2000PASP..112..320B

Roughly 10% of all quasars exhibit broad absorption line (BAL) features which appear to arise in material outflowing at high velocity from the active galactic nucleus. The details of this outflow are, however, very poorly constrained, and the particular nature of the BAL material is essentially unknown. Recently, new clues have become available through polarimetric studies, which have found that BAL troughs are more polarized than the quasar continuum radiation. To explain these observations, researchers have developed models where the BAL material outflows equatorially across the surface of the dusty torus. In these models, however, several sources of the BAL polarization are possible. Here we demonstrate how polarimetric monitoring of gravitationally lensed quasars, such as H1413+117, during microlensing events not only can distinguish between two currently popular models but also can provide further insight into the structure at the cores of BAL quasars.