The eclipsing bursting X-ray binary EXO 0748-676 revisited by XMM-Newton

Abstract

The bright eclipsing and bursting low-mass X-ray binary EXO 0748-676 has been observed at several occasions by XMM-Newton during the initial calibration and performance verification (CAL/PV) phase. We present here the results obtained from observations with the EPIC cameras. Apart from several type-I X-ray bursts, the source shows a high degree of variability with the presence of soft flares. The wide energy coverage and high sensitivity of XMM-Newton allows for the first time a detailed description of the spectral variability. The source is found to be the superposition of a central ( ~ 2 10⁸ cm) Comptonized emission, most probably a corona surrounding the inner edge of an accretion disk, associated with a more extended ( ~ 3 10¹⁰ cm) thermal halo at a typical temperature of ~ 0.6 keV with an indication of non-solar abundances. Most of the variations of the source can be accounted for by a variable absorption affecting only the central comptonized component and reaching up to N_H ~ 1.3 10²³ cm^-2. The characteristics of the surrounding halo are found compatible with an irradiated atmosphere of an accretion disc which intercepts the central emission due to the system high inclination.