Magneto Rotational Instability in Magnetized AGN Tori
  It is widely believed that in active galactic nuclei (AGNs) a supermassive
black hole with an accretion disk is surrounded by an optically and
geometrically thick torus at sub-parsec scale. However, it is not clear how is
the mass supply toward the central engine caused and how it is related with the
internal structures of the tori. The magnetic field in the tori may contribute
to the accretion process via the magneto-rotational instability (MRI). Using
global three dimensional magnetohydrodynamic (MHD) simulations taking the
effects of X-ray heating and radiative cooling into account studied the
numerical resolution for azimuthal direction for MRI driving. We found that a
strongly magnetized disk consisted of a cold ($< 10^3$ K) and warm ($10^4$ K)
gas is developed in about 30 rotational periods. We also found in high
resolution model that the mean azimuthal magnetic fields reverse their
direction quasi-periodically. We confirmed that the typical wave length of the
MRI should be resolved with a least 20 azimuthal grid cells.
