  The determination of the size and geometry of the broad line region (BLR) in
active galactic nuclei is one of the major ingredients for determining the mass
of the accreting black hole. This can be done by determining the delay between
the optical continuum and the flux reprocessed by the BLR, in particular via
the emission lines. We propose here that the delay between polarized and
unpolarized light can also be used in much the same way to constrain the size
of the BLR; we check that meaningful results can be expected from observations
using this technique. We use our code STOKES for performing polarized radiative
transfer simulations. We determine the response of the central source
environment (broad line region, dust torus, polar wind) to fluctuations of the
central source that are randomly generated; we then calculate the cross
correlation between the simulated polarized flux and the total flux to estimate
the time delay that would be provided by observations using the same method. We
find that the broad line region is the main contributor to the delay between
the polarized flux and the total flux; this delay is independent on the
observation wavelength. This validates the use of polarized radiation in the
optical/UV band to estimate the geometrical properties of the broad line region
in type I AGNs, in which the viewing angle is close to pole-on and the BLR is
not obscured by the dust torus.
