The basic theoretical ideas in the models of regularly pulsating X-ray sources are discussed, and put in relation to the observations. The topics covered include physics of the magnetosphere of an accreting neutron star, hydrodynamics of the accretion column, physical processes close to the surface of the ...

Pulsars with pulsation periods in the millisecond range are thought to be neutron stars that have acquired an extraordinarily short spin period through the accretion of stellar material spiraling down onto the neutron star from a nearby companion. Nearly all the angular momentum and most of the mass of the ...

4U 2206+54 is a high-mass X-ray binary which has been suspected to contain a neutron star accreting from the wind of its companion, BD +53{sup 0} 2790. Reig et al. have recently detected 5560 s period pulsations in both Rossi X-ray Timing Explorer (RXTE) and International Gamma-ray Astrophysics Laboratory observations which they ...

The report deals with the question of whether mass accretion on a star can cause pulsational instability by itself. The principal result is a formula for the effect of accretion on the growth (or decay) rate of a radial pulsation mode. Application of this...

Analysis of experimental data shows that the pulsations of X-ray flux from the sources Her X-1 and Cen X-3 cannot be explained without invoking a special mechanism for the formation of X-ray pulses of the observed shape. In disk accretion onto a magnetized neutron star, the layer of plasma flowing along the Alfven surface rotates along ...

A model for disk accretion by a rotating magnetic neutron star is proposed which includes a detailed

HETE J1900.1-2455 is a highly peculiar accreting millisecond pulsar, as its pulses disappeared soon after the discovery of the source. Therefore, it can be viewed as a prototype of a system in between pulsating and non pulsating low mass X-ray binaries. We propose to observe it for the first time with XMM-Newton, to discriminate ...

The space-time around Neutron Stars is indeed an extreme environment. Whether they are in accreting binary systems, isolated or in non-accreting binaries (perhaps with another Neutron Star), Neutron Stars provide a window onto physical processes not accessible by other means. In particular, the ...

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 Rossi X-ray Timing Explorer Proportional Counter Array data reveal a pulsation in the iron line at the spin frequency of the neutron star. However, fitting more ...

It is now ten years ago that the first accreting millisecond X-ray pulsar (AMP) was discovered in the low-mass X-ray binary SAX J1808.4-3658. This RXTE discovery confirmed long-standing predictions that low magnetic field neutron stars can be spun up to high spin frequencies by accretion in X-ray binaries. AMPs have since been ...

The discovery of orbitally-modulated, periodic X-ray pulsations from Cen ...... Ariel 5 discovered 103 s pulsations from A 0535+26 in 1975 (Rosenberg et al. ...

We have shown previously that many of the properties of persistent accretion-powered millisecond pulsars can be understood if their X-ray emitting areas are near their spin axes and move as the accretion rate and structure of the inner disk vary. Here, we show that this 'nearly aligned moving spot model' may also explain the intermittent ...

Rossi X-Ray Timing Explorer (RXTE) All-Sky Monitor observations of the X-ray source 4U 2206+54, previously proposed to be a Be star system, show the X-ray flux to be modulated with a period of approximately 9.6 days. If the modulation is due to orbital variability, then this would be one of the shortest orbital periods known for a Be star X-ray source. However, the X-ray luminosity is relatively ...

The self-consistency of the standard model for accreting X-ray pulsars is reexamined, using observational data on two X-ray sources, Her X-1 and 4U0115 + 63, interpreted in the context of the MHD accretion torque theory of Ghosh and Lamb (1979). Within a phenomenologically extended version of this theory, it is shown that the inner radius of the ...

Nuclear reactions in the hot accretion plasma surrounding a collapsed star are a source of neutrons,

I review the present status of the pulsation studies of close binary systems, focusing on pulsating gainers of semi-detached Algol type eclipsing binaries. I discuss the advantages of pulsation studies of eclipsing binaries, influence of the activity cycles of a mass-losing star on mass transfer and accretion rate ...

In this review I describe the basic properties of white dwarfs and their pulsations. I then discuss some of the areas in which the pulsations can provide meaningful results, such as internal chemical profiles, possible emission of ``exotic'' particles, planet detection, crystallization, convection, accretion, and cosmochronology.

