The X-ray emission from accreting black-holes and neutron stars features strong variability on sub-second time scales, with very complex and broad phenomenology. From high-frequency quasi-periodic oscillations to rapidly changing X-ray burst oscillations to millisecond pulsations, these are weak signals immersed in strong noise and their study is pushing instrument capabilities to their limit. The scientific significance of fast time variability studies are both astronomical (properties of accretion flows, nature and evolution of sources) and physical (effects of General Relativity, equation of state of degenerate matter). I first review the main observational properties, then discuss the future prospects and observational needs.

Anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs) are two small classes of X-ray sources strongly suspected to host a magnetar, i.e. an ultra-magnetized neutron star with $B\approx 10^14-10^15 G. Many SGRs/AXPs are known to be variable, and recently the existence of genuinely "transient" magnetars was discovered. Here we present a comprehensive study of the pulse profile and spectral evolution of the two transient AXPs (TAXPs) XTE J1810-197 and CXOU J164710.2-455216. Our analysis was carried out in the framework of the twisted magnetosphere model for magnetar emission. Starting from 3D Monte Carlo simulations of the emerging spectrum, we produced a large database of synthetic pulse profiles which was fitted to observed lightcurves in different spectral bands and at different epochs. This allowed us to derive the physical parameters of the model and their evolution with time, together with the geometry of the two sources, i.e. the inclination of the line-of-sight and of the magnetic axis with respect to the rotation axis. We then fitted the (phase-averaged) spectra of the two TAXPs at different epochs using a model similar to that used to calculate the pulse profiles ntzang in XSPEC) freezing all parameters to the values obtained from the timing analysis, and leaving only the normalization free to vary. This provided acceptable fits to XMM-Newton data in all the observations we analyzed. Our results support a picture in which a limited portion of the star surface close to one of the magnetic poles is heated at the outburst onset. The subsequent evolution is driven both by the cooling/varying size of the heated cap and by a progressive untwisting of the magnetosphere.

The Fermi Large Area Telescope (LAT) data have confirmed the pulsed emission from all six high-confidence gamma-ray pulsars previously known from the EGRET observations. We report results obtained from the analysis of 13 months of LAT data for three of these pulsars (PSR J1057-5226, PSR J1709-4429, and PSR J1952+3252) each of which had some unique feature among the EGRET pulsars. The excellent sensitivity of LAT allows more detailed analysis of the evolution of the pulse profile with energy and also of the variation of the spectral shape with phase. We measure the cutoff energy of the pulsed emission from these pulsars for the first time and provide a more complete picture of the emission mechanism. The results confirm some, but not all, of the features seen in the EGRET data.

Boutloukos et al. (2006) discovered twin-peak quasi-periodic oscillations (QPOs) in 11 observations of the peculiar Z-source Circinus X-1. Among several other conjunctions the authors briefly discussed the related estimate of the compact object mass following from the geodesic relativistic precession model for kHz QPOs. Neglecting the neutron star rotation they reported the inferred mass M_0 = 2.2 +/- 0.3 M_\sun. We present a more detailed analysis of the estimate which involves the frame-dragging effects associated with rotating spacetimes. For a free mass we find acceptable fits of the model to data for (any) small dimensionless compact object angular momentum j=cJ/GM^2. Moreover, quality of the fit tends to increase very gently with rising j. Good fits are reached when M ~ M_0[1+0.55(j+j^2)]. It is therefore impossible to estimate the mass without the independent knowledge of the angular momentum and vice versa. Considering j up to 0.3 the range of the feasible values of mass extends up to 3M_\sun. We suggest that similar increase of estimated mass due to rotational effects can be relevant for several other sources.

We present results from Swift, XMM-Newton, and deep INTEGRAL monitoring in the region of GRB 050925. This short Swift burst is a candidate for a newly discovered soft gamma-ray repeater (SGR) with the following observational burst properties: 1) galactic plane (b=-0.1 deg) localization, 2) 150 msec duration, and 3) a blackbody rather than a simple power-law spectral shape (with a significance level of 97%). We found two possible X-ray counterparts of GRB 050925 by comparing the X-ray images from Swift XRT and XMM-Newton. Both X-ray sources show the transient behavior with a power-law decay index shallower than -1. We found no hard X-ray emission nor any additional burst from the location of GRB 050925 in ~5 Ms of INTEGRAL data. We discuss about the three BATSE short bursts which might be associated with GRB 050925, based on their location and the duration. Assuming GRB 050925 is associated with the H II regions (W 58) at the galactic longitude of l=70 deg, we also discuss the source frame properties of GRB 050925.

We have observed the 3.8 s pulsar CXOU J171405.7-381031 with XMM-Newton, and discovered the significant dP/dt of 6.40+/-0.14X10^-11 s/s from this source for the first time, with the aid of archival Chandra data. The characteristic age (950 yr), the magnetic field strength (5X10^14 G), and the spin-down luminosity (4.5X10^34 erg/s) derived from P and dP/dt lead us to conclude that CXOU J171405.7-381031 should be identified as a new magnetar. The obtained characteristic age indicates that CXOU J171405.7-381031 is youngest among all known anomalous X-ray pulsars, which is consistent with the age estimation from the thermal X-rays of the associated supernova remnant. The ratio between 2-10 keV luminosity and spin-down luminosity is almost unity, which implies that CXOU J171405.7-381031 is the key source to connect magnetars and traditional radio pulsars.

Nonaxisymmetric, meridional circulation inside a neutron star, excited by a glitch and persisting throughout the post-glitch relaxation phase, emits gravitational radiation. Here, it is shown that the current quadrupole contributes more strongly to the gravitational wave signal than the mass quadrupole evaluated in previous work. We calculate the signal-to-noise ratio for a coherent search and conclude that a large glitch may be detectable by second-generation interferometers like the Laser Interferometer Gravitational-Wave Observatory. It is shown that the viscosity and compressibility of bulk nuclear matter, as well as the stratification length-scale and inclination angle of the star, can be inferred from a gravitational wave detection in principle.

Pulsar timing arrays act to detect gravitational waves by observing the small, correlated effect the waves have on pulse arrival times at Earth. This effect has conventionally been evaluated assuming the gravitational wave phasefronts are planar across the array, an assumption that is valid only for sources at distances $R\gg2\pi{}L^2/\lambda$, where $L$ is physical extent of the array and $\lambda$ the radiation wavelength. In the case of pulsar timing arrays (PTAs) the array size is of order the pulsar-Earth distance (kpc) and $\lambda$ is of order pc. Correspondingly, for point gravitational wave sources closer than $\sim100$~Mpc the PTA response is sensitive to the source parallax across the pulsar-Earth baseline. Here we evaluate the PTA response to gravitational wave point sources including the important wavefront curvature effects. Taking the wavefront curvature into account the relative amplitude and phase of the timing residuals associated with a collection of pulsars allows us to measure the distance to, and sky position of, the source.

We calculate stationary configurations of rapidly rotating compact stars in general relativity, to study the properties of circular orbits of test particles in the equatorial plane. We seek for simple, but precise, analytical formulae for the orbital frequency, specific angular momentum and binding energy of a test particle, valid for any equation of state and for any rotation frequency of the rigidly rotating compact star, up to the mass shedding limit. Numerical calculations are performed using precise 2-D codes based on multi-domain spectral methods. Models of rigidly rotating neutron stars and the spacetime outside them are calculated for several equations of state of dense matter. Calculations are also performed for quark stars built of self-bound quark matter. At the mass shedding limit, the rotational frequency converges to a Schwarzschildian orbital frequency at the equator. We show that orbital frequency for any orbit outside equator is also well-approximated by a Schwarzschildian formula. Using a simple approximation for the frame-dragging term, we obtain approximate expressions for the specific angular momentum and specific energy on the corotating circular orbits in the equatorial plane of neutron star, valid down to the stellar equator. The formulae recover reference numerical values with typically 1% of accuracy for neutron stars with M > 0.5 M_sun. They are less precise for quark stars built of self-bound quark matter.

Neutron rich matter is at the heart of many fundamental questions in Nuclear Physics and Astrophysics. What are the high density phases of QCD? Where did the chemical elements come from? What is the structure of many compact and energetic objects in the heavens, and what determines their electromagnetic, neutrino, and gravitational-wave radiations? Moreover, neutron rich matter is being studied with an extraordinary variety of new tools such as Facility for Rare Isotope Beams (FRIB) and the Laser Interferometer Gravitational Wave Observatory (LIGO). We describe the Lead Radius Experiment (PREX) that is using parity violation to measure the neutron radius in 208Pb. This has important implications for neutron stars and their crusts. Using large scale molecular dynamics, we model the formation of solids in both white dwarfs and neutron stars. We find neutron star crust to be the strongest material known, some 10 billion times stronger than steel. It can support mountains on rotating neutron stars large enough to generate detectable gravitational waves. Finally, we describe a new equation of state for supernova and neutron star merger simulations based on the Virial expansion at low densities, and large scale relativistic mean field calculations.

We report the analysis of high-resolution, high-S/N spectra of an extremely metal-poor, extremely C-rich red giant, Seg 1-7, in the Segue 1 system - described in the literature alternatively as an unusually extended globular cluster or an ultra-faint dwarf galaxy. The radial velocity of Seg 1-7 coincides precisely with the systemic velocity of Segue 1, and its chemical abundance signature of [Fe/H] = -3.52, [C/Fe] = +2.3, [N/Fe] = +0.8, [Na/Fe] = +0.53, [Mg/Fe] = +0.94, [Al/Fe] = +0.23 and [Ba/Fe] < -1.0 is similar to that of the rare and enigmatic class of Galactic halo objects designated CEMP-no (Carbon-rich, Extremely Metal-Poor and with no enhancement (over solar ratios) of heavy neutron-capture elements). This is the first star in a Milky Way ``satellite'' that unambiguously lies on the metal-poor, C-rich branch of the Aoki et al. (2007) bimodal distribution defined by field halo stars in the ([C/Fe], [Fe/H])-plane. Available data permit us only to identify Seg 1-7 as a member of an ultra-faint dwarf galaxy or as debris from the Sgr dwarf spheroidal galaxy. In either case, this demonstrates that at extremely low abundance, [Fe/H ] < -3.0, star formation and associated chemical evolution proceeded similarly in the progenitors of both the field halo and satellite systems. By extension, this is consistent with other recent suggestions the most metal-poor dwarf spheroidal and ultra-faint dwarf satellites were the building blocks of the Milky Way's outer halo.

