AT2019aalc: An obscured tidal disruption event candidate in an active galactic nucleus revealed by its first flare?

AT2019aalc is considered a repeating tidal disruption event (TDE) candidate occurring in an active galactic nucleus (AGN). In this paper, we highlight previously unnoticed but intriguing features that include a brief optical dimming prior to the rise of the main flare and a significantly lower post-flare luminosity compared to the pre-flare level. By applying a time-dependent obscured TDE model to AT2019aalc, we successfully reproduce its light curves with the tidal disruption of a 1.122-0.176+0.246 M main-sequence star by a 1.862-0.259+0.255 times 10 7 M supermassive black hole (SMBH). Both the pre-flare dimming and the reduced post-flare luminosity are attributed to obscuration of the intrinsic AGN emission. The total energy of the event derived from our fit is 1.24 times10 51 ergs and about 0.2 M of debris mass is accreted by the SMBH. In addition, the g-r color of the net flare in AT2019aalc exhibits a continuous reddening trend during the first flare, consistent with a gradual increase in E(B-V) predicted by the obscured TDE model. These results suggest that AT2019aalc can be considered a second member of the recently proposed class of obscured TDE candidates hosted in AGNs. galaxies: active-galaxies: nuclei-quasars: supermassive black holes-quasars: individual (AT2019aalc)-transients: tidal disruption events.