Study Of GRB X-RAY Flares:Lightcurves And Spectral Evolution

Bright X-ray flares are observed in about50%Swift Gamma-Ray bursts (GRBs). Usually it is believed that they are produced from internal shock by restarting the central engine. So X-ray flare is a good probe for indicating the central engine activity. This thesis briefly reviews the observational and theoretical progress of GRBs, then we mainly focuse on the statistical results of X-ray flare lightcurve behavior and spectral evolution and derive the Lorentz factor of X-ray flare according to curvature effect.We select60bright X-ray flares and perform time-resolved spectral analysis. Strong spectral evolution is found.86percent of flares show hard-to-soft evolution.4percent of flares show the opposite pattern and the rest10percent are intensity tracking. The evolution intensity involves with the peak luminosity and doesn’t involve with the time of flare occurring and how long they last. The more luminous the flares, the stronger the spectral evolution. Different flares in a burst may show different evolution pattern.Analyzing the lightcurves of354X-ray flares, we find that they are asymmetry with tr/td=0.4, which is similar to the prompt emission pulses. The peak luminosity and isotropic energy of X-ray flares cluster around1050.2±0.9erg/s and1051.4±0.64erg, respectively, which are1or2orders of magnitude lower than prompt emission. There is an anti-relation between peak luminosity and peak time. These imply that the later flares are dimmer and wider than the early one. If we define the burst time as the peak time of the last X-ray flare, the central engine activity time will fall in [100,1000]s, even more reach to the106s, which is longer than the previous T90. If we treat the flare zero point at its peak time, we fit the decaying wing of X-ray flares based on the curvature effect and then work out the Lorentz factor. The12Lorentz factors in our sample are from a few to twenty, which is smaller than the prompt emission. Combined the smaller peak luminosity and flux of later X-ray flares, If the X-ray flares and prompt emission both are produced from central engine, we consider that the central engine activity goes weakly.