Correlated X-ray and optical variability in intermediate polars during their outbursts

TL;DR

This study investigates the correlated optical and X-ray flux variations during outbursts in two intermediate polars, revealing a strong correlation and a higher amplitude ratio compared to non-magnetic dwarf novae, supporting the magnetic nature of FS Aur.

Contribution

It provides new observational evidence of correlated flux variations in intermediate polars during outbursts and highlights differences from non-magnetic dwarf novae, suggesting magnetic accretion processes.

Findings

X-ray and optical fluxes are well correlated during outbursts.

The amplitude ratio of X-ray to optical flux is about 0.6.

The flux dependence steepens at very low accretion rates.

Abstract

We present a study of the evolution of the optical and X-ray fluxes during outbursts of two short-period cataclysmic variables, the confirmed intermediate polar CC Scl and the intermediate polar candidate FS Aur. We found that the X-ray and optical light curves are well correlated in both objects, although the amplitudes of outbursts in X-rays are smaller than those in the optical. The ratio of the outburst amplitudes in X-rays and the optical in both objects is close to ~0.6. This is significantly higher than was observed during the outburst of the non-magnetic dwarf nova U Gem, in which this ratio was only ~0.03. The obtained data also suggest that the dependence between the X-ray and optical fluxes must steepen significantly toward very low accretion rates and very low fluxes. Similarities in the behaviour of CC Scl and FS Aur indicate strongly the magnetic nature of the white dwarf in FS Aur.