An X-ray corona in SS Cygni?

Abstract

A recent model¹ for the X-ray emission of non-magnetic cataclysmic variables suggests that most of the observed hard X-ray flux originates in a radiatively-cooling quasi-hydrostatic corona surrounding the white dwarf as it accretes from its companion. We present here some results from a ~7.5-h EXOSAT observation of the dwarf nova SS Cygni in its quiescent state, which confirm many of the predictions of this model. In particular, they show that the X-ray luminosity, L_x, and bremsstrahlung temperature, T, obey the predicted relationship L_x α T^3/2+2ɛ. The results further suggest that the emitting region covers an appreciable fraction f~0.1-1 of the white dwarf's surface, and also that transport processes into the white dwarf cause most of the luminosity to emerge at soft X-ray/extreme ultraviolet wavelengths.