In order to study precession and interstellar magnetic field variations, we measured the polarized position angle of 81 pulsars at several-month intervals for four years. We show that the uncertainties in a single-epoch measurement of position angle is usually dominated by random pulse-to-pulse jitter of the polarized subpulses. Even with these uncertainties, we find that the position angle variations in 19 pulsars are significantly better fitted (at the 3 {\sigma} level) by a sinusoid than by a constant. Such variations could be caused by precession, which would then indicate periods of ~ (200 - 1300) d and amplitudes of ~(1 - 12) degrees. We narrow this collection to four pulsars that show the most convincing evidence of sinusoidal variation in position angle. Also, in a handful of pulsars, single discrepant position angle measurements are observed which may result from the line of sight passing across a discrete ionized, magnetized structure. We calculate the standard deviation of position angle measurements from the mean for each pulsar, and relate these to limits on precession and interstellar magnetic field variations.

The gamma-ray binaries LS 5039 and LS I +61 303 have been detected by Cerenkov telescopes at TeV energies, exhibiting periodic behavior correlated with the orbital period. These gamma-ray binary systems have also been recently detected by the Fermi Gamma-ray Telescope at GeV energies, and combination of GeV and TeV observations are providing both, expected and surprising results. We summarize these results, also considering the multi-frequency scenario, from the perspective of pulsar systems. We discuss similarities and differences of models in which pulsar wind/star wind shocks, or pulsar wind zone processes lead to particles accelerated enough to emit TeV photons. We discuss in detail the caveats of the current observations for detecting either accretion lines or pulsations from these objects. We also comment on the possibility for understanding the GeV to TeV emission from these binaries with a 2-components contribution to their spectrum. We show that it would be possible to accommodate both, normal pulsar emission and GeV / TeV fluxes that vary with orbital phase. We point out several aspects of this idea that are subject to test with data being currently taken.

The radio, optical, X-ray and gamma-ray nebulae that surround many pulsars are thought to arise from synchrotron and inverse Compton emission. The energy powering this emission, as well as the magnetic fields and relativistic particles, are supplied by a "wind" driven by the central object. The inner parts of the wind can be described using the equations of MHD, but these break down in the outer parts, when the density of charge carriers drops below a critical value. This paper reviews the wave properties of the inner part (striped wind), and uses a relativistic two-fluid model (cold electrons and positrons) to re-examine the nonlinear electromagnetic modes that propagate in the outer parts. It is shown that in a radial wind, two solutions exist for circularly polarised electromagnetic modes. At large distances one of them turns into a freely expanding flow containing a vacuum wave, whereas the other decelerates, corresponding to a confined flow.

Gamma-ray binaries are suitable sources to study high-energy processes in jets and outflows in general. In the last years, there has been a lot of activity in the field of gamma-ray binaries to identify the different factors that shape their non-thermal spectra, which ranges from radio to very high energies, as well as their lightcurves. In this work, I discuss the main aspects of the non-thermal emission in this class of objects, which presently includes high-mass microquasars, high-mass binaries hosting a non-accreting pulsar and, probably, massive star binaries; few potential candidates to be gamma-ray binaries are also presented. Finally, the importance of gamma-ray absorption is discussed, and the main physical ingredients, which are likely involved in the non-thermal radiation in gamma-ray binaries, are briefly considered.

High Time Resolution Astrophysics (HTRA) concerns itself with observations on short scales normally defined as being lower than the conventional read-out time of a CCD. As such it is concerned with condensed objects such as neutron stars, black holes and white dwarfs, surfaces with extreme magnetic reconnection phenomena, as well as with planetary scale objects through transits and occultations. HTRA is the only way to make a major step forward in our understanding of several important astrophysical and physical processes; these include the extreme gravity conditions around neutron stars and stable orbits around stellar mass black holes. Transits, involving fast timing, can give vital information on the size of, and satellites around exoplanets. In the realm of fundamental physics very interesting applications lie in the regime of ultra-high time resolution, where quantum-physical phenomena, currently studied in laboratory physics, may be explored. HTRA science covers the full gamut of observational optical/IR astronomy from asteroids to {\gamma}-rays bursts, contributing to four out of six of AstroNet's fundamental challenges described in their Science Vision for European Astronomy. Giving the European-Extremely Large Telescope (E-ELT) an HTRA capability is therefore importance. We suggest that there are three possibilities for HTRA and E-ELT. These are, firstly giving the E-ELT first light engineering camera an HTRA science capability. Secondly, to include a small HTRA instrument within another instrument. Finally, to have separate fibre feeds to a dedicated HTRA instrument. In this case a small number of fibres could be positioned and would provide a flexible and low cost means to have an HTRA capability. By the time of E-ELT first light, there should be a number of significant developments in fast detector arrays, in particular in the infra-red (IR) region.

We report the discovery of multi-scale X-ray jets from the accreting neutron star X-ray binary, Circinus X-1. The bipolar outflows show wide opening angles and are spatially coincident with the radio jets seen in new high-resolution radio images of the region. The morphology of the emission regions suggests that the jets from Circinus X-1 are running into a terminal shock with the interstellar medium, as is seen in powerful radio galaxies. This and other observations indicate that the jets have a wide opening angle, suggesting that the jets are either not very well collimated or precessing. We interpret the spectra from the shocks as cooled synchrotron emission and derive a cooling age of approximately 1600 yr. This allows us to constrain the jet power to be between 3e35 erg/s and 2e37 erg/s, making this one of a few microquasars with a direct measurement of its jet power and the only known microquasar that exhibits stationary large-scale X-ray emission.

Cross-sections for Rutherford scattering, Coulomb bremsstrahlung and pair creation, have been calculated at very high magnetic fields in order to investigate the photo-production of protons at the polar caps of pulsars whose spin is antiparallel with the polar magnetic flux density. The Landau-Pomeranchuk-Migdal effect at very high magnetic fields is included in a simple electron Green function.

This paper summarizes our recent results on tidal interaction in high mass X-ray binaries and symbiotic stars. We demonstrate that the giant in symbiotic stars with orbital periods <1200 d are co-rotating (synchronized). The symbiotics MWC 560 and CD-4314304 probably have high orbital eccentricity. The giants in symbiotic binaries rotate faster than the field giants, likely their rotation is accelerated by the tidal force of the white dwarf.
The giant/supergiant High mass X-ray binaries with orbital periods <40 d are synchronized. However the Be/X-ray binaries are not synchronized. In the Be/X-ray binaries the circumstellar disks are denser and smaller than those in isolated Be stars, probably truncated by the orbiting neutron star.

Novel method of calculating Nuclear Statistical Equilibrium is presented. Basic equations are carefully solved using arbitrary precision arithmetic. Special interpolation procedure is then used to retrieve all abundances using tabulated results for neutrons and protons, together with basic nuclear data. Proton and neutron abundance tables, basic nuclear data and partition functions for nuclides used in calculations are provided. Simple interpolation algorithm using pre-calculated p and n abundances tabulated as a functions of kT, rho and Ye is outlined. Unique properties of this method are: (1) ability to pick-up out of NSE selected nuclei only (2) computational time scaling linearly with number of re-calculated abundances (3) relatively small amount of stored data: only two large tables (4) slightly faster than solving NSE equations using traditional Newton-Raphson methods for small networks (few tens of species); superior for huge (800-3000) networks (5) do not require initial guess; works well on random input (6) can tailored to specific application (7) ability to use third-party NSE solvers to obtain fully compatible tables (8) encapsulation of the NSE code for bug-free calculations.
Range of applications for this approach is possible: coverage test of traditional NSE Newton-Raphson codes, generating starting values, code-to-code verification and possible replacement of the old legacy procedures in supernova simulations.

Nonlinear dissipative systems in the state of self-organized criticality release energy sporadically in avalanches of all sizes, such as in earthquakes, auroral substorms, solar and stellar flares, soft gamma-ray repeaters, and pulsar glitches. The statistical occurrence frequency distributions of event energies $E$ generally exhibit a powerlaw-like function $N(E)\propto E^{-\alpha_E}$ with a powerlaw slope of $\alpha_E \approx 1.5$. The powerlaw slope $\alpha_E$ of energies can be related to the fractal dimension $D$ of the spatial energy dissipation domain by $D=3/\alpha_E$, which predicts a powerlaw slope $\alpha_E=1.5$ for area-rupturing or area-spreading processes with $D=2$. For solar and stellar flares, 2-D area-spreading dissipation domains are naturally provided in current sheets or separatrix surfaces in a magnetic reconnection region. Thus, this universal scaling law provides a useful new diagnostic on the topology of the spatial energy dissipation domain in geophysical and astrophysical observations.

After the initiation of the explosion of core-collapse supernovae, neutrinos emitted from the nascent neutron star drive a supersonic baryonic outflow. This neutrino-driven wind interacts with the more slowly moving, earlier supernova ejecta forming a wind termination shock (or reverse shock), which changes the local wind conditions and their evolution. Important nucleosynthesis processes (alpha-process, charged-particle reactions, r-process, and vp-process) occur or might occur in this environment. The nucleosynthesis depends on the long-time evolution of density, temperature, and expansion velocity. Here we present two-dimensional hydrodynamical simulations with an approximate description of neutrino-transport effects, which for the first time, follow the post-bounce accretion, onset of the explosion, wind formation, and the wind expansion through the collision with the preceding supernova ejecta. Our results demonstrate a great impact of the anisotropic ejecta distribution on the position of the reverse shock, wind profile, and long-time evolution and show a big effect of multidimensional features on nucleosynthesis-relevant conditions.

Recent neutron star observations suggest that the masses and radii of neutron stars may be smaller than previously considered, which would disfavor a purely nucleonic equation of state. In our model, we use a the flavor SU(3) sigma model that includes delta resonances and hyperons in the equation of state. We find that if the coupling of the delta resonances to the vector mesons is slightly smaller than that of the nucleons, we can reproduce both the measured mass-radius relationship and the extrapolated equation of state.

We report on observations of the unusual neutron-star binary system FIRST J102347.6+003841 carried out using the XMM-Newton satellite. This system consists of a radio millisecond pulsar in an 0.198-day orbit with a ~0.2 solar-mass Roche-lobe-filling companion, and appears to have had an accretion disk in 2001. We observe a hard power-law spectrum (\Gamma = 1.26(4)) with a possible thermal component, and orbital variability in X-ray flux and possibly hardness of the X-rays. We also detect probable pulsations at the pulsar period (single-trial significance ~4.5 sigma from an 11(2)% modulation), which would make this the first system in which both orbital and rotational X-ray pulsations are detected. We interpret the emission as a combination of X-rays from the pulsar itself and from a shock where material overflowing the companion meets the pulsar wind. The similarity of this X-ray emission to that seen from other millisecond pulsar binary systems, in particular 47 Tuc W (PSR J0024-7204W) and PSR J1740-5340, suggests that they may also undergo disk episodes similar to that seen in J1023 in 2001.

