Energizing Photospheres of Gamma-Ray Bursts

探测到中子星合并（GW 170817）与伽马射线暴（GRB 170817A）同时发生的引力波事件，是现代天体物理学的一项重大成就。GRB是宇宙中最极端的爆炸，GRB研究可以通过了解极端条件下物质的新特性来影响基础物理学。为了更好地了解GRB 170817A和其他GRB，哥伦比亚大学的一个研究小组将研究GRB光球（即辐射光线的外壳）是如何被激发而变得如此明亮的。这将使用由该小组开发的最先进的数值工具来完成。GRB中冲击波的模拟源自第一性原理，将自一致地包括电子-正电子（反电子）对的产生，并预测产生的辐射的光谱，这可以与观测结果进行比较。这些结果将用于开发GRB 170817A的具体物理场景。该小组将通过公开演讲和与新闻界的联系继续其外联活动，并将在国际会议、座谈会和研讨会上传播其结果。研究方法和结果将作为哥伦比亚大学天体物理学课程的一部分教授，该项目将涉及博士后学者和学生的培训。不透明相对论性抛射的光球发射在宇宙伽玛射线暴中起着关键作用。一个关键的物理问题是，为什么grb中的光球如此明亮，以及是什么过程形成了观测到的非热光谱。提出的研究将集中于建立两种加热机制的物理模型：(1)内部辐射介导的冲击和(2)湍流级联的阻尼。一个重要的目标是研究冲击是如何在光球中爆发并释放辐射的。该代码将直接跟踪亚光球激波的演变，加上其周围单个光子的传播，并计算它们的爆发，伴随着大量电子-正电子对的产生。这种方法特别适用于中子星合并的伽马射线对应物的研究。它可以为GRB 170817A提供一个强大的物理模型，并为未来的引力波探测提供具体的预测。该结果将应用于短、长宇宙学伽马射线暴以及超新星爆炸中的激波爆发。计划中的研究还包括一个新的GRB射流湍流阻尼物理模型和自由中子的辐射效应。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The detection of a gravitational wave event from a neutron star merger, GW 170817, coincident with a gamma-ray burst, GRB 170817A, is a major achievement of modern astrophysics. GRBs are the most extreme explosions in the Universe and GRB research can impact fundamental physics through understanding new properties of matter under extreme conditions. In order to better understand GRB 170817A and other GRBs, a research group at Columbia University will investigate how the GRB photosphere, or outer shell from which light is radiated, is energized to become so bright. This will be accomplished using state-of-the-art numerical tools developed by the group. The simulations of shock waves in the GRB, derived from first principles, will self-consistently include the creation of electron-positron (anti-electron) pairs, and predict the spectrum of the radiation produced, which can be compared with observations. The results will be used to develop a concrete physical scenario for GRB 170817A. The group will continue with its outreach activities through both public lectures and communications with the press, and the results will be disseminated at international conferences, colloquia, and seminars. Methods and results of the research will be taught as part of astrophysics courses at Columbia University, and the project will involve training of a postdoctoral scholar and students.Photospheric emission from opaque relativistic ejecta plays a key role in cosmological gamma-ray bursts. A key physics question is why the photosphere is so bright in GRBs and what processes shape its observed nonthermal spectrum. The proposed research will focus on building physical models for two heating mechanisms: (1) internal radiation-mediated shocks and (2) damping of a turbulent cascade. An important goal is to investigate how shocks break out at the photosphere, releasing their radiation. The code will directly follow the evolution of sub-photospheric shocks, coupled with propagation of individual photons around it, and calculate their breakout, accompanied by copious electron-positron pair creation. This method is particularly applicable to studies of gamma-ray counterparts of neutron star mergers. It can give a robust physical model for GRB 170817A and lead to specific predictions for counterparts of future gravitational wave detections. The results will have applications to short and long cosmological GRBs as well as shock breakout in supernova explosions. The planned research also includes a novel physical model for turbulence damping in GRB jets and the radiative effects of free neutrons.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.