Suppression of x-rays during an optical outburst of the helium dwarf nova kl dra

Abstract

KL Dra is a helium-accreting AM CVn binary system with an orbital period close to 25min. Approximately every 60d there is a 4-mag optical outburst lasting ∼10d. We present the most sensitive X-ray observations made of an AM CVn system during an outburst cycle. A series of eight observations were made using XMM-Newton which started shortly after the onset of an optical outburst. We find that X-rays are suppressed during the optical outburst. There is some evidence for a spectral evolution of the X-ray spectrum during the course of the outburst. A periodic modulation is seen in the ultraviolet data at three epochs - this is a signature of the binary orbital or the superhump period. The temperature of the X-ray-emitting plasma is cooler compared to dwarf novae, which may suggest that a wind is the origin of a significant fraction of the X-ray flux. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.