弱宇宙Shock Waves中非热粒子的再加速
Re-acceleration of Nonthermal Particles at Weak Cosmological Shock Waves
摘要：
我们研究扩散冲击加速（DSA）的pre-brackiting以及新注入的人口的非热，宇宙射线（CR）粒子在弱宇宙学冲击。假设简单的模型，热漏注入和Alfvénic漂移，我们推导出分析，时间依赖的解决方案的两个人口的CR加速试验粒子制度。然后，我们将它们与冲击波的动力学DSA模拟的结果进行比较，这些冲击波预计将在大尺度结构形成的过程中形成于团内介质和团簇外围。我们表明，测试粒子的解决方案提供了一个很好的近似的压力和光谱的CR加速在这些弱冲击。由于注入是非常低效的弱冲击，预先存在的CR人口占主导地位的注入人口。如果预先存在的CR质子产生的压力约为上游流中气体热压力的5%，则下游CR压力通常可吸收马赫数为$M \la 3$的冲击时冲击冲压压力的几%至10%。然而，CR电子的再加速可以导致在冲击后面的大量同步辐射。在整个冲击的同步辐射的增强估计为几个到几个$M \sim 1.5$和$10^2-10^3$的$M \sim 3$，取决于详细的模型参数。讨论了我们的研究结果对观测到的明亮射电遗迹的影响。
英文摘要：
We examine diffusive shock acceleration (DSA) of the pre-exisiting as well as freshly injected populations of nonthermal, cosmic-ray (CR) particles at weak cosmological shocks. Assuming simple models for thermal leakage injection and Alfvénic drift, we derive analytic, time-dependent solutions for the two populations of CRs accelerated in the test-particle regime. We then compare them with the results from kinetic DSA simulations for shock waves that are expected to form in intracluster media and cluster outskirts in the course of large-scale structure formation. We show that the test-particle solutions provide a good approximation for the pressure and spectrum of CRs accelerated at these weak shocks. Since the injection is extremely inefficient at weak shocks, the pre-existing CR population dominates over the injected population. If the pressure due to pre-existing CR protons is about 5 % of the gas thermal pressure in the upstream flow, the downstream CR pressure can absorb typically a few to 10 % of the shock ram pressure at shocks with the Mach number $M \la 3$. Yet, the re-acceleration of CR electrons can result in a substantial synchrotron emission behind the shock. The enhancement in synchrotron radiation across the shock is estimated to be about a few to several for $M \sim 1.5$ and $10^2-10^3$ for $M \sim 3$, depending on the detail model parameters. The implication of our findings for observed bright radio relics is discussed.
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