X-ray Spectra from MHD Simulations of Accreting Black Holes. (arXiv:1207.2693v1 [astro-ph.HE])

X-ray Spectra from MHD Simulations of Accreting Black Holes. (arXiv:1207.2693v1 [astro-ph.HE]):
We present the results of a new global radiation transport code coupled to a
general relativistic magneto-hydrodynamic simulation of an accreting,
non-rotating black hole. For the first time, we are able to predict in a
self-consistent way the X-ray spectra observed from stellar-mass black holes,
including a thermal peak, Compton reflection hump, power-law tail, and broad
iron line. Varying only the mass accretion rate, we are able to reproduce the
low/hard, steep power-law, and thermal-dominant states seen in most galactic
black hole sources. The temperature in the corona is T_e ~ 10 keV in a boundary
layer near the disk and rises smoothly to T_e >~ 100 keV in low-density regions
far above the disk. Even as the disk's reflection edge varies from the horizon
out to ~6M as the accretion rate decreases, we find that the shape of the Fe
K\alpha line is remarkably constant. This is because photons emitted from the
plunging region are strongly beamed into the horizon and never reach the
observer. We have also carried out a basic timing analysis of the spectra and
find that the fractional variability increases with photon energy and viewer
inclination angle, consistent with the coronal hot spot model for X-ray
fluctuations.