THE X-RAY AND EUV SPECTRUM OF THE DWARF NOVA VW HYDRI IN OUTBURST ANDQUIESCENCE

We combine ROSAT, Ginga, and EXOSAT observations to investigate the X- ray and extreme-ultraviolet fluxes of VW Hyi in quiescence and through out an ordinary dwarf-nova outburst. We show that the quiescent spectr um is consistent with emission from material heated to similar to 12 k eV and cooling through the X-ray band to temperatures below our sensit ivity range. During outburst the X-ray flux is suppressed, and recover s only at the very end of the optical outburst. The recovery starts in termittently with similar to 100% modulations on a timescale of about 200 s. A very soft component is detectable only in the extreme ultravi olet, after outburst maximum, and disappears before the end of the opt ical outburst. The luminosity of this component is limited to less tha n that expected from the boundary layer. The late recovery of the hard X-ray flux indicates that this flux is regulated by processes occurri ng very close to the white dwarf.