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伽玛射线暴单脉冲光变曲线和能谱的研究
其他题名The Studies of Single Pulse Light Curves and Energy Spectra of Gamma-ray Bursts
彭朝阳
学位类型博士
导师张力 ; 覃一平
2007-06-12
学位授予单位中国科学院研究生院(云南天文台)
学位授予地点北京
学位专业天体物理
关键词伽玛暴 多普勒效应 光变曲线 脉冲宽度 谱延迟 能谱
摘要伽玛射线暴(简称伽玛暴)是一种来自宇宙空间的伽玛射线在短时间内突然增强的现象,是目前观测到的最剧烈的爆发现象。伽玛暴在1967年首次被探测以来,就一直是极具吸引力的谜。虽然在短短的三十多年来,人们对伽玛暴的研究取得了一些进展,但还有很多问题没有被认识清楚。本论文首先对伽玛暴的研究概况做一综述,然后详细介绍了本人在博士期间做的几个研究工作。 第一章到第四章为综述部分。第一章比较详细地介绍了伽玛暴的主要观测仪器;第二章简要介绍了伽玛暴在四个观测阶段的基本观测和统计特征;第三章介绍了伽玛暴的主要理论研究成果;第四章主要介绍了与伽玛暴有关的两个重要问题。 第五章到第八章是工作部分,主要介绍本人在伽玛暴的光变曲线和能谱方面的几个研究工作。其中第五章主要介绍我们工作的一个主要模型Qin多普勒模型。 第六章是基于第五章介绍的Qin多普勒模型及其它的应用所做的一个工作。在伽玛暴脉冲宽度和能量之间存在幂律关系,我们首先简要列出了前人研究的结果。最近,在假设以相对论速度膨胀的火球表面的多普勒效应很重要的基础上,Qin等研究表明:在大多数情况下,上述的幂律关系存在于特定的能量范围内,而且在同一个暴的相同的能量范围内,上升宽度和下降宽度的比值和能量之间存在一个趋势相反的幂律关系。我们用两个包含很好的脉冲的伽玛暴样本检验了这个关系。在BATSE能量范围内,我们两个样本中的大多数暴(大约65%)的脉冲宽度和能量之间存在幂律反相关,而在脉冲宽度比值和能量之间存在幂律相关关系。这些表明,这大多数暴很可能产生于那些发生在相对论膨胀火球表面的辐射。而且我们发现,两个样本的宽度比的上限不会超过0.9, 这和以前多普勒模型预测的一致。根据两个幂律指数位于不同的平面区域,我们把这些暴分成三个不同的子类,我们怀疑这些位于不同平面区域的暴产生于不同的辐射机制。 第七章探讨伽玛暴谱延迟和伽玛暴脉冲宽度之间的关系。我们主要研究了相对谱延迟和相对脉冲宽度的关系。伽玛暴谱延迟现象很普遍,但是这个问题的明确答案还没有给出。我们运用一个包含82个伽玛暴脉冲的样本研究发现:伽玛暴谱延迟和脉冲宽度之间存在一个较强的相关关系,而相对谱延迟和相对脉冲宽度之间却没有相关性。我们怀疑谱延迟和脉冲宽度之间的相关性是由于伽玛暴的洛仑兹因子引起的。我们对相对量的分析表明,内禀的谱延迟可能反映脉冲的其它方面,而既不是和激波动力学时间有关也不是和由于曲率效应引起的时间延迟有关。 第八章研究了伽玛暴单脉冲谱的演化规律。我们仔细研究了Kaneko等最新的BATSE谱样本,发现有一类脉冲的峰值能量Epeak 遵循软-硬-软的演化规律,我们选取了82个分离得较好的这类伽玛暴脉冲研究了它们的Epeak演化的统计特征。当统一研究这些脉冲时,我们发现:a) 它们的Epeak演化确实遵循软-硬-软的规律; b) 软到硬的前段相对硬到软的后段的时间要短; c)后段最软的谱要比前段最软的谱要软;d) 前段的谱比100 keV要硬,而后段的谱比50 keV的谱要硬,但有的比100 keV要软。这和目前伽玛暴产生的普遍观点一致。当把两类脉冲按脉冲形态分成I类(上升宽度小于下降宽度)和II类(上升宽度大于下降宽度)两类时,我们发现只有I类和我们的普遍理论一致。而II类除了前段比后段要长外,其它演化特征都相同。我们怀疑这两类脉冲的产生机制可能和内激波的不同过程有关。I类可能产生于前激波,而II类可能来自于反激波,这值得进一步探索。 第九章列举了一些与伽玛暴有关的问题和展望。
其他摘要Gamma-ray burst (GRB) is a flash from space, with most energy in gamma-ray and with short duration. It is the most drastic burst since we observed. GRBs are first detected in 1967, and have been regarded as a great mystery since then.Although much progress has been made only within 30 years, many problems still puzzle us. In this thesis, I first present a brief review on both theories and observations of GRB, and then introduce some detailed works finished by my collaborators and me. Chapters 1-4 are the review of GRB. In Chapter 1, we introduce in detail some main instruments of GRB; We summarize the characteristic of GRB in four different phases in Chapter 2; In Chapter 3, we introduce the results of GRB theory; In Chapter 4, two issues associated with GRB are presented. Chapters 5-8 are my works on GRB single pulse light curves and energy spectra. In Chapter 5, we introduce Qin Doppler model, which is base of my first work. Chapter 6 is my work based on Qin model. A power law relationship between the pulse width and energy of GRBs was found by many authors. In this Chapter, we first introduce some results related to this work. Recently, under the assumption that the Doppler effect of the relativistically expanding fireball surface is important, Qin et al. showed that in most cases the mentioned power law relationship would exist in a certain energy range and within a similar range a power law relationship of an opposite trend between the ratio of the rising width to the decaying width and energy would be expectable for the same burst.We check this prediction with two GRB samples which contain well identified pulses. A power law anti-correlation between the full pulse width and energy