Dependence of linear polarization of radiation in accretion disks on the spin of central black hole

摘要

We suppose that linear optical polarization is due to multiple scattering inoptically thick magnetized accretion disk around central black hole. Thepolarization degree is very sensitive to the spin of black hole - for Kerrrotating hole the polarization is higher than for Schwarzschild non-rotatingone if both holes have the same luminosities and masses. The reason of thiseffect is that the radius of the first stable orbit for non-rotating hole isequal to three gravitational radiuses, and for fast rotating Kerr hole isapproximately 6 times lesser. Magnetic field, decreasing from first stableorbits, is much larger in the region of escaping of optical radiation for thecase of Schwarzschild hole than for Kerr one. Large magnetic field gives riseto large depolarization of radiation due to Faraday rotation effect. Thisexplains the mentioned result. It seems that the ensemble of objects withobserved polarization mostly consists of Kerr black holes.