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Neutron Stars (neutron + star)
Kinds of Neutron Stars Selected AbstractsNeutron star with C atmosphereASTRONOMY & GEOPHYSICS, Issue 6 2009Article first published online: 23 NOV 200 The neutron star at the heart of the Cassiopeia A supernova remnant has a thin carbon atmosphere, masking the X-ray emission that was expected, but not detected. [source] Asymptotic behaviour for a non-monotone fluid in one dimension: the positive temperature caseMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 8 2001B. Ducomet We consider a one-dimensional continuous model of neutron star, described by a compressible Navier,Stokes system with a non-monotone equation of state, due to the effective Skyrme nuclear interaction between particles. We study the asymptotic behaviour of globally defined solutions of a mixed free boundary problem for our model, for large time, assuming that a sufficient thermal dissipation is present. Copyright © 2001 John Wiley & Sons, Ltd. [source] Be/X-ray binary SXP6.85 undergoes large Type II outburst in the Small Magellanic CloudMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2010L. J. Townsend ABSTRACT The Small Magellanic Cloud (SMC) Be/X-ray binary pulsar SXP6.85 = XTE J0103,728 underwent a large Type II outburst beginning on 2008 August 10. The source was consistently seen for the following 20 weeks (MJD = 54688,54830). We present X-ray timing and spectroscopic analysis of the source as a part of our ongoing Rossi X-ray Timing Explorer (RXTE) monitoring campaign and INTEGRAL key programme monitoring the SMC and 47 Tuc. A comparison with the Optical Gravitational Lensing Experiment (OGLE) III light curve of the Be counterpart shows the X-ray outbursts from this source coincide with times of optical maximum. We attribute this to the circumstellar disc increasing in size, causing mass accretion on to the neutron star. Ground based infrared photometry and H, spectroscopy obtained during the outburst are used as a measure of the size of the circumstellar disc and lend support to this picture. In addition, folded RXTE light curves seem to indicate complex changes in the geometry of the accretion regions on the surface of the neutron star, which may be indicative of an inhomogeneous density distribution in the circumstellar material causing a variable accretion rate on to the neutron star. Finally, the assumed inclination of the system and H, equivalent width measurements are used to make a simplistic estimate of the size of the circumstellar disc. [source] Accreting millisecond pulsar SAX J1808.4,3658 during its 2002 outburst: evidence for a receding discMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2009Askar Ibragimov ABSTRACT An outburst of the accreting X-ray millisecond pulsar SAX J1808.4,3658 in 2002 October,November was followed by the Rossi X-ray Timing Explorer for more than a month. A detailed analysis of this unprecedented data set is presented. For the first time, we demonstrate how the area covered by the hotspot at the neutron star surface is decreasing in the course of the outburst together with the reflection amplitude. These trends are in agreement with the natural scenario, where the disc inner edge is receding from the neutron star as the mass accretion rate drops. These findings are further supported by the variations of the pulse profiles, which clearly show the presence of the secondary maximum at the late stages of the outburst after October 29. This fact can be interpreted as the disc receding sufficiently far from the neutron star to open the view of the lower magnetic pole. In that case, the disc inner radius can be estimated. Assuming that disc is truncated at the Alfvén radius, we constrain the stellar magnetic moment to ,= (9 ± 5) × 1025 G cm3, which corresponds to the surface field of about 108 G. On the other hand, using the magnetic moment recently obtained from the observed pulsar spin-down rate we show that the disc edge has to be within factor of 2 of the Alfvén radius, putting interesting constraints on the models of the disc,magnetosphere interaction. We also demonstrate that the sharp changes in the phase of the fundamental are intimately related to the variations of the pulse profile, which we associate with the varying obscuration of the antipodal spot. Using the phase-resolved spectra, we further argue that the strong dependence of the pulse profiles on photon energy and the observed soft time lags result from the different phase dependence of the normalizations of the two spectral components, the blackbody and the Comptonized tail, being consistent with the model, where these components have significantly different angular emission patterns. The pulse profile amplitude allows us to estimate the colatitude