伽玛射线暴辐射效率、辐射能及早期余辉研究
文献类型：学位论文
| 作者 | 赵晓红 |
| 学位类别 | 博士 |
| 答辩日期 | 2007-06-12 |
| 授予单位 | 中国科学院研究生院（云南天文台） |
| 授予地点 | 北京 |
| 导师 | 白金明 |
| 关键词 | 伽玛暴 喷流 边缘膨胀 非热辐射 数值 统计 |
| 其他题名 | Study on Gamma-Ray Burst effciency,energy and early afterglow |
| 学位专业 | 天体物理 |
| 中文摘要 | 伽玛射线暴（简称伽玛暴）是来自宇宙空间的伽玛射线短时间内大爆发的 现象。这种现象最初由美国的Vela军事卫星于1967年偶然发现。1973年，美国著 名的ApJ杂志在其Letter上发表了Vela卫星观测到的16个伽玛暴，标志着伽玛暴 的正式发现。由于伽玛暴时标很短，光变复杂，并释放出甚至超过超新星爆炸 的巨大能量，因此引起了天文学家们的广泛关注。目前虽然伽玛暴研究已经取 得了许多重要进展，但仍有些根本性的问题没有解决。比如，伽玛暴起源于什 么样的天体，如何产生高能伽玛射线等等。最近，Swift卫星发射上天，观测到了 许多新现象，为我们研究伽玛暴早期余辉性质，进而揭示伽玛暴本身性质奠定 了观测基础。 本文综述了伽玛暴到目前所取得的观测和理论成果，并介绍了本人在攻 读博士期间对伽玛暴效率、能量和早期余辉性质等问题所做的探索。本论文包 括三部分，综述部分（第一章），工作部分（第二章到第四章）和问题和展望部 分（第五章）。 第一章我们简单介绍了伽玛暴及其余辉的观测进展，并较为详细地介绍了 伽玛暴目前的主流模型，包括火球激波模型，极早期正反激波过程，标准余辉模 型，以及后标准效应等。 第二章我们研究了边缘膨胀效应对伽玛暴辐射效率估计的影响。过去，通 常用晚期余辉（约10小时）和早期的瞬时伽玛辐射数据来计算各向同性等价能 量，从而估计出伽玛暴的辐射效率。这在喷流张角在瞬时辐射和晚期余辉阶段 基本不变的情况下是正确的，但伽玛暴喷流可能存在边缘膨胀，这种情况下用 各向同性等价辐射能和动能会高估效率。我们用前人推导的动力学演化方程 组用数值方法计算了共动系声速膨胀下喷流张角的演化，得到喷流改正的能 量。我们发现用典型参数，考虑边缘膨胀后，伽玛暴的辐射效率比原来的典型 值（0.1）降低了约1/2。如果暴周是致密介质，则效率降低会更显著。我们取了 两个微观物理参数限定比较好的pre-Swift暴（GRB 980703和GRB 000926），详 细计算了他们的张角演化和效率，确认了我们前面的结果。因此，在利用晚期 余辉来估计效率时，喷流边缘膨胀效应可能需要考虑。 第三章我们用数值方法来计算了伽玛暴喷流的张角，并计算了喷流改正 的能量。通常用解析近似的动力学演化方程，假设光速边缘膨胀并利用观测到 的余辉光变拐折时间来计算伽玛暴喷流的初始张角。这对于喷流极端相对论 膨胀情况是近似合理的。但伽玛暴喷流到晚期余辉阶段已经处于中等相对论 阶段，此时仍假定边缘膨胀为光速已不太合理，而用演化的共动系声速边缘膨 胀可能更合理些。我们用前人给出的声速边缘膨胀演化方程，并结合晚期观测 到的余辉拐折反推出伽玛暴喷流的初始张角。我们取了一个较新的样本重新 计算伽玛暴的能量并做了统计研究，发现伽玛暴的能量成团性并不好。我们还 检验了Ep-Egamma关系，发现它们的相关性略有改善，但幂率指数由原来的0.71降 为0.64，这可能为理论上解释这一关系提供限制。 第四章我们考虑了伽玛暴喷流可能象活动星系核等天体的喷流一样存在运 动方向发生变化现象。由于伽玛暴喷流的体洛仑兹因子>100，因此运动方向微 小的变化都可能引起显著的光变。目前还不清楚喷流“弯曲”的原因，因此我们 假定了两个观测时间与喷流视角的关系，并计算了早期余辉的光变曲线，发现 有些与观测的结果相似。我们认为对于某些暴，早期X-ray余辉可能产生于喷流 的“弯曲”。 最后一章，我们总结了目前伽玛暴中还存在的一些问题，并对一些具体的 问题提出了一些个人看法。我们还简单介绍了一下GLAST卫星，并对GLAST时 代伽玛暴的研究进行了展望。 |
| 英文摘要 | Gamma-ray burst (GRB) is a kind of phenomenon that is the energy burst in gamma rays with a short duration. It was discovered for the first time by Vela satellite in 1976 by chance. Though many progresses have been made to date, some intrinsic issues haven't solved. Recently, Swift is launched successfully, some new characters have been observed, which is the base for us to study the early afterglow properties and then understand the properties of GRB. My thesis consists of threeparts. The first chapter is review, the second to the fourth ones are my works and the last chapter is the problems and prospects. In the second chapter, we study jet sideways expansion effect on estimating the GRB efficiency. Usually, the isotropic equivalent energy is calculated with the prompt emission and late afterglow data and the efficiency is derived. This is only valid for the case that jet opening angles are the same during the two phases. However, jet sideways expansion can exist