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Preprint H/00

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

J.M. Bonnet-Bidaud (1), F. Haberl (2), P. Ferrando (1), P.J. Bennie (3) E. Kendziorra (4)

(1) Service d'Astrophysique, DSM/DAPNIA/SAp, CE Saclay, F-91191 Gif sur Yvette Cedex, France
(2) Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
(3) Department of Physics & Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
(4) Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany

2001, Astronomy & Astrophysics 365, L282 - L287

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 10⁸cm) Comptonized emission, most probably a corona surrounding the inner edge of an accretion disk, associated with a more extended (~3 10¹⁰cm) 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 10²³cm^-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.

Key words: Stars: individual (EXO 0748-676/UY Vol) - binaries: eclipsing - X-rays: stars - accretion disc

Paper (184k gzip'ed Postscript including figures)

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