Flickering in Black Hole Accretion discs

Abstract

We present an extension of the King et al. (2004) model for the flickering of black hole accretion discs by taking proper account for the thermal properties of the disc. First we develop a one-dimensional, vertically averaged, one-zone model for an optically thick accretion disc and study the temporal evolution. This limits the current model to the so-called high/soft state, where the X-Ray spectrum is dominated by a thermal black-body component. Then we couple this disc model to the flickering process as described in King et al. (2004). Thus we consider the evolution of a poloidal magnetic field subject to a magnetic dynamo. By comparing to observations of X-Ray binaries in the high-soft state, we can constrain the strength of the energy density of the poloidal magnetic field to a few percent of the energy density of the intrinsic disc magnetic field.