and a power law correlation between the pulse width ratio and energy are seen in the light curves of the majority (around 65%) of bursts of the two samples within the energy range of BATSE, suggesting that these bursts are likely to arise from the emission associated with the shocks occurred on a relativistically expanding fireball surface. In addition, we find that the upper limits of the width ratio for the two samples do not exceed 0.9, in agrement with what predicted previously by the Doppler model. According to the distinct values of two power law indices, we divide the bursts into three subsets which are located in different areas of the two indices plane. We suspect that different locations of two indices might correspond to different mechanisms. In Chapter 7, we investigate the relationship between the spectral lag and the pulse width. We focus on the relationships between relative spectral lags and relative widths of GRBs. The phenomenon of GRB spectral lags is very common. But the definite answer to this issue has not yet been given. Employing a sample consisting of 82 GRB pulses we find that the spectral lags are correlated with the pulse widths. However, there have no correlation between the relative spectral lags and the relative pulse widths. We suspect that the correlations between spectral lags and pulse widths might be caused by the Lorentz factor of the GRBs concerned. Our analysis on the relative quantities suggests that the intrinsic spectral lag might reflect other aspect of pulses than the aspect associated with the dynamical time of shocks or that associated with the time delay owing to the curvature effect. In Chapter 8, we study the spectral evolution of GRB single pulse. We investigate carefully the BATSE spectral sample analyzed by Kaneko et al. and find that there are some especial single pulses, whose spectral peak energy, Epeak, follow the evolution of soft-hard-soft. Therefore we select 82 well identi¯ed pulses whose Epeak follow soft-hard-soft evolution and study their evolution characteris- tics of Epeak. When we analyze these pulses as a whole, we find that: a) the Epeak follow indeed soft-hard-soft evolution; b) the fore phase of soft-hard is shorter than the back phase of hard-soft; c) the softest spectra of back phase are much softer than the softest spectra of fore phase; d) the spectra of fore phase are harder than 100 keV and the back phase are harder than 50 keV but some are softer than 100 keV, which are consistent with current view on the generation of GRBs. When we classify these pulses into type I (the rise widths are less than the decay widths) and type II (the rise widths are larger than the decay widths) according to their profiles, we only find that the fore phase of type II are much longer than the back phase. The other characteristics are consistent. We suspect that the type I and type II might be related to the di®erent process of internal shock. Type I might be result from forward shock, while the type II might be come from reverse shock, which deserve the further investigation. Finally, we present a summary of the open questions and prospects in the current GRB research field in Chapter 9.
学科领域天文学
页数184
语种中文
文献类型学位论文
条目标识符http://ir.ynao.ac.cn/handle/114a53/7164
专题星系研究组
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彭朝阳. 伽玛射线暴单脉冲光变曲线和能谱的研究[D]. 北京. 中国科学院研究生院(云南天文台),2007.
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