We present a coherent timing analysis of the 2003 outburst of the accreting millisecond pulsar (AMXP) XTE J1807-294. We find a 95% confidence interval for the pulse frequency derivative of (+0.7, + 4.7) x 10{sup -14} Hz s{sup -1} and (-0.6, + 3.8) x 10{sup -14} Hz s{sup -1} for the fundamental and second harmonics, respectively. The sinusoidal fractional amplitudes of the ...

Recent observations suggest that neutron stars in low-mass X-ray binaries rotate within a narrow range of spin frequencies clustered around 300 Hz. A proposed explanation for this remarkable fact is that gravitational radiation from a steady state r-mode oscillation in the neutron star's core halts the spin-up due to accretion. For the ...

X-ray timing of neutron stars in low-mass X-ray binaries (LMXBs) with the Rossi X-ray Timing Explorer has since 1996 revealed several distinct high-frequency phenomena. Among these are oscillations during thermonuclear (type-I) bursts, which (in addition to persistent X-ray pulsations) are thought to trace the neutron star spin. The ...

Context. In addition to coherent pulsation, many accreting neutron stars exhibit flaring activity and strong aperiodic variability on time scales comparable to or shorter than their pulsation period. This behavior shows that the accretion flow in the vicinity of the accretor must be highly ...

Neutron viscosity is investigated as a possible mechanism for the dissipation of kinetic energy into

Millisecond pulsars are neutron stars that are thought to have been spun-up by mass accretion from a stellar companion. It is not known whether there is a natural brake for this process, or if it continues until the centrifugal breakup limit is reached at submillisecond periods. Many neutron stars that are ...

They could see details as fine as the neutron star's accretion disk, a ring of gas swirling around and flowing onto the neutron star, as the disk buckled ...

Two very promising candidates for isolated old neutron stars (IONS) accreting interstellar matter were found so far in ROSAT data. {RXJ1856.5--3754} and {RXJ0720.4--3125} are soft X-ray sources with very similar X-ray spectrum , long term temporal behaviour and faint optical counterpart. In addition {RXJ0720.4--3125} shows 8.4 s ...

We report on a 70 ks XMM-Newton Target of Opportunity (ToO) observation of the newly discovered accreting millisecond pulsar, IGR J17511-3057. Pulsations at 244.8339512(1)Hz are observed throughout the outburst with an rms-pulsed fraction of 14.4(3) per cent. Pulsations have been used to derive a precise solution for the Porb = ...

Problems connected with theories linking the pulsating radio sources ('pulsars') to the rotation of neutron stars are discussed. (Author)

Accreting white dwarfs in cataclysmic variables (CVs) have also recently been shown to exhibit non-radial pulsations similar to their non-interacting counterparts; GW Librae was the first accreting pulsator discovered in 1998 (Warner & van Zyl 1998; van Zyl et al. 2000, 2004). When the orbital period of a CV is ...

A neutron star high mass X-ray binary (HMXB) is a system consisting of a neutron star and a massive O- or B-type companion star. OB stars, which are young giant stars, have powerful stellar winds and are spreading a fraction of their mass continuously. As the neutron star revolves around the companion star, it sweeps up the matter ...

The capabilities of XMM-Newton have been fully exploited to detect a broadened iron K? emission line from the 2.5 ms Accreting Millisecond Pulsar, SAX J1808.4-3658. The energy of the transition is compatible with fluorescence from neutral/lowly ionized iron. The observed large width (FWHM more than 1 keV) can be explained through Doppler and relativistic broadening from the ...

Radial oscillations resulting from axisymmetric perturbations in viscous accretion disks surrounding

I review the X-ray observations of galactic accreting black holes and neutron stars and interpretations of these in terms of solutions of the accretion flow equations. PMID:12804240

at nearly the same frequency as the persistent pulsations have verified the interpretation of burst oscillations as arising from neutron star spin ...

Nov 4, 2009 ... This would explain the lack of X-ray pulsations because -- like a ... Interpreting the hydrogen atmosphere model without pulsations would ...

Context: The source 4U 2206+54 is one of the most enigmatic high-mass X-ray binaries. In spite of intensive searches, X-ray pulsations have not been detected in the time range 10-3-103 s. A cyclotron line at ~30 keV has been suggested by various authors but never detected with significance. The stellar wind of the optical companion is abnormally slow. The orbital period, ...

