Understanding extreme quasar optical variability with CRTS – I. Major AGN flares

• Main Authors: Graham, Matthew J., Djorgovski, S. G., Drake, Andrew J., Stern, Daniel, Mahabal, Ashish A., Glikman, Eilat, Larson, Steve, Christensen, Eric
• Other Authors: Univ Arizona, Dept Planetary Sci, Lunar & Planetary Lab
• Language: en
• Published: OXFORD UNIV PRESS 2017
• Subjects: methods: data analysis; techniques: photometric; surveys; quasars: general
• Online Access: http://hdl.handle.net/10150/625731; http://arizona.openrepository.com/arizona/handle/10150/625731

There is a large degree of variety in the optical variability of quasars and it is unclear whether this is all attributable to a single (set of) physical mechanism(s). We present the results of a systematic search for major flares in active galactic nucleus (AGN) in the Catalina Real-time Transient Survey as part of a broader study into extreme quasar variability. Such flares are defined in a quantitative manner as being atop of the normal, stochastic variability of quasars. We have identified 51 events from over 900 000 known quasars and high-probability quasar candidates, typically lasting 900 d and with a median peak amplitude of Delta m = 1.25 mag. Characterizing the flare profile with a Weibull distribution, we find that nine of the sources are well described by a single-point single-lens model. This supports the proposal by Lawrence et al. that microlensing is a plausible physical mechanism for extreme variability. However, we attribute the majority of our events to explosive stellar-related activity in the accretion disc: superluminous supernovae, tidal disruption events and mergers of stellar mass black holes.