The soft X-ray spectrum of transient pulsars in the Small Magellanic Cloud

Abstract

The Small Magellanic Cloud is characterized by a high number of transient accreting pulsars, which can reach luminosities up to 10^{38} erg s^{-1} during their outbursts. Due to the low Galactic interstellar absorption in the SMC direction, these sources offer a unique opportunity to investigate the soft end of the X-ray spectrum in accreting pulsars. In the last two years we observed with XMM-Newton the large outburst of two of these transient pulsars (RX J0059.2-7138 and SMC X-2). Thanks to the high throughput and spectral resolution of XMM, these observations allowed us to investigate at an unprecedented level of detail their spectral and timing properties at soft X-ray energies. We found that both sources show a pulsed emission also at low energies, and that they are characterized by a thermal component which dominates the source spectrum below 0.5 keV; moreover, we discovered several emission and absorption features, which are very likely produced by photoionization of plasma located above the inner regions of the accretion disc. <P />