Determine the mechanisms powering AGN nuclear transients

Determine the physical mechanisms responsible for the observed classes of AGN-related nuclear transients—namely changing-look AGN, changing-state AGN, periodic AGN, quasi-periodic eruptors, quasi-periodic oscillators, ambiguous nuclear transients, extreme nuclear transients, and tidal disruption events—and ascertain to what extent interactions between AGN accretion disks and stars from nuclear star clusters account for these phenomena.

Background

The paper summarizes that AGN exhibit diverse nuclear transient phenomena (e.g., changing-look and changing-state AGN, QPEs, QPOs, ANTs, ENTs, and TDEs) that are currently classified phenomenologically by timescales, energetics, and spectral behavior. Despite extensive monitoring from wide-field time-domain surveys, the underlying physical drivers of these phenomena are not well established.

The authors present J2245+3743, an extreme, highly energetic nuclear flare, and discuss multiple plausible mechanisms (including AGN TDEs, supernovae within disks, and gravitational lensing). The difficulty in uniquely attributing events like J2245+3743 underscores the broader unresolved question of what physical processes power different AGN nuclear transient classes and when disk–star interactions dominate.

References

The physical mechanisms behind these events are still unclear, but the nature and location of the activity strongly suggests at least some are caused by interactions between the AGN accretion disk and a star, most likely from the nuclear star cluster gravitationally bound to the SMBH \cite[e.g.,][]{Graham20, Starfall22}.

— An Extremely Luminous Flare Recorded from a Supermassive Black Hole  (2511.02178 - Graham et al., 4 Nov 2025) in Main Text, opening paragraph

Perhaps most importantly, the ability of the wind model to kinetically power the radiation and simultaneously reproduce the spectral line evolution disfavors accretion-powered models, as it is unclear whether they can produce the same result.

— Relativistic outflows power a quasi-periodic eruption: constraints on energetics, mass loss, and emission mechanisms  (2608.28507 - Chakraborty et al., 28 Aug 2026) in Section 3.1, “Constraints on energetics, long-term evolution, and QPE models”

Current data cannot firmly establish whether the mid-infrared flare is the dust echo of a micro-TDE or an SMBH TDE, though, in the latter case, the data prefer a retrograde TDE over a prograde TDE.

— Extreme AGN Variability in WISE: Powerful Flares and Candidate Tidal Disruption Events in AGN  (2609.01421 - Upadhyayula et al., 1 Sep 2026) in Section 6.4, “J2150-1132”

The origin of QPEs remains uncertain, and several physical scenarios have been proposed to explain their recurrent eruptions.

— A Unified Timescale Relation for Quasi-Periodic Eruptions and Repeated Nuclear Transients  (2609.08737 - Huang et al., 8 Sep 2026) in Section 4.1, “Implications for the origin of QPEs”

Thus, the physical origin of the apparent continuity between QPEs and RNTs remains an open question.

— A Unified Timescale Relation for Quasi-Periodic Eruptions and Repeated Nuclear Transients  (2609.08737 - Huang et al., 8 Sep 2026) in Section 4.2, “A possible connection between QPEs and RNTs”