2025MNRAS.537...84G

We report a high-redshift ($z=1.404$) tidal disruption event (TDE) candidate in SDSS J000118.70+003314.0 (SDSS J0001), which is a quasar with apparent broad Mg II emission line. The long-term variability in its nine-year photometric $ugriz$-band light curves, obtained from the SDSS Stripe82 and the PHOTOOBJALL data bases, can be described by the conventional TDE model. Our results suggest that the TDE is a main-sequence star with mass of $1.905_{-0.009}^{+0.023}\,{\rm M_\odot }$ tidally disrupted by a black hole (BH) with mass $6.5_{-2.6}^{+3.5}\times 10^7\,{\rm M_\odot }$. The BH mass is about 7.5 times smaller than the virial BH mass derived from the broad Mg II emission line, which can be explained by non-virial dynamic properties of broad emission lines from TDEs debris. Furthermore, we examine the probability that the event results from intrinsic variability of quasars, which is about $0.009{{\ \rm per\ cent}}$, through applications of the DRW/CAR process. Alternative explanations for the event are also discussed, such as the scenarios of dust obscurations, microlensing and accretion. Our results provide clues to support that TDEs could be detectable in broad line quasars as well as in quiescent galaxies, and to indicate the variability of some active galactic nuclei may be partly attributed to central TDEs.