XMM-Newton observations of MR Vel/RX J0925.7-4758

¹ Observatoire Astronomique, UA 1280 CNRS, 11 rue de l'Université, 67000 Strasbourg, France
² Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
³ Terschelling 120, 3524 AZ Utrecht, The Netherlands
⁴ Sterrenkundig Instituut Anton Pannekoek, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands

Corresponding author: C. Motch, motch@astro.u-strasbg.fr

Received: 21 May 2002
Accepted: 27 June 2002

Abstract

We report on XMM-Newton observations of the galactic supersoft X-ray source RX J0925.7-4758. The RGS spectrum exhibits a wealth of spectral features from iron and oxygen. XMM-Newton data confirm the finding of previous Chandra HETGS/MEG observations that NLTE models of hot white dwarf atmospheres fail to represent the complex spectrum. There are clear evidences for P Cygni profiles with wind velocities of up to 2000 km s^-1. Small flux variations with time scales larger than 1000 s are present. The strongest power is at ~0.21 d, a period close to that seen in V band optical light curves. A detailed analysis of the associated changes in the RGS and EPIC pn spectra hint at a mostly grey mechanism suggesting a variation of the visibility of the white dwarf due to occulting material in the accretion disk. Finally, we detect radial velocity changes of 173 ± 47 km s^-1 between two RGS observations obtained half an orbital cycle apart. The amplitude of the RGS velocity shift is consistent with that of the optical λ 4686 and thus supports the idea that most of the optical line emission arises from the accretion disk.