We present an analysis of the spin and orbital properties of the newly discovered accreting pulsar IGR J17480-2446, located in the globular cluster Terzan 5. Considering the pulses detected by the Rossi X-ray Timing Explorer at a period of 90.539645(2) ms, we derive a solution for the 21.27454(8) hr binary system. The binary mass function is estimated to be 0.021275(5) M?, ...

Context: Monitoring of pulse period variations in accreting binary pulsars is an important tool to study the interaction between the magnetosphere of the neutron star and the accretion disk. While the X-ray flux of the brightest X-ray pulsars have been successfully monitored over many years (e.g. with RXTE/ASM, CGRO/BATSE, Swift/BAT), ...

X-ray flashes from accreting neutron stars are considered. A number of possible explanations for the phenomenon are reviewed. A physical picture is drawn, and numerical models are discussed. 3 figures. (RWR)

Jan 22, 2010 ... Many astrophysical objects, including neutron stars and accretion disks, are powered by a combination of very strong magnetic fields and ...

Accreting white dwarfs have recently been shown to exhibit non-radial pulsations similar to their non-interacting counterparts. This allows us to probe the interior of the accreting white dwarf using seismology, and may be the only way to determine masses for non-eclipsing cataclysmic variables. Improving our understanding of ...

The key contribution of the discovery of nuclear-powered pulsations from the accretion-powered millisecond pulsars (AMPs) has been the establishment of burst oscillation frequency as a reliable proxy for stellar spin rate. This has doubled the sample of rapidly-rotating accreting neutron stars and revealed the ...

... Abstract : The prototype of accreting, pulsating white dwarfs (GW Lib) underwent a large amplitude dwarf nova outburst in 2007. ...

We show that equations governing pulsations of superfluid neutron stars can be split into two sets of weakly coupled equations, one describing the superfluid modes and another one, the normal modes. The coupling parameter s is small, |s|�0.01-0.05, for realistic equations of state. Already an approximation s=0 is sufficient to calculate the ...

We propose a 100-ks XMM-Newton observation of the transiently accreting neutron star Swift J1749.4-2807 during its quiescent state. The detection of coherent pulsations at a frequency of 518 Hz and X-ray eclipses recurring every 8.82 h during an outburst observed in 2010 have recently established Swift J1749.4-2807 as the first ...

Our past HST studies of the temperatures of 9 accreting, pulsating white dwarfs in cataclysmic variables show that 3 are in the normal instability strip for single white dwarfs, but the other 6 are much hotter {15,000-16,500K}. This dual strip has been proposed to be due to mass differences in the white dwarfs related to evolutionary history and driven by ...

A large number of neutron stars (NSs), approximately 10(exp 9), populate the Galaxy, but only a tiny

The image-tube scanner at the 3 m telescope at Lick Observatory was employed to study the spectral changes which occur during the pulse period in the optical pulsars HZ Herculis (1.2 s period) and DQ Herculis (71 s period). The data acquisition is described and the tools needed for the data analysis developed. Then the results of the observations are presented. In the case of HZ Herculis (Hercules ...

Aims: A fraction of massive stars are expected to collapse into compact objects (accreting black holes or rapidly rotating neutron stars) that successfully produce gamma-ray bursts (GRBs). We examine the possibility of directly observing these gamma-ray burst compact objects (GCOs) using post-explosion observations of past and future GRB sites. Methods: ...

Radio pulsars with millisecond spin periods are thought to have been spun up by the transfer of matter and angular momentum from a low-mass companion star during an x-ray-emitting phase. The spin periods of the neutron stars in several such low-mass x-ray binary (LMXB) systems have been shown to be in the millisecond regime, but no radio pulsations have ...

Radio pulsars with millisecond spin periods are thought to have been spun up by the transfer of matter and angular momentum from a low-mass companion star during an x-ray-emitting phase. The spin periods of the neutron stars in several such low-mass x-ray binary (LMXB) systems have been shown to be in the millisecond regime, but no radio pulsations have ...

4U2206+54 has recently been found from observations with the RXTE ASM to have a period of approximately 10 days. If due to orbital modulation this would be one of the shortest known for a Be star system. However, the X-ray luminosity is relatively modest whereas a high luminosity would be predicted if the system contains a neutron star accreting from the ...

