Constraining the spectral parameters of RX J0925.7-4758 with the BeppoSAX LECS

The Super Soft Source RX J0925.7-4758 (RX J0925 hereafter) was observed by BeppoSAX LEGS and MECS on January 25-26 1997. The source was clearly detect ed by the LEGS but only marginally detected by the MECS. We apply detailed Non-Local Thermodynamic Equilibrium (Non-LTE) models including metal line o pacities to the observed LEGS spectrum. We test whether the X-ray spectrum of RX J0925 is consistent with that of a white dwarf and put constraints up on the effective temperature and surface gravity by considering the presenc e or absence of spectral features such as absorption edges and line blends in the models and the observed spectrum. We find that models with effective temperatures above similar to 10(6)K or below similar to 7.5 x 10(5)K can be excluded. If we assume a single model component for RXJ0925 we observe a significant discrepancy between the mode l and the data above the Ne IX edge energy at 1.19 keV. This is consistent with earlier observations with ROSAT and ASCA. The only way to account for the emission above similar to 1.2 keV is by introducing a second spectral ( plasma) component. This plasma component may be explained by a shocked wind originating from the compact object or from the irradiated companion star. If we assume log g = 9 then the derived luminosity is consistent with: that of a nuclear burning white dwarf at a distance of similar to 4 kpc.