Determination of magnetic field strength on the event horizon of
  supermassive black holes in active galactic nuclei
  We estimated the magnetic field strength at the event horizon for a sample of
supermassive black holes (SMBHs) in active galactic nuclei (AGNs). Our
estimates were made using the values of the inclination angles of the accretion
disk to the line of sight, that we obtained previously from spectropolarimetric
observations in the visible spectrum. We also used published values of full
width at half maximum (FWHM) of spectral line $H_\beta$ from broad line region,
masses of SMBHs and luminosity of AGNs at 5100 angstrom. In addition we used
literature data on the spins of SMBHs obtained from their X-ray spectra. Our
estimates showed that the magnetic field strength at the event horizon of the
majority of SMBHs in AGNs ranges from several to tens of kG and have mean
values of about $10^4$G. At the same time, for individual objects, the fields
are significantly larger - of the order of hundreds kG or even 1 MG.
