Conditions for Changing-Look AGNs from Accretion Disk-Induced Tidal Disruption Events

TL;DR

This paper explores the conditions under which changing-look AGNs can result from tidal disruption events, linking SMBH properties, disk characteristics, and star cluster IMF to observed phenomena.

Contribution

It predicts the frequency of AGN TDEs and identifies key SMBH and disk parameters that influence changing-look AGN behavior, providing testable observational constraints.

Findings

Most CL-AGNs have SMBHs with spin > 0.9

AGN inner disks likely have high surface density

Typical AGN lifetimes are 10-100 million years

Abstract

The phenomenon of changing-look (CL) behavior in active galactic nuclei (AGN) is characterized by dramatic changes in luminosity and/or emission line profiles over relatively short periods, ranging from months to years. The origin of CL-AGNs remains a mystery, but one proposed explanation involves the response of the inner AGN disk to tidal disruption events (TDEs) around the supermassive black hole (SMBH). In this Letter, we calculate the predicted frequency of AGN TDEs as a function of SMBH mass and compare the results to the observed CL-AGN distribution. We find that if the fraction of CL-AGNs caused by AGN-TDEs is high, then: (1) most SMBHs in CL-AGN are near maximal spin, with the dimensionless spin parameter $a>0.9$; (2) AGN inner disks have a high surface density ($\geq 10^{7}\, {\rm g\, cm^{-2}}$); (3) typical AGN lifetimes are $\sim 10$-$100$ Myr; and (4) a nuclear star cluster initial mass function (IMF) that scales as $\sim m_*^{-1.6}$ is preferred. Future observations of CL-AGN will help constrain the fraction of CL-AGNs caused by AGN-TDEs, SMBH spins, AGN lifetimes, and the nuclear star cluster IMF.