The Dynamics And Radiation Processes In Tidal-disruption Events And The Applications In Sw J1644+57

A star may be disrupted by tidal forces when it passes close enough by a supermassive black hole(SMBH). These events are named as tidal disruption eventes(TDEs), which are important tools for identifying SMBH in a dormant galaxy and investigating its properties.In this thesis, we focus on TDEs with relativistic jets, and study the physics behind the high energy emissions. Our researches include the raidation from accretion disk, jets and ejecta. The thesis is arragned as follows:Firstly, we review the basic theory of TDEs, including the physical processes during fallback, orbital cirularization, disk accretion, ejecta/outflow and jet propagting. We make special emphasis on dynamcis and emission in the super-Eddington accretion flow(i.e., slim disk model), Poynting flux-dominated jet(such as the jet powered by the Blandord-Znajek mechanism) and ejecta driven by disk raidiation.Secondly, we give a briefly introduction on TDE candidates, especially on those with relativistic jets, like Sw J1644+57, Sw J2058+05 and Sw J1112.2-8238. We collect the multi-band observational data of Sw J2058+05 and Sw J1112.2-8238, which will be investigated in future study.Finally, we study the late X-ray emission in Sw J1644+57. Recently, Swift/XRT, XMM-Newton and Chandra have found a flat X-ray lightcurve from Sw J1644+57 that appeared at ~500 days and was visible until ~1500 days after the disruption. This nearly constant X-ray component can not be interpreted by the exteral shock emission from the interaction between the relativistic jet and cirucumnuclear medium. We propose a model in which interaction between the disk driven ejecta and a gas cloud might account for the late X-ray lightcurve. Our model has the advantages in explaining both the behavior and non-thermal feature in the X-ray emission.