Effects Of Magnetic Field On Neutrino-dominated Accretion Disk

Gamma-ray bursts (GRBs) are flashes of gamma-ray occurring at cosmological distances, being the most powerful explosions since the Big Bang. GRBs became one of the biggest enigmas in astrophysics since they had been discovered by Vela satellite. Long GRBs root in core collapses of massive, rapidly rotating stars, for some of which, supernovae in spiral galaxies have been observed coincidently; by contrast, Short GRBs may arise from coalescence of neutron stars or black hole binary systems as a result of damping of gravitational radiation, and associatations between Short GRBs and elliptical galaxies have been reported. The standard shock model for GRBs afterglows has been established, and jet in GRBs and their afterglows are widely believed, so that the ture energy of GRB jets around 10⁵¹ergs are commonly accepted.The researches in my thesis focus on the mechanisms of GRBs central engine. Sagnificant progress has been made in two types of mechanisms of GRBs central engine: the baryonic energy and the Poynting flux energy, which is corresponding with the model of neutrino-dominated accretion disk and magnetic accretion disk, respectively. Based on these two kinds of model, we investigate the effects of magnetic field on neutrino-dominated accretion disk, and we also suggest a possible mechanism for X-ray flares which were observed in GRBs afterglows. Thesis is arranged as follows:Firstly, we present a general review in Chapter 1 on the observations of GRBs and their afterglows and detailed review on the GRBs central engine; we also introduce the milestone results in the theory of BH accretion disk.Secondly, the two types of mechanisms of GRBs central engine are discussed in details and we focus our study mainly on the effects of magnetic field on neutrino-dominated accretion disk. By numerical analysing, We find that the electromagnetic processes during the Bursts are much more important than the neutrino processes, and we compare the power of neutrino emission with of BZ process and BP process as well.Thirdly, we introduce the main observational property of X-ray flares in the afterglows of GRBs and some of central engine restarting mechanisms for internal shock model of it as well. And then, we suggest a model in which the magnetic field magnifying and B-bomb occur alternately that might interpret the several flares in one Burst.Finally, we summarize some of the open questions in the current GRBs research field and we also give a review on the polarization of GRBs and their flares emission, which might be the biggest observational difference between the baryonic energy and the Poynting flux energy model.