两类伽马暴X射线余辉光变特性的比较研究

A Comparative Study on the Characteristics of X-ray Afterglow Variation in Two Types of Gamma Bursts

伽马射线暴(Gamma-Ray Bursts,GRBs)的分类是伽马暴领域未解决的热点问题,为了解决这个问题,我们搜集了Swift观测具有缓慢衰减和随后衰减特征的X射线余辉光变曲线样本(180个已知红移的伽马暴),其中长伽马暴(Long Gamma-Ray Bursts,LGRBs)172个,短伽马暴(Short Gamma-Ray Bursts,SGRBs)8个,并选择平滑拐折幂律函数使用马尔可夫链蒙特卡罗(Markov Chain Monte Carlo,MCMC)方法拟合了这些X射线余辉光变曲线,获得光变特性参数后,分析两类暴的光变特性参数α_(1)(缓慢衰减指数)、α_(2)(正常衰减指数)、T_(a)(静止系下缓慢衰减结束时间)的分布是否存在差异以及两类暴是否遵循相同的相关关系。研究发现,(1)两类暴的光变特性参数α_(1),α_(2)和T_(a)的分布范围、中值和平均值都非常接近,没有显示出明显的不同,随后的K-S检验结果进一步表明,这两类暴的光变特性参数分布没有显著差异。(2)我们选取的两类暴均遵循如下相关关系:L_(x)-T_(a),L_(x)-E_(γ,iso),S-T_(90)和E_(γ,iso)-T_(90),而且它们在散点图上不可区分。这些统计结果表明,两类暴的这些光变特性是相似的,因而,我们推断两类伽马暴具有同一物理起源,它们的喷流结构也可能相同。

The classification of gamma-ray bursts(GRBs)is an unsolved hot issue in the field of GRBs.To solve this problem,we collected a samples of X-ray afterglow curves including 180 known redshift GRBs observed by Swift with slow attenuation and subsequent attenuation characteristics,in which there are 172 Long GRBs and 8 Short GRBs.We adopt the smooth broken power law function and the Markov chain Monte Carlo(MCMC)method to fit these X-ray afterglow light curves.After obtaining these light curve characteristic parametersα_(1)(slow decay index),α_(2)(normal attenuation index),and T_(a)(slow attenuation end time in rest frame),we analyze the characteristic parameters of the two types of bursts to check whether there are differences in the distribution of these parameters and whether the two types of storms follow the same correlation.Our research findings are as follows:(1)The distribution range,median value,and average value of the characteristic parameters(α_(1)、α_(2),T_(a))of two types of bursts are very close,and there is no significant difference.The subsequent K-S test further indicates that there is no significant difference in the distribution of parameters between the two types of bursts.(2)The two types of bursts we selected follow the following correlation:L _(x)-T_(a),L_(x)-E_(γ,iso)、S-T_(90)、E_(γ,iso)-T_(90),and they are not distinguishable on a scatter chart.These statistical results indicate that the optical variability characteristics of the two types of bursts are similar.Therefore,we infer that the two types of GRBs have the same physical origin,and their jet structures may also be the same.