Probing the Disk-Corona Systems and Broad-line Regions of Changing-look Quasars with X-Ray and Optical Observations
Green, Paul J.; Anderson, Scott F.; Eracleous, Michael; Jin, Xiangyu; Haggard, Daryl; Runnoe, Jessie C.; MacLeod, Chelsea L.; Ruan, John J.; Gingras, Marie-Joëlle; Hountalas, Joseph; Doan, Anh
Canada, United States
Abstract
"Changing-look" quasars are a new class of highly variable active galactic nuclei that have changed their spectral type over surprisingly short timescales of just a few years. The origin of this phenomenon is debated, but is likely to reflect some change in the accretion flow. To investigate the disk-corona systems in these objects, we measure optical/UV-X-ray spectral indices ( ${\alpha }_{\mathrm{OX}}$ ) and Eddington ratios ( ${\lambda }_{\mathrm{Edd}}$ ) of 10 previously discovered changing-look quasars at two or more epochs. By comparing these data with simulated results based on the behavior of X-ray binaries, we find possible similarities in spectral indices below the 1% Eddington ratio. We further investigate the Eddington ratios of changing-look quasars before and after their spectral type changes, and find that changing-look quasars cross the 1% Eddington ratio boundary when their broad emission lines disappear/emerge. This is consistent with the disk-wind model as the origin of broad emission lines.