AT2022zod: An Unusual Tidal Disruption Event in an Elliptical Galaxy at Redshift 0.11

TL;DR

AT2022zod is a short-lived, luminous optical flare in an elliptical galaxy, likely caused by a star disrupted by an intermediate-mass black hole, providing insights into black hole demographics.

Contribution

This paper reports the discovery and analysis of AT2022zod, an unusual TDE candidate, highlighting its potential origin from an intermediate-mass black hole in a UCD.

Findings

AT2022zod's luminosity and duration suggest a non-SMBH origin.

The event is likely caused by a star disrupted by a MBH in a UCD.

Implications for future searches of intermediate-mass black holes.

Abstract

Tidal Disruption Events (TDEs) have long been hypothesized as valuable indicators of black holes, offering insight into their demographics and behaviour out to high redshift. TDEs have also enabled the discovery of a few Massive Black Holes (MBHs) with inferred masses of $10^4$--$10^6\,M_\odot$, often associated with the nuclei of dwarf galaxies or ultra-compact dwarf galaxies (UCDs). Here we present AT2022zod, an extreme and short-lived optical flare in an elliptical galaxy at z=0.11, residing within 3kpc of the galaxy's centre. Its luminosity and ~30-day duration make it unlikely to have originated from the host galaxy's central supermassive black hole (SMBH), which estimate to have a mass around $10^8\,M_\odot$. Assuming that the emission mechanism is consistent with known observed TDEs, we find that such a rapidly evolving transient could either be produced by a MBH in the intermediate-mass range or, alternatively, result from the tidal disruption of a star on a non-parabolic orbit around the central SMBH. We suggest that the most plausible origin for AT2022zod is the tidal disruption of a star by a MBH embedded in a UCD. As the Vera C. Rubin Observatory's Legacy Survey of Space and Time comes online, we propose that AT2022zod serves as an important event for refining search strategies and characterization techniques for intermediate-mass black holes.