Particle Acceleration at Relativistic Shocks: Implications for Models of Gamma-Ray Bursts and Active Galaxies

巴林伽马射线暴（GRB）是宇宙中已知的最迷人的天体之一，其短暂的性质体现了其独特性。大约30年前他们的发现导致了一系列令人困惑的谜团和惊人的发现。 其中最新的进展是在1997年发现了衰落的X射线，光学和无线电余辉，这些余辉使人们能够准确地确定它们与地球的距离，将它们置于宇宙中最遥远的领域。因此，天体物理学家得出结论，伽玛暴是宇宙中最明亮和最强大的物体。 目前的想法是，它们是由灾难性事件产生的，也许是一颗大质量星星的爆炸。 本项目的目标是研究伽玛暴的灾变事件模型。 在这些模型中，当从星星喷射出的物质以高度超音速和相对论速度冲入周围的环境气体时，伽马射线暴就会发生，从而产生极其强大的宇宙冲击波。能量以热的形式和极端相对论性的基本粒子的形式被释放。这些高速粒子然后产生辐射发射，在地球上被检测为伽马射线，X射线，无线电波和可见光。 这种耗散冲击情景的不确定性主要来自两个限制：（i）相对较短的持续时间和窄的能量带宽的即时伽马射线数据，（ii）目前的粗糙的理论模型。该项目解决了这些限制。它探讨了相对论粒子如何获得必要的极端能量。 它包括比以前更准确的确定可达到的最大能量。它还试图建立粒子加速特性和我们看到的辐射之间的明确的相关性和趋势，使用后者作为加速物理学的诊断探针。这项工作试图回答的大问题包括：（i）GRB环境是否是一个有序的大尺度现象，或者它是否拥有大量混乱的，纠缠的，磁化的细胞，（ii）如果这两种情况都可以出现，从而影响对观测可能性的解释，即可能有两类爆发，而不仅仅是一类，（iii）GRB中的平均磁场有多大，以及（iv）爆发时的粒子加速是否足够快，以解释不断地淋浴地球的超相对论性核（宇宙射线）的普遍存在。伽马射线暴的天体物理环境与其背后的物理学之间的这种联系以前从未被研究过。此外，这项工作还将涉及活动星系的模型，因为它们的发射可能是由类似类型的物理驱动的。这些目标的成功将提供一个合适的平台，在未来几十年内进一步提高我们对奇异和诱人的伽马射线爆发源的认识。该项目的资金由美国国家科学基金会的河外天文宇宙学计划（AST/EXC）提供。

AST 0098705BaringGamma Ray Bursts (GRBs) are among the most fascinating objects known in the universe, possessing a uniqueness embodied in their ephemeral nature. Their discovery around 30 years ago has led to a sequence of baffling mysteries and startling revelations. The latest advance among these was the discovery in 1997 of fading X-ray, optical and radio afterglows that have permitted accurate determination of their distance from Earth, placing them in the most remote realms of the universe. Consequently, astrophysicists have arrived at the conclusion that GRBs are the most luminous and powerful objects in the universe. Current thinking is that they are spawned by a catastrophic event, perhaps an explosion of a massive star. The goals of this project are to investigate catastrophic event models of GRBs. In these models, the GRB occurs when the ejected material from the star ploughs into the surrounding ambient gas at highly supersonic and relativistic speeds, creating an enormously powerful cosmic shock wave. Energy is liberated, both in thermal forms and in the form of extremely relativistic elementary particles. These high-speed particles then produce radiative emission, which is detected on Earth as gamma rays, X-rays, radio waves and optical light. The uncertainties in this dissipative shock scenario essentially stem from two constraints: (i) the relatively short duration and narrow energy bandwidth of the prompt gama-ray data, and (ii) the present crudeness of theoretical models. This project addresses these limitations. It explores how the relativistic particles can obtain the necessary extreme energies. It includes much more accurate determinations than previously available of the maximum energies attainable. It also seeks to establish definitive correlations and trends between particle acceleration properties and the radiation we see, using the latter as a diagnostic probe on the acceleration physics. The big questions this work seeks to answer include (i) whether the GRB environment is an ordered large scale phenomenon, or whether it possesses a multitude of chaotic, entangled, magnetized cells, (ii) if both of these situations can arise and thereby effect an explanation of the observational possibility that there might be two classes of bursts, not just one, (iii) how large the mean magnetic field is in a GRB, and (iv) whether particle acceleration in bursts is sufficiently rapid to account for the pervasive population of ultrarelativistic nuclei (cosmic rays) that shower Earth incessantly. This connection between the astrophysical environment of gamma-ray bursts and the underlying physics has not been studied before. In addition, this work will also address models for active galaxies, since their emission is probably driven by similar types of physics. Success in these goals will provide a suitable platform for further advancement of our knowledge of the exotic and alluring gamma-ray burst sources over the coming decades. Funding for this project was provided by the NSF program for Extragalactic Astronomy & Cosmology (AST/EXC).***