Probing the disk-corona systems and broad line regions of changing-look quasars with X-ray and optical observations

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 ten 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 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.

31 pages, 9 figures, accepted for publication in ApJ

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Cited by in corpus (5)

• Probing the Origin of Changing-look Quasar Transitions with Chandra
• Extreme Variability and Episodic Lifetime of Quasars
• Investigating Changing-Look Active Galactic Nuclei with Long-term Optical and X-Ray Observations
• Modeling Star Formation Histories of Changing-Look AGN Host Galaxies with Prospector
• Identifying Changing-Look AGN Transitions in Light Curve Data with the Zwicky Transient Facility