Polarization and Beaming of Accretion Disk Radiation

The beaming and the polarization of finite optical depth plane-parallel accretion disks are calculated using both a Feautrier radiative transfer scheme and, independently, an iteration scheme, for the case where the opacity is dominated by nonrelativistic electron scattering. In addition to internal sources of photons, the important case of external illumination of the disk is included. The angular distribution and the polarization as a function of the angle of the emergent radiation are found to depend sensitively on the total optical depth. It is shown that the disk polarization can significantly exceed the classical limit of 11.7 percent for the case where the scattering half-thickness of the disk is small compared to unity, corresponding to subcritical conditions. The radiation pattern emerging from these scattering disks becomes more anisotropic as the optical depth decreases, alleviating some current difficulties encountered with apparent super-Eddington luminosities.