Time-resolved low resolution Hubble Space Telescope ultraviolet spectra together with ground-based optical photometry and spectra are used to constrain the temperatures and pulsation properties of six cataclysmic variables containing pulsating white dwarfs (WDs). Combining our temperature determinations for the five pulsating WDs that ...

The newly discovered 11-Hz accreting pulsar, IGR J17480-2446, located in the globular cluster Terzan 5, has shown several bursts with a recurrence time as short as a few minutes. The source shows the shortest recurrence time ever observed from a neutron star. Here we present a study of the morphological, spectral and temporal properties of 107 bursts ...

Anomalous X-ray pulsars (AXPs) differ from ordinary radio pulsars in that their X-ray luminosity is orders of magnitude greater than their rate of rotational energy loss, and so they require an additional energy source. One possibility is that AXPs are highly magnetized neuron stars or 'magnetars' having surface magnetic fields greater than 10(14) G. This would make them similar to the soft ...

Matter spirals toward the neutron star in the form of an accretion disk, a journey visible in X-ray radiation. In doing so, it transfers its orbital energy to the neutron ...

The accretion-powered millisecond pulsar IGR J00291+5934 underwent two ~10 day long outbursts during 2008, separated by 30 days in quiescence. Such a short quiescent period between outbursts has never been seen before from a neutron star X-ray transient. X-ray pulsations at the 599 Hz spin frequency are detected throughout both ...

Spherically symmetric, time-dependent accretion of an ionized hydrogen plasma onto a neutron star is

Feb 23, 2004 ... "Accretion disks are known to flow around many objects in the universe ... Under normal conditions, accretion disks appear far too minute to ...

Neutrino emissions from stellar collapse followed by a supernova or formation of a black hole are quantified in terms of the rise-time and magnitude of the leading pulse and the average energy of the neutrinos emitted. The characteristics of the pulse at the shock breakout is examined to optical depths below unity. The resulting neutrino energy is expressed in terms of the shock-strength ...

The model of pulsar emission through superluminally induced polarization currents (SLIP) predicts that pulsations produced by such currents, induced at many light cylinder radii by a rotating, magnetized body, as would be the case for a neutron star born within any star of more than 1.4 solar masses, will drive pulsations close to the ...

Intermittent optical pulsations at the 0.1--0.3 percent level have been detected from this binary system in over 500 hours of optical observations. These pulsations are present only for well defined values of the 1.7-day (binary) and 35-day phases. Positions of the pulsation-emitting regions, projected onto the orbital plane, have been ...

The authors examine the possibility of neutron viscosity as the mechanism responsible for the dissipation of kinetic energy into luminosity in the innermost parts (r < 100 R sub s) of accretion disks surrounding compact objects. They present simplified models of such self-consistent, steady state accretion flows in which the ...

4U 1822-37 is a low mass X-ray binary (LMXB) system with an accretion disc corona. It is one of the very few LMXBs that shows narrow X-ray eclipses and small amplitude pulsations of the neutron star. The X-ray eclipse is an excellent reference for measurement of orbital evolution of the binary, and we have obtained 16 new mid-eclipse ...

The dwarf nova VSX J0747+0650 has pulsations at 238.2 s and 684.2 s (found only two years after its superoutburst), and is therefore a CV/ZZ star. Our observations of the accreting white dwarf SDSS0919+08 show that it occasionally has a brightness modulation at 214 s in addition to the known one near 260 s, establishing its credentials as a CV/ZZ ...

We report on the discovery of the second accreting millisecond X-ray pulsar (AMXP) in the globular cluster NGC 6440. Pulsations with a frequency of 205.89 Hz were detected with RXTE on 2009 August 30, October 1 and October 28, during the decays of lsim4 day outbursts of a newly X-ray transient source in NGC 6440. By studying the Doppler shift of the ...

We report on the discovery of the second accreting millisecond X-ray pulsar (AMXP) in the globular cluster NGC 6440. Pulsations with a frequency of 205.89 Hz were detected with RXTE on 2009 August 30, October 1 and October 28, during the decays of {approx}<4 day outbursts of a newly X-ray transient source in NGC 6440. By studying the Doppler shift ...

X-ray timing of the accretion-powered pulsations during the 2003 outburst of the accreting millisecond pulsar XTE J1814-338 has revealed variation in the pulse time of arrival residuals. These can be interpreted in several ways, including spin-down and wandering of the fuel impact point around the magnetic pole. In this Letter we show ...

