Soft X-ray emission of VY Scl stars during optical high state

Abstract

I have collected all available ROSAT observations of VY Scl stars including those during the all-sky survey to investigate the presence, strength and spectrum of soft X-ray emission (0.1-2.4 keV) of this group of nova-like variables. A total of 9 out of the 14 VY Scl stars are detected with ROSAT, mostly during optical high states. Interestingly, all detections during the optical high state have very similar X-ray spectral characteristics. I find that a simple blackbody model gives a reasonably good fit in all cases, with temperatures falling in the narrow range between 0.25-0.5 keV. Possible emission mechanisms are discussed.