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arXiv 0807.4259astro-ph
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粒子从cosmic ray修正激波中逃逸的研究

On the escape of particles from cosmic ray modified shocks

D. Caprioli, P. Blasi, E. Amato

摘要:

在非线性状态下,当被加速粒子对激波的动力学反应不可忽略时,激波处粒子加速问题的定态解显示出从激波向上游无穷远逃逸的显著能流。从物理学的角度来看,在所有加速粒子的最大动量$p_{max}$随时间减小的情况下,粒子从激波上游区域逃逸都是可以预料的,就像超新星遗迹壳层膨胀的Sedov-Taylor相的情况一样,此时激波速度和宇宙线感生磁化都减小了。在这种情况下,在每一次$t$,动量大于$p_{max}(t)$的粒子从上游离开系统,如果激波被宇宙射线的存在强烈地改变,则带走大部分能量。这一现象对于解释在地球上探测到的宇宙射线光谱至关重要。在本文中,我们讨论如何出现这种逃逸通量在不同的方法来非线性扩散激波加速,特别是在准定常半解析动力学的。我们将计算结果应用于一个典型超新星遗迹的Sedov-Taylor相,以自洽的方式包括粒子加速、磁场放大以及粒子和场对激波结构的动力学反应。在这个框架内,我们计算的时间演化的最大能量达到的加速粒子和逃逸通量向上游无穷大。后一个量与在地球上探测到的宇宙射线光谱直接相关。

英文摘要:

Stationary solutions to the problem of particle acceleration at shock waves in the non-linear regime, when the dynamical reaction of the accelerated particles on the shock cannot be neglected, are known to show a prominent energy flux escaping from the shock towards upstream infinity. On physical grounds, the escape of particles from the upstream region of a shock has to be expected in all those situations in which the maximum momentum of accelerated particles, $p_{max}$, decreases with time, as is the case for the Sedov-Taylor phase of expansion of a shell Supernova Remnant, when both the shock velocity and the cosmic ray induced magnetization decrease. In this situation, at each time $t$, particles with momenta larger than $p_{max}(t)$ leave the system from upstream, carrying away a large fraction of the energy if the shock is strongly modified by the presence of cosmic rays. This phenomenon is of crucial importance for explaining the cosmic ray spectrum detected at Earth. In this paper we discuss how this escape flux appears in the different approaches to non-linear diffusive shock acceleration, and especially in the quasi-stationary semi-analytical kinetic ones. We apply our calculations to the Sedov-Taylor phase of a typical supernova remnant, including in a self-consistent way particle acceleration, magnetic field amplification and the dynamical reaction on the shock structure of both particles and fields. Within this framework we calculate the temporal evolution of the maximum energy reached by the accelerated particles and of the escape flux towards upstream infinity. The latter quantity is directly related to the cosmic ray spectrum detected at Earth.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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