AT 2022csn: A Photometrically Peculiar Optical/UV Tidal Disruption Event in a Type II AGN

The emission mechanism and host galaxy preference of optical/UV tidal disruption events (TDEs) are still not entirely understood. We present observations of the TDE AT 2022csn, which is one of the most distant ( d L ∼ 726 Mpc) and luminous ( L peak = 2.48 7 − 0.067 + 0.073 × 1 0 44 erg s − 1 ) optical/UV TDEs observed to date. Although it is a spectroscopically normal H + He TDE, it shows some photometric peculiarities, exhibiting a pronounced double-peaked light curve (with peaks separated by 18.30 ± 2.84 days in the g band) and lying in the low-temperature and large-radius end of the optical/UV TDE population. The host galaxy of AT 2022csn shows evidence for a significant starburst within the last gigayear, consistent with hosts of other optical/UV TDEs, as well as narrow emission lines, consistent with hosts of Type II AGN. Interaction between the TDE and a preexisting AGN accretion disk might explain the peculiar photometric properties. However, it is puzzling that a TDE would be visible in a Type II AGN, where according to the AGN unification picture the central region around the supermassive black hole is obscured. We suggest a few scenarios to reconcile this. AT 2022csn together with AT 2019ahk, which shows similar properties, may belong to a new subset of low-temperature, high-radius TDEs in galaxies with Type II AGN emission features.