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伽玛暴脉冲时变特征及其对能量的依赖
Alternative TitlePulse Temporal Characteristics and Their Energy Dependence of Gamma-Ray Bursts
张富文
Subtype博士
Thesis Advisor白金明 ; 覃一平
2008-06-11
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
Keyword伽玛暴 光变曲线 脉冲 谱延迟 统计
Abstract伽玛暴是人类至今观测到的最强烈的爆发事件。伽玛暴光变曲线非常复杂,往往包含许多叠合的脉冲。这些脉冲是构成伽玛暴光变曲线的基本单元,其时变特征反映着伽玛暴的基本物理过程。本人研究了伽玛暴脉冲的时变特征,并探讨它们对伽玛暴辐射理论模型的限制。本文首先综述了伽玛暴的重要观测和理论研究进展,然后详细介绍了本人的研究工作。 长延迟宽脉冲的伽玛暴普遍是低光度暴,其是否是一个特殊的暴类至今仍是一个谜。它们简单的结构可能反映的是比较简单的物理过程。我们研究了这类暴的时变特征及其跟能量的关联性,其主要结果如下:(1)发现脉冲在高能段变窄并变得更加对称;脉冲峰值时间、宽度、上升时标和下降时标对光子能量都具有显著的幂律依赖关系,但是这些幂律指数在不同暴间的分布很弥散,表明不同的暴脉冲时变特征对能量的依赖行为是不相同的;(2)发现脉冲的峰值时间在低能段移向较晚的时刻,呈现显著的谱延迟;我们计算了三种谱延迟:峰值延迟(τpeak)、互相关函数(CCF)延迟(τCCF)和质心延迟(τcen),并且发现它们之间是相关的,但τcen系统性地比τpeak和τCCF的值要大,而τCCF和τpeak的相关性要比其它两对量之间的相关性强,表明不同的延迟测量可能反映脉冲不同方面的演化特征,τCCF可能主要是由于脉冲峰值的移动导致,而τcen则主要描述脉冲辐射时标的延展;另外,相对于同一个低能段的谱延迟随着对应高能段能量的增加而增加,但到较高的能段时谱延迟对能量的依赖性变弱;(3)GRB 980425和GRB 060218是两个已证认的低红移、低光度暴,我们发现其时变特征跟其它长延迟宽脉冲暴非常相似,表明这两个暴可能与普通的长延迟宽脉冲暴有类似的辐射物理。 伽玛暴的脉冲宽度跟能量之间的依赖关系已经被广泛地研究,并发现其幂律指数约为−0.4。这一关系是否可以延伸到X射线能段的辐射?这是一个令人感兴趣的问题。GRB 060124从X射线到伽玛射线能段的辐射同时被Swift卫星探测到,并且其脉冲形态能在很宽的能段内被识别。以此暴为例,我们研究其X射线到伽玛射线能段辐射的时变特征,发现脉冲在高能段变窄,X射线和伽玛射线都遵循同样的宽度-能量依赖关系,并且脉冲上升宽度与下降宽度的比值不随能量演化,其值与在典型伽玛暴中得到的值是一致的。这些结果表明X射线与伽玛射线辐射的能谱行为是一致的,可能具有同样的物理机制。
Other AbstractGamma-ray bursts (GRBs) are the most luminous events observed so far. Their light curves are complicated with many overlapping pulses. The pulses are the ``building blocks'' of the light curves, which may represent the fundamental physical process of this phenomenon. I investigate the temporal characteristics of the pulses and explore their possible implications to the GRB physics. This thesis summarizes the progress of our understanding the nature of this phenomenon from both observations and theory, and then presents our research work in detail. It is generally suggested that long-lag, wide-pulse GRBs are subluminous. Whether they form a peculiar subclass of GRBs is still a puzzle. Their simple temporal structures might have simpler physics. We study the pulse temporal characteristics and their energy dependence of these bursts. Our main results are as following: (1) We find that the pulses tend to be narrower and more symmetry at higher energies, and the pulse peak time, width, rise time scale and decay time scale are power-law functions of energy, but the distributions of the power-law indices in different bursts have large dispersions. This implies that the energy dependence of the temporal characteristics may not be the same for different bursts. (2) We find that the pulse peaks shift to later times at lower energies, and their light curves show significant spectral lags. We measure the three types of pulse spectral lags: peak lag (\tau_{peak}), cross correlation function (CCF) lag (\tau_{CCF}) and centroid lag (\tau_{cen}), and find that the three quantities are correlated, but \tau_{cen} is systematically larger than both \tau_{peak} and \tau_{CCF}, and \tau_{CCF} and \tau_{peak} are highly correlated, while the other pairs of variables are less well correlated. These indicate that the different types of lag measurements could represent the different aspects of pulse evolution, with \tau_{CCF} representing the shifting of pulse peaks and \tau_{cen} describing the stretching of pulses. In addition, we also find that the pulse spectral lags relative to the same low-energy band increase with the energy of the corresponding high-energy band, but the energy dependence of the lags is shallower at higher energy bands. (3) GRB 980425 and GRB 060218 are two prototypes of low-redshift, low-luminosity GRBs. We find that the temporal characteristics of the two bursts are well consistent with those of other long-lag, wide-pulse GRBs. This suggests that the two bursts may share the similar radiation physics with normal long-lag, wide-pulse GRBs. The relationship between pulse width and energy has been studied extensively, with the power-law index being about -0.4. It is very interesting whether this correlation can be extended to X-ray bands. The prompt emission of GRB 060124 from X-ray to gamma-ray bands are simultaneously observed by Swift, and its pulses can be well identified over a broad energy bands. Take GRB 060124 as an example, we present a detailed analysis on the temporal properties of the two well identified pulses of this burst from X-ray to gamma-ray bands. We find that the pulses are narrower at higher energies, and both X-rays and gamma-rays follow the same width-energy relation for an individual pulse. We also find that the rise-to-decay ratio seems not to evolve with energy and the ratio values are well consistent with that observed in typical GRBs. These results indicate that the X-ray emission is consistent with the spectral behavior of the gamma-ray emission and the emissions in the two energy bands are likely to be originated from the same physical mechanism.
Subject Area天文学
Pages149
Language中文
Document Type学位论文
Identifierhttp://ir.ynao.ac.cn/handle/114a53/7167
Collection星系研究组
Recommended Citation
GB/T 7714
张富文. 伽玛暴脉冲时变特征及其对能量的依赖[D]. 北京. 中国科学院研究生院(云南天文台),2008.
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