2011MNRAS.415.1409K

Recent observations have provided strong evidence for the presence of an electron-scattering region (ESR) within the central regions of active galactic nuclei. This is responsible for reprocessing emission from the accretion disc into polarized radiation. The geometry of this scattering region is, however, poorly constrained. In this paper, we consider the influence of gravitational microlensing on polarized emission from the ESR in the quadruply imaged quasar, Q2237+0305, demonstrating how correlated features in the resultant light-curve variations can determine both the size and orientation of the scattering region. This signal is due to differential magnification between perpendicularly polarized views of the ESR, and is clearest for a small ESR width and a large ESR radius. Cross-correlation and autocorrelation measures appear to be independent of lens image shear and convergence parameters, making it ideal to investigate ESR features. As with many microlensing experiments, the time-scale for variability, being of order decades to centuries, is impractically long. However, with a polarization filter oriented appropriately with respect to the path that the quasar takes across the caustic structure, the ESR diameter and radius can be estimated from the autocorrelation and cross-correlation of polarized light curves on much shorter time-scales.

Research undertaken as part of the Commonwealth Cosmology Initiative (CCI:), an international collaboration supported by the Australian Research Council.