Testing the Propagating Fluctuations Model with a Long, Global Accretion
  Disk Simulation
  The broad-band variability of many accreting systems displays characteristic
structure; log-normal flux distributions, RMS-flux relations, and long
inter-band lags. These characteristics are usually interpreted as inward
propagating fluctuations in an accretion disk driven by stochasticity of the
angular momentum transport mechanism. We present the first analysis of
propagating fluctuations in a long-duration, high-resolution, global
three-dimensional magnetohydrodynamic (MHD) simulation of a geometrically-thin
($h/r\approx0.1$) accretion disk around a black hole. While the
dynamical-timescale turbulent fluctuations in the Maxwell stresses are too
rapid to drive radially-coherent fluctuations in the accretion rate, we find
that the low-frequency quasi-periodic dynamo action introduces low-frequency
fluctuations in the Maxwell stresses which then drive the propagating
fluctuations. Examining both the mass accretion rate and emission proxies, we
recover log-normality, linear RMS-flux relations, and radial coherence that
would produce inter-band lags. Hence, we successful relate and connect the
phenomenology of propagating fluctuations to modern MHD accretion disk theory.
