Understanding extreme quasar optical variability with CRTS: II. Changing-state quasars

Matthew J. Graham, Nicholas P. Ross, Daniel Stern, Andrew J. Drake, Barry McKernan, K. E. Saavik Ford, S. G. Djorgovski, Ashish Mahabal, Eilat Glikman, Steve Larson, Eric Christensen

Research output: Contribution to journalArticlepeer-review


We present the results of a systematic search for quasars in the Catalina Real-time Transient Survey exhibiting both strong photometric variability and spectroscopic variability over a decadal baseline. We identify 111 sources with specific patterns of optical and mid-infrared photometric behaviour and a defined spectroscopic change. These ‘changing-state’ quasars (CSQs) form a higher luminosity sample to complement existing sets of ‘changing-look’ AGNs and quasars in the literature. The CSQs (by selection) exhibit larger photometric variability than the changing-look quasars (CLQs). The spectroscopic variability is marginally stronger in the CSQs than CLQs as defined by the change in H β/[OIII] ratio. We find 48 sources with declining H β flux and 63 sources with increasing H β flux, and discover 8 sources with z > 0.8, further extending the redshift arm. Our CSQ sample compares to the literature CLQ objects in similar distributions of H β flux ratios and differential Eddington ratios between high (bright) and low (dim) states. Taken as a whole, we find that this population of extreme varying quasars is associated with changes in the Eddington ratio and the time-scales imply cooling/heating fronts propagating through the disc.
Original languageEnglish
Pages (from-to)4925-4948
Number of pages24
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date20 Nov 2019
Publication statusPublished - 1 Feb 2020


  • astro-ph.GA

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