Comparison of two methods for determining the magnetic fields near black holes |
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| Authors: | N A Silant’ev M Yu Piotrovich Yu N Gnedin T M Natsvlishvili |
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| Institution: | 1.Pulkovo Observatory,Russian Academy of Sciences,St. Petersburg,Russia |
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| Abstract: | We compare two methods for estimating the magnetic field near a black hole—based on a statistical formula that relates the
magnetic field on the horizon of the black hole to its mass and on a direct magnetic field determination from optical polarimetric
observations. An optically thick magnetized accretion disk is usually formed around the black hole in active galactic nuclei.
The linear polarization of the radiation emerging from the disk is related to the local magnetic field and the polarization
in Milne’s classical problem. The magnetic field in the region from where the radiation with the observed wavelength comes
can be estimated by measuring this polarization. On the other hand, this field can be estimated from the above statistical
formula if the field near the black hole is extrapolated into the accretion disk using a standard power law. Comparison of
the magnetic field obtained from the observed polarization with the extrapolated field can serve to estimate the accuracy
of the latter and the exponent in the adopted extrapolation law. As an example, we compare these two methods for the source
NGC 4258. |
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