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Gamma射线暴的光变曲线和谱硬度比
Alternative TitleThe Light Curves and the Spectral Harness Ratios of Gamma-Ray Bursts
梁恩维
Subtype博士
Thesis Advisor覃一平
2002
Degree Grantor中国科学院研究生院(云南天文台)
Place of Conferral北京
Degree Discipline天体物理
KeywordGamma 射线暴 观测 光变曲线 脉冲 能谱 潜硬度比 统计
Abstract本文综述gamma射线暴的观测和理论研究现状,详细介绍本人在攻读博士学位期间在gamma射线暴的光变曲线和谱硬度比统计特征方面的研究工作。我们运用小波分析技术和新的脉冲识别算法研究了BATsE观测的2044个暴光变曲线中脉冲的统计特征:(1)发现脉冲宽度、强度、Rise-to-Deeay等参量分布很广,不同暴间脉冲特征差异很大;(2)给出了新的脉冲辐射率曲线,并研究其形态参量随能量的变化规律,发现脉冲宽度、上升时标、下降时标随能量增加以幂率规律递减,而形状因子随能量增加以指数函数规律递增;而且发现脉冲宽度随能量的变化规律跟同步辐射理论结果符合;(3)通过光子流量归一、持续时间归一的方法研究不同能道脉冲的特征结构,发现脉冲特征结构跟能量无关,表明不同能道脉冲辐射的相对过程是一样的;(4)研究了两类暴的平均脉冲辐射曲线及其特征结构的差异,发现长暴的脉冲辐射率曲线宽度要比短暴的大,说明短暴中产生脉冲辐射的相对论电子冷却时标比长暴中的短,这意味着两类暴的辐射区域有本质的区别,短暴辐射的光子能量比长暴中的高,这跟持续时间与谱硬度比的反相关性是吻合的;然而,两类暴的脉冲的特征时间结构差异不大,说明两者的火球演化、辐射机制、辐射过程是一致的。我们系统地研究了谱硬度比的统计特征,包括:(1)指出持续时间和谱硬度比的反相关性是由两类暴各自不同的持续时间和硬度比的分布造成的,这个反相关性在两类暴中并不存在:并这个反相关性给出更贴切的解释,即:短暴硬谱、软谱长暴;(2)通过研究谱硬度比跟总流量之间的相关性,发现支持长暴一短暴分类方法的新证据,并且发现在全体暴样本中,脉冲辐射总流量跟谱硬度比不存在相关,但在两类暴中两者存在正相关;(3)通过研究不同谱硬度比的相关性,发现谱的高能段和低能段有很显著的差异,这跟能谱拟合中发现的分段幂率谱的结果是一致的;(4)在研究各个能道辐射流量之间相关性的基础上,定义了描述高端谱行为特征和低端谱行为特征的谱硬度比,研究了谱指数跟这些谱硬度比的相关性,发现折断能(峰值能量)跟高能端谱硬度比和低能端谱硬度比都相关,高端谱指数跟高端谱硬度比相关,协但跟低端谱指数无关,低端谱指数跟低端谱硬度比不相关;(5)引入了时间分辨谱硬度比的定义,研究了其演化特征,发现平均谱硬度比随时间以"由硬到软"规律演化,77%暴谱硬度比以"由硬到软"规律演化,而23%暴以"由软到硬"规律演化,而且不同持续时间、不同强度的暴的谱硬度比随时间演化特征有较大差异。
Other AbstractWe summarize the observational and theoretical studies of gamma-ray bursts (GRBs), and present the results of our studies on the statistical properties of the light curves and the spectral hardness ratios of GRBs. We study the statistical properties of the pulses in GRB temporal profiles using 2044 burst data detected by BATSE on board CGRO with a wavelet package analysis technique and a developed pulse-finding algorithm. Our results are as following:(l)We presented the distributions of the width, intensity, and ratios of rise-to-decay of pulses, and found these properties of pulses are varied from burst to burst. (2)We presented the average curves of emissivity (ACEs) of pulses by a beginning-aligned method, and analyzed the relations between their shape parameters and energy. We found that the width, the rising time scale, and the decaying time scale decay with energy with a power law. However, their peakness and ratio of rise-to-decay are exponential increase with energy. The relation between pulse width and energy are consistent with the result of synchrotron emission. (3)We studied the characteristic structures of pulses in different channels by a duration-and-fiuence-normalized method, and found that the characteristic structures of pulses in four channels are the sam (4)We investigated the difference of the ACEs of the long and short GRBs. The results show that the ACEs of pulses in two groups have a significant difference. The ACEs of the pulses in short group are shorter and narrower than that in long group, suggesting that the cooling tirnescale of the relativistic electrons in short bursts are shorter than that in long bursts. The short bursts may emit more higher energy photons than that in the long bursts. The result is quite consistent with the well-known anti-correlation between hardness ratio (HR) and burst duration. The sources of them likely have intrinsic difference. Compared to the ACEs, the normalized ACEs of the pulses in the two groups seem to be similar. This suggests that the emission mechanisms are the same in the two groups of bursts. We systematically studied statistical properties of the HR of GRBs. (l)We further confirmed the anti-correlation between HR and duration and pointed out that it is caused by the different distributions of the two quantities in the two groups. This anti-correlation does not exist in each groups. We also proposed a more accurate interpretation of this anti-correlation, i.e., the shorter bursts tend to be harder, and the softer bursts tend to be longer. (2)We studied correlation between the total fluence and HR. We found a new evidence that is consistent with the classification of the long and short GRBs, and found that the total fluence is not correlated with HR in the entire set, but it is in each subsets. (3)We investigated the correlations between various HRs and reached conclusions that the slope of the higher part of the spectrum of most GRBs is independent of that of the lower part; emissions at higher energy bands from the bursts of both short- and long-duration classes are significantly different for different sources, but radiations at lower energy bands are similar; the spectra of the short-duration bursts is harder than that of the long-duration bursts. (4)We presented defines of HRs of high energy band and low energy bands, and presented the result of correlation studies, examining the association between the hardness ratios and the spectral fitting parameters. We found that the break energy(or peak energy) are correlated with the HRs in high and low energy bands. The spectral index of high energy band only correlated with the HRs of high energy band. The spectral index of low energy band is not correlated with any hardness ratios. (5)We also presented a define of time-resolved HR to study the evolution of HR during a burst. The results show that the average HR monotonously decreases with time. There are 77% of GRBs showing "hard-to-soft" evolutional feature, the rest showing "soft-to-hard" evolutional feature. We also found that the HRs in different groups of GRBs with different duration and peak flux show different evolutional characteristics.
Subject Area天文学
Pages133
Language中文
Document Type学位论文
Identifierhttp://ir.ynao.ac.cn/handle/114a53/7149
Collection星系研究组
Recommended Citation
GB/T 7714
梁恩维. Gamma射线暴的光变曲线和谱硬度比[D]. 北京. 中国科学院研究生院(云南天文台),2002.
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