Power spectra from 'spotted' accretion discs

We are carrying out a project to calculate power spectra of variability, assuming a model of a 'spotted' accretion disc near a black hole. We consider relativistic effects that change photon energy and produce light-bending and time-delays acting on the X-ray signal received by an observer. We assume that the life-time and the intrinsic emissivity of individual flaring events are described in terms of a simple stochastic process. This allows us to give approximate analytical formulae and compare them with numerical computations.