We present the evolution of the radio emission from the 2.8-s pulsar of the double pulsar system PSR J0737-3039A/B. We provide an update on the Burgay et al. (2005) analysis by describing the changes in the pulse profile and flux density over five years of observations, culminating in the B pulsar's radio disappearance in 2008 March. Over this time, the flux density decreases by 0.177 mJy/yr at the brightest orbital phases and the pulse profile evolves from a single to a double peak, with a separation rate of 2.6 deg/yr. The pulse profile changes are most likely caused by relativistic spin precession, but can not be easily explained with a circular hollow-cone beam as in the model of Clifton & Weisberg (2008). Relativistic spin precession, coupled with an elliptical beam, can model the pulse profile evolution well. This particular beam shape predicts geometrical parameters for the two bright orbital phases which are consistent and similar to those derived by Breton et al. (2008). However, the observed decrease in flux over time and B's eventual disappearance cannot be easily explained by the model and may be due to the changing influence of A on B.

We present results from observations of the magnetar 1E 1547.0-5408 (SGR J1550-5418) taken with the Chandra X-ray Observatory and the Rossi X-ray Timing Explorer (RXTE) following the source's outbursts in 2008 October and 2009 January. During the time span of the Chandra observations, which covers days 4 through 23 and days 2 through 16 after the 2008 and 2009 events, respectively, the source spectral shape remained stable, while the pulsar's spin-down rate in the same span in 2008 increased by a factor of 2.2 as measured by RXTE. The lack of spectral variation suggests decoupling between magnetar spin-down and radiative changes, hence between the spin-down-inferred magnetic field strength and that inferred spectrally. We also found a strong anti-correlation between the phase-averaged flux and the pulsed fraction in the 2008 and 2009 Chandra data, but not in the pre-2008 measurements. We discuss these results in the context of the magnetar model.

Resluts of 3D numerical simulations in the framework of pair starved polar cap model (PSPC) for millisecond pulsars are presented. In the investigated PSPC model electric field structure highly depends on the pulsar inclination which is clearly visible in the computed spectra of electrons escaping pulsar magnetosphere which become bimodal with the increasing inclination. This is an important result for modelling very high energy radiation from globular clusters where currently the standard power law or monoenergetic electron distributions are used.

We describe our newly developed two different, three dimensional magneto hydrodynamical codes. One of our code is written in the Newtonian limit (NMHD) and the other is in the full general relativistic code (GRMHD). Both codes employ Adaptive Mesh Refinement and, in GRMHD, the metric is evolved with the "Baumgarte-Shapiro-Shibata- Nakamura" formalism known as the most stable method at present. We have done several test problems and calculated the gravitational collapse of a 15Msun as our first practical test. This is the first 3DMHD simulation for the collapse of a massive star on the fully dynamical background. Main results are; (1) High velocity bipolar outflow is driven from the proto-neutronstar and rolls through along the rotational axis in the strongly magnetized models (~10^12G at pre-collapse stage); (2) A one-armed spiral structure appears which we consider originated from the low-|T/W| instability; (3) In weakly magnetized model (10^9G at pre-collapse stage), the convective over turn highly deforms the magnetic field configuration. However, we do not find exponential growth of the magnetic field seen if the magneto rotational instability operates. We estimate the wave length of the magneto rotational instability in linear mode and found that our numerical resolution is not adequate, approximately 10 times, to capture the linear mode amplification; (4) By comparing GRMHD and NMHD models, the maximum density increases about ~30% in the vicinity of the center. Roughly speaking, however, the dynamical evolutions, such as the time of core bounce or formation of the bipolar outflow, are similar.

We report results of a numerical-relativity simulation for the merger of a black hole-neutron star binary with a variety of equations of state (EOSs) modeled by piecewise polytropes. We focus in particular on the dependence of the gravitational waveform at the merger stage on the EOSs. The initial conditions are computed in the moving-puncture framework, assuming that the black hole is nonspinning and the neutron star has an irrotational velocity field. For a small mass ratio of the binaries (e.g., MBH/MNS = 2 where MBH and MNS are the masses of the black hole and neutron star, respectively), the neutron star is tidally disrupted before it is swallowed by the black hole irrespective of the EOS. Especially for less-compact neutron stars, the tidal disruption occurs at a more distant orbit. The tidal disruption is reflected in a cutoff frequency of the gravitational-wave spectrum, above which the spectrum amplitude exponentially decreases. A clear relation is found between the cutoff frequency of the gravitational-wave spectrum and the compactness of the neutron star. This relation also depends weakly on the stiffness of the EOS in the core region of the neutron star, suggesting that not only the compactness but also the EOS at high density is reflected in gravitational waveforms. The mass of the disk formed after the merger shows a similar correlation with the EOS, whereas the spin of the remnant black hole depends primarily on the mass ratio of the binary, and only weakly on the EOS. Properties of the remnant disks are also analyzed.

In this paper, we discuss our first attempts to model the broadband persistent emission of magnetars within a self consistent, physical scenario. We present the predictions of a synthetic model that we calculated with a new Monte Carlo 3-D radiative code. The basic idea is that soft thermal photons (e.g. emitted by the star surface) can experience resonant cyclotron upscattering by a population of relativistic electrons threated in the twisted magnetosphere. Our code is specifically tailored to work in the ultra-magnetized regime; polarization and QED effects are consistently accounted for, as well different configurations for the magnetosphere. We discuss the predicted spectral properties in the 0.1-1000 keV range, the polarization properties, and we present the model application to a sample of magnetars soft X-ray spectra.

We have redetermined the parallax and proper motion of the nearby isolated neutron star RX~J185635-3754. We used eight observations with the high resolution camera of the HST/ACS taken from 2002 through 2004. We performed the astrometric fitting using five independent methods, all of which yielded consistent results. The mean estimate of the distance is 123 (+11, -15) pc (1 sigma), in good agreement with our earlier published determination.

There is a general consensus about the fact that the magnetar scenario provides a convincing explanation for several of the observed properties of the Anomalous X-ray Pulsars and the Soft Gamma Repeaters. However, the origin of the emission observed at low energies is still an open issue. We present a quantitative model for the emission in the optical/infrared band produced by curvature radiation from magnetospheric charges, and compare results with current magnetars observations.

Pulsar timing is a promising technique for detecting low frequency sources of gravitational waves. Historically the focus has been on the detection of diffuse stochastic backgrounds, such as those formed from the superposition of weak signals from a population of binary black holes. More recently, attention has turned to members of the binary population that are nearer and brighter, which stand out from the crowd and can be individually resolved. Here we show that the timing data from an array of pulsars can be used to recover the physical parameters describing an individual black hole binary to good accuracy, even for moderately strong signals. A novel aspect of our analysis is that we include the distance to each pulsar as a search parameter, which allows us to utilize the full gravitational wave signal. This doubles the signal power, improves the sky location determination by an order of magnitude, and allows us to extract the mass and the distance to the black hole binary.

We report on sensitive new 1.4-GHz VLA radio observations of the pulsar wind nebula G21.5-0.9, powered by PSR J1833-1034, and its environs. Our observations were targeted at searching for the radio counterpart of the shell-like structure seen surrounding the pulsar wind nebula in X-rays. Some such radio emission might be expected as the ejecta from the <~ 1000 yr old supernova expand and interact with the surrounding medium. We find, however, no radio emission from the shell, and can place a conservative 3-sigma upper limit on its 1-GHz surface brightness of 7 x 10^-22 W/m^2/Hz/sr, comparable to the lowest limits obtained for radio emission from shells around other pulsar-wind nebulae. Our widefield radio image also shows the presence of two extended objects of low-surface brightness. We re-examine previous 327-MHz images, on which both the new objects are visible. We identify the first, G21.64-0.84, as a new shell-type supernova remnant, with a diameter of ~13' and an unusual double-shell structure. The second, G21.45-0.59, ~1' in diameter, is likely an HII region.

(Abridged) In 1999, Chandra revealed a 150"-radius X-ray halo surrounding the 40"-radius PWN G21.5-0.9. A 2005 imaging study showed that the halo is limb-brightened, and suggested this feature is a candidate for the long-sought SNR shell. We present a spectral analysis of G21.5-0.9, using the longest effective observation to date (578.6 ks with ACIS, 278.4 ks with HRC) to study unresolved questions about the spectral nature of remnant features, such as the limb-brightening of the X-ray halo and the bright knot in the northern part of the halo. The Chandra analysis favours the non-thermal interpretation of the limb. Its spectrum is well fit with a power-law model with a photon index $\Gamma$ = 2.13 (1.94-2.33) and a luminosity of L_x (0.5-8 keV) = (2.3 +/- 0.6) x 10^33 erg/s (at an assumed distance of 5.0 kpc). An srcut model was also used to fit the spectrum between radio and X-ray energies. We find that the maximum energy to which electrons are accelerated at the shock ranges from ~60-130 TeV (B/10$\mu$G)^(-1/2), where B is the magnetic field in units of $\mu$G. For the northern knot, we constrain previous models and find that a two-component power-law (or srcut) + pshock model provides an adequate fit, with the pshock model requiring a very low ionization timescale and solar abundances for Mg and Si. Our spectroscopic study of J1833-1034, the highly energetic pulsar powering G21.5-0.9, shows that its spectrum is dominated by hard non-thermal X-ray emission with some evidence of a thermal component that represents ~9% of the observed non-thermal emission and that suggests non-standard rapid cooling of the neutron star. Finally, the ACIS and HRC-I images provide the first evidence for variability in the PWN, a property observed in other PWNe such as the Crab and Vela.

The goal of this article is to summarize the current state of play in the field of radio pulsar statistics. Simply put, from the observed sample of objects from a variety of surveys with different telescopes, we wish to infer the properties of the underlying sample and to connect these with other astrophysical populations (for example supernova remnants or X-ray binaries). The main problem we need to tackle is the fact that, like many areas of science, the observed populations are often heavily biased by a variety of selection effects. After a review of the main effects relevant to radio pulsars, I discuss techniques to correct for them and summarize some of the most recent results. Perhaps the main point I would like to make in this article is that current models to describe the population are far from complete and often suffer from strong covariances between input parameters. That said, there are a number of very interesting conclusions that can be made concerning the evolution of neutron stars based on current data. While the focus of this review will be on the population of isolated Galactic pulsars, I will also briefly comment on millisecond and binary pulsars as well as the pulsar content of globular clusters and the Magellanic Clouds.

