AT2021acak: a Candidate Tidal Disruption Event Found in the Zwicky Transient Facility Survey

We report a candidate tidal disruption event (TDE) found in the Zwicky Transient Facility survey data. This candidate, with its transient name AT2021acak, showed brightness increases of ~1 mag around MJD 59500 and subsequent power-law-like brightness declines. We have conducted multiple optical spectroscopic observations with the 2.4 m Lijiang telescope and one observation at X-ray and ultraviolet (UV) bands with the Neil Gehrels Swift Observatory (Swift). The optical spectra of the source show broad H and He emission lines and Fe emission features. Possible 0.3-2 keV X-ray and bright UV emission of the source was detected. We analyze the declines of the optical light curves, the emission features of the optical spectra, and the constructed broad-band UV and optical spectra. The properties derived from the analyses are consistent with those of reported (candidate) TDEs, and in particular very similar to those of ASASSN-18jd. The identification is complicated by the host being likely an AGN, and thus further observations of the event and quiescent host are required in order to have a clear understanding of the nature of this transient event.