Gamma-Ray Bursts And Afterglows: A Multi-Wavelength Study In The Swift Era

Gamma-ray bursts(GRBs) are short and intense pulses of gamma-rays observed from the sky in arbitrary directions.Since the discovery in 1967 by the Vela satellite,GRBs have always been one of the most mysterious phenomena in astrophysics.The discovery of afterglows in 1997 made it possible to measure GRBs' redshifts and find their host galaxies,and also favored the so-called standard model,i.e.,the prompt emission arises from the internal dissipation(e.g.,internal shocks or magnetic reconnection) of GRB ejecta.while the afterglow emission is produced by the external shock due to the interaction between the GRB ejecta and circum-burst media.In order to observe earlier multi-wavelength emissions,NASA launched the Swift satellite on 2004 November 20,which can localize GRBs within about 10 seconds.In the past four years,Swift has discovered the afterglows and host galaxies of short-duration GRBs,uncovered the detailed features of the early afterglow light curves,detected high redshift GRBs,and performed multi-wavelength observations for the prompt emission of some GRBs.A brief review on the recent progress in observations and theories in the Swift era will be given in Chapter 1.This paper will focus on the features of the afterglows and multi-wavelength prompt emission.In Chapter 2 and 3,we will try to explain the shallow decay phase of X-ray afterglows and X-ray fares,both of which are unaccountable in the standard afterglow model.(1) It is widely accepted that the shallow decay phase indicates a continuous energy injection to the GRB blastwave,and this energy could be released from the central object after the burst.Based on the knowledge of the evolution of a Poynting outflow,we argue that the injecting flow interacting with the GRB blastwave is an ultra-relativistic kinetic-energy flow(i.e.,wind) rather than pure electromagnetic waves.Therefore,a relativistic wind bubble(RWB) including a pair of shocks will occur.Our numerical calculations and two example fits show that the emission from a RWB can account for the X-ray shallow decay phase well.(2) For the X-ray flares that are attributed to some intermediate late activities of the central object,we analyze the detailed dynamics of late internal shocks that produce the flare emission directly.Comparing the lower observational luminosity limit and profiles of flare light curves with the theoretical results,we find some constraints on the properties of the pre-collision shells that are directly determined by the central object.In Chapter 4,we investigate high-energy afterglow emission during the shallow decay phase in two models,i.e.,RWB model and the model where a wide radially spread of Lorentz factor is in GRB ejecta(RSE).We provide a unified description for the dynamics of the two models and calculate the high-energy emission by considering the inverse-Compton(IC) scattering between the electrons and low-energy synchrotron photons.Our results show that,in both models,there is a plateau(even a hump) in high-energy light curves during the shallow decay phase.In particular, the high-energy flux predicted by the RWB model is about one order of magnitude higher than that by the RSE model.These observational signatures would be used to discriminate between these two different energy-injection models.In addition,a similar study on high-energy emission due to the IC mechanism in the late internal shock model shows that the high-energy flares accompanying with the relatively brighter X-ray flares could be detected by the Fermi LAT.In Chapter 5,neutrino emission for early afterglows of GRB 060218-like GRBs is concerne where neutrinos are expected to be produced from photon-pion interactions in a GRB blast wave that propagates into a dense wind.Relativistic protons for the interactions are accelerated by an external shock,while target photons are basically provided by the incoming thermal emission from the shock breakout and its inverse-Compton scattered component.Because of a high estimated event rate of low-luminosity GRBs,we would have more opportunities to detect afterglow neutrinos from a single nearby GRB event of this type by IceCube.In Chapter 6,We show that the synchrotron emission produced by internal forward and reverse shocks respectively could peak at two quite different energy bands if the Lorentz factors of these two types of shocks are significantly different with each other(e.g.,one shock is relativistic and the other is Newtonian).We then investigate whether this scenario is applicable to the case of GRB 080319B and find that a bimodal distribution of the shell Lorentz factors,peaking at about 400 and 100,000,is required.In addition,this scenario predicts an accompanying inverse-Compton (IC) GeV emission with a luminosity comparable to(not much higher than) that of the synchrotron MeV emission,which can be tested with future Fermi observations.In Chapter 7,we carefully investigate long-term spin and thermal evolutions of isolated neutron stars and neutron stars in low-mass X-ray binaries(LMXBs),by considering the effects of reheating due to r-mode dissipation,magnetic braking,and accretion are taken into account.The role of the r-mode induced differential rotation on the evolution of neutron stars are investigated.Finally,we give some discussions and an outlook in ChaDter 8.