Diffusive nuclear burning of H by an underlying material capable of capturing protons can readily consume H from the surface of neutron stars (NSs) during their early cooling history. In the absence of subsequent accretion, it will be depleted from the photosphere. We now extend diffusive nuclear burning to He, motivated by the recent observation by Ho \& Heinke of a carbon atmosphere on the NS in the Cassiopeia A supernova remnant. We calculate the equilibrium structure of He on an underlying $\alpha$ capturing material, accounting for thermal, mass defect, and Coulomb corrections on the stratification of material with the same zeroth order $\mu_e = A/Z$. We show that Coulomb corrections dominate over thermal and mass defect corrections in the highly degenerate part of the envelope. We also show that the bulk of the He sits deep in the envelope rather than near the surface. Thus, even if the photospheric He abundance is low, the total He column could be substantially larger than the photospheric column, which may have implications for rapid surface evolution ($\approx 1$ yr timescales) of neutron stars. When nuclear reactions are taken into account, we find that for base temperatures $\gtrsim 1.6 \times 10^8$ K, He is readily captured onto C. As these high temperatures are present during the early stages of NS evolution, we expect that the primordial He is completely depleted from the NS surface like the case for primordial H. We also find that magnetic fields $\lesssim 10^{12}$ G do not affect our conclusions. Armed with the results of this work and our prior efforts, we expect that primordial H and He are depleted, and so any observed H or He on the surfaces of these NS must be due to subsequent accretion (with or without spallation). If this subsequent accretion can be prevented, the underlying mid-Z material would be exposed.

The flux of gamma rays with energies >100MeV is dominated by diffuse emission from CRs illuminating the ISM of our Galaxy through the processes of Bremsstrahlung, pion production and decay, and inverse-Compton scattering. The study of this diffuse emission provides insight into the origin and transport of CRs. We searched for gamma-ray emission from the SMC in order to derive constraints on the CR population and transport in an external system with properties different from the Milky Way. We analysed the first 17 months of continuous all-sky observations by the Large Area Telescope of the Fermi mission to determine the spatial distribution, flux and spectrum of the gamma-ray emission from the SMC. We also used past radio synchrotron observations of the SMC to study the population of CR electrons specifically. We obtained the first detection of the SMC in high-energy gamma rays, with an integrated >100MeV flux of (3.7 +/-0.7) x10e-8 ph/cm2/s, with additional systematic uncertainty of <16%. The emission is steady and from an extended source ~3{\deg} in size. It is not clearly correlated with the distribution of massive stars or neutral gas, nor with known pulsars or SNRs, but a certain correlation with supergiant shells is observed. The observed flux implies an upper limit on the average CR nuclei density in the SMC of ~15% of the value measured locally in the Milky Way. The population of high-energy pulsars of the SMC may account for a substantial fraction of the gamma-ray flux, which would make the inferred CR nuclei density even lower. The average density of CR electrons derived from radio synchrotron observations is consistent with the same reduction factor but the uncertainties are large. From our current knowledge of the SMC, such a low CR density does not seem to be due to a lower rate of CR injection and rather indicates a smaller CR confinement volume characteristic size.

Binary radio pulsars are generally believed to have been spun up to millisecond periods (i.e. recycling) via mass accretion from their donor stars, and they are the descendants of neutron star low-mass X-ray binaries. However, some studies indicate that the formation of pulsars from the accretion-induced collapse (AIC) of accreting white dwarfs (WDs) cannot be excluded. In this work, we use a population synthesis code to examine if the AIC channel can produce eccentric binary millisecond pulsars (BMSPs) in the Galaxy. Our simulated results indicate that, only when the natal MSPs receive a relatively strong kick ($\ga100\rm km\,s^{-1}$), can the AIC channel produce $\sim 10-180$ eccentric ($e>0.1$) BMSPs in the Galaxy, most of which are accompanied by a Helium star. Such a kick seems to be highly unlikely in the conventional AIC process, hence the probability of forming eccentric BMSPs via the AIC channel can be ruled out. Even if a high kick is allowed, the AIC channel cannot produce eccentric BMSPs with an orbital period of $\ga 20$ days. Therefore, we propose that the peculiar BMSP PSR J1903+0327 cannot be formed by the AIC channel. However, the AIC evolutionary channel may produce some fraction of isolated millisecond pulsars, and even sub-millisecond pulsars if they really exist.

We report on observations of a SSS in M31, r1-25, that has exhibited spectral changes to harder X-ray states. We document these spectral changes. In addition, we show that they have important implications for modeling the source. Quasisoft states in a source that has been observed as an SSS represent a newly-discovered phenomenon. We show how such state changers could prove to be examples of unusual black hole or neutron star accretors. Future observations of this and other state changers can provide the information needed to determine the nature(s) of these intriguing new sources.

Einstein@Home aggregates the computer power of hundreds of thousands of volunteers from 192 countries to "mine" large data sets. It has now found a 40.8 Hz isolated pulsar in radio survey data from the Arecibo Observatory taken in February 2007. Additional timing observations indicate that this pulsar is likely a disrupted recycled pulsar. PSR J2007+2722's pulse profile is remarkably wide with emission over almost the entire spin period; the pulsar likely has closely aligned magnetic and spin axes. The massive computing power provided by volunteers should enable many more such discoveries.

The light curves observed from X-ray pulsars and magnetars reflect the radiation emission pattern, the geometry of the magnetic field, and the neutron star compactness. We study the statistics of X-ray pulse profiles in order to constrain the neutron star compactness and the magnetic field geometry. We collect the data for 124 X-ray pulsars, which are mainly in high-mass X-ray binary systems, and classify their pulse profiles according to the number of observed peaks seen during one spin period, dividing them into two classes, single- and double-peaked. We find that the pulsars are distributed about equally between both groups. We also compute the probabilities predicted by the theoretical models of two antipodal point-like spots that emit radiation according to the pencil-like emission patterns. These are then compared to the observed fraction of pulsars in the two classes. Assuming a blackbody emission pattern, it is possible to constrain the neutron star compactness if the magnetic dipole has arbitrary inclinations to the pulsar rotational axis. More realistic pencil-beam patterns predict that 79% of the pulsars are double-peaked independently of their compactness. The theoretical predictions can be made consistent with the data if the magnetic dipole inclination to the rotational axis has an upper limit of 40+/-4 deg. We also discuss the effect of limited sensitivity of the X-ray instruments to detect weak pulses, which lowers the number of detected double-peaked profiles and makes the theoretical predictions to be consistent with the data even if the magnetic dipole does have random inclinations. This shows that the statistics of pulse profiles does not allow us to constrain the neutron star compactness. In contrast to the previous claims by Bulik et al. (2003), the data also do not require the magnetic inclination to be confined in a narrow interval.

Since the discovery of the first double neutron star (DNS) system in 1975 by Hulse and Taylor, there are currently 8 confirmed DNS in our galaxy. For every system, the masses of both neutron stars, the orbital semi- major axis and eccentricity are measured, and proper motion is known for half of the systems. Using the orbital parameters and kinematic information, if available, as constraints for all system, we investigate the immediate progenitor mass of the second-born neutron star and the magnitude of the supernova kick it received at birth, with the primary goal to understand the core collapse mechanism leading to neutron star formation. Compared to earlier studies, we use a novel method to address the uncertainty related to the unknown radial velocity of the observed systems. For PSR B1534+12 and PSR B1913+16, the kick magnitudes are 150 - 270 km/s and 190 - 450 km/s (with 95% confidence) respectively, and the progenitor masses of the 2nd born neutron stars are 1.3 - 3.4 Msun and 1.4 - 5.0 Msun (95%), respectively. These suggest that the 2nd born neutron star was formed by an iron core collapse supernova in both systems. For PSR J0737-3039, on the other hand, the kick magnitude is only 5 - 120 km/s (95%), and the progenitor mass of the 2nd born neutron star is 1.3 - 1.9 Msun (95%). Because of the relatively low progenitor mass and kick magnitude, the formation of the 2nd born neutron star in PSR J0737-3039 is potentially connected to an electron capture supernova of a massive O - Ne - Mg white dwarf. For the remaining 5 Galactic DNS, the kick magnitude ranges from several tens to several hundreds of km/s, and the progenitor mass of the 2nd formed neutron star can be as low as ~1.5 Msun, or as high as ~8 Msun. Therefore in these systems, it is not clear which type of supernova is more likely to form the 2nd neutron star.

We obtained a second Chandra timing measurement of the 3.82 s pulsar CXOU J171405.7-381031 in the supernova remnant (SNR) CTB 37B, which shows that it is spinning down rapidly. The average period derivative of (5.88+/-0.08)E-11 over the 1 year time span corresponds to a dipole magnetic field strength B = 4.8E14 G, well into the magnetar range. The spin-down power E-dot = 4.2E34 erg/s is among the largest for magnetars, and the corresponding characteristic age Tau = P/2P-dot = 1030 years is comparable to estimates of the age of the SNR. The period derivative enables us to recover probable pulsations in an ASCA observation taken in 1996, which yields a mean characteristic age of 860 years over the longer 13 year time span. The source is well detected up to 10 keV, and its composite spectrum is typical of a magnetar. CTB 37B hosts HESS J1713-381, the first TeV source that is coincident with a magnetar. While the TeV emission has been attributed to the SNR shell, it is possibly centrally peaked, and we hypothesize that this particularly young, energetic magnetar may contribute to the HESS source. We also searched for pulsations from another source in a HESS SNR, XMMU J173203.3-344518 in HESS J1731-347/G353.6-0.7 but could not confirm pulsations or long-term flux variability, making it more likely that this source is a weakly magnetized central compact object.

abbreviated:
Massive gravitons are features of some alternatives to general relativity. This has motivated experiments and observations that, so far, have been consistent with the zero mass graviton of general relativity, but further tests will be valuable. A basis for new tests may be the high sensitivity gravitational wave experiments that are now being performed, and the higher sensitivity experiments that are being planned. In these experiments it should be feasible to detect low levels of dispersion due to nonzero graviton mass. One of the most promising techniques for such a detection may be the pulsar timing program that is sensitive to nano-Hertz gravitational waves.
Here we present some details of such a detection scheme. The pulsar timing response to a gravitational wave background with the massive graviton is calculated, and the algorithm to detect the massive graviton is presented. We conclude that, with $90\%$ probability, massles gravitons can be distinguished from gravitons heavier than $3\times 10^{-22}$\,eV (Compton wave length $\lambda_{\rm g}=4.1 \times 10^{12}$ km), if biweekly observation of 60 pulsars are performed for 5 years with pulsar RMS timing accuracy of 100\,ns. If 60 pulsars are observed for 10 years with the same accuracy, the detectable graviton mass is reduced to $5\times 10^{-23}$\,eV ($\lambda_{\rm g}=2.5 \times 10^{13}$ km); for 5-year observations of 100 or 300 pulsars, the sensitivity is respectively $2.5\times 10^{-22}$ ($\lambda_{\rm g}=5.0\times 10^{12}$ km) and $10^{-22}$ eV ($\lambda_{\rm g}=1.2\times 10^{13}$ km). Finally, a 10-year observation of 300 pulsars with 100\,ns timing accuracy would probe graviton masses down to $3\times 10^{-23}$\,eV ($\lambda_{\rm g}=4.1\times 10^{13}$ km).

