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KL Dra is a helium‐accreting AM CVn binary system with an orbital period close to 25 min. Approximately every 60 d there is a 4‐mag optical outburst lasting ∼10 d. 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.

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