Global Radiation Magneto-hydrodynamic Simulations of Sub-Eddington Accretion Disks around Supermassive Black Holes. (arXiv:1904.01674v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Jiang_Y/0/1/0/all/0/1">Yan-Fei Jiang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blaes_O/0/1/0/all/0/1">Omer Blaes</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stone_J/0/1/0/all/0/1">James Stone</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Davis_S/0/1/0/all/0/1">Shane W. Davis</a>
We use global three dimensional radiation magneto-hydrodynamic simulations to
study the properties of inner regions of accretion disks around a 5times 10^8
solar mass black hole with mass accretion rates reaching 7% and 20% of the
Eddington value. This region of the disk is supported by magnetic pressure with
surface density significantly smaller than the values predicted by the standard
thin disk model but with a much larger disk scale height. The disks do not show
any sign of thermal instability over many thermal time scales. More than half
of the accretion is driven by radiation viscosity in the optically thin corona
region for the lower accretion rate case, while accretion in the optically
thick part of the disk is driven by the Maxwell and Reynolds stresses from MRI
turbulence. Coronae with gas temperatures > 10^8 K are generated only in the
inner approx 10 gravitational radii in both simulations, being more compact in
the higher accretion rate case. In contrast to the thin disk model, surface
density increases with increasing mass accretion rate, which causes less
dissipation in the optically thin region and a relatively weaker corona. The
simulation results may explain the formation of X-ray coronae in Active
Galactic Nuclei (AGNs), the compact size of such coronae, and the observed
trend of optical to X-ray luminosity with Eddington ratio for many AGNs.
We use global three dimensional radiation magneto-hydrodynamic simulations to
study the properties of inner regions of accretion disks around a 5times 10^8
solar mass black hole with mass accretion rates reaching 7% and 20% of the
Eddington value. This region of the disk is supported by magnetic pressure with
surface density significantly smaller than the values predicted by the standard
thin disk model but with a much larger disk scale height. The disks do not show
any sign of thermal instability over many thermal time scales. More than half
of the accretion is driven by radiation viscosity in the optically thin corona
region for the lower accretion rate case, while accretion in the optically
thick part of the disk is driven by the Maxwell and Reynolds stresses from MRI
turbulence. Coronae with gas temperatures > 10^8 K are generated only in the
inner approx 10 gravitational radii in both simulations, being more compact in
the higher accretion rate case. In contrast to the thin disk model, surface
density increases with increasing mass accretion rate, which causes less
dissipation in the optically thin region and a relatively weaker corona. The
simulation results may explain the formation of X-ray coronae in Active
Galactic Nuclei (AGNs), the compact size of such coronae, and the observed
trend of optical to X-ray luminosity with Eddington ratio for many AGNs.
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