Mass evolution of broad line regions to explain the luminosity variability of broad H$\alpha$ in the TDE ASASSN-14li

TL;DR

This paper proposes a simple model linking the mass evolution of broad line regions to the luminosity variability of broad Hα emission in TDEs, successfully explaining observations in ASASSN-14li and ASASSN-14ae.

Contribution

It introduces an oversimplified, parameter-efficient model for the mass evolution of BLRs to explain Hα luminosity variability in TDEs, applicable to multiple events.

Findings

Model with one free parameter fits ASASSN-14li data

Model roughly describes ASASSN-14ae Hα luminosity

Mass evolution of BLRs correlates with accreted debris

Abstract

In this manuscript, an oversimplified model is proposed for the first time to explain the different variability trends in the observed broad H$\alpha$ emission line luminosity $L_{H\alpha}(t)$ and in the TDE model determined bolometric luminosity $L_{bol}(t)$ in the known TDE ASASSN-14li. Considering broad emission line regions (BLRs) lying into central accretion disk related to accreted materials onto central black hole in TDEs, mass evolution $M_{BLRs}(t)$ of central BLRs can be determined by 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 mass of BLRs, the mass evolution $M_{BLRs}(t)$ of central BLRs can be applied to describe the observed $L_{H\alpha}(t)$. Although the proposed model is oversimplified with only one free model parameter $M_{BLRs,0}$, the model with $M_{BLRs,0}\sim0.02{\rm M_\odot}$ can be applied to well describe the observed $L_{H\alpha}(t)$ in the TDE ASASSN-14li. Meanwhile, the oversimplified model can also be applied to roughly describe the observed $L_{H\alpha}(t)$ in the TDE ASASSN-14ae. The reasonable descriptions to the observed $L_{H\alpha}(t)$ in ASASSN-14li and ASASSN-14ae indicate the oversimplified model with only one free model parameter is probably efficient enough to describe mass evolutions of $M_{BLRs}$ related to central accreted debris in TDEs.