Outflow Structure And Radiation Characteristics Of Short Gamma-ray Burst

Gamma Ray Bursts(GRBs)are the most violent explosions of gamma-ray emissions that last from milliseconds to thousands of seconds in the universe and the typical isotropic energy usually ranges in 1051-1054 erg.Since its discovery in 1967 by Vela satellites,GRB researches have been rapidly developed as one hot topic in astrophysics.Based on their durations,GRBs are divided into long GRBs(1GRBs)and short GRBs(sGRBs).Generally,1GRBs are believed to likely originate from the collapse of massive stars,while sGRBs originate from mergers of compact binaries involving double neutron stars or neutron star-black hole systems.The main properties of GRBs can be described by the "standard fireball" and the internal-external shocks models.Some pieces of evidences,such as a clear break in multi-wavelength afterglow light-curves,suggest that not all GRB outflows are spherical ejecta but may be collimated into narrow jets.GRB jet is assumed to be uniform,but observations and some numerical simulations,especially the first gravitational-wave associated GRB event(GRB 170817A),suggest that at least some GRBs should have structured jets.In this thesis,we focus on the temporal and spectral characteristics of GRBs detected by various satellites and constrain jet structures and the radiation mechanisms.In particular,we pay more attention to three prompt gamma-ray components,namely main peaks,precursors and extended emissions.In addition,we also analyze the observational properties of fast radio bursts(FRBs)and propose a new classification method of FRBs.The thesis is organized as follows.In Chapter 1,we briefly review the progress on the observational and theoretical studies of GRBs and FRBs.Firstly,we present a brief introduction on the history and the theorietial models of GRBs.Next,we introduce the observational characteristics of prompt emission and their afterglows,respectively.Finally,we present a brief introduction on the history,observational characteristics and models of FRBs.In Chapter 2,we investigate the properties of CGRO/BATSE sGRB pulses and study the evolution modes of pulses across differently adjacent energy channels.We find that the first pulse of two types of double-peaked sGRBs is similar to the singlepeaked one and may share the same origin from the central engine,while the two types of double-peaked short GRBs might originate from different mechanisms.We find different dependence of the FWHM on the photon energy among different energy bands.We propose that the diverse power-law indexes together with the profile evolution of the GRB pulse can be used as an effective probe to diagnose the structure and evolution of the relativistically jetted outflows.In Chapter 3,we examine in detail the temporal properties of the three components in the prompt gamma-ray emission phase of Swift/BAT sGRBs,including precursors,main peaks,and extended emissions.We investigate the similarity of the main peaks between one-component and two-component short GRBs.It is found that there is no substantial difference among their main peaks,suggesting that they are produced from similar central engine activities.Importantly,comparisons are made between the singlepeaked and the double-peaked sGRBs.Interestingly,we find more evolution modes of pulses across different adjacent energy channels in view of the Swift/BAT observations.We verify the power-law correlations related with peak fluxes of the three components,strongly suggesting that they are produced from similar central engine activities.In particular,we compare the temporal properties of GRB 170817A with other sGRBs with EE and find no obvious differences between them.In Chapter 4,we introduce the research of spectral properties of prompt emissions with multiple components in Swift/BAT sGRBs.It has been found that peak energies in each pulse are uncorrelated with the pulse duration.Meanwhile,we find that there is no obvious correlation between peak energy and energy fluence.There is no obvious spectral evolution from earlier precursors to later extended emissions in view of the correlations of pulse duration with either the peak energies or the low-energy spectrum index.A power-law correlation between the average flux and the energy fluence is found to exist in the individual segments instead of mean peaks.On the basis of all the above analyses,we conclude that three emissive components could share the same radiation mechanisms,but they might be dominated by diverse physical processes.In Chapter 5,the multi-wavelength properties of the nearby low-luminosity GRB 171205A associated with SN 2017iuk are investigated in depth to constrain its pyhsical origin synthetically,including time lags,spectral energy relation,host properties,offset,etc.We compare its properties with nonnal 1GRBs,other low-luminosity 1GRBs associated with supernovae,and sGRBs associated with kilonovae.Finally,we put an upper limit on the viewing angle of GRB 171205A.In Chapter 6,we firstly classify 133 FRBs into short FRBs and long FRBs according to the clear bimodal distribution of pulse width.Then,we systematically investigate their observational properties,including observational pulse width,peak flux density,fluence and energy,etc.Finally,we investigate the dependence of the peak flux density on the redshift and predict the detectability of FRB at a higher redshift by FAST and the Square Kilometre Array in the near future.In Chapter 7,we comprehensively summarize the thesis and make some prospects in the relevant fields.