Issue |
A&A
Volume 507, Number 1, November III 2009
|
|
---|---|---|
Page(s) | 171 - 182 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/200810892 | |
Published online | 08 September 2009 |
Magnetic fields of AGNs and standard accretion disk model: testing by optical polarimetry
1
Instituto Nacional de Astrofísica, Óptica y Electrónica, Luis Enrique Erro 1, Apartado Postal 51 y 216, 72840, Tonantzintla, Puebla, México e-mail: silant@inaoep.mx
2
Central Astronomical Observatory at Pulkovo of Russian Academy of Sciences, 196140, Saint-Petersburg, Pulkovskoe shosse 65, Russia
Received:
1
September
2008
Accepted:
15
July
2009
We have developed the method that allows us to estimate the
magnetic field strength at the horizon of a supermassive black
hole (SMBH) through the observed polarization of optical emission of
the accreting disk surrounding SMBH. The known asymptotic formulae for
the Stokes parameters of outgoing radiation are azimuthal averaged, which
corresponds to an observation of the disk as a whole. We consider two
models of the embedding 3D-magnetic field, the regular field, and
the regular field with an additional chaotic (turbulent) component.
It is shown that the second model is preferable for estimating the
magnetic field in NGC 4258. For estimations we used the standard
accretion disk model assuming that the same power-law dependence of the
magnetic field follows from the range of the optical emission down to
the horizon. The observed optical polarization from NGC 4258 allowed us to
find the values Gauss at the horizon, depending on
the particular choice of the model parameters. We also discuss the
wavelength dependencies of the light polarization, and possibly
applying them for a more realistic choice of accretion disk parameters.
Key words: black hole physics / magnetic fields / accretion, accretion disks / polarization
© ESO, 2009
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