Investigating The Thermal Component In The Prompt Eission Of Fermi Gamma-ray Bursts

Gamma-Ray Burst(GRB)is the most intense astrophysical phenomenon in the universe,it will release huge energy in a short time and which has always been a hot issue in astrophysics.The study of GRB helps to understand the high-energy gamma-ray radiative mechanism,the physical process,and the ability to limit other theoretical models.In this paper,we analysis the spectral components and spectral evolutions through the fitting results with different models in the prompt emission of GRB.In Chapter 1,we review the history and achievements of the observations in GRBs at first.Then,we briefly introduce some open questions and the standard fireball model,in which the non-thermal radiative mechanisms of the prompt emissions of GRBs.Recent researches shows that the time-intergrated spectra can be best modeled with a combination of non-thermal and thermal component.Therefore,we presents some important physical conclusions about the onset process of GRBs by the fitting results of the theoretical models and empirical functions at the end of this part.In Chapter 2 we give the detailed accounts of the Fermi satellite,selections of GRB data,backgroud fitting and the methods of spectral fitting.According to the fitting results in Chapter 2,we discuss the spectal components,the evolutions of spectral parameters,and its physical process in Chapter 3.The spectra of prompt emission can be fitted with the non-thermal components and the thermal component.The non-thermal component Band(CPL)very likely satisfy with the optically thin synchrotron radiation above the photosphere,and the thermal component is relevant to the photospheric emission.Moreover,the most likely interpretation of the Power Law in the keV~MeV band is that the acceleration process does not accelerate all the electrons in the shock,then these electrons will produce the PL photons by inverse-Compoton scatterings in Thomson regime with hot photons.In Chapter 4 we present the spectral evolutions between the specral parameters and their physical significances.First of all,we find that there are a little bursts satisfied with the synchrotron radiation through the analysis of the low-energy power-law index ?.Although we notice that the jitter radiation can explain the evolutions of ? in three bursts,the possibility of the occurrence is too low according to the envirmental limitations surrouding the bursts.At the same time,comparing the particals acceleration models in GRBs,we find that the magnetic reconnection is more suitable to the prompt emission than the internal shock model.Next,the correlation between spectral peak enenrgy Ep and thermal temperature kT shows that there are a magnetically-dominent jet in the GRBs which we have choosed,and the index ? of this correlation is approximately equal to +0.5 in Band+BB.Thirdly,we imply the relation between Ep and spectal peak flux Fp,and the average value of the index k of this relation is about +1.45,which is similar to others.The cosmological redshift can be measured if this relation is truly intrinsical.What's more,the Ep—Fp relation is weak in Band+BB,which can be regarded as one of the evidences of the existence of the thermal radiation in GRB prompt emission.The conclusion of this paper,some problems about the prompt emission and the fireball model of GRBs from recent observations have been listed in the last part.