Compton scattering of polarized radiation in two-phase accretion disks in active galactic nuclei

We present results of radiative transfer calculations of Compton scattering of polarized radiation in a corona above an accretion disk. The corona has a plane-parallel geometry and is assumed to be homogeneous with a fixed te mperature. We employ a Feautrier method to calculate the radiative transfer , incorporating the full relativistic, polarized Compton redistribution mat rix. This allows us to explore a broad range of parameter space, in particu lar large optical depths and/or low corona temperatures, for which the iter ative scattering method is very inefficient. Compared with Thomson scatteri ng, Compton scattering generally produces smaller polarizations for feature less spectra. Distinct frequency-dependent patterns in polarization are pro duced near lines and edges, which can be used as diagnostics for the corona . We discuss the physics that gives rise to these results. Compton scatteri ng can smear out Lyman edges in total flux and at the same time produce lar ge increases in polarization. This might help explain the rises in polariza tion observed near the Lyman limit in some quasars, although in general Com pton scattering does not appear able to produce polarization changes that a re as steep as observed.