After more than 40 years of studies, surprisingly little is known on the emission of accreting pulsars at low-luminosity. It was suggested that already at 10^{35} ergs/s the onset of a centrifugal barrier should inhibit the accretion. On the other hand, pulsations during quiescence were reported for three transient pulsars, namely 1A ...

The primary white dwarf of the cataclysmic variable SDSS J074531.92+453829.6 was discovered to exhibit non-radial pulsations in 2006 January. This accreting white dwarf underwent its first recorded dwarf nova outburst in 2006 October, during which its brightness increased by more than 5 mag. A Hubble Space Telescope (HST) ultraviolet spectrum, obtained one ...

The present study of hypercritical accretion flows onto neutron stars considers steady-state, spherically symmetric flows whose accretion rate range is characterized by the carrying away of gravitational-accretion energy by neutrinos. The models used encompass pair production, radiation diffusion, and general ...

Abstract. The accretion process onto a magnetized isolated neutron star, which captures material from the interstellar medium, is discussed. The evolutionary track of such a star can be presented as a sequence of four states: ejector, supersonic propeller, subsonic propeller, andsteady accretor. Ishowthatsubsonic propeller ? accretor transition does not ...

59, X-ray Variability and Evidence for Pulsations from the Unique Radio .... 455 , X-ray Pulsations from the Radio-quiet Gamma-ray Pulsar in CTA 1, Caraveo, ...

pulsations. In several cases, these mass esti- mates have provided convincing ... pulsations show clearly that the X-ray compo- nent is a neutron star. ...

Highly nonstationary accretion onto a magnetized neutron star from a surrounding accretion disc is considered. Nonstationary accretion has been considered before in terms of droplets or rain or as a necessary consequence of instabilities in the accretion column flow. Here, the extreme of very ...

THE presence of rotating neutron stars in binary systems is revealed by the existence of X-ray pulsators which are generally associated with massive companions. The evolutionary history of these systems is now relatively clear (see ref. 1 and refs therein). The X-ray phase, which corresponds to accretion on the ...

We report the detection of pulsations at 552 Hz in the rising phase of two type-I (thermonuclear) X-ray bursts observed from the accreting neutron star EXO 0748-676 in 2007 January and December, by the Rossi X-ray Timing Explorer. The fractional amplitude was 15% (rms). The dynamic power density spectrum for each burst revealed an ...

We report the detection of pulsations at 552 Hz in the rising phase of two type-I (thermonuclear) X-ray bursts observed from the accreting neutron star EXO 0748-676 in 2007 January and December, by the Rossi X-ray Timing Explorer. The fractional amplitude was 15% (rms). The dynamic power density spectrum for each burst revealed an ...

Important aspects of the theory of accretion are reviewed and the theory of the spherical accretion of a polytropic gas is presented. The effect of the termination of the flow at the surface of a neutron star or white dwarf is studied with consideration given to the interaction with a magnetic field anchored to the star. Spherical ...

We study the effects of finite stellar temperatures on the oscillations of superfluid neutron stars. The importance of these effects is illustrated with a simple example of a radially pulsating general relativistic star. Two main effects are taken into account: (i) temperature dependence of the entrainment matrix and (ii) the variation of the size of ...

velocities and to magnetic #12;eld decay. 2 The Ejector, Propeller and Accretion Phases Over the stellar challenge. In Section 2 we trace the evolution of a neutron star in the Ejector, Propeller and Accretion close to their mass shedding threshold, a limit sensitive to the equation of state for nuclear matter

We consider the structure and emission spectra of nonthermal accretion disks around both strongly and weakly magnetized neutron stars. Such disks may be dissipating their gravitational binding energy and transferring their angular momentum via semicontinu...

A model for emission of the hard photons of gamma bursts is presented. The model assumes accretion at nearly the Eddington limited rate onto a neutron star without a magnetic field. Initially soft photons are heated as they are compressed between the accr...

A model for emission of the hard photons of gamma bursts is presented. The model assumes accretion at nearly the Eddington limited rate onto a neutron star without magnetic a field. Initially soft photons are heated as they are compressed between the accr...

The basic ideas of accretion onto magnetized neutron stars are outlined. These are applied to a simple model of the structure of the plasma mound sitting at the magnetic poles of such a star, in which upward diffusion of photons is balanced by their downw...

thermonuclear flashes on accreting neutron stars are compared. ... An ignition mechanism of the bursts is proposed in terms of elemental mixing and ...