of the hotspot centroid to be ,4°,10°. [source] Delayed X-ray emission from fallback in compact-object mergersMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2009Elena M. Rossi ABSTRACT When double neutron star or neutron star,black hole binaries merge, the final remnant may comprise a central solar-mass black hole surrounded by a ,0.01,0.1 M, torus. The subsequent evolution of this disc may be responsible for short ,-ray bursts (SGRBs). A comparable amount of mass is ejected into eccentric orbits and will eventually fallback to the merger site after ,0.01 s. In this paper, we investigate analytically the fate of the fallback matter, which may provide a luminous signal long after the disc is exhausted. We find that matter in the eccentric tail returns at a super-Eddington rate and eventually (,0.1 s) is unable to cool via neutrino emission and accrete all the way to the black hole. Therefore, contrary to previous claims, our analysis suggests that fallback matter is not an efficient source of late-time accretion power and unlikely to cause the late-flaring activity observed in SGRB afterglows. The fallback matter rather forms a radiation-driven wind or a bound atmosphere. In both the cases, the emitting plasma is very opaque and photons are released with a degraded energy in the X-ray band. We therefore suggest that compact binary mergers could be followed by an ,X-ray renaissance', as late as several days to weeks after the merger. This might be observed by the next generation of X-ray detectors. [source] Toroidal magnetic fields in type II superconducting neutron starsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2008T. Akgün ABSTRACT We determine constraints on the form of axisymmetric toroidal magnetic fields dictated by hydrostatic balance in a type II superconducting neutron star with a barotropic equation of state. Using Lagrangian perturbation theory, we find the quadrupolar distortions due to such fields for various models of neutron stars with type II superconducting and normal regions. We find that the star becomes prolate and can be sufficiently distorted to display precession with a period of the order of years. We also study the stability of such fields using an energy principle, which allows us to extend the stability criteria established by R. J. Tayler for normal conductors to more general media with magnetic free energy that depends on density and magnetic induction, such as type II superconductors. We also derive the growth rate and instability conditions for a specific instability of type II superconductors, first discussed by P. Muzikar, C. J. Pethick and P. H. Roberts, using a local analysis based on perturbations around a uniform background. [source] Measuring the spin up of the accreting millisecond pulsar XTE J1751,305MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008A. Papitto ABSTRACT We perform a timing analysis on RXTE data of the accreting millisecond pulsar XTE J1751,305 observed during the 2002 April outburst. After having corrected for Doppler effects on the pulse phases due to the orbital motion of the source, we performed a timing analysis on the phase delays, which gives, for the first time for this source, an estimate of the average spin frequency derivative . We discuss the torque resulting from the spin-up of the neutron star deriving a dynamical estimate of the mass accretion rate and comparing it with the one obtained from X-ray flux. Constraints on the distance to the source are discussed, leading to a lower limit of , 6.7 kpc. [source] The dynamical formation of LMXBs in dense stellar environments: globular clusters and the inner bulge of M31MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007R. Voss ABSTRACT The radial distribution of luminous (LX > 1036 erg s,1) X-ray point sources in the bulge of M31 is investigated using archival Chandra observations. We find a significant increase in the specific frequency of X-ray sources, per unit stellar mass, within 1 arcmin from the centre of the galaxy. The radial distribution of surplus sources in this region follows the ,2* law, suggesting that they are low-mass X-ray binaries (LMXBs) formed dynamically in the dense inner bulge. We investigate dynamical formation of LMXBs, paying particular attention to the high-velocity regime characteristic for galactic bulges, which has not been explored previously. Our calculations suggest that the majority of the surplus sources are formed in tidal captures of black holes by main-sequence stars of low mass, M*, 0.3,0.4 M,, with some contribution of neutron star (NS) systems of same type. Due to the small size of the accretion discs, a fraction of such systems may be persistent X-ray sources. Some of the sources may be ultracompact X-ray binaries with helium