Suppression of X-rays during an optical outburst of the helium dwarf nova KL Dra

Gavin Ramsay, Peter J. Wheatley, Simon Rosen, Thomas Barclay, Danny Steeghs

Figure 4. The X-ray spectrum of KL Dra observed during the faint optical state. The best-fit model using an absorbed single temperature thermal model with metalicity appropriate for CNO processed material is shown as a solid line.


KL Dra is a helium accreting AM CVn binary system with an orbital period close to 25 mins. Approximately every 60 days there is a 4 mag optical outburst lasting ∼10 days. 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 UV data at three epochs – this is a signature of the binary orbital or the super-hump period. The temperature of the X-ray emitting plasma is cooler compared to dwarf novae, which may suggest a wind is the origin of a significant fraction of the X-ray flux.

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Last Revised: 2012 July 5th