Changing-look Seyfert galaxies with optical linear polarization
  measurements
  In this lecture note, we make the case for new (spectro)polarimetric
measurements of "changing-look" AGNs (CLAGNs), a subclass of the AGN family
tree that shows long-term (months to years) large flux variability associated
with the appearance or disappearance of optical broad emission lines. We
discuss how polarization measurements could help to distinguish which of the
several scenarios proposed to explain such variations is/are the most likely.
We collected past polarization measurements of nearby, Seyfert-like CLAGNs and
take stock that almost all polarimetric information we have on those
fascinating objects dates from the 80's and 90's. We thus explain how
polarization could help us understand the physical processes happening in the
first parsecs of CLAGNs and why new polarization monitoring campaigns are
strongly needed.
