lnsight on quasar changing-look physics from optical polarimetry

A handful of quasars changing from type 1 (strong broad and narrow emission lines) to type 1.9 (strong narrow lines only and dim continuum) on timescales of a few years have been recently uncovered. If the disappearance of the broad emission lines observed in changing-look quasars were caused by the obscuration of the quasar core through moving dust clouds in the torus, high linear polarization typical of type 2 quasars would be expected. We measured the polarization of the changing-look quasar J1011+5442 in which the broad emission lines have disappeared between 2003 and 2015. We found a polarization degree compatible with null polarization. This measurement suggests that the observed change of look is not due to a change of obscuration in a torus hiding the continuum source and the broad line region. Our results thus support the idea that the vanishing of the broad emission lines in J1011+5442 is due to an intrinsic dimming of the ionizing continuum source that is most likely caused by a rapid decrease in the rate of accretion onto the supermassive black hole. New polarization measurements have been secured for a sample of changing-look quasars. They essentially confirm our previous results.