Identifying Changing-Look AGN Transitions in Light Curve Data with the Zwicky Transient Facility

TL;DR

This paper develops a photometric method using ZTF light curve data to identify Changing-Look AGN transitions, providing insights into their duration, frequency, and potential physical mechanisms.

Contribution

The authors introduce a new photometric criterion for detecting CL-AGN transitions using light curve changes, enabling large-scale identification without repeat spectroscopy.

Findings

A criterion of |Δg| > 0.4 mag and |Δ(g-r)| > 0.2 mag recovers 9.6% of CL-AGN transitions.

Estimated false positive rate among simulated Seyferts is 1.6%.

Photometric CL-AGN transitions last between 21 and 560 days, median 360 days.

Abstract

Changing-Look AGN (CL-AGN) are AGN which transition between Seyfert types, challenging AGN unification models. Most CL-AGN have been identified via repeat spectroscopy, making it difficult to determine the duration and magnitude of the CL-AGN transition. As such, the physical mechanisms behind this transition are still unknown. We use synthetic photometry in combination with ZTF light curve data to develop a new criterion to identify photometric CL-AGN transitions based on changes in g-band magnitude and g-r color. We find that a CL-AGN criterion of $| \Delta g| > 0.4$ mag and $| \Delta (g-r)| > 0.2$ mag recovers a photometric transition in $9.6^{+4.9}_{-3.4}\%$ of CL-AGN hosts over the six-year ZTF survey, including a candidate repeating changing-look event in SDSS J084957.78+274728.9. Using simulated AGN light curves, we estimate the false positive rate among the simulated Seyferts to be $1.6^{+0.19}_{-0.17}\%$. We find that the rate of similar flares among Type 1 Seyferts is $1.2^{+0.87}_{-0.50}\%$ , and among Type 2 Seyferts is $\leq 0.39\%$ over six years. Photometric CL-AGN transitions last between 21 and 560 days, with a median duration of 360 days, consistent with the thermal or orbital timescales for AGN disks. We do not detect a correlation between black hole mass and transition duration, likely due to the small sample of detected photometric transitions. This method can be applied to the upcoming Legacy Survey of Space and Time to identify CL-AGN candidates and test theories of their origins