Coronal Electron Scattering of Hot Spot Emission Around Black Holes
  Using a Monte Carlo ray-tracing code in full general relativity, we calculate the transport of photons from a geodesic hot spot emitter through a corona of hot electrons surrounding a black hole. Each photon is followed until it is either captured by the black hole or is detected by a distant observer. The source is assumed to be a low-energy thermal emitter (T_em ~ 1 keV), isotropic in the rest frame of a massive geodesic test particle. The coronal scattering has two major observable effects: the Comptonization of the photon spectrum due to the high energy electrons, and the convolution of the time-dependent light curve as each photon is effectively scattered into a different time bin. Both of these effects are clearly present in the Rossi X-Ray Timing Explorer (RXTE) observations of high frequency quasi-periodic oscillations (QPOs) seen in black hole binaries. These QPOs tend to occur when the system is in the Steep Power Law spectral state and also show no evidence for significant power at higher harmonic frequencies, consistent with the smoothing out of the light curve by multiple random time delays. We present simulated photon spectra and light curves and compare with RXTE data, allowing us to infer the properties of the corona as well as the hot spot emitter. 
Jeremy D. Schnittman (MIT)