Mass evolution of broad-line regions to explain the luminosity variability of broad H<i>α</i> in the tidal disruption event ASASSN-14li

We propose an oversimplified model to explain the different variability trends in the observed broad H α emission line luminosity, L H α ( 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 H α ( 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 H α ( t ) in the TDE ASASSN-14li well. Meanwhile, the oversimplified model also roughly describes the observed L H α ( t ) in the TDE ASASSN-14ae. The reasonable descriptions of the observed L H α ( 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.