Multiwavelength monitoring of the dwarf nova VW Hydri. V. EXOSAT observations.

Abstract

Exosat X-ray observations of VW Hyi during three normal outbursts and one superoutburst were obtained in 1984. The decrease in X-ray flux by a factor of 1.2-1.6 during the quiescent periods between outbursts implies that the accretion rate onto the white dwarf decreases by about the same factor, consistent with emission from an optically thin hot corona. The outburst spectrum is characterized as extremely soft with dominant emission at wavelength above 170 A, and the spectral shape remains constant while the flux changes by a factor of 100. The onset of the superoutburst is shown to be similar to that of a normal outburst. The origin of the X-ray emission with respect to the boundary layer between the accretion disk and the white dwarf is considered.