Polarization of the changing-look quasar J1011+5442^⋆

¹ Institut d’Astrophysique et de Géophysique, Université de Liège, , Allée du 6 Août 19c, B5c, 4000 Liège, Belgium
e-mail: hutsemekers@astro.ulg.ac.be
² Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, Bus 2401, 3001 Leuven, Belgium
³ Instituto de Astrofisica de Canarias, Calle Via Lactea, s/n, 38205 La Laguna, Tenerife, Spain
⁴ Departamento de Astrofisica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain

Received: 19 June 2017
Accepted: 13 July 2017

Abstract

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 hiding the continuum source and the broad line region, and that the quasar is seen close to the system axis. 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.