Mar 1, 2011 ... thermonuclear flashes on accreting neutron stars are compared. ... An ignition mechanism of the bursts is proposed in terms of elemental ...

Magnetic compact objects (neutron stars or white dwarfs) are currently thought to be present in many

It is shown here that the behavior of nuclear burning on accreting neutron stars depends on the mass

An initial study of the evolution of a neutron star in a close-binary orbit of high eccentricity discloses a special class of systems that will never achieve a state of pure, steady accretion: the neutron star will continually oscillate between an accreting state and a propeller state. This may be what is happening ...

... the hard X-ray Galactic continuum could be the superposition of unresolved point sources such as accreting neutron stars or black holes. ...

... the hard X-ray Galactic continuum could be the superposition of unresolved point sources such as accreting neutron stars or black holes. ...

The current generation of gamma-ray telescopes (SIGMA, GRO) provides a new opportunity for observing

Neutron Stars, Pulsars, Millisecond Pulsars, and Gravitational Radiation: GLOSSARY. Accretion disk: The flattened, pancake-like structure formed by matter ...

Abstracts of individual items from the workshop were prepared separately for the data base. (ERA citation 08:044825)

of these phenomena, the one supported by the data is the following. Accreting black holes and neutron stars are observed to launch relativistic puffs of plasma:...

We constrain the distribution of calcium across the surface of the white dwarf star G29-38 by combining time-series spectroscopy from Gemini-North with global time-series photometry from the Whole Earth Telescope. G29-38 is actively accreting metals from a known debris disk. Since the metals sink significantly faster than they mix across the surface, any inhomogeneity in the ...

We constrain the distribution of calcium across the surface of the white dwarf star G29-38 by combining time-series spectroscopy from Gemini-North with global time-series photometry from the Whole Earth Telescope. G29-38 is actively accreting metals from a known debris disk. Since the metals sink significantly faster than they mix across the surface, any inhomogeneity in the ...

Neutron viscosity is investigated as a possible mechanism for the dissipation of kinetic energy into luminosity in the innermost parts of accretion disks around compact objects. Simplified models are presented of the self-consistent, steady-state accretion flows in which viscosity is provided by neutron collisions ...

neutron stars would have important implications for nuclear and particle physics. While many of these objects are in binary systems ( X-ray binaries ), where ...

Feb 23, 2004 ... The gas spirals toward the neutron star like water going down a drain, forming what scientists call an accretion disk. ...

Dec 31, 2008 ... The line widths are influenced by rotation of the star via the Doppler effect. Since the spin rates of many of these accreting neutron stars ...

The shape of the Alfven surface separating the magnetosphere of a neutron star from the stream of accreting plasma and the velocity and scattering optical depth of the gas layer flowing along the Alfven surface are calculated. Calculations are made both for spherically symmetrical fall of the gas and for disk accretion. It is shown ...

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 (PSR J1023+0038) in a 0.198 day orbit with a ~0.2 M sun Roche-lobe-filling companion and appears to have had an accretion disk in 2001. We observe a hard power-law spectrum ...

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 (PSR J1023+0038) in a 0.198 day orbit with a {approx}0.2 M{sub sun} Roche-lobe-filling companion and appears to have had an accretion disk in 2001. We observe a hard ...

The wind-accreting X-ray binary pulsar Vela X-1 has been observed by INTEGRAL during two extended periods in 2003 as part of the Core Program observations of the Vela region. Here we report about the timing behaviour, particular the intense flaring which happened in Nov/Dec 2003. A preliminary spectral analysis is reported in Kretschmar et al. (2004). Several flares, typically ...

1610 in quiescence GW Lib after April 2007 outburst Implications and future work #12;Background Some pulsation modes is crucial Irregular heating events from accretion-driven outbursts (none observed before for this fainter source #12;April 2007 outburst in GW Lib On 12th April 2007, GW Lib went into outburst � the first

Abstract: Linear, adiabatic, Newtonian, nonradial pulsation analyses have been performed for finite-temperature neutron star models with a fluid core, ...

Nov 4, 2009 ... Defying astronomers' expectations, this object did not show any X-ray or radio pulsations or any signs of radio pulsar activity. ...

