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Keywords:

  • accretion, accretion discs;
  • black hole physics;
  • binaries: close;
  • novae, cataclysmic variables;
  • stars: oscillations;
  • stars: individual: MV Lyrae

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 d at a cadence of 58.8 s and allow us to probe four 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 light curve 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 with either the viscous or dynamical time-scale for different source types (accreting black holes or neutron stars), we here systematically explore both scenarios and place constraints on the accretion disc structure. In the viscous case we employ the fluctuating accretion disc model to infer parameters for the viscosity and disc scale height, and infer uncomfortably high parameters to be accommodated by the standard thin disc, whilst in the dynamical case we infer a large accretion disc truncation radius of ≈10RWD. 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.