| Gamma-ray burst (GRB) is the most violent event in the deep universe. There are two emission stages. One is the prompt emission. After the prompt emission, we see its afterglow. The light curve of the prompt emission is very complex. It often consists of one or more pulse. The spectrum of the prompt emission is usually described by Band function. The light curve of the afterglow is relatively simple, commonly described by some power laws. For explaining the observational signature of the GRB, the internal shock model for the prompt emission and the standard model for the afterglow are proposed. With the detection going on, more and more fresh observational signatures are observed. And different models are put forward. The emis-sion mechanism for GRB is mainly synchrotron emission. As we know synchrotron emission is highly polarized. With the development of the polarimetry, now there are some facilities in commission, e.g. LT, VLT, and INTEGRAL. Polarization observations can be used to dis-cuss the magnetic field configuration and jet structure of the source. This thesis focuses on the polarization of the GRB and other Astrophysical process.In chapter 1, we present the detailed review on the observations and theories of GRB and on the observations and theories of the polarization. We introduce the main models for the prompt emission, i.e. the internal shock model, the ICMART model and the dissipative pho-tosphere model. Then we present the models for the afterglow, i.e. the standard model, the forward-reverse shock model for the optical flash, the generic dynamic model, other dynami-cal model, energy injection model and the synchrotron-self Compton model. The theoretical models for polarization is discussed in Section 1.3. The synchrotron emission in random mag-netic field model, the synchrotron emission in the ordered magnetic field model, the inverse Compton scattering model and the structured ejecta model are included. Finally, we present the polarization observations in other astrophysical processes.From Chapter 2 to Chapter 5, we introduce our works on the polarization evolution of the GRB and other astrophysical sources. In Chapter 2, we discuss the polarization evolution of the early optical afterglow of the GRB. Based on the generic dynamic model, we deduced a dynamics that include the contributions of the reverse shock. Our dynamics can also evolve from early relativistic phase to late non-relativistic phase. Then, we calculate the polarization evolution of the early afterglow, under two ordered magnetic field configurations. We found that if position angle changes gradually or if the position angle changes abruptly by 90° with non-zero polarization degree, the magnetic field configuration in the reverse shock region may be aligned and the corresponding central engine could be a magnetar. If the position angle changes abruptly by 90° with zero polarization degree, the magnetic field configuration in the reverse shock region might be toroidal and the corresponding central engine might be a black hole. We finally use our polarization model to fit the observational data of GRB 120308A. And we found that both ordered magnetic field configurations can fit the data equally well. Therefore, for this burst, we can not tell what kind central engine it is.In Chapter 3, we use the polarization evolution during the shallow decay phase to test the models. One half of the GRBs which have X-ray afterglow detection have the shallow decay phase. Two popular model can explain this observational signature, i.e. the relativistic wind bubble (RWB) model and structured ejecta model. For the RWB model, the relative central engine is a millisecond pulsar. The late time energy injection is Poynting flux and the magnetic field in this outflow is very likely to be aligned. For the structured ejecta model, the relative central engine is a rotating black hole. The main injected energy is dynamical energy and whether there is an ordered magnetic field in the outflow remains unknown. There is often one energy band having the shallow decay phase for the structured ejecta model. But in the RWB model, the shallow decay phase will appear in both optical and X-ray band. From our results, the polarization degree evolution of the RWB model have a bump which will not appear in the structured ejecta model. The maximum value of the polarization degree will be reached at the end of the shallow decay phase for the RWB model. Therefore, with the polarization degree observations, we can distinguish different model for shallow decay phase.In Chapter 4, the polarization evolutions in the early optical afterglow of the GRBs with the two-component jet model is discussed. The black hole and accretion disk system is one kind of the GRB central engine. Because of the accretion, there will be jets around the black hole. The inner narrow one is generated by the Blandford-Znajek mechanism. The outer wider one is drived by the disk. Therefore, it is very likely that a ordered, large-scale toroidal magnetic field will be in the narrow jet. Under the parameters we take, the early light curve is dominated by the narrow jet. For appropriate observational angles, there will be bump in the polarization degree evolutions.In Chapter 5, the polarization properties of the precessing jet is calculated. The black hole and the accretion disk system is commonly thought to be the central engine of many astrophys- ical sources. If the spin of the black hole and the angular momentum of the disk is not aligned, the jet which is powered by the black hole or the disk will precess. Our preliminary results show that the temporal and polarization properties of the emission from the precessing jet exhibit a periodic evolution.Finally, in Chapter 6, we give our summary. We summarize the observational properties of the GRB prompt emission and afterglow. From our works, we can distinguish the central engine and tell the composition of jet through polarization observation. What can we learn from the polarization observations needs more explorations. |
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