The origin of the shallow decay segment in gamma-ray burst's (GRB) early light curves remains a mystery, especially those cases with a long-lived plateau followed by an abrupt falloff. In this paper, we propose a mechanism to understand the origin of the abrupt falloff after plateau by considering solidification of newborn quark stars with latent heat released as energy injection to GRB afterglow. We estimate the total latent heat released during the phase transition of quark stars from liquid to solid states, to be order of ~ 10^{51}ergs, which is comparable to the emission energy in the shallow decay segment. We also estimate the time scale of radiating the latent heat through thermal photon emission, and find that the time scale agrees with observations. Based on our estimation, we analyze the process of energy injection to GRB afterglow. We show that the steady latent heat of quark star phase transition would continuously inject into GRB afterglow in a form similar to that of a Poyntingflux- dominated outflow and naturally produce the shallow decay phase and the abrupt falloff after plateau. We conclude that the latent heat of quark star phase transition would be an important contribution to the shallow decay radiation in GRB afterglow, and would explain the general features of GRB light curves (including the plateau), if pulsar-like stars are really (solid) quark stars.

G54.1+0.3 is a Crab-like pulsar wind nebula (PWN) with the highest $\gamma$-ray to X-ray luminosity ratio among all the nebulae driven by young rotation-powered pulsars. We model the spectral evolution of the PWN and find it difficult to match the observed multi-band data with leptons alone using reasonable model parameters. In lepton-hadron hybrid model instead, TeV photons come mainly from $\pi^0$ decay in proton-proton interaction and the observed photon spectrum can be well reproduced. The newly discovered infrared loop and molecular cloud in or closely around the PWN can work as the target for the bombardment of the PWN protons.

We perform phase-resolved spectroscopy of the accreting millisecond pulsar, SAX J1808.4-3658, during the slow-decay phase of the 2002 outburst. Simple phenomenological fits to RXTE PCA data reveal a pulsation in the iron line at the spin frequency of the star. However, fitting more complex spectral models reveals a degeneracy between iron-line pulsations and changes in the underlying hotspot blackbody temperature with phase. By comparing with the variations in reflection continuum, which are much weaker than the iron line variations, we infer that the iron-line is not pulsed. The observed spectral variations can be explained by variations in blackbody temperature associated with rotational Doppler shifts at the neutron star surface. By allowing blackbody temperature to vary in this way, we also find a larger phase-shift between the pulsations in the Comptonised and blackbody components than has been seen in previous work. The phase-shift between the pulsation in the blackbody temperature and normalisation is consistent with a simple model where the Doppler shift is maximised at the limb of the star, ~90 degrees prior to maximisation of the hot-spot projected area.

After a long quiescence of three decades, the transient X-ray pulsar 4U 1901+03 became highly active in 2003 February. From the analysis of a large number of Rossi X-ray Timing Explorer/ Proportional Counter Array (RXTE/PCA) observations of this source, we report here the detection of X-ray flares, a broadening of the pulse frequency peak and Quasi Periodic Oscillations (QPOs). The X-ray flares showed spectral changes, had a duration of 100 s - 300 s, and were more frequent and stronger during the peak of the outburst. In most of the observations during the outburst we also detected a broadening of the pulse frequency peak. We have also found intensity dependent changes in the pulse profile at very short timescales. This reveals a coupling between the periodic and the low frequency aperiodic variabilities. In addition, near the end of the outburst we have detected a strong QPO feature centered at ~ 0.135 Hz. The QPO feature is broad with a quality factor of 3.3 and with an rms value of 18.5+/-3.1%. Using the QPO frequency and the X-ray luminosity during the QPO detection period we estimated the magnetic field strength of the neutron star as 0.31*10^12 G which is consistent with the value inferred earlier under the assumption of spin equilibrium.

Westerlund 1 is a young, massive Galactic starburst cluster that contains a rich coeval population of Wolf-Rayet stars, hot- and cool-phase transitional supergiants, and a magnetar. We use spectroscopic and photometric observations of the eclipsing double-lined binary W13 to derive dynamical masses for the two components, in order to determine limits for the progenitor masses of the magnetar CXOU J164710.2-455216 and the population of evolved stars in Wd1. W13 has an orbital period of 9.2709+/-0.0015 days and near-contact configuration. The shallow photometric eclipse rules out an inclination greater than 65 degrees, leading to lower limits for the masses of the emission-line optical primary and supergiant optical secondary of 21.4+/-2.6Msun and 32.8+/-4.0Msun respectively, rising to 23.2 +3.3/-3.0Msun and 35.4 +5.0/-4.6 Msun for our best-fit inclination 62 +3/-4 degrees. Comparison with theoretical models of Wolf-Rayet binary evolution suggest the emission-line object had an initial mass in excess of 35Msun, with the most likely model featuring highly non-conservative late-Case-A/Case-B mass transfer and an initial mass in excess of 40Msun. This confirms the high magnetar progenitor mass inferred from its membership in Wd1, and represents the first dynamical constraint on the progenitor mass of any magnetar. The red supergiants in Wd1 must have similar progenitor masses to W13 and are therefore amongst the most massive stars to undergo a red supergiant phase, representing a challenge for population models that suggest stars in this mass range end their redwards evolution as yellow hypergiants. [ABRIDGED]

The SKA at mid and low frequencies will be constructed in two distinct phases, the first being a subset of the second. This document defines the main scientific goals and baseline technical concept for the SKA Phase 1 (SKA_1). The major science goals for SKA_1 will be to study the history and role of neutral Hydrogen in the Universe from the dark ages to the present-day, and to employ pulsars as probes of fundamental physics. The baseline technical concept of SKA_1 will include a sparse aperture array operating at frequencies up to 450 MHz, and an array of dishes, initially operating at frequencies up to 3 GHz but capable of 10 GHz in terms of antenna surface accuracy. An associated Advanced Instrumentation Program (AIP) allows further development of new technologies currently under investigation. Construction will take place in 2016-2019 at a total capital cost of 350M\texteuro, including an element for contingency. The cost estimates of the SKA_1 telescope are now the subject of a more detailed and thorough costing exercise led by the SKA Project Development Office (SPDO). The 350 M\texteuro total for SKA_1 is a cost-constrained cap; an additional contingency is to reduce the overall scope of the project. The design of the SKA_1 is expected to evolve as the major cost estimates are refined, in particular the infrastructure costs at the two sites. The SKA_1 facility will represent a major step forward in terms of sensitivity, survey speed, image fidelity, temporal resolution and field-of-view. It will open up new areas of discovery space and demonstrate the science and technology underpinning the SKA Phase 2 (SKA_2).

X-ray emission is a common feature of all varieties of isolated neutron stars (INS) and, thanks to the advent of sensitive instruments with good spectroscopic, timing, and imaging capabilities, X-ray observations have become an essential tool in the study of these objects. Non-thermal X-rays from young, energetic radio pulsars have been detected since the beginning of X-ray astronomy, and the long-sought thermal emission from cooling neutron star's surfaces can now be studied in detail in many pulsars spanning different ages, magnetic fields, and, possibly, surface compositions. In addition, other different manifestations of INS have been discovered with X-ray observations. These new classes of high-energy sources, comprising the nearby X-ray Dim Isolated Neutron Stars, the Central Compact Objects in supernova remnants, the Anomalous X-ray Pulsars, and the Soft Gamma-ray Repeaters, now add up to several tens of confirmed members, plus many candidates, and allow us to study a variety of phenomena unobservable in "standard'' radio pulsars.

We discuss CXOU~1229410+075744, a new black hole candidate in a globular cluster in the elliptical galaxy NGC~4472. By comparing two Chandra observations of the galaxy, we find a source that varies by at least a factor of 4, and has a peak luminosity of at least $2\times10^{39}$ ergs/sec. As such, the source varies by significantly more than the Eddington luminosity for a single neutron star, and is a strong candidate for being a globular cluster black hole. The source's X-ray spectrum also evolves in a manner consistent with what would be expected from a single accreting stellar mass black hole. We consider the properties of the host cluster of this source and the six other strong black hole X-ray binary candidates, and find that there is suggestive evidence that black hole X-ray binary formation is favored in bright and metal rich clusters, just as is the case for bright X-ray sources in general.

In previous papers, we have shown that, as the rotation of a neutron star slows down, it will be internally heated as a consequence of the progressively changing mix of particles (rotochemical heating). In previously studied cases non-superfluid neutron stars or superfluid stars with only modified Urca reactions), this leads to a quasi-steady state in which the star radiates thermal photons for a long time, possibly accounting for the ultraviolet radiation observed from the millisecond pulsar J0437-4715. For the first time, we explore the phenomenology of rotochemical heating with direct Urca reactions and uniform and isotropic superfluid energy gaps of different sizes. We first do exploratory work by integrating the thermal and chemical evolution equations numerically for different energy gaps, which suggests a rich phenomenology of stable and unstable solutions. In order to understand these, we do a stability analysis around the quasi-steady state, identifying the characteristic times of growing, decaying, and oscillating solutions. For small gaps, the phenomenology is similar to the previously studied cases, in the sense that the solutions quickly converge to a quasi-steady state. For large gaps ($\gtrsim 0.05$ MeV), these solutions become unstable, leading to a limit-cycle behavior with periodicity $\sim 10^{6-7}$ yr, in which the star is hot ($T_s\gtrsim 10^5$ K) for a small fraction of the cycle ($\sim 5- 20 \%$ ), and cold for a longer time.

