XMM-Newton observations of persistent Be binary pulsars
Abstract
Thanks to its high throughput and good spatial, timing and spectral resolution, the XMM-Newton X-ray space telescope is well suited to perform detailed studies also of faint X-ray sources. Here we report the results we obtained on the persistent Be binaries, a sub-class of the accreting X-ray binary pulsars which are characterized by non-transient emission, low luminosity (L < 1036 erg s-1 ) and long pulse period (P > 100 s); in these systems the neutron star has a wide and low-eccentricity orbit around the Be star, and accretes matter from its wind. The XMM-Newton observations of these sources have provided better source localizations, which were used to pinpoint possible candidate counterparts. The new measures of the pulse periods have shown that most pulsars are characterized by a low long-term spin down (dP/dt 10-8 s s-1 ). In nearly all pulsars the spectra show a significant excess above the main power-law component. In most cases this excess can be described by a black-body of high temperature (kT > 1 keV) and small emitting region (R < 0.5 km), whose properties are consistent with a polar-cap origin. On the other hand, other persistent binaries have shown a "soft" excess (kT < 0.4 keV), which can be described with a "mekal" model for a hot plasma in collisional equilibrium: the luminosity of this component is proportional to the total X-ray luminosity and can be due to either thermal emission or reprocessing of the primary hard X-ray radiation in a diffuse, optically thin gas around the neutron star. Finally, two pulsars have also a strong Iron line, which originates in the accreting matter far from the NS surface.
- Publication:
-
38th COSPAR Scientific Assembly
- Pub Date:
- 2010
- Bibcode:
- 2010cosp...38.2434L