energy (VHE) gamma-ray sources are associated with Pulsar Wind Nebulae, which is the most populous Galactic source category at TeV energies. The extended synchrotron nebulae of these objects observed in the X-ray band are a hallmark of the relativistic winds, generated by the young, energetic neutron stars, that interact with the matter ejected by the supernova explosion and the surrounding interstellar gas. Relativistic electrons, or protons, accelerated in the pulsar winds, or at their shock boundaries, interact with the magnetic field and low energy seed photons to produce the observed VHE gamma-ray emission. The VERITAS array of four imaging atmospheric Cherenkov telescopes was designed to study astrophysical sources of gamma rays in the energy domain from about 100 GeV up to several tens of TeV. The sensitivity of the VERITAS array allows detailed studies of the morphology and spectral features of gamma-ray emission from PWNe. Three northern sky PWNe, G75.2+0.1, G106.6+2.9, and 3C58, were observed with VERITAS during 2006. No evidence for TeV gamma-ray emission at the position of the pu lsar associated with these PWNe is demonstrated.

Cross-lists for Wed, 26 Sep 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[46]  arXiv:0709.3527 (cross-list from gr-qc) [ps, pdf, other]
Title: Type II critical phenomena of neutron star collapse Authors: Scott C. Noble, Matthew W. Choptuik Comments: 24 pages, 22 figures, RevTeX 4, submitted to Phys. Rev. D Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)

We investigate spherically-symmetric, general relativistic systems of collapsing perfect fluid distributions. We consider neutron star models that are driven to collapse by the addition of an initially "in-going" velocity profile to the nominally static star solution. The neutron star models we use are Tolman-Oppenheimer-Volkoff solutions with an initially isentropic, gamma-law equation of state. The initial values of 1) the amplitude of the velocity profile, and 2) the central density of the star, span a parameter space, and we focus only on that region that gives rise to Type II critical behavior, wherein black holes of arbitrarily small mass can be formed. In contrast to previously published work, we find that--for a specific value of the adiabatic index (Gamma = 2)--the observed Type II critical solution has approximately the same scaling exponent as that calculated for an ultrarelativistic fluid of the same index. Further, we find that the critical solution computed using the ideal-gas equations of state asymptotes to the ultrarelativistic critical solution.

Replacements for Wed, 26 Sep 07

0 abstracts or titles contain neutron star, magnetar or pulsar


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[9]  arXiv:0709.4062 [ps, pdf, other]
Title: The Burst Spectra of EXO 0748-676 during a Long 2003 XMM-Newton Observation Authors: J. Cottam (1), F. Paerels (2,3), M. Méndez (3), L. Boirin (4), W.H.G. Lewin (5), E. Kuulkers (6), J.M. Miller (7) ((1) NASA/GSFC, (2) Columbia Astrophysics Laboratory, (3) SRON, (4) Observatoire Astronomique de Strasbourg, (5) MIT/Kavli Institute for Astrophysics and Space Research, (6) ESA/ESAC, (7) University of Michigan) Comments: 18 Pages, 3 Figures. Accepted for publication in ApJ Subjects: Astrophysics (astro-ph)

Gravitationally redshifted absorption lines from highly ionized iron have been previously identified in the burst spectra of the neutron star in EXO 0748-676. To repeat this detection we obtained a long, nearly 600 ks observation of the source with XMM-Newton in 2003. The spectral features seen in the burst spectra from the initial data are not reproduced in the burst spectra from this new data. In this paper we present the spectra from the 2003 observations and discuss the sensitivity of the absorption structure to changes in the photospheric conditions.

[15]  arXiv:0709.4094 [ps, pdf, other]
Title: Establishing a connection between high-power pulsars and very-high-energy gamma-ray sources Authors: S. Carrigan, J.A. Hinton, W. Hofmann, K. Kosack, T. Lohse, O. Reimer, for the H.E.S.S. Collaboration Comments: Proceedings of the 30th ICRC, Merida, Mexico Subjects: Astrophysics (astro-ph)

In the very-high-energy (VHE) gamma-ray wave band, pulsar wind nebulae (PWNe) represent to date the most populous class of Galactic sources. Nevertheless, the details of the energy conversion mechanisms in the vicinity of pulsars are not well understood, nor is it known which pulsars are able to drive PWNe and emit high-energy radiation. In this paper we present a systematic study of a connection between pulsars and VHE gamma-ray sources based on a deep survey of the inner Galactic plane conducted with the High Energy Stereoscopic System (H.E.S.S.). We find clear evidence that pulsars with large spin-down energy flux are associated with VHE gamma-ray sources. This implies that these pulsars emit on the order of 1% of their spin-down energy as TeV gamma-rays.

