Study On Spectral Components Of Short GRBs

A gamma-ray burst is a sudden brightening of gamma rays in space for a short period of time,ranging in duration from a few milliseconds to hundreds of seconds,and ranging in energy from kiloelectron volts(ke V)to teraelectron volts(Te V).With the improvement of satellite observation capabilities,more and more GRBs have been recorded,and GRB events are now detected almost every day.At the same time,more and more theoretical models of gamma-ray bursts have been proposed,the most widely accepted is the so-called "fireball" model,and there is a lot of observational work,which provides comprehensive statistics of gamma-ray bursts and correlations between parameters.Despite many studies have been done by astronomers around the world,some basic information about gamma-ray bursts still remains unclear.Gamma-ray bursts are classified into short and long bursts according to duration,and are generally believed to originate from different precursor,which must have different physical explanations.Because of the long duration,the process is more complicated,relatively short bursts of less than two seconds are not so complicated.We have done some analysis of light curve and energy spectrum of short gamma-ray bursts,this paper is organized as follows:The first chapter briefly introduces the basic information of gamma-ray bursts,including observation and theoretical interpretation,respectively from the time domain and spectra domain of GRBs.In theory,we briefly introduce the current relatively accepted model and radiation mechanism.In chapter 2,I introduced our analysis of 9 bright short bursts,we analyzed the nine bright short gamma-ray bursts from the light curve and energy spectrum respectively.FRED function was selected to fit each pulse of gamma-ray bursts,and the rising time scale and FWHM of these pulses were obtained,and their correlation was obtained by analyzing the data: "log(FWHM)=(-0.17±0.14)+(0.78±0.15)log(Trise)",and illustrates the different pulse may have originated from the same area.For energy spectrum analysis of gamma-ray bursts,we selected four models BAND,CPL,BAND+BB and CPL+BB to fit their energy spectra and obtain their spectral parameters.According to these data,their correlation is as follows: "log Epeak =(-1.40±0.31)+(1.11±0.12)log(k T)".Finally,the possible origin of the thermal and non-thermal components and the possible radiation mechanism are speculated based on the analysis of light curve and energy spectrum.In chapter 3,I introduced another work,in which we analyzed a multi-pulse short gamma-ray burst GRB 170206 A with complex light curve.We try to fit the time-integrated spectrum and time-resolved spectrum of this short burst with various possible model combinations.In the time-resolved spectrum analysis,we divide the T90 of gamma-ray bursts into six time intervals,and select a time period before and after T90,for a total of eight time bins.As a result,we found a strong thermal component in the burst,and a strong positive correlation between the flux of the thermal component and the non-thermal component.In addition,the low-energy photon index obtained by our fitting was harder than predicted by synchrotron radiation theory.Finally,according to the result,we suggest that the thermal component may come from the optically thick photosphere,and the non-thermal component may come from the inverse Compton scattering of high-energy photons on the photosphere,so that the hard low-energy photon index can be well explained.