star/white dwarf companions. We also predict a large number of faint transients, both NS and BH systems, within ,1 arcmin from the M31 galactic centre. Finally, we consider the population of dynamically formed binaries in Galactic globular clusters, emphasizing the differences between these two types of stellar environments. [source] Mountains on neutron stars: accreted versus non-accreted crustsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006B. Haskell ABSTRACT The aim of this paper is to compare the two cases of an isolated neutron star, with a non-accreted crust, and that of an accreting neutron star, with an accreted crust, and try to estimate which one of the two would make a better source of gravitational waves. In order to do this, we must evaluate the maximum ,mountain' that the crust can sustain in these two cases. We first do this using the formalism of Ushomirsky, Cutler & Bildsten and find that the maximum quadrupole is very similar in the two cases, with the non-accreted crust sustaining a slightly larger mountain. We then develop a perturbation formalism for the problem, that allows us to drop the Cowling approximation and have more control over the boundaries. The use of this formalism confirms that there is not much difference between the two cases, but leads to results approximately one order of magnitude larger than those we obtain with the formalism of Ushomirsky et al. [source] Constraints on the dense matter equation of state from the measurements of PSR J0737,3039A moment of inertia and PSR J0751+1807 massMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005M. Bejger ABSTRACT The moment of inertia of the pulsar A in the neutron star binary J0737,3039 will soon be measurable through detailed measurements of the periastron advance. We present the calculation of the moment of inertia of neutron stars with the masses of the components of the binary J0737,3039 for a broad range of equations of state of dense matter, and we discuss the implications of such measurement for constraining the equation of state. An observational determination of the moment of inertia of the pulsar A in J0737,3039 with the accuracy of 10 per cent will narrow down considerably the range of viable equations of state. We also show that limits on the maximal mass of a neutron star provide a complementary set of constraints on the properties of dense nuclear matter. [source] Can a slowly rotating neutron star be a radio pulsar?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2005Ya. N. Istomin ABSTRACT It is shown that the radius of curvature of magnetic field lines in the polar region of a rotating magnetized neutron star can be significantly less than the usual radius of curvature of the dipole magnetic field. The magnetic field in the polar cap is distorted by toroidal electric currents flowing in the neutron star crust. These currents close up the magnetospheric currents driven by the electron,positron plasma generation process in the pulsar magnetosphere. Owing to the decrease in the radius of curvature, electron,positron plasma generation becomes possible even for slowly rotating neutron stars, with PB,2/312 < 10 s, where P is the period of star rotation and B12=B/1012 G is the magnitude of the magnetic field on the star surface. [source] Radio detections of the neutron star X-ray binaries 4U 1820 , 30 and Ser X-1 in soft X-ray statesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2004S. Migliari ABSTRACT We present the analysis of simultaneous X-ray (RXTE) and radio (VLA) observations of two atoll-type neutron star X-ray binaries: 4U 1820 , 30 and Ser X-1. Both sources were steadily in the soft (,banana') X-ray state during the observations. We have detected the radio counterpart of 4U 1820 , 30 at 4.86 and 8.46 GHz at a flux density of ,0.1 mJy. This radio source is positionally coincident with the radio pulsar PSR 1820 , 30A. However, the radio emission of the pulsar falls rapidly with frequency (,,,3), and we argue that the radio emission of the X-ray binary is dominant above ,2 GHz. Supporting this interpretation, comparison with previous observations reveals variability at the higher radio frequencies that is likely to be due to the X-ray binary. We have detected for the first time the radio counterpart of Ser X-1 at 8.46 GHz, also at a flux density of ,0.1 mJy. The position of the radio counterpart has allowed us to identify its optical counterpart unambiguously. We briefly discuss similarities and differences between the disc,jet coupling in neutron star and black hole X-ray binaries. In particular, we draw attention to the fact that, contrary to other states, neutron star X-ray binaries seem to be more radio-loud than persistent black hole candidates when the emission is ,quenched' in the soft