Cross-lists for Thu, 27 Sep 07

0 abstracts or titles contain neutron star, magnetar or pulsar


Replacements for Thu, 27 Sep 07

0 abstracts or titles contain neutron star, magnetar or pulsar


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5 abstracts or titles contain neutron star, magnetar or pulsar


[15]  arXiv:0709.4287 [ps, pdf, other]
Title: Magnetic Field Upper Limits for Jet Formation Authors: M. Massi, M. Kaufman Bernado Comments: 7 pages, 6 figures, A&A in press Subjects: Astrophysics (astro-ph)

{Context: Very high magnetic fields at the surface of neutron stars or in the accretion disk of black holes inhibit the production of jets.} {Aims: We quantify here the magnetic field strength for the jet formation.} {Methods: By using, the Alfven Radius, R_{A}, in its dependency with the magnetic field strength and the mass accretion rate.} {Results: The association of a classical X-ray pulsar (i.e. B~10^{12} G) with jets is excluded even if accreting at the Eddington critical rate. Z-sources may develop jets for B < 10^{8.2} G whereas Atoll-sources are potential sources for jets if B< 10^{7.7} G. It is not ruled out that a millisecond X-ray pulsar could develop jets, at least for those sources where B< 10^{7.5} G. In this case the millisecond X-ray pulsar could switch to a microquasar phase during its maximum accretion rate. For stellar-mass black hole X-ray Binaries, the condition is that B<1.35x10^8 G and B< 5x10^8 G at the last stable orbit for a Schwarzschild and a Kerr black hole respectively. For Active Galactic Nuclei it reaches B <10^{5.9} G for each kind of black hole. Most of these general and theoretical results are in complete agreement with observational data. Radio emission in classical X-ray pulsars is up to now ruled out (Fender et al. 1997, Fender & Hendry 2000; Migliari & Fender 2006). The magnetic field strength has been determined in a Z-source (Scorpius X-1) using magnetoacoustic oscillations in kHz QPO reaching values of 10^{7-8} G (Titarchuk et al. 2001). In the accreting millisecond X-ray pulsar SAX J1808.4-3658 hints for a radio jet have been found (Gaensler et al. 1999).}

[20]  arXiv:0709.4298 [ps, pdf, other]
Title: Observation of the Supernova Remnant IC 443 with VERITAS Authors: VERITAS Collaboration: T. B. Humensky Comments: 4 pages; contribution to the 30th International Cosmic Ray Conference, Merida, Mexico, July 2007 Subjects: Astrophysics (astro-ph)

Shell-type supernova remnants (SNRs) accelerate particles at the shock front between the expanding remnant and the swept-up interstellar medium. If these particles include protons and nuclei, very-high-energy gamma-ray emission may result from the decay of pions produced in interactions between cosmic rays and the local insterstellar medium. For SNRs that are interacting with a nearby molecular cloud, such as IC 443, the enhanced matter density provides a target medium that can amplify the gamma-ray emission. IC 443 also contains the pulsar wind nebula (PWN) CXOU J061705.3+222127. PWNe are the most plentiful galactic sources of very-high-energy gamma rays, which are produced in the shock formed at the collision of the pulsar wind with the ambient medium.
VERITAS is an array of four 12-m telescopes dedicated to gamma-ray astronomy in the energy band above 100 GeV. Located on Mt. Hopkins in southern Arizona, VERITAS operated during the 2006-2007 season in 2-, 3-, and 4-telescope observation modes. In this talk, results from three-telescope observations of the composite supernova remnant IC 443 during the 2006-2007 season are discussed.

