Multi-wavelength observations of the helium dwarf nova KL Dra through its outburst cycle

TL;DR

This study presents multi-wavelength observations of the helium-dominated dwarf nova KL Dra, revealing its ~60-day outburst cycle, consistent with the Disc Instability Model, and highlighting its potential as a key target for studying helium accretion flows.

Contribution

First detailed multi-wavelength observational analysis of KL Dra's outburst cycle, supporting helium accretion models and comparing it to hydrogen dwarf novae.

Findings

Outbursts recur approximately every 60 days.

Outbursts have similar amplitude in UV and optical wavelengths.

X-ray flux shows no significant variation during outbursts.

Abstract

We present multi-wavelength observations of the helium-dominated accreting binary KL Dra which has an orbital period of 25 mins. Our ground-based optical monitoring programme using the Liverpool Telescope has revealed KL Dra to show frequent outbursts. Although our coverage is not uniform, our observations are consistent with the outbursts recurring on a timescale of ~60 days. Observations made using Swift show that the outbursts occur with a similar amplitude at both UV and optical energies and a duration of 2 weeks. Although KL Dra is a weak X-ray source we find no significant evidence that the X-ray flux varies over the course of an outburst cycle. We can reproduce the main features of the 60 day outburst cycle using the Disc Instability Model and a helium-dominated accretion flow. Although the outbursts of KL Dra are very similar to those of the hydrogen accreting dwarf novae, we cannot exclude that they are the AM CVn equivalent of WZ Sge type outbursts. With outbursts occurring every ~2 months, KL Dra is an excellent target to study helium-dominated accretion flows in general.