Polarization from magnetized optically thick accretion disks

¹ Instituto Nacional de Astrofísica, Óptica y Electrónica, Apartado Postal 51 y 216, Z.P. 72000, Pue. México
² Main Astronomical Observatory of Russian Academy of Sciences, Pulkovo, 196140 St.-Petersburg, Russia

Corresponding author: silant@inaoep.mx

Received: 24 April 2001
Accepted: 25 October 2001

Abstract

We present simple approximate formulae for intensity and the other Stokes parameters of outgoing radiation for magnetized, plane-parallel optically thick atmospheres. We assume that the polarization arises as a result of the light scattering on free electrons in magnetized plasma of an atmosphere. Our asymptotic formulae take place when the Faraday rotation angle ψ at the optical length is large, , and magnetic field ≤ 10⁵ G, when the scattering cross-section has the Thomson value. The formulae describe the radiation for an arbitrary direction of the magnetic field. The Milne problem, the atmospheres with homogeneous and linearly distributed thermal sources, as well as exponential sources are considered. The superposition of these “standard" sources can represent practically any real distribution of sources in optically thick accretion disks. Polarization for some particular models of magnetic fields on the surface of flat accretion disks are considered (chaotic fields in turbulent plasma, axially symmetric plane magnetic fields and the field of the magnetic dipole). The presented results allow us to calculate or estimate the polarization for a large variety of optically thick magnetized accretion disks.