Speaker: Dr. Rongfeng Shen (Toronto University, Canada)

Time: 2:00PM, September 21

Location: 3rd floor

Title: The Evolution of Accretion Disk in Tidal Disruption Events

Abstract:

　　　　 In a super massive black hole (BH) tidal disruption event (TDE), the tidally disrupted star feeds the BH via an accretion disk. Most often it is assumed that the accretion rate history, hence the emission light curve, tracks the rate at which new debris mass falls back onto the disk, notably the t^-5/3 power law. But this is not the case when the disk evolution due to viscous spreading - the driving force for accretion - is carefully considered. We construct a simple analytical model that comprehensively describes the accretion rate history across 4 different phases of the disk evolution, in the presence of mass fallback and taking into account disk wind loss. Accretion rate evolves differently in those phases which are governed by how the disk heat energy is carried away, early on by advection (i.e., an ADAF) and later by radiation. The accretion rate can decline as steeply as t^-5/3 only if copious disk wind loss is present during the early ADAF phase. Later, the accretion rate history is t^-8/7 or shallower. These have great implications on the TDE flare light curve. I will also talk about the application of our results on the recently discovered jetted TDE candidate Swift J1644+57.