Study The Lightcurve And Spectra Of X-Ray Flares In Gamma-Ray Bursts

Gamma-ray bursts (GRBs) are most luminous y-ray explosions in the universe. After the prompt y-ray emission, X-ray flares are usually observed. It is generally believed that X-ray flares are produced in a relativistic fireball which is due to the late activities of GRB central engine. In this thesis, the light curve and spectral evolution behavior of X-ray flares are studied. The investigation on the GRBs with X-ray bump are also presented.The observation and theoretical progress about GRBs are presented in Chapter 1. The research progress of GRBs in the Swift era are presented in Chapter 2.In Chapter 3, out work about the X-ray flares is presented. We present joint fits to the light curve and spectral index evolution behaviors to the steep decay segments of 29 bright X-ray flares with the curvature effect model. Our results show that both the light curves and spectral evolution can be well fit with the model, and the derived characteristic timescales (tc) of this effect are in the range of 35-351 seconds. Using the relation between the peak luminosity and the Lorentz factor derived from the prompt gamma-rays, we estimate the Lorentz factors of the flares and find Γx=10-78. With the derived tc and Γx, we constrain the radiating region of the X-ray flares as Rx～7.1×1014-2.7×1016cm, which are smaller than the radii of the afterglow fireballs at the peak times of the flares.In Chapter 4, we present a systematic analysis about the GRBs with X-ray bump component. For these bumps, it is found that the spectral index does not vary significantly with time and the light curve can be fitted with several power-law functions. In addition, it is found that the properties of X-ray bumps does not present significantly differences with those of optical onset bumps and re-brightening bumps. With the assumption that the X-ray bumps are produced in the deceleration of GRB prompt emission fireball, the Lorentz factor and radiation efficiency of prompt emission fireball are estimated in the range of 20-130 and 0.02%-3.55%, respectively.