Evolution of broad emission lines from double-peaked to single-peaked to support a central tidal disruption event

TL;DR

This study models how the evolution of fallback debris in a tidal disruption event causes broad emission lines to change from double-peaked to single-peaked, providing potential observational indicators for TDEs.

Contribution

It introduces a model linking the evolution of broad emission line profiles to the changing outer boundaries of disk-like BLRs in TDEs, supported by simulations and observations.

Findings

Probability of profile change is about 3.95%.

Observed profile changes in AT 2018hyz support the model.

Outer boundary ratios of BLRs match TDE debris predictions.

Abstract

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 into central accretion disk will lead expected broad emission lines changed from double-peaked to single-peaked. Considering common elliptical orbitals for the accreting fallback TDEs debris, based on simulated results through the preferred standard elliptical accretion disk model, a probability about 3.95\% can be estimated for cases with double-peaked profile changed to single-peaked profile in multi-epoch broad emission lines, indicating such unique profile variability could be indicator for BLRs related to TDE debris. Meanwhile, among the reported optical TDE candidates with apparent broad lines, such profile changes in broad H$\alpha$ can be found in the AT 2018hyz. After accepted the outer boundaries of the disk-like BLRs increased with time, the observed multi-epoch broad H$\alpha$ 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.