[23]  arXiv:0709.4301 [ps, pdf, other]
Title: A bright millisecond radio burst of extragalactic origin Authors: D. R. Lorimer, M. Bailes, M. A. McLaughlin, D. J. Narkevic, F. Crawford Comments: 18 pages, 4 figures. Accepted by Science. Published electronically via Science Express on September 27, 2007 Subjects: Astrophysics (astro-ph)

Pulsar surveys offer one of the few opportunities to monitor even a small fraction (~0.00001) of the radio sky for impulsive burst-like events with millisecond durations. In analysis of archival survey data, we have discovered a 30-Jy dispersed burst of duration <5 ms located three degrees from the Small Magellanic Cloud. The burst properties argue against a physical association with our Galaxy or the Small Magellanic Cloud. Current models for the free electron content in the Universe imply a distance to the burst of <1 Gpc No further bursts are seen in 90-hr of additional observations, implying that it was a singular event such as a supernova or coalescence of relativistic objects. Hundreds of similar events could occur every day and act as insightful cosmological probes.

[27]  arXiv:0709.4315 [ps, pdf, other]
Title: Pulsar Magnetic Field Oscillation Model and Verification Method Authors: Zhu-Xing Liang, Yi Liang Comments: 21 pages, 4 figures Subjects: Astrophysics (astro-ph)

We constructed the magnetic field oscillation model (hereafter the MO model) by analogizing the periodically reversing phenomenon of the solar magnetic field to pulsars. Almost all kinds of pulsar radiation phenomena are best explained using the MO model, especially polarization characteristics, glitch, generation rate, the geodetic precession of pulsars and the configuration of pulsar-wind nebula of the Crab. The MO model also provides a satisfactory explanation of other characteristics of pulsars, e.g., interpulse, spin-down, pulse nulling, beat and pulse drift, the loss rate of the rotating energy, and the accuracy of frequency. We present six verification methods for the MO model. In addition, we predict that the pulsar PSR B1913+16 will not disappear from our line of sight after the year 2025, which is antithetical to the prediction made by some astronomers.

[33]  arXiv:0709.4380 [ps, pdf, other]
Title: Discovery of the candidate pulsar wind nebula HESS J1718-385 in very-high-energy gamma-rays Authors: H.E.S.S Collaboration: S. Carrigan, Y.A. Gallant, J. A. Hinton, Nu. Komin, K. Kosack, C. Stegmann Comments: Proceedings of the 30th ICRC, Merida, Mexico Subjects: Astrophysics (astro-ph)

Motivated by recent detections of pulsar wind nebulae in very-high-energy (VHE) gamma rays, a systematic search for VHE gamma-ray sources associated with energetic pulsars was performed, using data obtained with the H.E.S.S. (High Energy Stereoscopic System) instrument. The search for VHE gamma-ray sources near the pulsar PSR J1718-3825 revealed the new VHE gamma-ray source HESS J1718-385. We report on the results from the HESS data analysis of this source and on possible associations with the pulsar and at other wavelengths. We investigate the energy spectrum of HESS J1718-385 that shows a clear peak. This is only the second time a VHE gamma-ray spectral maximum from a cosmic source was observed, the first being the Vela X pulsar wind nebula.

Cross-lists for Fri, 28 Sep 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[48]  arXiv:0709.4081 (cross-list from nucl-th) [ps, pdf, other]
Title: Non-rotating and rotating neutron stars in the extended field theoretical model Authors: Shashi K. Dhiman, Raj Kumar, B. K. Agrawal Comments: 28 pages, 12 figures. Phys. Rev. C (in press) Subjects: Nuclear Theory (nucl-th); Astrophysics (astro-ph)

We study the properties of non-rotating and rotating neutron stars for a new set of equations of state (EOSs) with different high density behaviour obtained using the extended field theoretical model. The high density behaviour for these EOSs are varied by varying the $\omega-$meson self-coupling and hyperon-meson couplings in such a way that the quality of fit to the bulk nuclear observables, nuclear matter incompressibility coefficient and hyperon-nucleon potential depths remain practically unaffected. We find that the largest value for maximum mass for the non-rotating neutron star is $2.1M_\odot$. The radius for the neutron star with canonical mass is $12.8 - 14.1$ km provided only those EOSs are considered for which maximum mass is larger than $1.6M_\odot$ as it is the lower bound on the maximum mass measured so far. Our results for the very recently discovered fastest rotating neutron star indicate that this star is supra massive with mass $1.7 - 2.7M_\odot$ and circumferential equatorial radius $12 - 19$ km.

