论文标题

流式宇宙射线的动荡重新计算

Turbulent Reacceleration of Streaming Cosmic Rays

论文作者

Bustard, Chad, Oh, S. Peng

论文摘要

亚音速,压缩湍流将能量转移到宇宙射线(CRS),这是一种称为非共振重新计算的过程。假设完全扩散的Cr传输,通常会调用以$ \ sim \ rm Gev $ engies的观察到的初级和次级CR的比率。但是,这样的估计值忽略了CR自我填充和流媒体的影响。我们在使用Athena ++的搅拌盒磁流失动力学(MHD)模拟中研究了这些问题,并具有与场对齐的扩散和流式CR传输。仅对于扩散,我们发现CR重新计算速率与分析预测非常吻合。包括流媒体时,重新计算率取决于等离子体$β$。由于CR和气体变量之间流媒体修饰的相移,因此在低$β$环境(如星际介质)(ISM)等低$β$环境中,它们的速度慢,但在高$β$环境中保持不变,如膨胀介质(ICM)。我们还量化了模拟中的流能量损失率。对于亚alfvénic湍流,与各向同性损耗率$ v_ {a} \ cdot \ cdot \ cdot \ nabla p _ {\ rm cr} / p _ {由于平均场和各向同性CR梯度之间的不对对准。违反直觉,并且与加速度的效率不同,CR损耗几乎独立于$β\ SIM 1-100 $上的磁场强度,因此,并不是包括流式传输时较低加速度速率的主要因素。尽管本文主要涉及湍流如何影响CRS,但在后续纸(Bustard和Oh,Prep中)中,我们考虑CRS如何通过从MHD Cascade转移能量来影响湍流,改变了加热气体的途径并使湍流功率频谱震荡。

Subsonic, compressive turbulence transfers energy to cosmic rays (CRs), a process known as non-resonant reacceleration. It is often invoked to explain observed ratios of primary to secondary CRs at $\sim \rm GeV$ energies, assuming wholly diffusive CR transport. However, such estimates ignore the impact of CR self-confinement and streaming. We study these issues in stirring box magnetohydrodynamic (MHD) simulations using Athena++, with field-aligned diffusive and streaming CR transport. For diffusion only, we find CR reacceleration rates in good agreement with analytic predictions. When streaming is included, reacceleration rates depend on plasma $β$. Due to streaming-modified phase shifts between CR and gas variables, they are slower than canonical reacceleration rates in low-$β$ environments like the interstellar medium (ISM) but remain unchanged in high-$β$ environments like the intracluster medium (ICM). We also quantify the streaming energy loss rate in our simulations. For sub-Alfvénic turbulence, it is resolution-dependent (hence unconverged in large scale simulations) and heavily suppressed -- by an order of magnitude -- compared to the isotropic loss rate $v_{A} \cdot \nabla P_{\rm CR} / P_{\rm CR} \sim v_{A}/L_{0}$, due to misalignment between the mean field and isotropic CR gradients. Counterintuitively, and unlike acceleration efficiencies, CR losses are almost independent of magnetic field strength over $β\sim 1-100$ and are, therefore, not the primary factor behind lower acceleration rates when streaming is included. While this paper is primarily concerned with how turbulence affects CRs, in a follow-up paper (Bustard and Oh, in prep), we consider how CRs affect turbulence by diverting energy from the MHD cascade, altering the pathway to gas heating and steepening the turbulent power spectrum.

扫码加入交流群

加入微信交流群

微信交流群二维码

扫码加入学术交流群,获取更多资源