state. [source] PSR J1829+2456: a relativistic binary pulsarMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2004D. J. Champion ABSTRACT We report the discovery of a new binary pulsar, PSR J1829+2456, found during a mid-latitude drift-scan survey with the Arecibo telescope. Our initial timing observations show the 41-ms pulsar to be in a 28-h, slightly eccentric, binary orbit. The advance of periastron yr,1 is derived from our timing observations spanning 200 d. Assuming that the advance of periastron is purely relativistic and a reasonable range of neutron star masses for PSR J1829+2456, we constrain the companion mass to be between 1.22 and 1.38 M,, making it likely to be another neutron star. We also place a firm upper limit on the pulsar mass of 1.38 M,. The expected coalescence time due to gravitational wave emission is long (,60 Gyr), and this system will not significantly impact upon calculations of merger rates that are relevant to upcoming instruments such as LIGO. [source] The , -ray burst phenomenon treated as the collapse of a QED magnetized vacuum bubble: analogy with sonoluminescenceMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2000YU. N. Gnedin We treat the phenomenon of a , -ray burst as the non-linear collapse of a magnetic cavity surrounding a neutron star with extremely large magnetic field B,1015,1016 G due to the process of bubble shape instability in the resonant MHD field of an accreting plasma or on a neutron star surface. The QED effect of vacuum polarizability by a strong magnetic field is taken into a consideration. We develop an analogy with the phenomenon of sonoluminescence in which the gas bubble is located in a surrounding liquid with a driven sound intensity. [source] OGLE observations of four X-ray binary pulsars in the Small Magellanic CloudMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2000M. J. Coe This paper presents analysis and interpretation of OGLE photometric data of four X-ray binary pulsar systems in the Small Magellanic Cloud (SMC): 1WGA J0054.9-7226, RX J0050.7-7316, RX J0049.1-7250 and 1SAX J0103.2-7209. In each case, the probable optical counterpart is identified on the basis of its optical colours. In the case of RX J0050.7-7316 the regular modulation of its optical light curve appears to reveal an ellipsoidal modulation with a period of 1.416 d. Using reasonable masses for the neutron star and the B star, we show that the amplitude and relative depths of the minima of the I -band light curve of RX J0050.7-7316 can be matched with an ellipsoidal model where the B star nearly fills its Roche lobe. For mass ratios in the range of 0.12 to 0.20, the corresponding best-fitting inclinations are about 55° or larger. The neutron star would be eclipsed by the B star at inclinations larger than ,60° for this particular mass ratio range. Thus RX J0050.7-7316 is a good candidate system for further study. In particular, we would need additional photometry in several colours, and most importantly, radial velocity data for the B star before we could draw more quantitative conclusions about the component masses. [source] Origin and evolution of magnetarsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2008Lilia Ferrario ABSTRACT We present a population synthesis study of the observed properties of the magnetars investigating the hypothesis that they are drawn from a population of progenitors that are more massive than those of the normal radio pulsars. We assume that the anomalous X-ray emission is caused by the decay of a toroidal or tangled up field that does not take part in the spin-down of the star. Our model assumes that the magnetic flux of the neutron star is distributed as a Gaussian in the logarithm about a mean value that is described by a power law , where Mp is the mass of the progenitor. We find that we can explain the observed properties of the magnetars for a model with ,0= 2 × 1025 G cm2 and ,= 5 if we suitably parametrize the time evolution of the anomalous X-ray luminosity as an exponentially decaying function of time. Our modelling suggests that magnetars arise from stars in the high-mass end (20 M,,Mp, 45 M,) of this distribution. The lower mass progenitors are assumed to give rise to the radio pulsars. The high value of , can be interpreted in one of two ways. It may indicate that the magnetic flux distribution on the main sequence is a strong function of mass and that this is reflected in the magnetic fluxes of the neutron stars that form from this mass range (the fossil field hypothesis). The recent evidence for magnetic fluxes similar to those of the magnetars in a high fraction (,25 per cent) of massive O-type stars lends support to such a hypothesis. Another possibility is that the spin of the neutron star is a strong function of the progenitor