Extreme AGN Variability in WISE: Powerful Flares and Candidate Tidal Disruption Events in AGN

Satya Teja Anuraag Upadhyayula, Daniel Stern, Kishalay De, Christos Panagiotou, Matthew J. Graham, K. E. Saavik Ford, Barry McKernan, Murray Brightman, J. A. Acevedo Barroso, Daniel H. McIntosh

First listed 2026-09-02 | Last updated 2026-09-01

Abstract

We present first results from a systematic study of extreme mid-infrared variability of active galaxies across the $>10$-year baseline of the Wide-field Infrared Survey Explorer (WISE) mission. WISE, which observed the full sky with a six-month cadence, is sensitive to transient events in both unobscured and obscured galaxies. This paper focuses on extreme flares in active galactic nuclei (AGNs). Previous studies identified flares such as tidal disruption events (TDEs) in inactive galaxies, typically from optical or X-ray surveys. However, flares are also expected in AGN and optical/X-ray searches are insensitive to events in dust-enshrouded AGN. In this pilot study, we present flares in two AGN identified from extreme mid-infrared color variability. One flare was also detected at optical wavelengths. While both events showed broadened H$α$ emission several years after the flare peak, more recent spectroscopy reveals continued broadened emission only from the source with the optical flare. After considering several potential physical causes of the flares, including supernovae and micro-lensing, we suggest both events are TDEs in AGN. Intriguingly, the optical flare decays much faster than the expected $t^{-5/3}$ fallback rate expected for TDEs in quiescent galaxies, suggesting either a partial disruption or the tidal disruption of a star by an intermediate mass black hole embedded in the accretion disk of an AGN. This work demonstrates the power of WISE to identify the full census of TDEs, including events in dust-obscured AGN. Mid-infrared data probes the nature of the event and provides a bolometric measure of the flare energetics.

Short digest

Using the 15-year, six-month-cadence WISE/NEOWISE baseline, the authors search the high-reliability WISE R90 AGN catalog for extreme mid-infrared color variability and isolate two powerful flares, J2244+0816 and J2150−1132. J2244+0816 has a near-simultaneous optical flare and persistent broadened Hα, whereas J2150−1132 is optically quiet and its initially broadened Hα subsequently weakens and narrows; both show dust-echo-like mid-infrared evolution and are argued to be candidate TDEs embedded in AGN. The unusually rapid optical decay of J2244+0816 relative to the canonical t^-5/3 expectation points to a partial disruption or a disruption by an intermediate-mass black hole in an AGN disk, while illustrating how mid-infrared selection can recover dust-obscured TDEs and constrain their bolometric energetics.

Key figures to inspect

• Figure 3. This is the core discovery figure: it places the W1/W2 flare histories, optical behavior, color evolution, and spectroscopic epochs of J2244+0816 and J2150−1132 side by side, making the optical counterpart in only one source immediately clear.
• Figure 5. The two-epoch spectra of J2150−1132 provide the key temporal line diagnostic for the obscured candidate: Hα weakens and narrows while narrow [O III] and [N II] remain strong, supporting a fading transient contribution rather than a static broad-line component.
• Figure 7. The monotonic W1/W2-derived cooling of J2150−1132 over roughly 900 days is direct physical evidence for a dust echo, linking the extreme mid-infrared flare to progressively more distant reprocessing material.
• Figure 10. This population-level phase-space comparison shows where the two WISE AGN flares fall in peak rest-frame 3.4 μm luminosity and decline timescale relative to optically selected TDEs, Type IIn supernovae, changing-look AGN, and prior mid-infrared TDE candidates.