The general-relativistic Ohm's law for a two-component plasma which includes the gravitomagnetic force terms even in the case of quasi-neutrality has been derived. The equations that describe the electromagnetic processes in a plasma surrounding a neutron star are obtained by using the general relativistic form of Maxwell equations in a geometry of slow rotating gravitational object. In addition to the general-relativistic effect first discussed by Khanna \& Camenzind (1996) we predict a mechanism of the generation of azimuthal current under the general relativistic effect of dragging of inertial frames on radial current in a plasma around neutron star. The azimuthal current being proportional to the angular velocity $\omega$ of the dragging of inertial frames can give valuable contribution on the evolution of the stellar magnetic field if $\omega$ exceeds $2.7\times 10^{17} (n/\sigma) \textrm{s}^{-1}$ ($n$ is the number density of the charged particles, $\sigma$ is the conductivity of plasma). Thus in general relativity a rotating neutron star, embedded in plasma, can in principle generate axial-symmetric magnetic fields even in axisymmetry. However, classical Cowling's antidynamo theorem, according to which a stationary axial-symmetric magnetic field can not be sustained against ohmic diffusion, has to be hold in the general-relativistic case for the typical plasma being responsible for the rotating neutron star.

We describe Monte Carlo models for the dynamical evolution of the massive globular cluster 47 Tuc (NGC 104). The code includes treatments of two-body relaxation, most kinds of three- and four-body interactions involving primordial binaries and those formed dynamically, the Galactic tide, and the internal evolution of both single and binary stars. We arrive at a set of initial parameters for the cluster which, after 12Gyr of evolution, gives a model with a fairly satisfactory match to surface brightness and density profiles, the velocity dispersion profile, the luminosity function in two fields, and the acceleration of pulsars. Our models appear to require a relatively steep initial mass function for stars above about turnoff, with an index of about 2.8 (where the Salpeter mass function has an index of 2.35), and a relatively flat initial mass function (index about 0.4) for the lower main sequence. According to the model, the current mass is estimated at 0.9 million solar masses, of which about 34% consists of remnants. We find that primordial binaries are gradually taking over from mass loss by stellar evolution as the main dynamical driver of the core. Despite the high concentration of the cluster, core collapse will take at least another 20Gyr.

We present X-ray and optical data on the Be/X-ray binary (BeXRB) pulsar IGR J01054-7253 = SXP11.5 in the Small Magellanic Cloud (SMC). Rossi X-ray Timing Explorer (RXTE) observations of this source in a large X-ray outburst reveal an 11.483 +/- 0.002s pulse period and show both the accretion driven spin-up of the neutron star and the motion of the neutron star around the companion through Doppler shifting of the spin period. Model fits to these data suggest an orbital period of 36.3 +/- 0.4d and Pdot of (4.7 +/- 0.3) x 10^{-10} ss^{-1}. We present an orbital solution for this system, making it one of the best described BeXRB systems in the SMC. The observed pulse period, spin-up and X-ray luminosity of SXP11.5 in this outburst are found to agree with the predictions of neutron star accretion theory. Timing analysis of the long-term optical light curve reveals a periodicity of 36.70 +/- 0.03d, in agreement with the orbital period found from the model fit to the X-ray data. Using blue-end spectroscopic observations we determine the spectral type of the counterpart to be O9.5-B0 IV-V. This luminosity class is supported by the observed V-band magnitude. Using optical and near-infrared photometry and spectroscopy, we study the circumstellar environment of the counterpart in the months after the X-ray outburst.

We re-assess the XMM-Newton and Swift observations of HLX1, to examine the evidence for its identification as an intermediate-mass black hole. We show that the X-ray spectral and timing properties are equally consistent with an intermediate-mass black hole in a high state, or with a foreground neutron star with a luminosity of about a few times 10^{32} erg/s ~ 10^{-6} L_{Edd}, located at a distance of about 1.5 to 3 kpc. Contrary to previously published results, we find that the X-ray spectral change between the two XMM-Newton observations of 2004 and 2008 (going from power-law dominated to thermal dominated) is not associated with a change in the X-ray luminosity. The thermal component becomes more dominant (and hotter) during the 2009 outburst seen by Swift, but in a way that is consistent with either scenario.

We investigate the effect of a new triple-alpha reaction rate from Ogata et al. (2009) on helium ignition conditions on accreting neutron stars and on the properties of the subsequent type I X-ray burst. We find that the new rate leads to significantly lower ignition column density for accreting neutron stars at low accretion rates. We compare the results of our ignition models for a pure helium accretor to observations of bursts in ultra-compact X-ray binary (UCXBs), which are believed to have nearly pure helium donors. For mdot > 0.001 mdot_Edd, the new triple-alpha reaction rate from Ogata et al. (2009) predicts a maximum helium ignition column of ~ 3 x 10^9 g cm^{-2}, corresponding to a burst energy of ~ 4 x 10^{40} ergs. For mdot ~ 0.01 mdot_Edd at which intermediate long bursts occur, the predicted burst energies are at least a factor of 10 too low to explain the observed energies of such bursts in UCXBs. This finding adds to the doubts cast on the triple-alpha reaction rate of Ogata et al. (2009) by the low-mass stellar evolution results of Dotter & Paxton (2009).

High-precision pulsar timing relies on a solar-system ephemeris in order to convert times of arrival (TOAs) of pulses measured at an observatory to the solar system barycenter. Any error in the conversion to the barycentric TOAs leads to a systematic variation in the observed timing residuals; specifically, an incorrect planetary mass leads to a predominantly sinusoidal variation having a period and phase associated with the planet's orbital motion about the Sun. By using an array of pulsars (PSRs J0437-4715, J1744-1134, J1857+0943, J1909-3744), the masses of the planetary systems from Mercury to Saturn have been determined. These masses are consistent with the best-known masses determined by spacecraft observations, with the mass of the Jovian system, 9.547921(2)E-4 Msun, being significantly more accurate than the mass determined from the Pioneer and Voyager spacecraft, and consistent with but less accurate than the value from the Galileo spacecraft. While spacecraft are likely to produce the most accurate measurements for individual solar system bodies, the pulsar technique is sensitive to planetary system masses and has the potential to provide the most accurate values of these masses for some planets.

We report on the first detection of ionospheric disturbances caused by short repeated gamma-ray bursts from the magnetar SGR J1550-5418. Very low frequency (VLF) radio wave data obtained in South America clearly show sudden amplitude and phase changes at the corresponding times of eight SGR bursts. Maximum amplitude and phase changes of the VLF signals appear to be correlated with the gamma-ray fluence. On the other hand, VLF recovery timescales do not show any significant correlation with the fluence, possibly suggesting that the bursts' spectra are not similar to each other. In summary, the Earth's ionosphere can be used as a very large gamma-ray detector and the VLF observations provide us with a new method to monitor high energy astrophysical phenomena without interruption such as Earth Occultation.

Here I will review the high time resolution radio sky, focusing on millisecond scales. This is primarily occupied by neutron stars, the well-known radio pulsars and the recently identified group of transient sources known as Rotating RAdio Transients (RRATs). The RRATs appear to be abundant in the Galaxy, which at first glance may be difficult to reconcile with the observed supernova rate. However, as I will discuss, it seems that the RRATs can be explained as pulsars which are either extreme nullers, highly variable or weak/distant. I will re-cap some recent results including a re-analysis of the Parkes Multi-beam Pulsar Survey, which has identified several new sources, as well as the unusual timing behaviour of RRAT J1819-1458. This leads to an examination of where RRATs fit within the evolution of neutron stars post-supernova.

We investigate medium effects due to density-dependent magnetic moments of baryons on neutron stars under strong magnetic fields. If we allow the variation of anomalous magnetic moments (AMMs) of baryons in dense matter under strong magnetic fields, AMMs of nucleons are enhanced to be larger than those of hyperons. The enhancement naturally affects the chemical potentials of baryons to be large and leads to the increase of a proton fraction. Consequently, it causes the suppression of hyperons, resulting in the stiffness of the equation of state. Under the presumed strong magnetic fields, we evaluate relevant particles' population, the equation of state and the maximum masses of neutron stars by including density-dependent AMMs and compare them with those obtained from AMMs in free space.

We present high spatial resolution optical imaging and polarization observations of the PSR B0540-69.3 and its highly dynamical pulsar wind nebula (PWN) performed with HST, and compare them with X-ray data obtained with the Chandra X-ray Observatory. We have studied the bright region southwest of the pulsar where a bright "blob" is seen in 1999. We show that it may be a result of local energy deposition around 1999, and that the emission from this then faded away. Polarization data from 2007 show that the polarization properties show dramatic spatial variations at the 1999 blob position arguing for a local process. Several other positions along the pulsar-"blob" orientation show similar changes in polarization, indicating previous recent local energy depositions. In X-rays, the spectrum steepens away from the "blob" position, faster orthogonal to the pulsar-"blob" direction than along this axis of orientation. This could indicate that the pulsar-"blob" orientation is an axis along where energy in the PWN is mainly injected, and that this is then mediated to the filaments in the PWN by shocks. We highlight this by constructing an [S II]-to-[O III]-ratio map. We argue, through modeling, that the high [S II]/[O III] ratio is not due to time-dependent photoionization caused by possible rapid Xray emission variations in the "blob" region. We have also created a multiwavelength energy spectrum for the "blob" position showing that one can, to within 2sigma, connect the optical and X-ray emission by a single power law. We obtain best power-law fits for the X-ray spectrum if we include "extra" oxygen, in addition to the oxygen column density in the interstellar gas of the Large Magellanic Cloud and the Milky Way. This oxygen is most naturally explained by the oxygen-rich ejecta of the supernova remnant. The oxygen needed likely places the progenitor mass in the 20 - 25 Msun range.

In the paper Pulsar Electrodynamics, published in 1969, Goldreich and Julian propose some basic properties of pulsars, such as the oft-cited Goldreich-Julian density, light cylinder, open and closed magnetic field lines, corotation and so on. However, inspection of their mathematics reveals three mistakes: first, the relative velocity is irrelevantly replaced by the corotation velocity; second, a hypothesis in their theory is contradictory to Maxwell's equations; and third, their theory neglected a special solution of the frozen-in field equation which is of particular importance for pulsar research. We additionally describe the results of a series of magnetohydrodynamic experiments that may be beneficial to the understanding of pulsar electrodynamics.

Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of interstellar magnetic fields. In the Milky Way, Faraday rotation of the polarized emission from pulsars and background sources indicate that the regular field follows the spiral arms and has one reversal inside the solar radius, but the overall field structure in our Galaxy is still unclear. In nearby galaxies, ordered fields with spiral structure exist in grand-design, barred and flocculent galaxies. The strongest ordered fields (10-15 \muG) are found in interarm regions. Faraday rotation of the diffuse polarized radio emission from the disks of spiral galaxies sometimes reveals large-scale patterns, which are signatures of regular fields generated by a mean-field dynamo. - The SKA and its precursor telescopes will open a new era in the observation of cosmic magnetic fields and help to understand their origin. All-sky surveys of Faraday rotation measures (RM) towards a dense grid of polarized background sources with the ASKAP (POSSUM), MeerKAT and the SKA are dedicated to measure fields in intervening galaxies and will be used to model the overall structure and strength of the magnetic fields in the Milky Way and beyond. Examples for joint polarimetric observations between the SKA and the E-ELT are given.

We present evidence for Quasi-Periodic Oscillations (QPOs) in the recurrent outburst emission from the soft gamma repeater SGR 1806-20 using NASA's Rossi X-ray Timing Explorer (RXTE) observations. By searching a sample of 30 bursts for timing signals at the frequencies of the QPOs discovered in the 2004 December 27 giant flare from the source, we find three QPOs at 84, 103, and 648 Hz in three different bursts. The first two QPOs lie within $\sim$ 1$\: \sigma$ from the 92 Hz QPO detected in the giant flare. The third QPO lie within $\sim$ 9$\: \sigma$ from the 625 Hz QPO also detected in the same flare. The detected QPOs are found in bursts with different durations, morphologies, and brightness, and are vindicated by Monte Carlo simulations, which set a lower limit confidence interval $\geq 4.3 \sigma$. We also find evidence for candidate QPOs at higher frequencies in other bursts with lower statistical significance. The fact that we can find evidence for QPOs in the recurrent bursts at frequencies relatively close to those found in the giant flare is intriguing and can offer insight about the origin of the oscillations. We confront our finding against the available theoretical models and discuss the connection between the QPOs we report and those detected in the giant flares. The implications to the neutron star properties are also discussed.

We present an analysis of highly magnetized neutron stars "magnetars", in search for high frequency oscillations in the recurrent emission from the soft gamma repeater SGR 1806-20, and we discuss the physical interpretation of these oscillations and its implications on the neutron star properties and structure. We present evidence for Quasi-Periodic Oscillations (QPOs) in the recurrent outburst activity from SGR 1806-20 using RXTE observations. By searching for timing signals at the frequencies of the QPOs discovered in the 2004 December 27 giant flare from the source, we find three QPOs at 84, 103, and 648 Hz in three different bursts. The first two QPOs lie within 8.85% and 11.83%, respectively, from the 92 Hz QPO detected in the giant flare. The third QPO lie within 3.75% from the 625 Hz QPO also detected in the same flare. The detected QPOs are found in bursts with different durations, morphologies, and brightness, and are vindicated by Monte Carlo simulations. We also find evidence for candidate QPOs at higher frequencies in other bursts with lower statistical significance. The fact that we can find evidence for QPOs in the recurrent bursts at frequencies relatively close to those found in the giant flare is intriguing and can offer insight about the origin of the oscillations. We confront our findings against the available theoretical models and discuss the physical interpretation of these QPOs. The leading interpretation for the origin of magnetar QPOs suggests that these toroidal seismic oscillatory modes are most likely to be excited by a crustquake of the neutron star crust. Other models have been proposed to explain the magnetar QPO phenomena including magnetospheric oscillations, magnetic flux tubes and modes of a passive debris disk. Theoretical modeling and observation of QPOs will be very useful in putting stringent constraints on neutron star equation of state.

We assess the detection prospects of a gravitational wave background associated with sub-luminous gamma-ray bursts (SL-GRBs). We assume that the central engines of a significant proportion of these bursts are provided by newly born magnetars and consider two plausible GW emission mechanisms. Firstly, the deformation-induced triaxial GW emission from a newly born magnetar. Secondly, the onset of a secular bar-mode instability, associated with the long lived plateau observed in the X-ray afterglows of many gamma-ray bursts (Corsi & Meszaros 2009a). With regards to detectability, we find that the onset of a secular instability is the most optimistic scenario: under the hypothesis that SL-GRBs associated with secularly unstable magnetars occur at a rate of (48; 80)Gpc^{-3}yr^{-1} or greater, cross-correlation of data from two Einstein Telescopes (ETs) could detect the GW background associated to this signal with a signal-to-noise ratio of 3 or greater after 1 year of observation. Assuming neutron star spindown results purely from triaxial GW emissions, we find that rates of around (130;350)Gpc^{-3}yr^{-1} will be required by ET to detect the resulting GW background. We show that a background signal from secular instabilities could potentially mask a primordial GW background signal in the frequency range where ET is most sen- sitive. Finally, we show how accounting for cosmic metallicity evolution can increase the predicted signal-to-noise ratio for background signals associated with SL-GRBs.

DSPSR is a high-performance, open-source, object-oriented, digital signal processing software library and application suite for use in radio pulsar astronomy. Written primarily in C++, the library implements an extensive range of modular algorithms that can optionally exploit both multiple-core processors and general-purpose graphics processing units. After over a decade of research and development, DSPSR is now stable and in widespread use in the community. This paper presents a detailed description of its functionality, justification of major design decisions, analysis of phase-coherent dispersion removal algorithms, and demonstration of performance on some contemporary microprocessor architectures.

We present a study of shape, spectra and polarization properties of giant pulses (GPs) from the Crab pulsar at the very high frequencies of 8.5 and 15.1 GHz. Studies at 15.1 GHz were performed for the first time. Observations were conducted with the 100-m radio telescope in Effelsberg in Oct-Nov 2007 at the frequencies of 8.5 and 15.1 GHz as part of an extensive campaign of multi-station multi-frequency observations of the Crab pulsar. A selection of the strongest pulses was recorded with a new data acquisition system, based on a fast digital oscilloscope, providing nanosecond time resolution in two polarizations in a bandwidth of about 500 MHz. We analyzed the pulse shapes, polarisation and dynamic spectra of GPs as well as the cross-correlations between their LHC and RHC signals. No events were detected outside main pulse and interpulse windows. GP properties were found to be very different for GPs emitted at longitudes of the main pulse and the interpulse. Cross-correlations of the LHC and RHC signals show regular patterns in the frequency domain for the main pulse, but these are missing for the interpulse GPs. We consider consequences of application of the rotating vector model to explain the apparent smooth variation in the position angle of linear polarization for main pulse GPs.
We also introduce a new scenario of GP generation as a direct consequence of the polar cap discharge. We find further evidence for strong nano-shot discharges in the magnetosphere of the Crab pulsar. The repetitive frequency spectrum seen in GPs at the main pulse phase is interpreted as a diffraction pattern of regular structures in the emission region. The interpulse GPs however have a spectrum that resembles that of amplitude modulated noise. Propagation effects may be the cause of the differences.

SGR~0501+4516 was discovered with the Swift satellite on 2008 August 22, after it emitted a series of very energetic bursts. Since then, the source was extensively monitored with Swift, the Rossi X-ray Timing Explorer (RXTE) and observed with Chandra and XMM-Newton, providing a wealth of information about its outburst behavior and burst induced changes of its persistent X-ray emission. Here we report the most accurate location of SGR~0501+4516 (with an accuracy of 0.11'') derived with Chandra. Using the combined RXTE, Swift/X-ray Telescope, Chandra and XMM-Newton observations we construct a phase connected timing solution with the longest time baseline (~240 days) to date for the source. We find that the pulse profile of the source is energy dependent and exhibits remarkable variations associated with the SGR~0501+4516 bursting activity. We also find significant spectral evolution (hardening) of the source persistent emission associated with bursts. Finally, we discuss the consequences of the SGR~0501+4516 proximity to the supernova remnant, SNR G160.9+2.6 (HB9).

In this Letter we report a spectroscopic confirmation of the association of HLX-1, the brightest ultra-luminous X-ray source, with the galaxy ESO 243-49. At the host galaxy distance of 95 Mpc, the maximum observed 0.2 - 10 keV luminosity is 1.2E42 erg/s. This luminosity is ~400 times above the Eddington limit for a 20 Msun black hole, and has been interpreted as implying an accreting intermediate mass black hole with a mass in excess of 500 Msun (assuming the luminosity is a factor of 10 above the Eddington value). However, a number of other ultra-luminous X-ray sources have been later identified as background active galaxies or foreground sources. It has recently been claimed that HLX-1 could be a quiescent neutron star X-ray binary at a Galactic distance of only 2.5 kpc, so a definitive association with the host galaxy is crucial in order to confirm the nature of the object. Here we report the detection of the Halpha emission line for the recently identified optical counterpart at a redshift consistent with that of ESO 243-49. This finding definitively places HLX-1 inside ESO 243-49, confirming the extreme maximum luminosity and strengthening the case for it containing an accreting intermediate mass black hole of more than 500 Msun.

We present an analysis of the gamma-ray data obtained with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the direction of SNR W49B (G43.3-0.2). A bright unresolved gamma-ray source detected at a significance of 38 sigma is found to coincide with SNR W49B. The energy spectrum in the 0.2-200 GeV range gradually steepens toward high energies. The luminosity is estimated to be 1.5x10^{36} (D/8 kpc)^2 erg s^-1 in this energy range. There is no indication that the gamma-ray emission comes from a pulsar. Assuming that the SNR shell is the site of gamma-ray production, the observed spectrum can be explained either by the decay of neutral pi mesons produced through the proton-proton collisions or by electron bremsstrahlung. The calculated energy density of relativistic particles responsible for the LAT flux is estimated to be remarkably large, U_{e,p}>10^4 eV cm^-3, for either gamma-ray production mechanism.

In this paper, we report a detailed investigation of the multiwavelength properties of a newly detected gamma-ray pulsar, PSR J2021+4026, in both observational and theoretical aspects. We firstly identify an X-ray source in the XMM-Newton serendipitous source catalogue, 2XMM J202131.0+402645, located within the 95% confidence circle of PSR J2021+4026. With an archival Chandra observation, this identification provides an X-ray position with arcsecond accuracy which is helpful in facilitating further investigations. Searching for the pulsed radio emission at the position of 2XMM J202131.0+402645 with a 25-m telescope at Urumqi Astronomical Observatory resulted in null detection and places an upper-limit of 0.1~mJy for any pulsed signal at 18~cm. Together with the emission properties in X-ray and gamma-ray, the radio quietness suggests PSR J2021+4026 to be another member of Geminga-like pulsars. In the radio sky survey data, extended emission features have been identified in the gamma-ray error circle of PSR J2021+4026. We have also re-analyzed the gamma-ray data collected by FERMI's Large Area Telescope. We found that the X-ray position of 2XMM J202131.0+402645 is consistent with that of the optimal gamma-ray timing solution. We have further modeled the results in the context of outer gap model which provides us with constraints for the pulsar emission geometry such as magnetic inclination angle and the viewing angle. We have also discussed the possibility of whether PSR J2021+4026 has any physical association with the supernova remnant G78.2+2.1 (gamma-Cygni).

