Mass evolution of broad-line regions to explain the luminosity variability of broad Hα in the tidal disruption event ASASSN-14li

Guangxi Key Laboratory for Relativistic Astrophysics, School of Physical Science and Technology, GuangXi University, Nanning 530004, PR China

^⋆ Corresponding author; xgzhang@gxu.edu.cn

Received: 29 August 2024
Accepted: 19 November 2024

Abstract

We propose an oversimplified model to explain the different variability trends in the observed broad Hα emission line luminosity, L_Hα(t), and the tidal disruption event (TDE) model-determined bolometric luminosity, L_bol(t), of the TDE ASASSN-14li. Assuming that broad emission line regions (BLRs) in the central accretion disk are related to materials accreted onto the central black hole of a TDE, the mass evolution of central BLRs, M_BLRs(t), can be determined as the maximum mass, M_BLRs, 0, of central BLRs minus the corresponding accreted mass in a TDE. Meanwhile, through the simple linear dependence of broad Balmer emission line luminosity on the mass of BLRs, the mass evolution of central BLRs, M_BLRs(t), can be applied to describe the observed L_Hα(t). Although our proposed model is oversimplified – with only one free model parameter, M_BLRs, 0 – with M_BLRs, 0 ∼ 0.02 M_⊙, it describes the observed L_Hα(t) in the TDE ASASSN-14li well. Meanwhile, the oversimplified model also roughly describes the observed L_Hα(t) in the TDE ASASSN-14ae. The reasonable descriptions of the observed L_Hα(t) in ASASSN-14li and ASASSN-14ae indicate that our oversimplified model is probably efficient enough to describe mass evolutions of M_BLRs related to central accreted debris in TDEs.