Replacements for Fri, 28 Sep 07

1 abstracts or titles contain neutron star, magnetar or pulsar


[61]  arXiv:0707.2100 (replaced) [ps, pdf, other]
Title: Relativistic Jets and Long-Duration Gamma-ray Bursts from the Birth of Magnetars Authors: N. Bucciantini (1), E. Quataert (1), J. Arons (1), B. D. Metzger (1), Todd A. Thompson (2) ((1)Astronomy Department, UC Berkeley, (2)Department of Astrophysical Sciences, Princeton) Comments: 5 pages, 3 figures, accepted in MNRAS letter, presented at the conference "Astrophysics of Compact Objects", 1-7 July, Huangshan, China Subjects: Astrophysics (astro-ph)
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6 abstracts or titles contain neutron star, magnetar or pulsar


[12]  arXiv:0709.4526 [ps, pdf, other]
Title: Exploring the origin of neutron star magnetic field: magnetic properties of the progenitor OB stars Authors: V. Petit, G.A. Wade, L. Drissen, T. Montmerle Comments: 40 Years of Pulsars conference: Millisecond Pulsars, Magnetars and More. McGill University, Montreal, Canada, August 12-17, 2007. 5 pages, 4 figures Subjects: Astrophysics (astro-ph)

Ferrario & Wickramasinghe (2006) explored the hypothesis that the magnetic fields of neutron stars are of fossil origin. In this context, they predicted the field distribution of the progenitor OB stars, finding that 5 per cent of main sequence massive stars should have fields in excess of 1kG. We have carried out sensitive ESPaDOnS spectropolarimetric observations to search for direct evidence of such fields in all massive B- and O-type stars in the Orion Nebula Cluster star-forming region. We have detected unambiguous Stokes V Zeeman signatures in spectra of three out of the eight stars observed (38%). Using a new state-of-the-art Bayesian analysis, we infer the presence of strong (kG), organised magnetic fields in their photospheres. For the remaining five stars, we constrain any dipolar fields in the photosphere to be weaker than about 200G. Statistically, the chance of finding three ~kG fields in a sample of eight OB stars is quite low (less than 1%) if the predictions of Ferrario & Wickramasinghe are correct. This implies that either the magnetic fields of neutron stars are not of fossil origin, that the flux-evolution model of Ferrario & Wickramasinghe is incomplete, or that the ONC has unusual magnetic properties. We are undertaking a study of other young star clusters, in order to better explore these possibilities.

[16]  arXiv:0709.4547 [ps, pdf, other]
Title: Probe into the interior of compact stars Authors: Pan Nana, Kang Miao Comments: 3 pages, to be published by American Institute of Physics, ed. D.Lai, X.D.Li and Y.F.Yuan, as the Proceedings of the conference Astrophysics of Compact Objects Subjects: Astrophysics (astro-ph)

The interior of neutron stars contains nuclear matter at very high density for numerous subatomic particles compete with each other. Therefore, confirming the components and properties there is our significant task. Here we summarize the possible methods especial the way of r-mode instability to probe into the neutron star and show our some results. The KHz pulsar in XTE J1739-285 may give a significant implication

[24]  arXiv:0709.4570 [ps, pdf, other]
Title: Gamma-Ray Emission from PWNe Interacting with Molecular Clouds Authors: H. Bartko, W. Bednarek Comments: Proceedings of the 30th ICRC, Merida, Mexico, 2007, in press Subjects: Astrophysics (astro-ph)

We consider a situation in which a pulsar (and its nebula) is formed inside or close to a high density regions of a molecular cloud. We apply a recent model for the gamma radiation of pulsar wind nebulae (PWN), which includes not only radiation processes due to injected leptons but also processes due to injection of relativistic hadrons, in order to calculate the expected gamma-ray emission from such interacting PWNe. The example calculations have been performed for two objects of this type from which directions TeV gamma-ray sources have recently been observed (IC443 and W41). We show that the gamma-ray emission below a few TeV can be produced by leptons accelerated in the past in the vicinity of the pulsars. gamma-rays with energies above ~10 TeV can be produced by hadrons interacting with the matter inside the supernova remnant and surrounding dense clouds. In contrary to the low energy TeV emission, this high energy TeV emission should be correlated with the location of dense clouds able to capture hadrons due to their strong magnetic fields.

