Polarimetric Tomography of Blazar Jets
  In this paper we propose a way to use optical polarisation observations to
provide independent constraints and guide to the modelling of the spectral
energy distribution (SED) of blazars, which is particularly useful when
two-zone models are required to fit the observed SED. As an example, we apply
the method to the 2008 multiwavelength campaign of PKS 2155-304, for which the
required polarisation information was already available. We find this approach
succesful in being able to simultaneously describe the SED and variability of
the source, otherwise difficult to interpret. More generally, by using
polarisation data to disentangle different active regions within the source,
the method reveals otherwise unseen correlations in the multiwavelength
behaviour which are key for the SED modelling.
