伽玛暴微光变特征时标研究  

Study on the characteristic timescales of micro-variability in Gamma-ray burst lightcurves

作　　者：吴汉成[1] 吕连忠[1] 邓家干[1] 

机构地区：[1]广西大学物理科学与工程技术学院,广西南宁530004

出　　处：《广西大学学报（自然科学版）》2011年第6期1048-1059,共12页Journal of Guangxi University（Natural Science Edition）

基　　金：国家自然科学基金资助项目(10847003);广西自然科学基金资助项目(2010GXNSFC013011)

摘　　要：伽玛暴光变曲线一般由若干个脉冲组成的"大轮廓"叠加着一些微光变组成的,大部分伽玛暴光变曲线没有呈现周期性,而这些微光变成分可能携带重要的辐射区性质。采用平滑滤波器把伽玛暴光变曲线中的"大轮廓"成分和微光变成分分离,然后采用"最大熵"功率谱密度估算法计算微光变信号的功率谱密度,并分析其周期特征时标。文中分析了Swift/BAT所探测的爆发持续时间大于20 s、采样间隔为1s的伽玛暴,发现有17个伽玛暴的微光变信号的功率谱密度函数曲线呈现显著的"峰"结构,表明这些微光变信号具有周期特征光变时标,这些时标一般约为4～8 s。如果"大轮廓"的脉冲信号和微光变信号是两个本质不同的辐射成分,根据火球模拟可计算微光变信号的辐射区尺度应该在1.5×1013～1.5×1015cm,比内激波辐射区尺度略大,在这一区域内有可能微光变信号受到能量较大的伽玛射线的调制而叠加到"大轮廓"光变信号中,从而形成复杂多样的伽玛暴光变曲线。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 suspected 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 lightcurve samples are binned with 1 s time interval and have a duration more than 20 s 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 s.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 ~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.

关 键 词：伽玛暴 功率谱密度 微光变特征时标 周期 光变曲线 

分 类 号：P172.3[天文地球—天文学]