Studying On The Characteristic Timescales Of Micro-Variability In Gamma-Ray Burst Lightcurves

It is a important way to research on the lightcurve for innate character in GRB,what this thesis discuss is about analysing GRBs lightcurves. Firstly,summarizing some achievement on the observation and theory in GRB Secondly,introducing some experience relationship about analysing GRB lightcurve; Finally, detailly introducing research results on the characteristic timescales of micro-variability in GRB. The thesis employ the maximum entropy method to analyse the spectrum of micro-variability in GRB,and then find out that the micro-variability in GRB exhibite periodicity, this result can provide some scientific clues for further realizing radiative property of GRB.Gamma-ray burst (GRB) lightcurves are generally composed of many pulses with superimposing micro-variability. No periodicity is found for the global lightcurves of most GRBs. It is suspended that the micro-variability may bring some signatures of radiation fields. With a smoothing filter method, A Swift/BAT GRB lightcurve decomposed into two components, micro-variability and pulse profile, then calculate the power spectrum density (PSD) of the micro-variability component with the maximum entropy method to search for possible characteristic timescale of this component. The lightcurves in our sample are binned with 1 seconds time interval and have a duration more than 20s of the bursts. It is found that there are 17 GRBs whose micro-variability PSD curves display a clear peak, which shows that there is a characteristic timescale in the micro-variability. The derived characteristic timescales are about 4～8 seconds. If the pulse profile and the micro-variability are two distinct radiation components, the scale of the micro-variability component should be 1.5×1013 cm～1.5×1015cm, which is more than that of internal shock region as expected from conventional fireball models. In the radiating region,it is probable that the micro-variability is modulated by high-energy gamma ray and superimposed into the pulse profile,then generate the various GRB lightcurves。To notarize that the characteristic timescales of micro-variability origins from gamma ray,but not noise, as well the analytical method adopted in the thesis is tested, and the testing result show that the analytical method is extremely right, and it is undoubted that the characteristic timescales origin from gamma ray.