The X-ray spectra of VW Hydri during the outburst cycle

We report six BeppoSAX X–ray observations of VW Hyi during and after the outburst of Sep 23 1998. The outburst flux is lower than the quiescent flux in the entire observed energy band (0.1–10 keV), in agreement with earlier observations. The X–ray spectra are fitted with two-temperature plasma and cooling flow spectral models. These fits show a clear spectral evolution in X–rays for the first time in VW Hyi: the hard X–ray turn-up after the outburst is reflected in the emission measure and the temperature. Moreover, during outburst the 1.5–10 keV flux decreases significantly. We argue that this is not consistent with the constant flux during a ROSAT outburst observation made eight years earlier. We conclude from this observation that there are significant differences between outburst X–ray lightcurves of VW Hyi.