Gamma-ray Bursts:the Propagation Of Relativistic Jets And Its Application

Gamma-ray bursts(GRBs)are phenomena of intensive spike in the cosmic gamma-ray background.Thanks to the prior satellites(e.g.,BeppoSAX,Swift,Fermi),people now understand that at least some long GRBs come from the collapse of massive stars after researches of nearly half a century.At the same time,the standard model for the GRB afterglows has been established.As multi-messenger windows,such as the opti-cal band,the X-ray band,the neutrinos,and the gravitational wave,are being opened for the observations of GRBs,it is time to try to solve the crucial questions on the phys-ical mechanisms of GRBs.Further researches are called to study the central engines,the jet properties(composition or launching mechanism),the energy dissipation and the radiation mechanisms during the prompt phase etc.In this thesis,we propose a numerical method to solve the dynamics of the forward shock-reverse shock system during the afterglow phase.After applying this method to specific scenarios,such as the delayed energy injection,the density jump,and the injection of relativistic positron-electron pais,we succeed in explaining some peculiar afterglows.We then move to study the propagation of intermittent jets through the envelope of a rotating,collapsing GRB progenitor star.As a next step,we would take magnetic fields into account in our future researches.Some investigations on fast radio bursts(FRBs)and strange stars are also done.In Chapter 1,we briefly introduce observations and theories on the GRB prompt emission and the afterglow.In Chapter 2,we discuss the possible physical processes that launch the relativistic jets of GRBs,including the Blandford-Znajek mechanism and the neutrino-driven-outflow mechanism.We propose a numerical method to cal-culate the dynamics of the system consisting of a forward shock and a reverse shock in Chapter 3.Then we use this method to calculate multi-wavelength afterglows from d-ifferent scenarios.In general,our results disfavor the density-jump origin for observed optical bumps.Two groups of afterglows are well interpreted by the delayed energy injection model and the ultrarelativistic electron-positron-pair wind model respective-ly.By relating the diverse features of afterglows to the central engines of GRBs,we find that the steep optical re-brightenings would be caused by the fall-back accretion of black holes,while the shallow optical re-brightenings are the consequence of the injection of the electron-positron-pair wind from the central magnetar.In Chapter 4,we perform a series of axisymmetric 2.5-dimensional simulations to study the propagation of relativistic,hydrodynamic,intermittent jets through the envelope of a GRB progenitor star.A realistic rapidly rotating star is incorporated as the background of jet propagation,and the star is allowed to collapse due to the gravity of the central black hole.For a jet pulse of duration T?1s,the reverse shock in the jet head crosses each pulse before the jet penetrates through the stellar envelope.As a result,after the breakout of the first group of pulses at the breakout time,several subsequent pulses vanish before penetrating the star,causing a quiescent gap.Our results may interpret the existence of a weak precursor in some long GRBs.In Chapter 5,we argue that the collision between neutron stars and asteroids would produce FRBs.This model is consistent with new observations.In Chapter 6,we discuss the gravitational wave signal from a strange star-strange planet binary.Our calculations indicate that strange planets with m? 10-5M? can result in gravi-tational wave outbursts detectable by the future Einstein Telescope up to a horizon of 3 Mpc.These events comprise a new kind of gravitational wave sources,which,if de-tected,will be strong evidence supporting the strange quark matter hypothesis.In the last chapter,we give a summary of the thesis,and also discuss some potential studies that could be done in the future.