The Universal Nature of Accretion-induced Variability: The RMS-Flux Relation in an Accreting White Dwarf

TL;DR

This study discovers a linear rms-flux relation in an accreting white dwarf, similar to other compact objects, implying a universal variability mechanism, but challenges existing disk instability models.

Contribution

It demonstrates the rms-flux relation in a white dwarf system, suggesting a common physical origin of variability across different accreting sources.

Findings

Linear rms-flux relation observed in MV Lyrae.

Viscosity parameter and disk scale height are higher than predicted by models.

Supports the universality of accretion-induced variability mechanisms.

Abstract

We report the discovery of a linear relationship between the root-mean-square (rms) variability amplitude and the mean flux in the accreting white dwarf binary system MV Lyrae. Our lightcurve, obtained with the Kepler satellite, spans 633 days with quasi-continuous 58.8 second cadence resolution. We show, for the first time, how this cataclysmic variable displays linear rms-flux relations similar to those observed in many other black hole binaries, neutron star binaries and Active Galactic Nuclei. The phenomenological similarity between the rms-flux relation observed here and in other X-ray binaries suggests a common physical origin for the broad-band variability, independent of source type, mass or size of the compact accretor. Furthermore, we infer the viscosity parameter, alpha, and disk scale height, H/R, using two independent methods. In both cases, both values are found to be uncomfortably high to be accommodated by the disk instability model.