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Title: Radiation magnetohydrodynamic simulations of the formation of hot accretion disk coronae

A new mechanism to form a magnetic pressure supported, high temperature corona above the photosphere of an accretion disk is explored using three dimensional radiation magnetohydrodynamic (MHD) simulations. The thermal properties of the disk are calculated self-consistently by balancing radiative cooling through the surfaces of the disk with heating due to dissipation of turbulence driven by magneto-rotational instability (MRI). As has been noted in previous work, we find the dissipation rate per unit mass increases dramatically with height above the mid-plane, in stark contrast to the α-disk model which assumes this quantity is a constant. Thus, we find that in simulations with a low surface density (and therefore a shallow photosphere), the fraction of energy dissipated above the photosphere is significant (about 3.4% in our lowest surface density model), and this fraction increases as surface density decreases. When a significant fraction of the accretion energy is dissipated in the optically thin photosphere, the gas temperature increases substantially and a high temperature, magnetic pressure supported corona is formed. The volume-averaged temperature in the disk corona is more than 10 times larger than at the disk mid-plane. Moreover, gas temperature in the corona is strongly anti-correlated with gas density, which implies themore » corona formed by MRI turbulence is patchy. This mechanism to form an accretion disk corona may help explain the observed relation between the spectral index and luminosity from active galactic nucleus (AGNs), and the soft X-ray excess from some AGNs. It may also be relevant to spectral state changes in X-ray binaries.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  2. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
  3. Canadian Institute for Theoretical Astrophysics. Toronto, ON M5S3H4 (Canada)
Publication Date:
OSTI Identifier:
22357236
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 784; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; BINARY STARS; DENSITY; GALAXY NUCLEI; INSTABILITY; LUMINOSITY; MAGNETOHYDRODYNAMICS; MASS; NMR IMAGING; PHOTOSPHERE; RADIANT HEAT TRANSFER; RADIATIVE COOLING; SIMULATION; SOFT X RADIATION; THERMODYNAMIC PROPERTIES; THREE-DIMENSIONAL CALCULATIONS; TURBULENCE