Gamma-Ray Burst Afterglows in the Multi-Messenger Era

伽马射线暴（GRB）是宇宙中最明亮的事件，能够为与周围星际介质相互作用的相对论喷流提供动力。伽马射线暴的两种变体与这项研究有关;长伽马射线暴，由超大质量恒星的死亡驱动，短伽马射线暴，由中子星星合并引起。由于这些事件产生的引力波，可以对相同的物体进行同步观测。这在2017年得到了证明，当时引力波事件GW 170817被用来三角测量和研究伽马射线暴GRB 170817 A，随后被光学望远镜看到。这种方法允许的伽玛射线暴的研究，不直接指向地球（离轴），允许整个喷流结构被潜在地viewed.Current模型的余辉发射调用同步辐射不能解释许多功能，发现在观测到的余辉光变曲线。此外，在TeV范围内的能量已被检测到在长（GRB 190114 C）和短（GRB 160821 B）GRB，这表明康普顿上散射也可能发生，并应占模型。对喷流的离轴研究也可以更好地研究其结构和发生在喷流不同部分的非热加速。在这个项目中，我将使用几个不同的软件包来模拟伽玛暴的喷流余辉。首先，使用移动网格流体动力学代码的数值射流模拟，Ayache为他的博士学位在巴斯，将进行研究结构射流的长期演变。使用ScaleFit模型拟合工具，对观测数据进行宽带分析，并与这些模拟结果进行比较。其次，动力学代码Katu，由Jimenez为他在巴斯的博士学位开发，沿着python模块afterglowpy，将用于研究喷流结构中发现的各种发射区。综合起来，将获得余辉射流的更全面的理论图象。虽然如果在博士期间没有观测成功，则可以获得存档数据，但希望下一次LIGO运行，沿着新的日本引力探测器KAGRA和切伦科夫望远镜阵列（CTA）将于2022年下半年上线，新数据将变得可用，允许模型进行测试和改进。在试图使理论模型与观察到的光相一致时，将考虑射流中的冲击加速和康普顿上散射的影响-曲线喷射环境的影响也将被研究，考虑喷射的边缘，看看它是否可以播种康普顿上散射所需的光子。这项研究还将通过研究喷流中的任何相似性或差异来调查短和长GRB是否具有可比性。结构射流模拟，TeV排放和两者的应用开发和比较模型的观测数据的出版物将被释放作为博士的进展。这项研究是在天体物理学，这是STFC的研究领域之一。

Gamma-ray bursts (GRBs) are the most luminous events in the Universe, and are capable of powering relativistic jets which interact with the surrounding interstellar medium. Two variants of GRBs are relevant for this research; long GRBs, which are driven by the death of supermassive stars, and short GRBs, which are caused by neutron star mergers. Because of gravitational waves generated by such events, coincident observations can be made on the same objects. This was demonstrated in 2017, when the gravitational wave event GW170817 was used to triangulate and study the gamma-ray burst GRB170817A, which was subsequently seen by optical telescopes. This approach allows for the study of GRB which do not point directly at Earth (off-axis), allowing for the full jet structure to be potentially viewed.Current models of afterglow emission which invoke synchrotron radiation do not explain many features which are found in observed afterglow light curves. Furthermore, energies in the range of TeV have been detected in both long (GRB190114C) and short (GRB160821B) GRBs, suggesting that Compton upscattering may also occur and should be accounted for in models. Off-axis studies of the jet also allows for better studies of its structure and the non-thermal acceleration occuring in different parts of the jet.For this project, I will be making use of several different packages to simulate the jet afterglow of GRBs. Firstly, numerical jet simulations using the moving-mesh hydrodynamic code GAMMA, developed by Ayache for his PhD in Bath, will be performed to study the long-term evolution of structured jets. Using the ScaleFit model fitting tool, a broadband analysis of observational data wil then be done and compared to the results of these simulations. Secondly, the kinetic code Katu, developed by Jimenez for his PhD in Bath, along with the python module afterglowpy, will be used to study the various emission zones found within the jet structure. Combined together, a fuller theoretical picture of the afterglow jet will be obtained. While archival data is available if no observations are successful during the PhD, it is hoped with the next LIGO run, along with the new Japanese gravitational detector KAGRA and the Cherenkov Telescope Array (CTA) coming online in the second half of 2022, that new data will be become available, allowing the model to be tested and refined.The shock acceleration in the jet and the impact of Compton upscattering will be considered in trying to reconcile theoretical models with the observed light-curve. The effect of the jet environment will also be studied, with the edge of the jet being considered to see if it could seed the photons necessary for Compton upscattering. This research will also investigate if short and long GRBs are comparable by studying any similarities or differences in the jet. Publications on the structured jet simulations, the TeV emissions and the application of both to develop and compare the model to observational data will be released as the PhD progresses.This research is in astrophysics, which is one of the research areas of the STFC.