Magnetic Fields of Black Holes and the Variability Plane
  We estimated the magnetic field strength at the horizon radius of black
holes, that is derived by the magnetic coupling process and depended on the
black hole mass $M_{BH}$ and the accretion rate $\dot{M}$. Our estimation is
based on the use of the fundamental variability plane for stellar mass black
holes, AGNs and QSOs. The typical values of magnetic field strength on the
black hole horizon are appeared at the level of $B_{BH}\sim 10^8$G for stellar
mass black holes and $B_{BH}\sim 10^4$G for the supermassive black holes. We
have obtained the relation $p_l\sim \nu^{-1/2}_b$ between the intrinsic
polarization of the accretion disk radiation and the characteristic frequency
of the black hole X-ray variability.
