Changing-look (CL) Active Galactic Nuclei (AGNs), characterized by appearance/disappearance of broad emission lines in the span of a few years, present a challenge for the AGN unified model, whereby the Type 1 vs. Type 2 dichotomy results from orientation effects alone. We present a systematic study of a large sample of spectroscopically classified AGNs, using optical variability data from the Zwicky Transient Facility (ZTF) as well as follow-up spectroscopy data. We demonstrate that Type 1 vs. 2 AGN can be neatly separated on the basis of the variability metric σQSO, which quantifies the resemblance of a light curve to a damp random walk model. For a small sub-sample, however, the ZTF light curves are inconsistent with their previous classification, suggesting the occurrence of a CL event. Specifically, we identify 35 (12) turn-on (turn-off) CL AGN candidates at z<0.35. Based on follow-up spectroscopy, we confirm 17 (4) turn-on (turn-off) CL AGNs out of 21 (5) candidates, presenting a high success rate of our method. Our results suggest that the occurrence rate of CL AGNs is ∼0.3% over timescales of 5 to 20 years, and confirm that the CL transition typically occurs at the Eddington ratio of ≤0.01.
@article{arxiv.2402.18131,
title = {Identifying changing-look AGNs using variability characteristics},
author = {Shu Wang and Jong-Hak Woo and Elena Gallo and Hengxiao Guo and Donghoon Son and Minzhi Kong and Amit Kumar Mandal and Hojin Cho and Changseok Kim and Jaejin Shin},
journal= {arXiv preprint arXiv:2402.18131},
year = {2024}
}