Afterglow Emission From Short Gamma-ray Bursts And Environmental Magnetic Field Of Fast Radio Bursts

Gamma-ray bursts(GRBs)are a class of bright gamma-ray flashes,which are the most intense high-energy explosions in the universe.Since the Vela satellite discovered the first gamma-ray burst in 1960s,GRBs have always been one of hot astrophysical researches.On one hand,the basic physical processes related to GRBs still remain to be solved,such as the origin of the jet,the central engine of GRBs and the generation mechanism of the prompt emission.On the other hand,the advent of multi-Messenger astronomical era with abundant observation data(e.g.,neutrino,electromagnetic radiation,gravitational wave)brings about the chance for us to understand the physical process under extreme conditions.According to the bimodel distribution of duration,GRBs fall into two groups,i.e.,long-duration GRB(1GRB)lasting for>2s and short-duration GRB(sGRB)lasting for<2s.Association between 1GRBs and supernova explosions supports that 1GRBs originate from the collapse of massive stars.SGRBs have long been proposed as the products of binary compact star mergers.The coalescence of binary neutron stars(BNS)or black hole-neutron stars(BH-NS)will eject neutron-rich matter.These ejecta synthesize a large number of unstable heavy nuclei through rapid neutron capture process(r-process),and then power a kilonova.Several kilonova candidates associated with sGRBs provide indirect evidence for the merger origin of sGRBs.A recently-discovered gravitational-wave(GW)event(GW 170817),has been identified as the signal from a BNS inspiral.The connection of GW 170817 with an sGRB(GRB 170817A)provides direct evidence for the BNS coalescences as progenitors of at least part of sGRBs.The central engines of GRBs are widely believed to be neutron stars or stellar black holes.GRBs and their afterglows would hint about properties of their central objects.For example,there could be a newborn magnetar if we observe extended emission,X-ray plateau or X-ray flares.In this dissertation,we focus on afterglow emission from sGRBs and the environmental magnetic field of fast radio bursts(FRBs).Chapter 1 introduces the background of research on the GRBs and their afterglows,including three sections.Section 1 is about observations and classical theories of GRBs and their afterglows.We make introduction of kilonova in section 2,including description of kilonova model and merger-nova model as well as research history of r-process.In section 3,we focus on the multi-messenger observations and theoretical research of GW170817.Importantly,observations connected with GW170817 confirm the association among sGRBs,kilonovae and BNS mergers.In the merger-nova model,a magnetar,born in a BNS merger,releases poynting flux and accelerates the merger ejecta.However,crab nebula observations imply that poynting flux would eventually turn into the relativistic fluid of positron/electron pairs.And then,leptons interact with surrounding matter and results in a pulsar wind nebula(PWN).Thus,we introduce in Chapter 2 observations of PWNe,followed by the application of PWN model to evolution of GRB jets and BNS merger ejecta.In the case of PWNe in GRB jets,reverse-shock emission is responsible for the X-ray bumps occurred at about 1 day.The interaction between magnetar wind and BNS merger ejecta could produce bumps at optical and X-ray band,where optical re-brightenings originate from the thermal radiation of ejecta and X-ray flares result from reverse-shock emission.In chapter 3,we start with the current research status of FRBs and find that FRBs might connect with GRBs and GW events.And we introduce a method of estimation of environmental magnetic field around FRBs,which opens a new window for studying their physical origin as well as the properties of their host galaxies.A brief summary and discussion of this thesis is presented in the last chapter.