Optical variability characterization of changing-state AGN candidates

Active galactic nuclei (AGN) are powered mainly through accretion of surrounding material onto their supermassive black hole, exhibiting flux variability across all wavelengths and timescales. A subclass known as changing-state AGN (CSAGN) displays dramatic variability, such as the almost complete appearance or disappearance of broad optical/UV emission lines and disk continuum emission, on timescales as short as 6–12 months. Such extreme variability appears inconsistent with the viscous timescales typically ascribed to accretion disks, suggesting a gap in our understanding of AGN accretion physics. As such, early detection and monitoring of CSAGN can provide clues that aid theoretical developments. However, most CSAGN have been identified from archival studies, well after their CS episodes. We present a statistical characterization of optical single-band and color variability of spectroscopically confirmed CSAGN based on 5-yr ZTF light curves, as well as results of an anomaly detection algorithm trained on these sources, aimed at identifying new CSAGN candidates for spectroscopic follow-up with the 4-metre Multi-Object Spectroscopic Telescope (4MOST) as part of the Chilean AGN/Galaxy Evolution Survey (ChANGES).