during the outward expansion of jet. In this case, the usual method to estimate the GRB efficiency is not valid. We calculate the evolution of jet opening angles numerically and derive the collimation-corrected emission and kinetic energy. We find that with the typical parameters, the GRB efficiency is decreased by a factor of 1/2 (for the typical efficiency 0.1). If the circumburst is dense, this effect is more significant. We also take two pre-swift bursts (GRB 980703 and GRB 000926) for case studies, which confirm our previous results. So when the efficiency is derived with the late afterglow data, jet sideways expansion effect needs to be considered. In the third chapter, we use the numerical method to calculate the initial jet opening angle of GRB. The opening angle is usually derived with the afterglow light curve breaks through an analytical method with the assumption that the speed of expanding laterally is the light speed. This is only valid approximately. At the late time, the jet enters a phase of a moderate relativistic expansion, so this assumption is invalid. A more reasonable assumption is that the jet expands laterally at the comoving sound speed cs. Using the hydrodynamic evolution equation group with the sideways expansion at the local sound speed derived by previous authors and the observed light curve breaks, we numerically derive the initial opening angles. With a new sample of GRB, we make a statistical study, and find that the energy clustering seems not to exist. We also test the Ep-Egamma relation, and find that the correlation improve slightly, while the power change from 0.71 to 0.64, which may provide constrain on model to interpret this relation in theory. In the fourth chapter, we consider a possible case that the GRB jet may travel in a curve line like the observed AGN jet. For a large Lorentz factor (> 100), a slight change of the view line angle will cause a significant light curve variation. Without knowing the mechanism of the bent of jet, we assume two relations between the view line angle and the observed time, and the light curve is calculated. We find some of the resulted light curves are similar to the observed ones. We argue that for some burst, the early X-ray afterglow may result from the bent of GRB jet. In the last chapter, we summarize the present problems in GRB. Some ideas are presented for some concrete problems. We also present a brief introduction to GLAST satellite and propose prospects. |
| 学科主题 | 天文学 |
| 语种 | 中文 |
| 页码 | 115 |
| 源URL | [http://ir.ynao.ac.cn/handle/114a53/5074]  |
| 专题 | 云南天文台_高能天体物理研究组 |
| 推荐引用方式 GB/T 7714 | 赵晓红. 伽玛射线暴辐射效率、辐射能及早期余辉研究[D]. 北京. 中国科学院研究生院（云南天文台）. 2007. |
入库方式： OAI收割
来源：云南天文台
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