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伽玛射线暴单脉冲光变曲线的研究
Alternative TitleInvestigations on the light curve of single pulses in Gamma-Ray Bursts
张志彬
Subtype博士
Thesis Advisor谢光中
2007-01-15
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伽玛射线暴 单脉冲 光变曲线 数据处理方法 观测 统计方法 理论 数值分析方法
Abstract本文首先概述伽玛射线暴(GRBs)及其余辉的观测和理论研究进展,这包括基本观测特征、主要理论模型以及与GRB相关的天体现象,如GRB-SN成协和GRB宇宙学。然后详细介绍作者在攻读博士学位期间所做的与GRB单脉冲光变曲线有关的研究工作。通过分析,我们得到以下几个主要结论: 一,利用Qin理论脉冲模型对KRL经验脉冲模型中的参数给予物理解释: 1)外流的洛伦兹因子(Γ)分别和脉冲的上升时标(tr)、下降时标(td)存在幂律关系,两者幂律指数都约为-2;2)当 (共动脉冲宽度)<2时,观测脉冲的非对称(tr/ td)随 的变宽而增大,这时可以用下降指数d来判定共动脉冲的大体形态;当 >2时,观测脉冲的非对称不再受 影响,则我们不能再由观测脉冲的形状指数判断共动脉冲的大致形态;3)只要取合适的共动脉冲宽度,如在0.1到2之间取值, 我们发现Kocevski样本中起码有一部分GRB脉冲能够用多普勒效应主导下的Qin脉冲模型来描述,即至少存在一部分GRBs可以用火球模型来解释。 二,对长暴脉冲在1、3能道间的相对谱延迟(RSLs)分析得到: RSL是以0.1为中心正态分布的;RSL与FWHM(=tr+td)、非对称、谱指数(α,β)、峰值能量(Ep)、峰值流量(Fp)和峰值计数率(Fm)存在弱的相关,而分别和谱延迟(τ31)、硬度比(HR31)和峰值计数的时间(tm)线性无关;最后,RSL与红移(z)和峰值光度(Lp)存在强线性相关,这使得RSL成为一个很好的红移/光度或距离指示器。 三,通过准确地分析短暴脉冲的谱延迟发现:短暴的谱延迟关于零点呈对称性高斯分布,并且绝大多数(94%)短暴的谱延迟可以忽略不计或在当前精度下不能被测量到;短暴的RSL也是在零附近(μ=0.082)正态分布的;如果假定谱延迟和Γ的幂律关系对短暴也成立,即τ∝±Γ^(-η)。由此可见,不仅大的Γ而且大的指数 或两者共同都能导致短暴具有可以忽略的或不能被测量的谱延迟。 四,通过讨论GRB三个典型时标(动力学、角延展和冷却时标)和观测脉冲轮廓之间的关系,我们发现:1)若忽略电子的辐射冷却时标, 分析脉冲在曲率效应作用下没有上升段,在动力学时标作用下没有下降段而呈尖峰结构;若仅在纯粹的电子辐射冷却时标主导下分析脉冲具有类FRED轮廓,呈平滑峰结构;2)壳层共动系中的内禀发射时间受到洛伦兹因子之比和爆发域半径之比的限制;3)我们把脉冲越宽越不对称的现象解释为脉冲和辐射区域的远近有关,即脉冲对称的短暴可能爆发在小半径区域,而脉冲非对称(绝大多数表现为FRED形态)的长暴可能爆发距中心较远的区域。 需要指出,这些结果或受到模型的限制或受样本容量的制约,因此,很有必要利用更真实的物理模型和更大的样本对这些初步结论给以检验或校正,甚至有些“发现”还有待于未来新的观测给予验证。
Other AbstractIn the thesis, we firstly review the actuality and progression of the observational and theoretical studies on gamma-ray bursts (GRBs) and their afterglows, which includes their underlying observational properties, primary theoretical models and other correlated phenomenon such as GRB-SN association and GRB cosmology. Subsequently, our investigations on the light curve of single pulses in gamma-ray bursts are summarized and discussed as follows: Firstly, using the Qin pulse model we have interpreted the parameters in KRL function describing the shape of GRB pulses. We find from our analysis that 1) The rise time (tr) and the decay time (td) of pulses are found to be related to the Lorentz factor by a power law, where the power-law for both cases is close to −2; 2) if the value of CPW can be suitably assigned, say 0.1≤CPW≤2, at least some sources in Kocevski sample could be described with Qin pulse model dominated by Doppler effect. By analyzing the relative spectral lags (RSLs) in long bursts between energy channels 1 and 3, we found that the RSLs are normally distributed and have a mean value of 0.1; that the RSLs are weakly correlated with the FWHM, the asymmetry, peak flux (Fp), peak energy (Ep) and spectral indexes α and β, while they are uncorrelated with spectral lag (τ31), the hardness ratio (HR31) and the peak time (tm). Our important discovery is that redshift (z) and peak luminosity (Lp) are strongly correlated with the RSL, which can be measured easily and directly, making the RSL a good redshift and peak luminosity or distance indicator. Thirdly, we restudy the spectral lag features of short bright gamma-ray bursts (T90 < 2.6s) with a BATSE time-tagged event (TTE) sample including 65 single pulse bursts. We conclude that spectral lags of short gamma ray bursts (SGRBs) are normally distributed and concentrated around the value of 0.014, with 40 percent of them having negative lags. With K-S tests, we find the lag distribution is identical with a normal one caused by white noises, which indicates the lags of the vast majority (~94%) of SGRBs are so small that they are negligible or unmeasurable, as Norris & Bonnell have suggested. On the assumption that there is the same relation τ∝±Γ-η as in long bursts, We interpret the negligible lag in SGRBs as a result of large lorentz factor or large power index η or both of them. Finally, we have clarified the relations between the observed pulses and their corresponding timescales. We find that the angular spreading timescale caused by curvature effect of fireball surface only contributes to the falling part of the observed pulses, while the dynamic one in the co-moving frame of the shell merely contributes to the rising portion of pulses provided the radiative time is negligible. In addition, the pulses resulted from the pure radiative cooling time of relativistic electrons exhibit properties of fast rise and slow decay (quasi-FRED) profile together with smooth peaks. we interpret the phenomena of wider pulses tending to be more asymmetric to be a consequence of the difference in emission regions. We here state that the above-mentioned results are more or less constrained by theoretical model or sample size. Therefore, they need to be updated and checked with much more physical model or larger sample, some findings are expected to be verified by new observations in the future.
Subject Area天文学
Pages142
Language中文
Document Type学位论文
Identifierhttp://ir.ynao.ac.cn/handle/114a53/7163
Collection星系研究组
Recommended Citation
GB/T 7714
张志彬. 伽玛射线暴单脉冲光变曲线的研究[D]. 北京. 中国科学院研究生院(云南天文台),2007.
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