伽玛暴前兆辐射和主暴时变特性的统计研究

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	伽玛暴前兆辐射和主暴时变特性的统计研究
其他题名	An Investigation of Temporal Properties of GRB Precursors and Main Bursts
	李联德
学位类型	硕士
导师	毛基荣
	2022-07-01
学位授予单位	中国科学院大学
学位授予地点	北京
培养单位	中国科学院云南天文台
学位专业	天体物理
关键词	伽玛射线暴辐射机制光变曲线
摘要	伽玛射线暴(Gamma-ray burst，简称伽玛暴)是来自宇宙空间的伽玛射线在短时间内突然增强的现象，是宇宙中恒星尺度上最剧烈的爆发事件。一个伽玛暴的光变曲线通常包含多个辐射事件，这些辐射事件被宁静时间隔开。在所有辐射事件中，其中一个辐射事件的峰值强度最大，这个辐射事件通常称为主暴。有时在主暴出现之前会探测到峰值强度较弱的辐射事件，我们称之为前兆辐射。第一个确认的前兆辐射事件于1990年由Ginga卫星发现，对应的伽玛暴为GRB 900126，这个前兆辐射的光谱可以用黑体谱拟合。自此，许多空间望远镜都探测到了前兆辐射。前兆辐射主要具有以下观测特征：(1)前兆辐射与主暴之间的宁静时间通常呈现出正态分布，典型的宁静时间是几十秒，其中也有一些伽玛暴的宁静时间长达几百秒；(2)宁静时间与主暴的持续时间相当；(3)主暴的持续时间总体上比前兆辐射的持续时间长；(4)除个别前兆辐射的光谱为黑体谱外，大多数的前兆辐射的光谱和主暴一样都是非热谱；(5)前兆辐射的光谱没有表现出比主暴更硬或更软的趋势。关于前兆辐射的理论模型主要有火球前兆模型、前身星模型、两步模型、相对论性强星风模型、推进模型。另外，也有一些研究人员专门对短暴前兆辐射的起源提出了理论解释，认为短暴的前兆辐射是由双星并合前的相关物理过程产生的，如中子星磁层相互作用模型、潮汐撕裂模型。之前关于前兆辐射与主暴是否具有相同物理起源的研究主要集中在分析两者的光谱特性，随着观测数据的增加，可以通过分析前兆辐射和主暴的时变特性来研究前兆辐射的起源。本文从Swift-BAT第三期星表中找到了52个伽玛暴具有前兆辐射，用Norris函数拟合了每一个前兆辐射和主暴的光变，并系统分析了前兆辐射和主暴的时变特性，得到的主要结果为：(1)K-S检验表明，前兆辐射和主暴的时变特性没有明显差别；(2)在大多数情况下，前兆辐射和主暴之间的宁静时间在暴源参考系下的范围为10-100 s，平均值为14.6 s，标准差为23.9 s，其中也有少数伽玛暴的宁静时间在暴源参考系下大于100 s；(3)前兆辐射的总光子数和主暴的总光子数之间存在相关性，可以表示为log Cp ~ 0.66log Cm，其中，额外误差σ = 0.41；(4)由总光子数估计的前兆辐射所释放的能量和宁静时间之间没有明显的相关性。此外，前兆辐射和主暴遵循相同的τp-ω关系，其中τp和ω分别表示脉冲峰值时间和脉冲宽度，这表明前兆辐射和主暴具有相同的物理起源。然而，前兆辐射和主暴的脉冲参数之间不存在明显的相关性。一些理论模型，如两步模型和前身星模型，有助于解释伽玛暴的前兆辐射。如果伽玛暴的喷流被磁化，那么推进模型也可以解释前兆辐射的一些特性。
其他摘要	Gamma-ray bursts (GRBs) are short and intense flashes of gamma-ray observed from the sky in random directions, which are the most violent explosion events in the universe. GRB lightcurve often shows multiple emission pulses. These pulses are separated by some quiescent intervals. One of the pulses has the largest peak intensity among all the pluses, and this pulse is usually called as the main burst. Sometimes a weaker pulse before the main burst is shown, and this weaker pulse is identified as the precursor. GRB 900126, as the first GRB with a clear precursor, was detected by Ginga satellite in 1990, and the precursor spectrum can be fitted by a blackbody spectrum. Since then, many space telescopes have detected GRB precursors.GRB precursors mainly have the following observation properties: (1) the quiescent time between the precursor and the main burst usually has a normal distribution. The typical quiescent time is tens of seconds, which can be up to hundreds of seconds; (2) the quiescent time is comparable to the duration of the main burst; (3) the duration of the main burst is generally longer than that of the precursor; (4) except that the individual precursors are characterized by thermal emission, most precursors are favorable to the nonthermal emission; (5) the spectral of GRB precursors shows no tendency to be harder or softer than that of the main bursts. The theoretical models of GRB precursors mainly include fireball precursor model, progenitor precursor model, two stage model, relativistic strongly magnetized winds model and propeller model. In addition, some literatures have put forward theoretical explanations for the origin of short GRB precursor, and believe that the short GRB precursors are generated by relevant physical processes before the merger of binary stars, such as interaction of neutron star magnetospheres model and tidal crust cracking model.Previous studies on whether the precursor and the main burst have the same physical origin mainly focused on analyzing the spectra properties. As the observational data increases, we can investigate the physical origin of GRB precursors by analyzing the temporal properties of the precursor and the main burst. We select 52 long GRBs having the precursor activity in the third Swift-BAT catalog. Each episode shown in both the precursors and the main bursts is fitted by the Norris function. We systematically analyze the temporal properties for both the precursors and the main bursts. We summarize the main findings obtained in our GRB-precursor sample below. (1) It is examined by the K-S test that the temporal profile of the main burst and that of the precursor have no major difference. (2) In most cases, the quiescent time in the rest frame between the precursor and the main burst has a range of 10-100 s. The mean value is 14.6 s with the deviation of 23.9 s. A few GRBs with the precursor activity have the quiescent time longer than 100 s. (3) There is a correlation between the photon count of the precursor and the photon count of the main burst. It is presented by log Cp ~ 0.66log Cm with the extrinsic scatter of 0.41. (4) There is no correlation between the energy release of the precursor estimated by the total number of photon counts and the quiescent time.We find that both the precursor and the main burst follow the same τp-ω relation, where τp and ω represent pulse peak time and pulse width respectively. It is suggested that the precursor and the main burst may have the same physical origin. However, we do not find any correlation in the FRED-fitting parameters between the precursor and the main burst. Some theoretical models, such as the two stage model and the progenitor precursor model, may be helpful to explain the GRB precursors. If GRB jet is magnetized, the propeller model is also a choice to explain the precursor features.
学科领域	天文学 ; 天体物理学 ; 高能天体物理学 ; 星系与宇宙学
学科门类	理学 ; 理学::天文学
页数	0
语种	中文
文献类型	学位论文
条目标识符	http://ir.ynao.ac.cn/handle/114a53/25775
专题	星系类星体研究组
推荐引用方式 GB/T 7714	李联德. 伽玛暴前兆辐射和主暴时变特性的统计研究[D]. 北京. 中国科学院大学,2022.

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