2002A&A...393..913M

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 2000km/s. Small flux variations with time scales larger than 1000s are present. The strongest power is at ∼0.21d, 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±47km/s between two RGS observations obtained half an orbital cycle apart. The amplitude of the RGS velocity shift is consistent with that of the optical HeII λ 4686 and thus supports the idea that most of the HeII optical line emission arises from the accretion disk.