Broad-band timing properties of the accreting white dwarf MV Lyrae

TL;DR

This study analyzes the broad-band timing properties of the accreting white dwarf MV Lyrae using Kepler data, revealing variability patterns similar to those in X-ray binaries and active galactic nuclei, and constraining accretion disk models.

Contribution

First systematic broad-band timing analysis of MV Lyrae with Lorentzian modeling, exploring viscous and dynamical scenarios to understand accretion disk structure.

Findings

Detected a frequency-varying Lorentzian component inversely correlated with flux.

Inferred high viscosity and disk scale height parameters inconsistent with standard thin disk.

Suggested a large disk truncation radius of about 10 white dwarf radii.

Abstract

We present a broad-band timing analysis of the accreting white dwarf system MV Lyrae based on data obtained with the Kepler satellite. The observations span 633 days at a cadence of 58.8 seconds and allow us to probe 4 orders of magnitude in temporal frequency. The modelling of the observed broad-band noise components is based on the superposition of multiple Lorentzian components, similar to the empirical modelling adopted for X-ray binary systems. We also present the detection of a frequency varying Lorentzian component in the lightcurve of MV Lyrae, where the Lorentzian characteristic frequency is inversely correlated with the mean source flux. Because in the literature similar broad-band noise components have been associated to either the viscous or dynamical timescale for different source types (accreting black holes or neutron stars), we here systematically explore both scenarios and place constraints on the accretion disk structure. In the viscous case we employ the fluctuating accretion disk model to infer parameters for the viscosity and disk scale height, and infer uncomfortably high parameters to be accommodated by the standard thin disk, whilst in the dynamical case we infer a large accretion disk truncation radius of ~10 white dwarf radii. More importantly however, the phenomenological properties between the broad-band variability observed here and in X-ray binaries and Active Galactic Nuclei are very similar, potentially suggesting a common origin for the broad-band variability.