Probing The Structure Of The Outflow In The Tidal Disruption Flare SW J1644+57 With Long-Term Radio Emission

The recently discovered high-energy transient SW J1644+57 is thought to arise from the tidal disruption of a passing star by a dormant massive black hole. The long-term, bright radio emission of Sw J1644+57 is believed to result from the blast wave syn-chrotron emission produced by the outflow expanding into the surrounding medium. Using the detailed multi-epoch radio spectral data, we are able to determine the num-ber of the total radiating electrons at different times, and hence the evolution of the cross section of the outflow. We find that the jet gradually transits from a conical jet to a cylindrical one and even become more collimated at later times. That may indicate a strong collimation mechanism, such as collimation of the outflow by the pressure of the shocked jet cocoon that forms while the outflow is propagating in the ambient medium. Since SW J1644+57 has the same central engine like AGNs, this process may be compared with the origin of AGNs.In chapter 1 we first simply introduced the background an observation features of SW J1644+57. We also compared and listed the same and different points of SW J1644+57 with GRBs and AGNs.In chapter 2 we mainly introduced the recent research of tidal disruption event and SW J1644+57 from other researchers. In this chapter we first analysed the possi-bility of SW J1644+57 being a tidal disruption event abd listed related evidence. We elaborated the sketch that how TDE evolves after a star being captured by a supermas-sive blackhole in detail. The timescales, luminosity, accretion rate and other physical parameters also being discussed. We especially focus on a white dwarf being tidal disrupted by a supermassive blackhole in galaxy central which is now being consid-ered as the most likely to be the origin of SW J1644+57. Last part we gave a simply introduction of the radio afterglow models of SW J1644+57.During chapter 3 and chapter 4 we showed an afterglow model which can be ap-plied to tidal disruption event SW J1644+57. This model was derived from basic GRB afterglow model. We also showed our fits of characteristic frequencies and peak flux of SW J1644+57 radio spectrum data. Due to the complete physical process of how a TDE produces a jet haven’t been fully resolved yet. The ambient density profile around the blackhole also not being completely researched because of its complexity. We can’t determine the evolution and initial condition of jet geometry during the propagation of jet itself. Moreover, if we give too much limits and assumptions before we start our calculation, we may not get a relative reality result or even can’t get a reasonable result. Thus in this article-we managed to calculate every physical parameters in each selected time spot and got the time/radius evolution in turn. Note that the model do not rely on the assumption of jet geometry, ambient density profile or initial conditions, so that we can manage to get the reality steller density profile around a blackhole in galaxy central and the physical parameters evolution during the propagation of jet.Finally we gave our conclusion and discussed the future prospect of radio after-glow research in SW J1644+57.