mass, and it is only for stars that are more massive than ,20 M, that magnetar-type fields can be generated by the ,,, dynamo mechanism (the convective dynamo hypothesis). In either interpretation, it has to be assumed that all or a subset of stars in the mass range ,20,45 M,, which on standard stellar evolution models lead to black holes via the formation of a fall-back disc, must give rise to magnetars. Unlike with the radio pulsars, the magnetars only weakly constrain the birth spin period, due to their rapid spin-down. Our model predicts a birthrate of ,1.5,3 × 10,3 yr,1 for the magnetars. [source] Detection of compact radio emission from Circinus X-1 with the first Southern hemisphere e-VLBI experimentMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2007C. J. Phillips ABSTRACT Circinus X-1 has recently returned to a state of strong radio flaring. Here we report on the first VLBI observations, and detection, undertaken in the 25 years since the 1975,1985 period of strong recurrent flaring activity. We detected Circinus X-1 with the first observations conducted by a recently developed Southern hemisphere e-VLBI array, at both 1.6 and 8.4 GHz, over a three-day period. At 1.6 GHz, the compact source has a total flux density of 11 mJy and a size of 60 ± 15 mas (Gaussian model full width at half maximum). At 8.4 GHz, the compact source is less than 60 mas. The size variation with frequency is consistent with a broadened image due to scattering in the turbulent, ionized interstellar medium of our Galaxy. However, these size measurements appear inconsistent with the ,2.2 variation expected for strong interstellar scattering and previous VLBI observations made at 2.3 GHz in the early 1980s. To explain this apparent inconsistency, we suggest that Circinus X-1 supports a weak, non-varying component of 35 mas extent (175 au at 5 kpc distance), corresponding to compact structure in the extended radio nebula. No significant variation in the flux density at 1.6 GHz is evident between two observations 24 h apart. No jet-like structures are evident on scales of tens of mas, simply a scatter broadened source, presumably coincident with the suggested neutron star in the binary system. [source] Masses and luminosities of O- and B-type stars and red supergiantsASTRONOMISCHE NACHRICHTEN, Issue 4 2010M.M. Hohle Abstract Massive stars are of interest as progenitors of supernovae, i.e. neutron stars and black holes, which can be sources of gravitational waves. Recent population synthesis models can predict neutron star and gravitational wave observations but deal with a fixed supernova rate or an assumed initial mass function for the population of massive stars. Here we investigate those massive stars, which are supernova progenitors, i.e. with O- and early B-type stars, and also all supergiants within 3 kpc. We restrict our sample to those massive stars detected both in 2MASS and observed by Hipparcos, i.e. only those stars with parallax and precise photometry. To determine the luminosities we calculated the extinctions from published multi-colour photometry, spectral types, luminosity class, all corrected for multiplicity and recently revised Hipparcos distances. We use luminosities and temperatures to estimate the masses and ages of these stars using different models from different authors. Having estimated the luminosities of all our stars within 3 kpc, in particular for all O- and early B-type stars, we have determined the median and mean luminosities for all spectral types for luminosity classes I, III, and V. Our luminosity values for supergiants deviate from earlier results: Previous work generally overestimates distances and luminosities compared to our data, this is likely due to Hipparcos parallaxes (generally more accurate and larger than previous ground-based data) and the fact that many massive stars have recently been resolved into multiples of lower masses and luminosities. From luminosities and effective temperatures we derived masses and ages using mass tracks and isochrones from different authors. From masses and ages we estimated lifetimes and derived a lower limit for the supernova rate of ,20 events/Myr averaged over the next 10 Myr within 600 pc from the sun. These data are then used to search for areas in the sky with higher likelihood for a supernova or gravitational wave event (like OB associations) (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] New photometry and astrometry of the isolated neutron star RX J0720.4,3125 using recent VLT/FORS observations,ASTRONOMISCHE NACHRICHTEN, Issue 3 2010T. Eisenbeiss Abstract Since the first optical detection of RX J0720.4,3125 various observations have been performed to determine astrometric and photometric data. We present the first detection of the isolated