Dec 31, 2008 ... The model for the pulsations is an expanding hot spot on the rotating neutron star surface. The contours denote the statistical quality ...

A model for emission of the hard photons of gamma bursts is presented. The model assumes accretion at nearly the Eddington limited rate onto a neutron star without magnetic a field. Initially soft photons are heated as they are compressed between the accreting matter and the star. A large electric field due to relatively small charge ...

Accreting neutron stars can produce jets only if they are weakly magnetized (B ~ 108 G). On the other hand, neutron stars are compact objects born with strong surface magnetic fields (B ~ 1012 G). In this work we study the conditions for jet formation in a binary system formed by a neutron star and a massive donor ...

It is pointed out that for galactic X-ray sources there exists an observational association between hard spectra (kT at least about 20 keV), pulsation, and early-type optical counterparts. The absence of pulsation in soft X-ray sources is attributed to the fact that photons produced at the surface of a magnetic neutron star are Compton ...

An analysis of the observed properties of the sub-dwarf O6 close binary system HD 49798 and its 13.18s ultrasoft X-ray pulsating companion (WGA J0648.0-4418) is presented. On evolutionary grounds we show that the subdwarf must have a degenerate CO core and is in the phase of shell helium burning, which explains its high luminosity. The subdwarf, which probably has a mass ...

With the help of a very simple two-zone model we deomonstrate the possiblity of periodic thermal relaxation (limit cycle) oscillations in the helium burning envelope of accreting neutron stars. Physically reasonable model parameters can be chosen which yield agreement with the observed features of X-ray bursts. We suggest that this limit cycle is operative ...

Many accreting neutron stars do so intermittently; that is, the accretion ceases for long quiescent intervals. During the accretion outburst, reactions are induced in the crust by the continual accumulation of matter. These reactions heat the crust out of thermal equilibrium with the core, and when ...

Many accreting neutron stars do so intermittently; that is, the accretion ceases for long quiescent intervals. During the accretion outburst, reactions are induced in the crust by the continual accumulation of matter. These reactions heat the crust out of thermal equilibrium with the core, and when ...

I perform and analyze the first ever calculations of rotating stellar iron core collapse in {3+1} general relativity that start out with presupernova models from stellar evolutionary calculations and include a microphysical finite-temperature nuclear equation of state, an approximate scheme for electron capture during collapse and neutrino pressure effects. Based on the results of these ...

An optical, intensified CCD observation of the field of the 3.49 s X-ray pulsar lE 2259+586 is discussed. Two stars with B = 22.0 and B = 21.3 are found to lie 4.''9 and 6.''3 away from the nominal X-ray position determined by the High Resolution Imager (HRI) camera of the Einstein Observatory. The fainter star is identified as the optical counterpart to the ...

Viscous accretion disks and rings are subject to pulsational overstability if the effective viscous stress is a rapidly increasing function of the disks' (or rings') surface density. Such a phenomenon is induced by the transfer of energy from shear to normal mode oscillations through viscous stress. The paper examines the global response ...

We examine the stability of geometrically thin and optically thick and thin accretion disks to axisymmetric perturbations. We show that the standard ..cap alpha..-disk models admit not only classical thermal and viscous instabilities, which are generally associated with regions where electron scattering and radiation pressure are dominant, but also radial ...

Bright pulsating X-ray sources (X-ray pulsars, AM Her stars,...) have been identified as strongly magnetized compact objects accreting matter from a binary companion. We give here a summary of some of the work which has been recently done to try to unders...

The aim of this paper is to compare the two cases of an isolated neutron star, with a non-accreted crust, and that of an accreting neutron star, with an accreted crust, and try to estimate which one of the two would make a better source of gravitational waves. In order to do this, we must ...

Rare isotopes from the proton drip line to the neutron drip line are produced on the surface and crust of accreting neutron stars. Understanding their properties is essential to address the open questions raised by a variety of new observations of X-ray binaries, in particular X-ray bursters and transients. This paper provides an ...

Pycnonuclear fusion processes take place at extreme density conditions of ?>10^10 g/cm^3, anticipated for the core of white dwarfs or the crust of neutron stars. A formalism was developed for predicting pycnonuclear reaction rates for neutron rich nuclei in the carbon to magnesium range. The reaction rates have been used to simulate pycnonuclear burning ...

