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

Published onJun 01, 2020
Probing the disk-corona systems and the broad line regions of changing-look quasars with optical and X-ray observations

“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 currently debated, but is likely to reflect some change in the accretion flow. To investigate the disk-corona systems in these objects, we measure optical/X-ray spectral slopes and Eddington ratios of ten previously discovered changing-look quasars at two or more epochs. By comparing these data with simulated results based on the behaviour of X-ray binaries, we find a similarity in spectral slopes 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 supports the disk-wind model as the origin of broad emission lines.

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