Modeling Comptonized Soft Gamma-Ray Flare Emission in Magnetars

中子星是磁星，是宇宙中最有趣的致密天体之一。 目前可能有多达30种，其中许多都表现出强大的高能X射线爆发。 磁星提供了一个独特的论坛，用于测试目前在陆地实验室无法访问的基础物理学。 由于对量子电动力学（QED）理论有很大的信心，天体物理学家通常通过使用未经检验的高磁场域理论预测来模拟中子星星环境。 由于磁星提供了进行这些测试的实验室，因此了解它们的特性对于将它们用作代理QED物理实验室至关重要。 该项目通过开发计算机模拟来研究磁星表面以上区域，在这一方向上迈出了重要一步。该研究项目为研究生和本科生的培训提供了一个重要因素，学生参与了研究和教学。 一名或两名博士生将作为工作的一个组成部分，其结果将导致博士论文。 这些学生将参与本科教育学，每年至少在适当的赖斯课程中讲授一次关于中子星的讲座。 一个或多个本科生将被招募工作的研究较小的，独立的部分，为他们的高级论文在赖斯。 这些学生将在研究小组研讨会上向赖斯的同行展示他们的研究成果。 继续与休斯敦天文学会建立的关系，PI还将向公众展示这项工作的各个方面和中子星的令人兴奋的领域的亮点。在更多的技术术语中，该项目开发了一个蒙特卡罗模拟来描述磁星磁层中的辐射传输，主要是在封闭的场区。 该代码将计算康普顿散射事件中X射线与热相对论电子之间的相互作用，跟踪它们之间的能量交换并解释光子偏振的变化。 新的物理形式主义的磁康普顿截面将开发占主导地位的不透明度的多个回旋共振。 其他过程将被建模，包括光子分裂和磁对的创建，并将评估其对衰减约100千电子伏以上的软伽马射线的影响。 磁双光子对产生截面的新物理发展将被执行，以促进衰减计算。对的创建将被纳入，偏振签名的生成将既是精度的必要条件，也是一个亮点，增加了建模的诊断潜力。 具体而言，捕获偏振信息可以提供解开几何源信息和强场QED物理特征的手段。 正电子-电子对产生和康普顿散射的关键物理分析发展将是这项工作的一个特点，并将为天体物理学家在其他问题上提供新的工具。 作为一个更广泛的科学元素，该计划的偏振考虑将有助于确定X射线和软伽马射线波段偏振望远镜的议程和动机，与这些目前处于科学兴趣前沿的源有关的三个突出问题将受到该项目的重大影响。 它们是（i）磁星是否本质上不同于正常的耀斑，或者它们的发射是由在中子星星参数空间的不同部分中运行的类似物理驱动的，（ii）是什么导致耀斑的最大能量通常被校准到100- 300 keV左右;以及（iii）在磁星中播种非热辐射的磁层中能量注入的确切位置，即，这个位置离恒星表面和/或磁赤道有多近？

Neutron stars that are magnetars are some of the most interesting compact objects in the Universe. There are perhaps as many as 30 presently identified with many of them exhibiting powerful outbursts of high energy X-rays. Magnetars present a unique forum for testing fundamental physics that is not presently accessible in terrestrial laboratories. Having great faith in the theory of quantum electrodynamics (QED), astrophysicists routinely model neutron star environments by using untested theoretical predictions for high magnetic field domains. Because magnetars provide the laboratory for performing these tests, understanding their character is central to using them as a proxy QED physics laboratory. This project makes significant steps in this direction by developing computer simulations to study the region above the surface of magnetars.This research project offers a significant element of graduate and undergraduate training with the involvement of students in research and teaching. One or two PhD students will be engaged as an integral part of the work with the results leading to doctoral theses. These students will be involved in undergraduate pedagogy by teaching at least one lecture per year on neutron stars in appropriate Rice courses. One or more undergraduates will be enlisted to work on smaller, self-contained portions of the research for their senior theses at Rice. These students are expected to present their research results to peers at Rice in research group seminars. Continuing an established relationship with the Houston Astronomical Society, the PI will also present aspects of this work and highlights of the exciting field of neutron stars to the general public.In more technical terms, this project develops a Monte Carlo simulation to describe radiative transfer in magnetar magnetospheres, mostly in closed field zones. The code will compute the interaction between X-rays and hot, relativistic electrons in Compton scattering events, tracking the energy exchange between them and accounting for changes in photon polarization. New physics formalism for the magnetic Compton cross section will be developed to account for the multiple cyclotron resonances that will dominate the opacity. Other processes will be modeled including photon splitting and magnetic pair creation, and their effect on attenuating soft gamma-rays above around 100 keV will be assessed. New physics developments of the magnetic two-photon pair creation cross section will be performed to facilitate the attenuation calculations.The creation of pairs will be incorporated and the generation of polarization signatures will be both a necessity for precision and also a highlight, increasing the diagnostic potential of the modeling. Specifically, capturing polarization information may provide the means to disentangle geometrical source information and the signatures of strong-field QED physics. Key physics analysis developments for positron-electron pair creation and Compton scattering will be a feature of the work and will provide new tools for astrophysicists to employ in other problems. As a broader scientific element, the polarization considerations of this program will aid in defining agendas and motivations for polarimetric telescopes in the X-ray and soft gamma-ray bands.Three outstanding questions pertaining to these sources that are at the forefront of scientific interest at the moment will be impacted significantly by this project. These are (i) whether or not magnetars are inherently different from normal pulsars, or is their emission driven by similar physics operating in different portions of neutron star parameter space, (ii) what causes the maximum energies of flares to be generally calibrated to around 100--300 keV; and (iii) where exactly is the site of energy injection in the magnetosphere that seeds non-thermal radiation in magnetars, i.e., how proximate is this locale to the stellar surface and/or the magnetic equator?