论文标题
对超热粒子加速度对低模型的形态的影响，高$β$ shocks
On the influence of supra-thermal particle acceleration on the morphology of low-Mach, high-$β$ shocks
论文作者
论文摘要
当两个星系簇相互遇到时，相互作用会导致无碰撞冲击，其特征是低（1-4）声音马赫数和高alfv {é} NIC MACH。我们的目标是确定此类冲击是否可以加速颗粒到足够的速度，以使它们有助于宇宙射线光谱。我们将两种不同的计算方法结合使用，磁水动力学（MHD）和粒子中的粒子（PIC），使我们能够利用MHD的高计算效率，同时保持对单个非热粒子的行为进行建模的能力。使用此方法，我们执行一系列模拟，涵盖了星系群碰撞冲击的预期参数空间。我们的结果表明，对于低于2.25的声音马赫数的冲击，由于磁场缺乏不稳定性，因此无法进行无扩散的冲击加速度，而对于具有声音马赫数的冲击，Sonic Mach Number $ \ GEQ \，3 $，加速度是有效的，并且可以加速粒子到相对速度。在这两个极端之间的状态中，可能会发生扩散的冲击加速度，但由于不稳定性的时间和空间依赖性，因此相对效率低。对于表现出有效加速的冲击，上游气体中的不稳定性会增加到改变冲击性质的程度，进而会影响颗粒注入过程。
When two galaxy clusters encounter each other, the interaction results in a collisionless shock that is characterized by a low (1-4) sonic Mach number, and a high Alfv{é}nic Mach number. Our goal is to determine if, and to what extent, such shocks can accelerate particles to sufficient velocities that they can contribute to the cosmic ray spectrum. We combine two different computational methods, magnetohydrodynamics (MHD) and particle-in-cell (PIC) into a single code that allows us to take advantage of the high computational efficiency of MHD while maintaining the ability to model the behaviour of individual non-thermal particles. Using this method, we perform a series of simulations covering the expected parameter space of galaxy cluster collision shocks. Our results show that for shocks with a sonic Mach number below 2.25 no diffusive shock acceleration can take place because of a lack of instabilities in the magnetic field, whereas for shocks with a sonic Mach number $\geq\,3$ the acceleration is efficient and can accelerate particles to relativistic speeds. In the regime between these two extremes, diffusive shock acceleration can occur but is relatively inefficient because of the time- and space-dependent nature of the instabilities. For those shocks that show efficient acceleration, the instabilities in the upstream gas increase to the point where they change the nature of the shock, which, in turn, will influence the particle injection process.
