Inflow Generated X-ray Corona Around Supermassive Black Holes and
  Unified Model for X-ray Emission
  Three-dimensional hydrodynamic simulations, covering the spatial domain from
hundreds of Schwarzschild radii to $2\ \mathrm{pc}$ around the central
supermassive black hole of mass $10^8 M_\odot$, with detailed radiative cooling
processes, are performed. Generically found is the existence of a significant
amount of shock heated, high temperature ($\geq 10^8\ \mathrm{K}$) coronal gas
in the inner ($\leq 10^4 r_\mathrm{sch}$) region. It is shown that the
composite bremsstrahlung emission spectrum due to coronal gas of various
temperatures are in reasonable agreement with the overall ensemble spectrum of
AGNs and hard X-ray background. Taking into account inverse Compton processes,
in the context of the simulation-produced coronal gas, our model can readily
account for the wide variety of AGN spectral shape, which can now be understood
physically. The distinguishing feature of our model is that X-ray coronal gas
is, for the first time, an integral part of the inflow gas and its observable
characteristics are physically coupled to the concomitant inflow gas. One
natural prediction of our model is the anti-correlation between accretion disk
luminosity and spectral hardness: as the luminosity of SMBH accretion disk
decreases, the hard X-ray luminosity increases relative to the UV/optical
luminosity.
