X-ray spectroscopic study of supersoft sources SSC_21

GT Luminous supersoft Xray sources are characterized by soft spectra and highbolometric luminosities of the order of 10^37 erg/s. We propose to observe oneof the brightest of the more than 30 known sources. EPIC and/or RGS Xrayspectra will allow us to derive essential information on the origin of theXray emission and thus to distinguish between white dwarf (WD) and neutronstar models. In the case of a WD origin, the modelling of the spectra willprovide measures of the temperature, gravity and abundances which in turnallows to estimate mass accretion rates, WD masses and possibly information onits C+O or O+Ne+Mg composition. This will enable us to test the most popularversion of the WD models, namely the closebinary supersoft source model. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]