Measuring the AGN sublimation radius with a new approach: reverberation
  mapping of the broad line polarization
  Here we give an observational method for measurements of the equatorial
scattering region radius using variability in the polarized broad lines in Type
1 active galactic nuclei (AGNs). The polarization in broad lines of Type 1 AGNs
is mostly caused by equatorial scattering, where specific features allow one to
separate its contribution from the total polarized flux. We propose to monitor
variability in the polarized line flux and find the time lag between the
nonpolarized continuum and polarized broad line variability. The distance to
the scattering screen can then be determined from the time delay. The method
was, for the first time, applied to the observations of the Type 1 AGN Mrk 6,
and we found that the size of the scattering region in this AGN is around 100
light days. That is significantly smaller than the dusty region size estimated
by the infrared interferometric observations and also larger than known broad
line region (BLR) size. This indicates that the scattering region lies between
the BLR and the dusty region and could be used as a probe of the dust
sublimation radius.
