Hidden No More: Spotlight on tidal disruption events in active galactic nuclei

TL;DR

This paper investigates tidal disruption events in active galactic nuclei and proposes that a hidden population of TDEs occurs in AGNs, identifiable through Bowen fluorescence flares. Using AT2019aalc as a case study, it compares it with analogues such as AT2021acak and ULIRG F01004-2237 to highlight dual optical flares, Bowen lines, coronal lines, and infrared echoes, consistent with a TDE-AGN interpretation in some cases. The authors argue that Bowen fluorescence flares (BFFs) may represent a broader class of TDEs in AGN environments, with diversity in X-ray emission and Balmer-line phenomenology, potentially explained by disk–debris interactions and disk precession. They discuss physical mechanisms, observational diagnostics, and the promise of upcoming surveys (e.g., LSST/LS4) to constrain TDE rates in AGNs and to illuminate SMBH feeding and disk dynamics in active galaxies.

Abstract

Tidal disruption events (TDEs) are typically discovered in previously quiescent galaxies. However, earlier studies have revealed a handful of TDEs occurring in pre-existing active galactic nuclei (AGNs). We discuss AT2019aalc, a promising TDE candidate in an AGN, and compare it to similar sources. We also explore Bowen fluorescence flares, a newly identified class of flaring supermassive black holes, as potential members of the TDE in AGN transient class. We aim to connect the observed properties of these flares with the expectations of TDE-in-AGN simulations.

Figures (2)

• Figure 1: ZTF and ATLAS differential light curves of AT2019aalc and AT2021acak, respectively, retrieved via forced photometry requests and binned to $14$-days. The red dotted line indicates the baseline flux level. The days are relative to the first flare's peak. The similarities of the optical light curve properties are remarkable. AT2019aalc is known as a BFF while AT2021acak is a candidate TDE.
• Figure 2: ZTF and ATLAS light curves of BFFs and BFF-like transients which show a late-time bump-like structure in their optical light curves. This bump feature differ from the distinct flares seen in a few other BFFs including AT2019aalc. The light curves are binned to $14$ days, except for AT2024rqe, which is binned to $7$ days. The black dashed lines represent the baseline flux levels for the different cases. Vertical offsets have been applied to all sources except AT2020afhd for clarity. A scaling factor of $1/2$ has been applied to AT2024rqe and AT2023dm to improve visibility. The peak of AT2024rqe and AT2020afhd are approximate due to lack of observations around that time.