High Energy Afterglow And Radiative Efficiency Of Gamma-RAY Burst

Gamma-ray bursts (GRBs) are transient events produced in the universe, which is increasing suddenly in short time and weakening fast. While they are on, they outshine the whole galaxy. It is one of the most active research fields in astrophysics. We first present a review of gamma-ray bursts in both observations and theories, including the significant observation progress in history, the light curves and spectra, the broadband afterglow emission, the fireball model, the observation features of high energy emission, the high energy emission processes in the GRBs and afterglows, the Fermi satellite introduction, which is related to my research.In Chapter 2, we present detailedly my postgraduate work—high energy afterglow and radiative efficiency of gamma-ray burst. High energy afterglow is gamma-ray emission which is above 100 MeV after prompt emission. The GRB radiative efficiency is an essential quantity to understand the nature of the bursts. It gives a direct measure of how efficient the burst dissipates the total energy into radiation during the GRB prompt emission phase. So far, the widely accepted model of GRB is the fireball model. According to fireball model, GRB radiative efficiency is very small. However, the X-ray afterglow observation show that the efficiency is high. So the observation data pose a challenge to the fireball model. We present 8 bright GRBs (fluence>3×105ergcm-2 during prompt emission phase of gamma-ray bursts) which are codetected by the GBM and the LAT onboard the Fermi satellite, give a systematic analysis of the prompt emission, estimate their isotropic energy in the 8 keV-100 GeV band. We use the standard afterglow model, make several simplifying assumptions including using a single typical value for se= 0.1, εB= 0.01 and n= 1 cm-3, to calculate the isotropic kinetic energy of the fireball right after the prompt gamma-ray emission is over. And then obtain their radiative efficiency. We find that all the bursts tend to have radiative efficiency varying from, ηγ～(1%～64%). We further explore the Eγ,iso-Ek relation, show Eγ,tso as a function of Ek for the eight bursts with the similar correlation with the paper of Racusin.As we all known, the kinetic energy of fireball is depend on the circumburst environment. So in Chapter 3, we discuss the radiative efficiency in different cases, respectively. There are two cases:in interstellar medium environment and in wind environment.