An Extremely Luminous Flare Recorded from a Supermassive Black Hole

TL;DR

This paper reports the discovery of an extremely luminous flare from a supermassive black hole, emitting an unprecedented amount of energy, likely caused by a tidal disruption event in an active galactic nucleus.

Contribution

It presents the observation of the most powerful AGN transient ever recorded and discusses potential mechanisms, favoring a tidal disruption of a massive star.

Findings

Flare brightness increased by over 40 times in 2018.

Total emitted energy is approximately 10^54 erg, converting about one solar mass.

The event is 30 times more energetic than previous AGN transients.

Abstract

Since their discovery more than 60 years ago, accreting supermassive black holes in active galactic nuclei (AGN) were recognized as highly variable sources, requiring an extremely compact, dynamic environment. Their variability traces to multiple phenomena, including changing accretion rates, temperature changes, foreground absorbers, and structural changes to the accretion disk. Spurred by a new generation of time-domain surveys, the extremes of black hole variability are now being probed. We report the discovery of an extreme flare by the AGN J224554.84+374326.5, which brightened by more than a factor of 40 in 2018. The source has slowly faded since then. The total emitted UV/optical energy to date is $\sim10^{54}$ erg, i.e., the complete conversion of approximately one solar mass into electromagnetic radiation. This flare is 30 times more powerful than the previous most powerful AGN transient. Very few physical events in the Universe can liberate this much electromagnetic energy. We discuss potential mechanisms, including the tidal disruption of a high mass $(>30\, M_\odot)$ star, gravitational lensing of an AGN flare or supernova, or a supermassive (pair instability) supernova in the accretion disk of an AGN. We favor the tidal disruption of a massive star in a prograde orbit in an AGN disk.