We present an extended set of model atmospheres and emergent spectra of X-ray bursting neutron stars in low mass X-ray binaries. Compton scattering is taken into account. The models were computed in LTE approximation for six different chemical compositions: pure hydrogen and pure helium atmospheres, and atmospheres with a solar mix of hydrogen and helium and various heavy elements abundances: Z = 1, 0.3, 0.1, and 0.01 Z_sun, for three values of gravity, log g =14.0, 14.3, and 14.6 and for 20 values of relative luminosity l = L/L_Edd in the range 0.001 - 0.98. The emergent spectra of all models are fitted by diluted blackbody spectra in the observed RXTE/PCA band 3 - 20 keV and the corresponding values of color correction factors f_c are presented. We also show how to use these dependencies to estimate the neutron star's basic parameters.Comment: 2 pages, 1 figure, conference "Astrophysics of Neutron Stars - 2010" in honor of M. Ali Alpar, Izmir, Turke
OAO 1657-415 is an eclipsing X-ray binary pulsar that has undergone several torque reversals throughout its long history of observation. We present a frequency history spanning nearly 19 years of observations from the Burst and Transient Source Experiment (BATSE) and from the Gamma-Ray Burst Monitor (GBM). Orbital ephemerides of the pulsar system is obtained at several intervals throughout this history. With these ephemerides, statistically significant orbital decay is established.
The rotational properties and X-ray luminosity of PSR J0726–2612 are close to those of dim isolated neutron stars (XDINs). It was proposed that the source could be the first XDIN with observable pulsed radio emission. We have investigated the long-term evolution of the source to test this possibility in the fallback disc model. Reasonable model curves that can account for the evolution of PSR J0726–2612 consistently with its radio pulsar property are similar to those of high-B radio pulsars with dipole field strength B0 ∼ a few × 1012 G at the pole of the star. In the same model, XDINs are estimated to have relatively weak fields (B0 ≲ 1012 G) locating them well below the pulsar death line. From the simulations, we estimate that PSR J0726–2612 is at an age of t ∼ 5 × 104 yr, and will achieve the rotational properties of a normal radio pulsar within ∼105 yr, rather than the XDIN properties.
We compiled X-ray and Optical observations of the accreting X-ray binary sytem A 0535+26 since its discovery in 1975, that will allow us to shed light on the unpredictible behavior of this binary system. We present the data in terms of the Be-disc interaction with the neutron star companion. In addition, we show recent results from the continous monitoring of this source by the Gamma-ray Burst Monitor (GBM), on board the Fermi observatory, since its launch in 2008 June 11.
Large pulsar glitches seem to be common to all radio pulsars and to exhibit a universal behaviour connecting the rate of occurrence, event size and interglitch relaxation that can be explained if the glitches are due to angular momentum exchange in the neutron star. This has implications for the energy dissipation rate. The large timing excursions observed in SGRs are not similar to the pulsar glitches. The one glitch observed in an AXP is very similar to pulsar glitches and demonstrates that typical neutron star glitch response occurs when the external torque is constant for an extended period of time. In the long run the timing variations of both the AXPs and the SGRs are much stronger than the timing noise of radio pulsars but comparable with the behaviour of accreting sources. For the DTNs, the thermal luminosities do not seem compatible with cooling ages and statistics if these sources are magnetars. The energy dissipation rates implied by the dynamical behaviour of glitching pulsars will provide the luminosities of the DTNs under propeller spindown torques supplied by fossil disks on neutron stars with conventional 10 12 G dipole magnetic fields.
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