A final report is given of two research projects dealing with magnetic fields of neutron stars. These are the modulation of thermal x-rays from cooling neutron stars and plasma instabilities in neutron star accretion columns. (DWL)

A final report is given of two research projects dealing with magnetic fields of neutron stars. These are the modulation of thermal x-rays from cooling neutron stars and plasma instabilities in neutron star accretion columns. (ERA citation 12:044375)

The magnetospheres of accreting compact stars (neutron stars and white dwarfs) are examined. It is assumed that the compact star possesses a multipole magnetic field. The shape of the magnetosphere for the two-dimensional analog of spherically symmetric accretion and the magnetic-field configuration for the case of disk ...

accreting star. Roughly half the known X�ray novae contain BH candidates and the rest contain NSs. X of the accreting star. As discussed in the Introduction, the accretion rate in a typical X�ray nova spans a wide in which the compact accreting primary stars are too massive to be neutron ...

The interest in X/ ?-ray Astronomy has grown enormously in the last decades thanks to the ability to send X-ray space missions above the Earth�s atmosphere. There are more than half a million X-ray sources detected and over a hundred missions (past and currently operational) devoted to the study of cosmic X/ ? rays. With the improved sensibilities of the currently active missions new detections ...

The aim of this work is to compare a neutron star with an accreted crust and one with a non-accreted crust, and estimate which one is potentially a better source of gravitational waves (i.e. can sustain a larger �mountain�). To do this we present a new formalism, and find that a non-accreted crust can sustain a ...

Millisecond pulsars, both during and after accretion, stand a class apart from the general pulsar population due to the much weaker field strength at their surface. The prevailing view is that accretion of matter on to a neutron star causes a decay of its magnetic field strength, as viewed by an external observer. In this paper we ...

The central region of the Galaxy is considered and the density of stars and interstellar matter is estimated. The power owed to accretion by neutron stars is calculated for an r.m.s. velocity of ~160 km/s as from the virial theorem. An upper limit for the accretion luminosity at x-ray wavelengths is proposed. The limit is ...

We calculate the rapid proton ( rp) capture process of hydrogen burning on the surface of an accreting neutron star with an updated reaction network that extends up to Xe, far beyond previous work. In both steady-state nuclear burning appropriate for rapidly accreting neutron stars (such as the magnetic polar caps ...

X-ray bursters are considered to be neutron stars with a weak magnetic field that are undergoing disk-type accretion. If the field is weak enough, the disk will reach to the neutron star surface; next to the surface, a narrow boundary layer will develop, girdling the star. Using available formulations for luminosity and for free ...

Envelope ionization variations during the pulsations of ..beta.. Cephei variables are known to be insufficient to drive pulsations in these stars in the presence of strong deeper radiative damping. If a model can be found with smaller than normal damping, or larger than normal helium ionization driving, then any intermittent core region driving will be ...

Cataclysmic variables (CVs) provide a rich laboratory to study the effects of mass transfer and accretion on the properties and evolution of white dwarfs. One interesting aspect is the effect of accretion on the instability strip. So far, there is only one ZZ Cet pulsator known to be a CV - GW Lib. Our UV spectra obtained with HST ...

Preliminary results of a study of the linear, nonadiabatic, radial-pulsation properties of neutron-star models are presented. Sequences of pure iron models with masses of 1.0 M/sub solar/ and 1.8 M/sub solar/ and a range of luminosities and effective temp...

The kilohertz frequencies of QPOs from accreting neutron star systems imply that they are generated in regions of strong gravity, close to the star. This suggests that observations of the QPOs can be used to constrain the properties of neutron stars thems...

Jan 13, 2011 ... High-resolution X-ray spectra of bursting, accreting neutron stars show redshifted absorption lines that reveal the neutron star mass and ...

We present results of 3D simulations of MHD instabilities at the accretion disk-magnetosphere boundary. The instability is Rayleigh-Taylor, and develops for a fairly broad range of accretion rates and stellar rotation rates and magnetic fields. It produces tall, thin tongues of plasma that penetrate the magnetosphere in the equatorial plane. The shape and ...

In this letter we show that the observed gamma -ray luminosity can be produced by an accretion disc around a non-magnetic neutron star or low mass black hole in which the dominant dissipative process in the disc is due to magnetic fields. The shearing mot...