Why Blazar Jets Shine: Radiative Relativistic Reconnection and the Minijet Model

耀变体是活跃星系核的一个子集，它们是星系的高能核心，它们的物质喷流以接近光速的速度流出，恰好排列成指向我们的方向。因此，耀变体提供了能量如何在快速移动的等离子体内部和周围被辐射和降解的直接视图。不幸的是，目前的解释已被证明是不充分的。这个研究小组提出了一个新的模型，在初步的近似研究中看起来非常有希望。该项目将使用新的计算技术来模拟大量高速等离子体的运动，以足够详细的研究问题，通过与天文观测相比较来区分可能的替代方案。为这项工作开发的研究工具将被打包，供其他人在等离子体科学的许多领域使用。耀变体是地面和天基天文台探测到的恒久星系外伽玛射线辐射的主要来源。它们提供了对相对论性无碰撞等离子体中耗散和辐射过程的直接观察。最近对快速强烈耀斑的观测表明，发射区域非常紧凑，传播的洛伦兹因子比从射电观测中推断出的大喷流值高得多。一种使用局部相对论子流的半解析模型，称为微型喷流，再现了耀变体的主要特征，但它是基于粗略的近似。该项目将使用一种全新的、完全辐射的粒子单元（PIC）代码来研究相对论性等离子体中的无碰撞重联，包括等离子体磁化、磁场引导强度和等离子体成分对大块等离子体运动、粒子加速和辐射特征的影响。模拟的随时间变化的光谱将与现有数据进行比较。来自蟹状星云的令人费解的伽马射线耀斑不可能是由于激波加速或任何其他磁流体动力学过程，该研究小组的综合模型是第一个令人信服的案例，证明重连是遥远天体物理系统的主要耗散机制。本工作将研究相对论性重联流出的整体运动学，等离子体成分对重联流出的影响，以及这些自相同流出中的辐射过程。这将是第一个模拟电子-离子等离子体中相对论性重连接的动力学模拟，也是第一个自洽地处理辐射损失的动力学模拟。这里使用的强大的研究工具将免费提供，包括所有必要的文档、测试问题、诊断工具和示例脚本。该研究本身不仅可以广泛应用于其他天体物理系统，如脉冲星风星云、伽马射线暴、吸积盘日冕等，还可以应用于空间物理应用和实验室等离子体。一名博士后研究员将获得高性能计算和模拟使用方面的支持、培训和指导。

Blazars are a subset of active galactic nuclei, which are highly energetic cores of galaxies, singled out by the fact that their jets of material, flowing out at speeds approaching that of light, just happen to be arranged so as to point towards us. As such, blazars provide a direct view of how energy is radiated away and degraded in and around fast moving plasmas. Unfortunately, the current explanations have proven inadequate. This research team has introduced a new model that looks very promising in initial, approximate, studies. This project will use new computational techniques to simulate the motions of large amounts of high-speed plasma, to study the problems in sufficient detail to distinguish between the possible alternatives by comparing with astronomical observations. The research tool developed for this work will be packaged for others to use in many areas of plasma science.Blazars are the primary sources of persistent extragalactic gamma-ray radiation detected by ground- and space-based observatories. They provide a direct view of dissipation and radiative processes in relativistic collisionless plasmas. Recent observations of rapid intense flares imply that the emitting regions are very compact and propagate with much higher Lorentz factors than the bulk jet values deduced from radio observations. A semi-analytical model using localized, relativistic sub-flows, called minijets, has reproduced the main features of flaring blazars, but is based on crude approximations. This project will use a new, fully radiative Particle-in-Cell (PIC) code to study collisionless reconnection in relativistic plasmas, including the effects that plasma magnetization, the strength of the magnetic guide field, and the plasma composition, can have on bulk plasma motions, particle acceleration, and radiative signatures. Simulated time-dependent spectra will be compared to existing data. The puzzling gamma-ray flares from the Crab Nebula cannot be due to shock acceleration or any other magnetohydrodynamic process, and this research team's comprehensive model is the first compelling case for reconnection as the main dissipation mechanism in a distant astrophysical system. The present work will study the bulk kinematics of relativistic reconnection outflows, the effects of plasma composition on reconnection outflows, and radiation processes in these self-same outflows. These will be the first kinetic simulations to model relativistic reconnection in an electron-ion plasma, and among the first to treat radiative losses self-consistently.The powerful research tool used here will be made freely available, with all necessary documentation, test problems, diagnostic tools, and sample scripts. The study itself applies widely not only to other astrophysical systems such as pulsar wind nebulae, gamma-ray bursts, and accretion disk coronae, but also to space physics applications and laboratory plasmas. One postdoctoral researcher will be supported, trained, and mentored in high-performance computing and the use of simulations.