Studies On The Radiation Process Of Gamma-ray Bursts And Trigger Mechanism Of Fast Radio Bursts

Gamma Ray Bursts(GRBs)are phenomena of intensive high-energy spike at cosmological distance,with relatively short duration times and extremely high released energy.The prompt emissions are mainly in gamma-ray band,thus they are named as Gamma-Ray Bursts.GRBs were discovered in late 1960 s by accident.After researches of about half a century,people have gained extensive knowledge of GRBs.With the multi-band observations of GRB long-lasting afterglows,people have established the standard models for the GRB afterglows,which help us to understand the physical origins of GRBs,the radiation mechanisms,the characteristics of central engines and the surrounding environment structures.The observed associations between long GRBs and supernovae implicate that at least some long GRBs originate from the death of some special massive stars.The association discovered between short GRBs and gravitational waves has proved that at least some short GRBs are originated from binary neutron star-neutron star mergers.The study of GRBs and their afterglows involves various electromagnetic observation methods,which include gamma-ray,X-ray,ultraviolet,optical,infrared,millimeter and radio bands.Besides,it is believed that various non-electromagnetic signals could be produced in GRBs,like gravitational waves,cosmic rays and neutrinos.The related theoretical researches play a significant role in high-energy astrophysics.In the forthcoming “Multi-Messenger Astronomy Era”,we believe that GRBs will bring us more surprises.Based on the recent observations from Fermi/LAT satellite,there are high-energy photons extending to ? Ge V in GRB prompt phase.Many people believe that the GRB prompt phase spectra originate mostly from electron synchrotron emission.However,the simple synchrotron radiation model could not interpret the origins of Ge V photons.It is generally believed that the production of such high-energy photons is related closely to the inverse Compton scattering(ICS)process.In this thesis,we discuss the observability of ICS component and whether the extra high-energy components can be produced via the ICS process,as well as the origin of another special bursting phenomena in the universe – Fast Radio Bursts.Chapter 1 introduces the study history and some fundamental observational characteristics of GRBs.GRBs can be divided into long GRBs and short GRBs according to their duration times.These two subgroups of GRBs are roughly corresponding to two kinds of astrophysical origins,the collapse of massive stars and the merging of binary compact stars.There are three kinds of components including Band-function,(quasi-)thermal and extra high-energy components in GRB prompt emission,and one or more of them could be found in one GRB.Some temporal features of the extra high-energy components are also introduced,such as the delayed arriving of high-energy photons.In the last part of this chapter,we introduce another special bursting phenomena: Fast Radio Bursts(FRBs),which may also be related to compact stars.In Chapter 2,we focus on the GRB physical origins,including the mechanisms of the relativistic electron acceleration and the prompt emission.There are mainly two models for electron acceleration mechanism,the internal shock model and the Poynting-flow dominated jet model.When it comes to the GRB prompt emission mechanisms,it becomes quite complicated due to the so-called “fast-cooling” problem.The GRB low-energy spectra is basically harder than that in common fast-cooling regimes.The simple synchrotron model,in which the prompt emission originates from powerlaw distributed electrons cooled in constant magnetic fields,could not explain this.We introduce previous works on this issue,taking the magnetic field spatial-dependence and the ICS in emission region into consideration,and then discuss the significance of these effects.Based on previous works,we discuss whether the extra component due to ICS in GRB prompt emission can be observed if we take both the ICS and the decaying of magnetic fields into consideration.We calculate the electron distribution,the corresponding photon spectra and their evolution with time,and discover that those parameter groups in which ICS components could be observed are usually with small low-energy spectrum index.In the end,we compare our numerical results withobservations and relative works.In Chapter 3,we introduce a possible model of FRBs.It is argued that some neutron stars(NSs)people observed are in fact strange stars(SSs).Due to the intrinsic characteristics of strange quark matter(SQM),there is a crust made up of normal baryon matter above the surface of SS.When the crust mass increases and reaches its critical value,it will collapse and fall into SS surface,and be converted into SQM.If the SS has strong magnetic fields and rotates,then a part of energy released during the collapse may trigger coherent radiation.Hereafter the FRBs are produced.In Chapter 4,we give a summary of our work and the prospect in future.We hope that more solid observations and detailed theoretical works will help us to unveil the mystery of high-energy components in GRB prompt phase.