We present the analysis of a 100ksec Integral(3-100kev) observation of the transient X-ray pulsar V0332+53 inoutburst. The source is pulsating at P=4.3751+/-0.0002s with a clear double pulse from 6 kev to 60 kev. The average flux was ~550mCrab between 20 kev and 60 kev. We modeled the broad band continuum from 5 kev to 100 kev with a power-law modified by an exponential cut off. We observe three cyclotron lines: the fundamental line at 24.9+/-0.1 kev, the first harmonic at 50.5+/-0.1 kev as well as the second harmonic at71.7+/-0.8 kev, thus confirming the discovery of the harmonic lines by Coburn et al. (2005) in RXTE data.
Magnetars comprise two classes of rotating neutron stars (Soft Gamma Repeaters (SGRs) and Anomalous X-ray Pulsars), whose X-ray emission is powered by an ultrastrong magnetic field, B ~ 10^15 G. Occasionally SGRs enter into active episodes producing many short X-ray bursts; extremely rarely (about once per 50 years per source), SGRs emit a giant flare, an event with total energy at least 1000 times higher than their typical bursts. Here we report that, on 2004 December 27, SGR 1806-20 emitted the brightest extra-solar transient event ever recorded, even surpassing the full moon brightness for 0.2 seconds. The total (isotropic) flare energy is 2x10^46 erg, 100 times higher than the only two previous events, making this flare a once in a century event. This colossal energy release likely occurred during a catastrophic reconfiguration of the magnetar's magnetic field. Such an event would have resembled a short, hard Gamma Ray Burst (GRB) if it had occurred within 40 Mpc, suggesting that extragalactic SGR flares may indeed form a subclass of GRBs.
The recent detection of a young pulsar powering ``the Mouse'', G359.23--0.82, as well as detailed imaging of surrounding nebular X-ray emission, have motivated us to investigate the structural details and polarization characteristics of the radio emission from this axisymmetric source with a supersonic bow shock. Using polarization data at 3.6 and 6cm, we find that the magnetic field wraps around the bow shock structure near the apex of the system, but downnstream runs parallel to the inferred direction of the pulsar's motion. The rotation measure (RM) distribution of the Mouse also suggests that the low degree of polarization combined with a high RM ahead of the pulsar result from internal plasma within the bowshock region. In addition, using sub-arcsecond radio image of the Mouse, we identify modulations in the brightness distribution of the Mouse that may be associated with the unshocked pulsar wind behind the pulsar. Lastly, we discuss the relationship between the Mouse and its neighboring shell-type supernova remnant G359.1--0.5 and argue that these two sources could potentially have the same origin.
Elemental abundance measurements have been obtained for a sample of 18 very metal-poor stars using spectra obtained with the Subaru Telescope High Dispersion Spectrograph. Seventeen stars, among which 16 are newly analyzed in the present work, were selected from candidate metal-poor stars identified in the HK survey of Beers and colleagues. The metallicity range covered by our sample is -3.1 ~< [Fe/H] ~< -2.4. The abundances of carbon, alpha-elements, and iron-peak elements determined for these stars confirm the trends found by previous work. One exception is the large over-abundance of Mg, Al and Sc found in BS16934--002, a giant with [Fe/H] = -2.8. By combining our new results with those of previous studies, we investigate the distribution of neutron-capture elements in very metal-poor stars, focusing on the production of the light neutron-capture elements (e.g., Sr, Y, and Zr).
The build up of the stress whose relaxation is presumed to account for pulsar frequency glitches can be attributed to various mechanisms, of which the most efficient involve differential rotation of the neutron superfluid in the inner layers of the (magnetically braked) solid crust of a rotating neutron star. In such a case it is usually supposed that the stress is attributable to pinning of superfluid vortices to crust nuclei. It was however suggested a few years ago that, even if the pinning effect is too weak, a comparably large stress can still arise just from the deficit of centrifugal buoyancy in the slowed down crust. The previous analysis of this effect was based on a simple description in terms of two (crustal and neutron superfluid) constituents that were supposed to be dynamically independent. However it has recently been shown that it is more realistic to suppose that the constituents will be mutually coupled by a strong (non dissipative) entrainment effect, whose consequences are the subject of the present investigation. It is shown here that allowance for this entrainment reduces the estimated values of the angular velocity differences, thus requiring upward revision of estimated moment of inertia of superfluid involved in observed pulsar gliches. However the entrainment does not substantially affect the previous conclusion that stresses due to a centrifugal buoyancy deficit can be comparable in magnitude (though opposite in sign) to those produced by pinning. An implication is that the glitch phenomenon will be able to occur under very general circumstances, as witnessed by recent observations of large glitches in anomalous X ray pulsars
We study, via a Monte Carlo simulation, a population of isolated asymmetric neutron stars where the magnitude of the magnetic field is low enough so that the dynamical evolution is dominated by the emission of gravitational waves. A starting population, with age uniformly distributed back to 100 Myr (or 500 Myr) and endowed with a birth kick velocity, is evolved in the Galactic gravitational potential to the present time. In describing the initial spatial distribution, the Gould Belt, with an enhanced neutron star formation rate, is taken into account. Different models for the initial period distribution are considered. The star ellipticity, measuring the amount of deformation, is drawn from an exponential distribution. We estimate the detectability of the emitted gravitational signals by the first and planned second generation of interferometric detectors. Results are parametrized by the fraction of the whole galactic neutron star population made of this kind of sources. Some possible mechanisms, which would make possible the existence of such a population, are discussed. A comparison of the gravitational spin-down with the braking due to a possible interaction of the neutron star with the interstellar medium is also presented.
We present our view of the main physical ingredients determining the evolution of neutron star magnetic fields. This includes the basic properties of neutron star matter, possible scenarios for the origin of the magnetic field, constraints and mechanisms for its evolution, and a discussion of our recent work on the Hall drift.
The breakdown of Lorentz's and CPT invariance, as described by the Extension of the Standard Model, gives rise to a modification of the dispersion relation of particles. Consequences of such a modification are reviewed in the framework of pulsar kicks induced by neutrino oscillations (active-sterile conversion). A peculiar feature of the modified energy-momentum relations is the occurrence of terms of the form $\delta {\bbox \Pi}\cdot {\bf {\hat p}}$, where $\delta {\bbox \Pi}$ accounts for the difference of spatial components of flavor depending coefficients which lead to the departure of the Lorentz symmetry, and ${\bf {\hat p}}={\bf p}/p$, being ${\bf p}$ the neutrino momentum. Owing to the relative orientation of ${\bf p}$ with respect to $\delta {\bbox \Pi}$, the {\it coupling} $\delta {\bbox \Pi}\cdot {\bf {\hat p}}$ may induce the mechanism to generate the observed pulsar velocities. Topics related to the velocity distribution of pulsars are also discussed.
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