An Off-Nuclear Tidal Disruption Event Discovered At Late Times: The Case Of TDE 2023mfm

The study presents the discovery and analysis of TDE 2023mfm, an optically selected tidal disruption event that originates from a wandering massive black hole in a massive host galaxy of about 10^11 solar masses. The host also contains a central low-luminosity active galactic nucleus (AGN), making the off-nuclear location of the flare especially notable.

Using observations from ZTF, Lick, Keck, Swift, Chandra, XMM-Newton, HST, and VLA, the team finds TDE 2023mfm is a TDE-H powered by a black hole of 10^6.2 ± 0.5 solar masses. The black hole is offset by 0.66 ± 0.02 arcseconds from the center of its host galaxy, corresponding to a projected distance of 1.08 ± 0.04 kpc. The event displays all the traits of optically selected TDEs.

The emission remains hot at a blackbody temperature of about 22,000 ± 1,000 K for more than a month after peak. Its g-band light curve peaks at (2.24 +0.10 -0.11) × 10^43 erg/s and stays above half-maximum luminosity for 47.8 +3.7 -3.5 days. Late-time optical-to-UV HST emission suggests an unresolved stellar population with a stellar mass of 10^7–10^8 solar masses at the TDE position, possibly a low-mass dwarf galaxy or a stripped galaxy left from a previous minor merger.

Radio emission from TDE 2023mfm emerges at least a year after the optical discovery, and the authors find it likely to originate from a delayed outflow, although further observations are needed to determine its true origin. The case adds to evidence that tidal disruption events can occur around wandering black holes well away from galactic nuclei.