Simulations of X-ray spectral/timing properties in a propagation model of variability of accreting black holes

Abstract

A phenomenological model of X-ray variability of accreting black holes is considered, where the variable emission is attributed to multiple active regions/perturbations moving radially towards the central black hole. The hard X-rays are produced by inverse Compton upscattering of soft photons coming from reprocessing/thermalization of the same hard X-rays. The heating rate of the Comptonizing plasma is assumed to scale with the rate of dissipation of gravitational energy while the supply of soft photons is assumed to diminish towards the center. Two scenarios are considered: (1) an inner hot flow with outer truncated standard accretion disc and (2) an accretion disc with an active corona and a thick hot ionized skin. A variant of the model is also considered, which is compatible with the currently discussed multi-Lorentzian description of power spectral densities of X-ray lightcurves. In the inner hot flow scenario the model can reproduce the observed Fourier frequency resolved spectra observed in X-ray binaries, in particular the properties of the reprocessed component as functions of Fourier frequency. In the accretion disc with ionized skin scenario the reduction of soft photons due to the ionized skin is insufficient to produce the observed characteristics.