Cosmic Evolution Of Long GRBs Luminosity And Anlysis Of GRBs Multi-wavelength Afterglows

Gamma-ray bursts (GRBs) are the most luminous events in the universe, happening at cosmological distance. A large number of red-shift known GRBs and their afterglows have been detected with continuous efforts in observation, especailly since the swift satellite was launched, and pushing GRBs theories study forward. My researches are focused on the cosmological evolution of luminosity of long GRBs, and analysis of their multi-wavelength afterglows, to test the standard model and constarin the circumburst environment, using the large swift GRBs sample. This thesis is organized as follows:We first present a detailed review in the Chapter 1 on both boservations and theories of GRBs and their aftergows, and using the GRBs as cosmic probe also including in this Chapter.In Chapter 2, we carry out the reserch on the cosmological evolution of long GRBs. GRBs can be used as cosmological probes, since they are originated from cosmological distance with highest red-shift 9.4 We revisit the cosmological evolution of long GRB luminosity based on a large and uniformed sample of 258 reshift-known GRBs observed within swift 10 operation years.We characterize the intrinsic cosmological evolution of long GRB luminosity asL∞(1+z)k, and measure the k value with the non-parameterized t statistics method. And k= 0.74 + 0.09 is obtained. Furthermore, we derive L ∞ (1+z)0.99+0.60/-0.45 from MC simulations method based on the assption that the long GRB rate follows the star formation rate incorporating with cosmic metallicity history. The consistency of the results from two different physically approaches, may infer that the observed excess of GRB rate at high red-shift can be explained with the cosmic evolution of the GRB luminosity. Our result is roughly consistent with the evolution of initial mass function (IMF) of massive stars, indicating that the luminosity evolution may be due to the mass evolutionof massive stars.In Chapter 3, we analyze the well sample of muti-wavelength optical aftergalows of GRBs, to test the standard model and constrain on the circumburst environment. Recently, Wang Yuan-Zhu found that there are spectra softening in the late time of X-ray afterglows in a small fraction of GRBs based on the systematically analysis of the X-ray afterglows of GRBs. However, the corresponding lightcurve have no difference behaviors, which is chanllege of standard external shock model. We collect a good sample of optical muti-wavelength GRBs afterglow, and then analyze their resolved spectra by jointing X-ray band afterglow, to test the standard external model of afterglow by checking if spectrum are softening in the late optical as in the X-ray band. Furthermore,we also try to study the extinction property of the GRBs’ host galaxy by using the optical afterglow.