[27]  arXiv:0709.4578 [ps, pdf, other]
Title: On the Nature of Precursors in the Radio Pulsar Profiles Authors: S. A. Petrova Comments: 5 pages, no figures. Accepted for publication in MNRAS Letters Subjects: Astrophysics (astro-ph)

In the average profiles of several radio pulsars, the main pulse is accompanied by the preceding component. This so called precursor is known for its distinctive polarization, spectral, and fluctuation properties. Recent single-pulse observations hint that the sporadic activity at the extreme leading edge of the pulse may be prevalent in pulsars. We for the first time propose a physical mechanism of this phenomenon. It is based on the induced scattering of the main pulse radiation into the background. We show that the scattered component is directed approximately along the ambient magnetic field and, because of rotational aberration in the scattering region, appears in the pulse profile as a precursor to the main pulse. Our model naturally explains high linear polarization of the precursor emission, its spectral and fluctuation peculiarities as well as suggests a specific connection between the precursor and the main pulse at widely spaced frequencies. This is believed to stimulate multifrequency single-pulse studies of intensity modulation in different pulsars.

[42]  arXiv:0709.4640 [ps, pdf, other]
Title: Two populations are better than one: Short gamma-ray bursts from SGR giant flares and NS-NS mergers Authors: Robert Chapman (1), Robert S. Priddey (1), Nial R. Tanvir (2) ((1) University of Hertfordshire, UK. (2) University of Leicester, UK.) Comments: 3 pages, 7 figures. To be included in the proceedings of "40 Years of Pulsars" held at McGill University, Montreal, 2007. Proceedings to be published by American Institute of Physics Subjects: Astrophysics (astro-ph)

With a peak luminosity of ~10^47 erg/s, the December 27th 2004 giant flare from SGR1806-20 would have been visible by BATSE (the Burst and Transient Source Experiment) out to ~50 Mpc. It is thus plausible that some fraction of the short duration Gamma-Ray Bursts (sGRBs) in the BATSE catalogue were due to extragalactic magnetar giant flares. According to the most widely accepted current models, the remaining BATSE sGRBs were most likely produced by compact object (neutron star-neutron star or neutron star-black hole) mergers with intrinsically higher luminosities. Previously, by examining correlations on the sky between BATSE sGRBs and galaxies within 155 Mpc, we placed limits on the proportion of nearby sGRBs. Here, we examine the redshift distribution of sGRBs produced by assuming both one and two populations of progenitor with separate Luminosity Functions (LFs). Using the local Galactic SGR giant flare rate and theoretical NS-NS merger rates evolved according to well-known Star Formation Rate parameterisations, we constrain the predicted distributions by BATSE sGRB overall number counts. We show that only a dual population consisting of both SGR giant flares and NS-NS mergers can reproduce the likely local distribution of sGRBs as well as the overall number counts. In addition, the best fit LF parameters of both sub-populations are in good agreement with observed luminosities.

[44]  arXiv:0709.4667 [ps, pdf, other]
Title: The Distance and Age of the SNR Kes 73 and AXP 1E 1841-045 Authors: Denis A. Leahy, Wenwu Tian Comments: submitted to Nature Physics. Only abstract, figures and references available in the website now. If interesting in the whole paper, email me by tww@iras.ucalgary.ca Subjects: Astrophysics (astro-ph)

We provide a new distance estimate to the supernova remnant (SNR) Kes 73 and its associated anomalous X-ray pulsar (AXP) 1E 1841-045. 21 cm HI images and HI absorption/ emission spectra from new VLA observations, and 13CO emission spectra of Kes 73 and two adjacent compact HII regions (G27.276+0.148 and G27.491+0.189) are analyzed. The HI images show prominent absorption features associated with Kes 73 and the HII regions. The absorption appears up to the tangent point velocity giving a lower distance limit to Kes 73 of 7.5 kpc, which has previously been given as the upper limit. Also, G27.276+0.148 and G27.491+0.189 are at the far kinematic distances of their radio recombination line velocities. There is prominent HI emission in the range 80--90 km/s for all three objects. The two HII regions show HI absorption at ~ 84 km/s, but there is no absorption in the Kes 73 absorption spectrum. This implies an upper distance limit of ~ 9.8 kpc to Kes 73. This corrected larger distance to Kes 73/ AXP 1E 1841-045 system leads to a refined age of the SNR of 500 to 1000 yr, and a ~ 50% larger AXP X-ray luminosity.

Cross-lists for Mon, 1 Oct 07

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Replacements for Mon, 1 Oct 07

0 abstracts or titles contain neutron star, magnetar or pulsar


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