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

TL;DR

This study presents sensitive X-ray observations of the helium dwarf nova KL Dra during an optical outburst, revealing X-ray suppression, spectral evolution, and periodic UV modulations linked to the binary system.

Contribution

First detailed X-ray analysis of KL Dra during an outburst, showing suppression of X-rays and spectral changes, advancing understanding of accretion processes in helium dwarf novae.

Findings

X-ray flux is suppressed during optical outburst

Spectral evolution observed in X-ray data

Periodic UV modulation detected at multiple epochs

Abstract

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.