AT2021acak: a candidate tidal disruption event found in the Zwicky Transient Facility survey

Abstract: We report a candidate tidal disruption event (TDE) found in the Zwicky Transient Facility (ZTF) survey data. This candidate, with its transient name AT2021acak, showed brightness increases of $\sim$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 {\it Neil Gehrels Swift Observatory (Swift)}. The optical spectra of the source show broad H and He emission line 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 spectrum. 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.