Here we report the detection of a 626 s periodic modulation from the X-ray source 2XMM J174016.0-290337 located in the direction of the Galactic center. We present temporal and spectral analyses of archival XMM-Newton data and photometry of archived near-infrared data in order to investigate the nature of this source. We find that the X-ray light curve shows a strong modulation at 626 +/- 2 s with a confidence level > 99.9% and a pulsed fraction of 54%. Spectral fitting demonstrates that the spectrum is consistent with an absorbed power law. No significant spectral variability was observed over the 626 s period. We have investigated the possibility that the 626 s period is orbital in nature (either that of an ultra-compact X-ray binary or an AM CVn) or related to the spin of a compact object (either an accretion powered pulsar or an intermediate polar). The X-ray properties of the source and the photometry of the candidate near-infrared counterparts are consistent with an accreting neutron star X-ray binary on the near-side of the Galactic bulge, where the 626 s period is most likely indicative of the pulsar spin period. However, we cannot rule out an ultra-compact X-ray binary or an intermediate polar with the data at hand. In the former case, if the 626 s modulation is the orbital period of an X-ray binary, it would be the shortest period system known. In the latter case, the modulation would be the spin period of a magnetic white dwarf. However, we find no evidence for absorption dips over the 626 s period, a low temperature black body spectral component, or Fe Kalpha emission lines. These features are commonly observed in intermediate polars, making 2XMM J174016.0-290337 a rather unusual member of this class if confirmed. We instead suggest that 2XMM J174016.0-290337 could be a new addition to the emerging class of symbiotic X-ray binaries.

Like the solar corona, the external magnetic field of magnetars is twisted by surface motions of the star. The twist energy is dissipated over time. We discuss the theory of this activity and its observational status. (1) Theory predicts that the magnetosphere tends to untwist in a peculiar way: a bundle of electric currents (the "j-bundle") is formed with a sharp boundary, which shrinks toward the magnetic dipole axis. Recent observations of shrinking hot spots on magnetars are consistent with this behavior. (2) Continual discharge fills the j-bundle with electron-positron plasma, maintaining a nonthermal corona around the neutron star. The corona outside a few stellar radii strongly interacts with the stellar radiation and forms a "radiatively locked" outflow with a high e+- multiplicity. The locked plasma annihilates near the apexes of the closed magnetic field lines. (3) New radiative-transfer simulations suggest a simple mechanism that shapes the observed X-ray spectrum from 0.1 keV to 1 MeV: part of the thermal X-rays emitted by the neutron star are reflected from the outer corona and then upscattered by the inner relativistic outflow in the j-bundle, producing a beam of hard X-rays.

A complex event observed in the radio pulses from the Crab pulsar in 1997 included echoes, a dispersive delay, and large changes in intensity. It is shown that these phenomena were due to refraction at the edge of a plasma cloud in the outer region of the Crab Nebula. Several similar events have been observed, although in less detail. It is suggested that the plasma cloud is in the form of filaments with diameter around 3 x 10^11m and electron density of order 10^4 cm-3

Some neutron star low-mass X-ray binaries have very long outbursts (lasting several years) which can generate a significant amount of heat in the neutron star crust. After the system has returned to quiescence, the crust then thermally relaxes. This provides a rare opportunity to study the thermal properties of neutron star crusts, putting constraints on the thermal conductivity and hence the structure and composition of the crust. KS 1731-260 is one of only four systems where this crustal cooling has been observed. Here, we present a new Chandra observation of this source approximately 8 years after the end of the last outburst, and 4 years since the last observation. We find that the source has continued to cool, with the cooling curve displaying a simple power-law decay. This suggests that the crust has not fully thermally relaxed yet, and may continue to cool further. A simple power law decay is in contrast to theoretical cooling models of the crust, which predict that the crust should now have cooled to the same temperature as the neutron star core.

The extended nebulae formed as pulsar winds expand into their surroundings provide information about the composition of the winds, the injection history from the host pulsar, and the material into which the nebulae are expanding. Observations from across the electromagnetic spectrum provide constraints on the evolution of the nebulae, the density and composition of the surrounding ejecta, the geometry of the central engines, and the long-term fate of the energetic particles produced in these systems. Such observations reveal the presence of jets and wind termination shocks, time-varying compact emission structures, shocked supernova ejecta, and newly formed dust. Here I provide a broad overview of the structure of pulsar wind nebulae, with specific examples from observations extending from the radio band to very-high-energy gamma-rays that demonstrate our ability to constrain the history and ultimate fate of the energy released in the spin-down of young pulsars.

The past decade has presented a revolution in the field of observational high energy gamma-ray astrophysics with the advent of a new generation in ground-based TeV telescopes and subsequent GeV space telescopes. The Fermi Large Area Telescope (LAT) was launched in August 2008 and has offered unprecedented sensitivity and survey capabilities in the 30 MeV - 300 GeV energy range.
Presented here are the results from the first two years of LAT observations of galactic binary systems including the definitive detections of LSI+61 303, LS 5039 and Cyg X-3. These sources and others are discussed in context with their known TeV and X-ray properties. The LAT data provides new understandings and pose new questions about the nature of these objects. The identification of an exponential cutoff in the spectra of both LSI+61 303 and LS 5039 was unexpected and poses challenges for explaining the emission mechanisms and processes which are in operation within these systems.

Context: Swift observations suggest that the X-ray afterglow emission of some gamma-ray bursts (GRB) may have internal origins, and the conventional external shock (ES) cannot be the exclusive source of the afterglow emission. Aims: If the central compact objects of some GRBs are millisecond magentars, the magnetar winds could play an important role in the (internal) X-ray afterglow emission, which is our focus here. Methods: The dynamics and the synchrotron radiation of the termination shock (TS) of the magmnetar winds, as well as the simultaneous GRB ES, are investigated by considering the magnetization of the winds. Results: As a result of the competition between the emission of the wind TS and the GRB ES, two basic types of X-ray afterglows are predicted, i.e., the TS-dominated and the ES-dominated types. Moreover, our results also show that both of the two types of afterglows have a shallow-decay phase and a normal-decay one, as observed by the \textit{Swift} satellite. This indicates that some observed X-ray afterglows could be (internally) produced by the magnetar winds, but not necessarily GRB ESs.

The curvature drift instability has long been considered as a viable mechanism for pulsar radio emission. We reconsidered this mechanism by finding an explicit solution describing propagation of short-wave electro-magnetic waves in a plasma flow along curved magnetic field lines. We show that even though the waves could be amplified, the amplification factor remains very close to unity therefore this mechanism is unable to generate high brightness temperature emission from initial weak fluctuations.

The steady equilibrium conditions for a mixed gas of neutrons, protons, electrons, positrons and radiation field (abbreviated as $npe^{\pm}$ gas) with/without external neutrino flux are investigated, and a general chemical potential equilibrium equation $\mu_n=\mu_p+C\mu_e$ is obtained to describe the steady equilibrium at high temperatures ($T>10^9$K). An analytic fitting formula of coefficient $C$ is presented for the sake of simplicity as the neutrino and antineutrino are transparent. It is a simple method to estimate the electron fraction for the steady equilibrium $npe^{\pm}$ gas that using the corresponding equilibrium condition. As an example, we apply this method to the GRB accretion disk and approve the composition in the inner region is approximate equilibrium as the accretion rate is low. For the case with external neutrino flux, we calculate the initial electron fraction of neutrino-driven wind from proto-neutron star model M15-l1-r1. The results show that the improved equilibrium condition makes the electron fraction decrease significantly than the case $\mu_n=\mu_p+\mu_e$ when the time is less than 5 seconds post bounce, which may be useful for the r-process nucleosynthesis

After the first prediction to expect geodetic precession in binary pulsars in 1974, made immediately after the discovery of a pulsar with a companion, the effects of relativistic spin precession have now been detected in all binary systems where the magnitude of the precession rate is expected to be sufficiently high. Moreover, the first quantitative test leads to the only available constraints for spin-orbit coupling of a strongly self-gravitating body for general relativity (GR) and alternative theories of gravity. The current results are consistent with the predictions of GR, proving the effacement principle of spinning bodies. Beyond tests of theories of gravity, relativistic spin precession has also become a useful tool to perform beam tomography of the pulsar emission beam, allowing to infer the unknown beam structure, and to probe the physics of the core collapse of massive stars.

So far, 24 Isolated neutron stars (INSs) of different types have been identified at optical wavelengths, from the classical radio pulsars to more peculiar objects, like the magnetars. Most identifications have been obtained in the last 20 years thanks to the deployment of modern technology telescopes, above all the HST, but also the NTT and, later, the 8m-class telescopes like the VLT. The larger identification rate has increased the impact factor of optical observations in the multi-wavelength approach to INS astronomy, opening interesting possibilities for studies not yet possible at other wavelengths. With the HST on the way to its retirement, 8m class telescopes will have the task of bridging neutron star optical astronomy into a new era, characterised by the advent of the generation of extremely large telescopes (ELTs), like the European ELT (E-ELT). This will mark a major step forward in the field, enabling one to identify many more INSs, many of which from follow-ups of observations performed with future radio and X-ray megastruscture facilities like SKA and IXO. Moreover, the E-ELT will make it possible to carry out observations, like timing, spectroscopy, and polarimetry, which still represent a challenge for 8m-class telescopes and are, in many respects, crucial for studies on the structure and composition of the neutron star interior and of its magnetosphere. In this contribution, I briefly summarise the current status of INS optical observations, describe the main science goals for the E-ELT, and their impact on neutron star physics.

The millisecond proto-magnetar model for the central engine of long-duration gamma-ray bursts is briefly reviewed. Limitations and uncertainties in the model are highlighted. A short discussion of the maximum energy, maximum duration, radiative efficiency, jet formation mechanism, late-time energy injection, and (non-)association with supernovae of millisecond magnetar-powered GRBs is provided.