The Observations And Theories Of Gamma-ray Bursts And A Magnetic-driving Model For Two-component Jets

Gamma-ray bursts (GRBs) are the brightest explosions in the universe. The intensityof these events may rank second only to that of the “big bang”. After the discovering since1960s, GRBs, with the features of short time scales, high energies, and complexlightcurves and spectra, have always been catching the attentions of the scientists. In half acentury, people have achieved a large amount of noticeable progresses both inobservational and theoretical fields of the GRB research. However, there are still manyproblems, such as the progenitor, the physical composition and structure of the GRB jetfrom the central engine, and so on yet to be resolved. This thesis introduces theobservational progresses and the standard fireball-shockwave model of the GRBs, andproposes a two-component jet model based on the Blandford-Znajek (BZ) andBlandford-Payne (BP) processes.Firstly, I make an introduction of the observational progresses of the GRBs. I reviewthe important discoveries achieved by the main telescopes in each era. The temporal andspectral characters and some empirical correlations of the GRBs are summarized in thispaper.Secondly, I introduce the standard fireball-shockwave model of the GRBs in detail.Specifically, I present the concept of “fireball”, the dynamical evolution and theshockwave emission of the fireball, so as to show a comparably clear outline of thestandard model for the lightcurves and spectra of the prompt emission and afterglowemission of the GRBs.Thirdly, I present a brief introduction of the magnetic driving mechanism, mainly theBZ and BP processes, of the jets from the central engines, and then I make a preliminaryquantitative analysis about the two-component jet model based on BZ and BP processes.In this model, the inner jet, whose ejection matter comes from the inner edge of theaccretion disk, is driven by BZ process of the Kerr black hole, while the outer jet is drivenby BP process happened on the accretion disk. On the the assumption of the large scalemagnetic field configuration and the disk matter accretion rate distribution versus the diskradius, I work out two analytical formulas for the two Lorentz factors of the two-component jet separately, in which the outer (BP) jet’s Lorentz factor is dictated bythe spin of the black hole, the magnetic configuration and the strength of the disk wind,while the inner (BZ) jet’s Lorentz factor is dictated by the spin of the black hole and theamount of mass injection from the inner edge of the accretion disk. This thesis concludesthat the BZ jet’s Lorentz factor is generally larger than that of the BP jet, which meansthat the combination of BZ process and BP process may perform as a natural origin of thespine/sheath structure of jet. In addition, by means of fitting the Lorentz factors of thetwo-component jets from three GRBs and three other AGNs, I find that the accretion disksof these two style of objects of different scale may be very different, specifically, theaccretion disk of AGN has a stong disk wind, while the GRB disk wind appears muchmore weaker.Finally, I discuss several problems to be sovled in GRB study, meanwhile, I point outthe probability of making a further research of the two-component jet from severalaspects.