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

We present the discovery and analysis of the optically selected tidal disruption event (TDE) 2023mfm, which originates from a wandering massive black hole (MBH) in a massive ($\sim {10}^{11}$M${}_{\odot }$) galaxy hosting a central low-luminosity active galactic nucleus (AGN). Our analysis of the ZTF, Lick, Keck, Swift, Chandra, XMM-Newton, HST, and VLA observations reveals that TDE 2023mfm is a TDE-H from a ${10}^{6.2\pm 0.5}$M${}_{\odot }$ black hole which is offset by $0.66\pm 0.02$" from the center of its host galaxy, corresponding to a projected distance of $1.08\pm 0.04$ kpc. TDE 2023mfm displays all the traits of optically selected TDEs. The emission remains hot, $T_{\mathrm{b}\mathrm{b}}\sim 22,000\pm 1,000$ K, for more than a month after peak, and the $g$-band light curve peaks at $\left(2.24_{-0.11}^{+0.10}\right)\times {10}^{43}\mathrm{e}\mathrm{r}\mathrm{g}{\mathrm{s}}^{-1}$ and stays above half-maximum luminosity for $47.8_{-3.5}^{+3.7}$ days. The late-time optical-to-UV emission observed with the HST suggests the presence of an unresolved stellar population with a stellar mass of ${10}^7-{10}^8$M${}_{\odot }$ at the position of the TDE, possibly being a low-mass dwarf galaxy or a stripped galaxy from a previous minor merger. The radio emission from TDE 2023mfm emerges at least a year after optical discovery, and we find it likely that it originates from a delayed outflow, however, further observations are needed to determine its true origin.