neutron star in the V Bessel filter to study the spectral energy distribution and derive a new astrometric position. At ESO Paranal we obtained very deep images with FORS 1 (three hours exposure time) of RX J0720.4,3125 in the V Bessel filter in January 2008. We derive the visual magnitude by standard star aperture photometry. Using sophisticated resampling software we correct the images for field distortions. Then we derive an updated position and proper motion value by comparing its position with FORS 1 observations of December 2000. We calculate a visual magnitude of V = 26.81 ± 0.09 mag, which is seven times in excess of what is expected from X-ray data, but consistent with the extant U, B, and R data. Over about a seven year epoch difference we measured a proper motion of , = 105.1 ± 7.4 mas yr,1 towards , = 296.951° ± 0.0063° (NW), consistent with previous data (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The estimations of neutron star mass and radius by the kHz QPOsASTRONOMISCHE NACHRICHTEN, Issue 4 2009C.M. Zhang Abstract The kHz quasi-periodic oscillations (QPOs) have been detected by the RXTE satellite in about thirty neutron stars (NSs) in low mass X-ray binaries (LMXBs), which are usually interpreted to be related to the Keplerian motions in the orbit close to NS surface where the accreted matter is sucked onto the star. Based on the MHD Alfvén wave oscillation model and the relativistic precession model for the neutron star (NS) kHz QPOs, estimations of mass M and radius R of some NSs are given, which can give clues to evaluate the models. Furthermore, comparisons with theoretical M - R relations by stellar equations of state (EOSs) are presented (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The X-ray source population of the Andromeda galaxy M 31,ASTRONOMISCHE NACHRICHTEN, Issue 2 2008W. Pietsch Abstract First studies of the X-ray source population of M 31 were performed with the Einstein Observatory and ROSAT. High resolution Chandra Observatory images not only spatially resolved the center area but also supernova remnants (SNRs) in the galaxy. Source catalogues of restricted areas were presented with high astrometric accuracy. Also luminosity function studies and studies of individual sources based on Chandra and XMM-Newton observations led to a better knowledge of the X-ray source population. An XMM-Newton source catalog based on archival observations revealed more than 850 sources down to a 0.2,4.5 keV luminosity of 1035 erg s,1. EPIC hardness ratios as well as informations from earlier X-ray, optical, and radio catalogues were used to distinguish between different source classes (SNRs, supersoft sources (SSSs), X-ray binaries (XRBs), globular cluster sources within M 31, and foreground stars and objects in the background). However, many sources could only be classified as "hard". These sources may either be XRBs or Crab-like SNRs in M 31 or background sources. Two of the globular cluster sources could be identified as low mass XRBs with a neutron star as compact object as they showed type I X-ray bursts. Many of the SSSs were identified as optical novae. Inspired by these results an XMM-Newton survey of the entire D25 disk of M 31 and a dedicated program to monitor X-ray counterparts of optical novae in M 31 was started. We discuss implications for further nearby galaxy studies. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The SGR 1806-20 magnetar signature on the Earth's magnetic fieldGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2006M. Mandea SUMMARY SGRs denote ,soft ,-ray repeaters', a small class of slowly spinning neutron stars with strong magnetic fields. On 2004 December 27, a giant flare was detected from magnetar SGR 1806-20. The initial spike was followed by a hard-X-ray tail persisting for 380 s with a modulation period of 7.56 s. This event has received considerable attention, particularly in the astrophysics area. Its relevance to the geophysics community lies in the importance of investigating the effects of such an event on the near-Earth electromagnetic environment. However, the signature of a magnetar flare on the geomagnetic field has not previously been investigated. Here, by applying wavelet analysis to the high-resolution magnetic data provided by the CHAMP satellite, a modulated signal with a period of 7.5 s over the duration of the giant flare appears in the observed data. Moreover, this event was detected by the energetic ion counters onboard the DEMETER satellite. [source] Unusual glitch activity in the RRAT J1819,1458: an exhausted magnetar?