2025A&A...699A.245Z

In this manuscript, considering evolution of fallback accreting debris in a central tidal disruption event (TDE), the outer boundary increased with time of the disk-like broad emission-line regions (BLRs) lying on the central accretion disk will lead to expected broad emission lines changing from double-peaked to single-peaked ones. Considering common elliptical orbitals for the accreting fallback TDE debris, based on simulated results through the preferred standard elliptical accretion disk model, a probability of about 3.95% can be estimated for cases with a double-peaked profile changed to a single-peaked profile in multi-epoch broad emission lines, indicating that such unique profile variability could signal BLRs being related to TDE debris. Meanwhile, among the reported optical TDE candidates with apparent broad lines, such profile changes in broad Hα can be found in the AT 2018hyz. After accepting the outer boundaries of the disk-like BLRs increased with time, the observed multi-epoch broad Hα can be described in AT 2018hyz. Moreover, the elliptical accretion-disk-model-determined time-dependent ratios of the outer boundaries of the disk-like BLRs are well consistent with the TDE-model-expected ratios of the outer boundaries of the fallback TDE debris. Furthermore, the evolution properties of disk-like BLRs can be applied to estimate the locations of the disk-like BLRs of which outer boundary could be about one sixth of the outer boundary of the fallback TDE debris in AT 2018hyz. Such unique profile changes from double-peaked to single-peaked could be applied as further clues to support a central TDE.