Shear Particle Acceleration in Astrophysical Jets

宇宙中带电粒子是在哪里以及如何加速到它们的极限能量的？也许最有希望的地点之一包括活动星系核（AGN）的准直、相对论性喷流或喷流。越来越多的人认识到这些射流可能表现出显著的速度剪切，近年来引发了各种研究，探索其对非热粒子加速和发射的影响。快速剪切流原则上可以通过几种方式促进高能粒子的加速。一个关键的可能性包括随机费米型过程，在这个过程中，粒子的激活是由于剪切背景流中嵌入的不同移动的磁不均匀性的弹性散射而发生的。在本项目中，我们将通过数值、解析和现象学的方法来解决AGN射流中费米型剪切粒子加速的关键问题。我们的具体目标是(a)剪切圆柱射流的相对论粒子传输方程的数值解，这将使评估目前使用的简化加速度模型的充分性成为可能；(b)通过蒙特卡罗模拟以及向各向异性散射的扩展，对剪切粒子加速度的基本概念进行数值验证。(c)基于详细的源建模，对其产生超高能宇宙射线的潜力进行现象学评估，以及最近在大规模AGN射流中检测到的TeV发射的起源。我们期望这些结果能够决定性地推进我们对宇宙粒子加速的概念理解，并允许对其现象学含义进行合格的判断。因此，这些结果有望成为进一步研究的中心参考。

Where and how are the charged particles seen in the Universe accelerated to their extreme energies? Perhaps one of the most promising sites includes the collimated, relativistic outflows or jets in Active Galactic Nuclei (AGN). The growing realisation that these jets are likely to exhibit significant velocity shearing has in recent times triggered a variety of studies exploring its consequences for non-thermal particle acceleration and emission. Fast shear flows can in principle facilitate energetic particle acceleration by several means. One key possibility includes a stochastic Fermi-type process, in which particle energisation occurs as a result of elastically scattering off differentially moving magnetic inhomogeneities embedded in a shearing background flow.In this project we will address and resolve key issues of Fermi-type shear particle acceleration in the jets of AGN by means of numerical, analytical and phenomenological methods.We specifically aim at (a) a numerical solution of the relativistic particle transport equation for sheared, cylindrical jets, that will enable assessing the adequacy of simplified acceleration models currently used, (b) a numerical verification of the fundamental concept of shear particle acceleration by means of Monte Carlo simulations along with extensions towards anisotropic scattering, and (c) a phenomenological assessment of its potential for ultra-high-energy cosmic-ray production and the origin of the recently detected TeV emission in large-scale AGN jets based on detailed source modelling. We expect these results to decisively advance our conceptual understanding of cosmic particle acceleration and to allow a qualified judgement of its phenomenological implications. As such the results are expected to become the central reference for further studies.