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009A. G. Lyne ABSTRACT We present an analysis of regular timing observations of the high magnetic field Rotating Radio Transient (RRAT) J1819,1458 obtained using the 64-m Parkes and 76-m Lovell radio telescopes over the past 5 years. During this time, the RRAT has suffered two significant glitches with fractional frequency changes of 0.6 × 10,6 and 0.1 × 10,6. Glitches of this magnitude are a phenomenon displayed by both radio pulsars and magnetars. However, the behaviour of J1819,1458 following these glitches is quite different to that which follows glitches in other neutron stars, since the glitch activity resulted in a significant long-term net decrease in the slow-down rate. If such glitches occur every 30 years, the spin-down rate, and by inference the magnetic dipole moment, will drop to zero on a time-scale of a few thousand years. There are also significant increases in the rate of pulse detection and in the radio pulse energy immediately following the glitches. [source] Upper limits on X-ray emission from two rotating radio transientsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009D. L. Kaplan ABSTRACT X-ray emission from the enigmatic rotating radio transients (RRATs) offers a vital clue to understanding these objects and how they relate to the greater neutron star population. An X-ray counterpart to RRAT J1819,1458 is known, and its properties are similar to those of other middle-aged (0.1 Myr) neutron stars. We have searched for X-ray emission with Chandra/Advanced CCD Imaging Spectrometer at the positions of two RRATs with arcsecond (or better) localization, J0847,4316 and J1846,0257. Despite deep searches (especially for RRAT J1846,0257) we did not detect any emission with 0.3,8 keV count-rate limits of 1 and 0.068 counts ks,1, respectively, at 3, confidence. Assuming thermal emission similar to that seen from RRAT J1819,1458 (a blackbody with radius ,20 km), we derive effective temperature limits of 77 and 91 eV for the nominal values of the distances and column densities to both sources, although both of those quantities are highly uncertain and correlated. If we instead fix the temperature of the emission (a blackbody with kT= 0.14 keV), we derive unabsorbed luminosity limits in the 0.3,8 keV range of 1 × 1032 and 3 × 1032 erg s,1. These limits are considerably below the luminosity of RRAT J1819,1458(4 × 1033 erg s,1), suggesting that RRATs J0847,4316 and J1846,0257 have cooled beyond the point of visibility (plausible given the differences in characteristic age). However, as we have not detected X-ray emission, it may also be that the emission from RRATs J0847,4316 and J1846,0257 has a different character from that of RRAT J1819,1458. The two non-detections may prove a counterpoint to RRAT J1819,1458, but more detections are certainly needed before we can begin to derive general X-ray emission properties for the RRAT populations. [source] Toroidal magnetic fields in type II superconducting neutron starsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2008T. Akgün ABSTRACT We determine constraints on the form of axisymmetric toroidal magnetic fields dictated by hydrostatic balance in a type II superconducting neutron star with a barotropic equation of state. Using Lagrangian perturbation theory, we find the quadrupolar distortions due to such fields for various models of neutron stars with type II superconducting and normal regions. We find that the star becomes prolate and can be sufficiently distorted to display precession with a period of the order of years. We also study the stability of such fields using an energy principle, which allows us to extend the stability criteria established by R. J. Tayler for normal conductors to more general media with magnetic free energy that depends on density and magnetic induction, such as type II superconductors. We also derive the growth rate and instability conditions for a specific instability of type II superconductors, first discussed by P. Muzikar, C. J. Pethick and P. H. Roberts, using a local analysis based on perturbations around a uniform background. [source] Radiative transitions of the helium atom in highly magnetized neutron star atmospheresMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Z. Medin ABSTRACT Recent observations of thermally emitting isolated neutron stars revealed spectral features that could be interpreted as radiative transitions of He in a magnetized neutron star atmosphere. We present Hartree,Fock calculations of the polarization-dependent photoionization cross-sections of the He atom in strong magnetic fields ranging from 1012 to 1014 G. Convenient fitting formulae for the cross-sections are given along with the related oscillator strengths for various bound,bound transitions. The effects of finite nucleus mass on the radiative absorption cross-sections are examined using perturbation theory. [source] Analysing the atolls: X-ray spectral transitions of