Study On The Light Curve And Spectra1 Evolution Of Grb Afterglow Base On Dust Scattering Model And Standard Model

This paper includes four chapters. In the first chapter we introduce the observation properties and basic theories of GRBs. We discuss the two of our works about the afterglows of GRB in chapter 2 and chapter 3. In the last chapter we give our prospects to the future research.In the standard model the X-ray afterglow photons are emitted from the synchrotron radiation of the electrons which are accelerated by the external shock. The spectral index of the emission is determined by the distribution of electrons and should remain the same during the "normal decay phase". However, in the observation of Swift, the hardness ratio of 0.3-1.5KeV/1.5-10KeV bands of some afterglows show significant variations at late time. We study the evolution properties and possible theorical explaination of these afterglows in chapter 2. We systemativally searched the XRT data and found 13 afterglows that have late time spectral evolution, and all of then evolve from hard to soft. We use the dust scattering model proposed by Shao & Dai (2007) to fit our samples, and the result shows the data is consistent with the theory. In addition, the statistics about these bursts show the distribution of their intrinsic hydrogen absorption and the duration of their central engine are not different from the normal ones.The follow up observations of ground telescopes can also help us study the afterglow. In Chapter 3 we introduce the optical observations and spectrum analysis of GRB111228A and GRB140629A, and fit the two bursts’X-ray and R band afterglows with external shock model. The result suggests in both of the afterglows the energy that is transferred to the electrons, ∈e, is very few and is even lower than ∈b. Besides, the dust extinction of optical radiation from GRB111228A’s host galaxy is very weak, and the energy that is injected into the fire ball is very large,～2×1053erg. This implies the central engine of GRB111228A is a black hole, rather than a magnetic star.