How Polarization and Scattering can reveal Geometries, Dynamics, and   Feeding of Active Galactic Nuclei
  Gaskell et al. (2007) introduced polarization reverberation mapping as a new technique to explore the structure of active galactic nuclei. We present modeling results for the time-dependent polarization signal expected from scattering inside a centrally illuminated spheroid. Such a model setup describes a larger corona surrounding the compact source of an active nucleus. Time-delays between the polarized and the total flux are computed and related to the geometry of the cloud and the viewing angle. When including the in-flow dynamics of the cloud, it is possible to constrain its optical depth and velocity, which enables estimations of the mass inflow rate. 
R. W. Goosmann, C. M. Gaskell, M. Shoji