Improving and Extending Models of Gamma-Ray Burst Afterglows

伽马射线暴(GRB)是最明亮的宇宙爆炸。它们是宇宙中一些比较极端的物体，既神秘又迷人。了解它们的起源和发展有助于深入了解恒星的形成和演化，以及对基础物理的测试。伽玛暴爆炸后留下的余辉是由于爆炸周围材料之间的相互作用造成的，可以在最初的爆炸后很长一段时间内观察到。这个项目将以新的方式探索余辉阶段，使用广泛的计算机模拟来超越简单的模型，并解释其他令人困惑的最近的观测。由于余辉的光谱随时间变化的方式，主要的发射机制被认为是来自冲击波加速的电子的同步辐射。然而，对能量超过最大同步加速器极限的光子的探测表明，对余辉发射的理论理解仍然不完整。由于对潜在的微观物理的忽视，目前的模型几乎没有预测能力。这项工作将超越标准的现象学方法，建立在这个研究小组最近的结果基础上，他们已经开始揭示伽玛暴余辉的微观物理。自洽的细胞内粒子模拟将在每个阶段提供物理上接地的微物理参数。这项研究将(1)解决磁化的起源问题；(2)研究早期伽玛暴余辉中的激波物理，研究电子-正电子-质子等离子体激波；(3)探索伽玛暴晚期余辉中的激波物理。这项研究将评估后期伽玛暴激波中电子和质子加速的效率，以及产生和放大的场的衰减长度。尽管涉及复杂的物理问题，但这项工作包含几个面向本科生的项目，甚至高中生也可以通过为期一天的研讨会接触到相对论激波的最新发展。该团队致力于大力参与既定的教育和指导计划，包括支持来自贫困社区的儿童和青少年。

Gamma-ray bursts (GRBs) are the most luminous cosmic explosions. They are some of the more extreme objects in the Universe, both mysterious and fascinating. Understanding their origin and development provides insights into star formation and evolution, as well as tests of basic physics. The afterglow left after a GRB goes off is due to interactions in the material around the explosion and can be observed long after the initial blast. This project will probe the afterglow phase in new ways using extensive computer simulations to go beyond the simple models and explain otherwise puzzling recent observations.Because of the way the spectrum of the afterglow changes with time, the dominant emission mechanism was thought to be synchrotron radiation from shock-accelerated electrons. However, the detection of photons with energies that violate the maximum synchrotron limit shows that theoretical understanding of the afterglow emission is still incomplete. Current models have little predictive power due to ignorance of the underlying microphysics. This work will go beyond standard phenomenological approaches, building on recent results by this research team that have started to unveil the microphysics of GRB afterglows. Self-consistent particle-in-cell simulations will provide physically grounded microphysical parameters at every stage. This study will (1) settle the question of the origin of the magnetization; (2) study the shock physics in early GRB afterglows, investigating the electron-positron-proton plasma shocks; and (3) explore the shock physics in late GRB afterglows. The research will assess the efficiencies of electron and proton acceleration in late GRB shocks, and the decay length of the generated and amplified fields.Despite the complex physics involved, this work contains several projects for undergraduate students, and even high school students can be exposed to the latest developments about relativistic shocks through day-long workshops. The team is committed to significant involvement with established educational and mentorship programs, including support for children and adolescents from disadvantaged neighborhoods.