accreting neutron starsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007Jeanette Gladstone ABSTRACT We systematically analyse all the available X-ray spectra of disc accreting neutron stars (atolls and millisecond pulsars) from the RXTE data base. We show that while all these have similar spectral evolution as a function of mass accretion rate, there are also subtle differences. There are two different types of hard/soft transition, those where the spectrum softens at all energies, leading to a diagonal track on a colour,colour diagram, and those where only the higher energy spectrum softens, giving a vertical track. The luminosity at which the transition occurs is correlated with this spectral behaviour, with the vertical transition at L/LEdd, 0.02 while the diagonal one is at ,0.1. Superimposed on this is the well-known hysteresis effect, but we show that classic, large-scale hysteresis occurs only in the outbursting sources, indicating that its origin is in the dramatic rate of change of mass accretion rate during the disc instability. We show that the long-term mass accretion rate correlates with the transition behaviour, and speculate that this is due to the magnetic field being able to emerge from the neutron star surface for low average mass accretion rates. While this is not strong enough to collimate the flow except in the millisecond pulsars, its presence may affect the inner accretion flow by changing the properties of the jet. [source] Thermal evolution of rotating hybrid starsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007Miao Kang ABSTRACT As a neutron star spins down, the nuclear matter is continuously converted into quark matter due to the core density increase, and then latent heat is released. We have investigated the thermal evolution of neutron stars undergoing such deconfinement phase transition. We have taken into account the conversion in the frame of the general theory of relativity. The released energy has been estimated as a function of changed rate of deconfinement baryon number. The numerical solutions to the cooling equation are seen to be very different from those without the heating effect. The results show that neutron stars may be heated to higher temperatures which is well matched with pulsar's data despite the onset of fast cooling in neutron stars with quark matter cores. It is also found that the heating effect has a magnetic field strength dependence. This feature could be particularly interesting for high temperatures of low-field millisecond pulsars at a later stage. The high temperature could fit the observed temperature for PSR J0437,4715. [source] Mountains on neutron stars: accreted versus non-accreted crustsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006B. Haskell ABSTRACT The aim of this paper is to compare the two cases of an isolated neutron star, with a non-accreted crust, and that of an accreting neutron star, with an accreted crust, and try to estimate which one of the two would make a better source of gravitational waves. In order to do this, we must evaluate the maximum ,mountain' that the crust can sustain in these two cases. We first do this using the formalism of Ushomirsky, Cutler & Bildsten and find that the maximum quadrupole is very similar in the two cases, with the non-accreted crust sustaining a slightly larger mountain. We then develop a perturbation formalism for the problem, that allows us to drop the Cowling approximation and have more control over the boundaries. The use of this formalism confirms that there is not much difference between the two cases, but leads to results approximately one order of magnitude larger than those we obtain with the formalism of Ushomirsky et al. [source] Minimal models of cooling neutron stars with accreted envelopesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006A. D. Kaminker ABSTRACT We study the ,minimal' cooling scenario of superfluid neutron stars with nucleon cores, where the direct Urca process is forbidden and enhanced cooling is produced by neutrino emission due to the Cooper pairing of neutrons. Extending our recent previous work, we include the effects of surface accreted envelopes of light elements. We employ the phenomenological density-dependent critical temperatures Tcp(,) and Tcnt(,) of singlet-state proton and triplet-state neutron pairing in a stellar core, as well as the critical temperature Tcns(,) of singlet-state neutron pairing in a stellar crust. We show that the presence of accreted envelopes simplifies the interpretation of observations of thermal radiation from isolated neutron stars in the scenario of our recent previous work and widens the class of models for nucleon superfluidity in neutron star interiors consistent with the observations. [source] | |||||||||||||