X-ray reverberation around accreting black holes: fitting complex GPU-based models to large datasets

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Black hole accretion flows are powerful sources of X-rays. These X-rays illuminate the accretion disc and produce a back-scattered spectrum that contains strong emission features. In addition, the X-ray source is highly variable. A combination of the variability, light travel time between the source and disc, and back-scattered spectrum result in a complex set of time lags between the light curves in different X-ray energy bands. The time lags are observed to depend on the frequency of variability, so this analysis is done in the Fourier domain. To model this behaviour we make use of GPUs to integrate photon paths from the X-ray source to the disc, taking into account all of the relativistic effects, and allowing for different X-ray source geometries. The goal of this project is to develop techniques that allow this complex, multi-dimensional model to be evaluated and fit to the large number of observations that are in the X-ray data archives.