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arXiv 1004.2771astro-ph.HEastro-ph.SR
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强超新星shock wave的结构及其过渡区电子的快速加速

Structure of a strong supernova shock wave and rapid electron acceleration confined in its transition region

Nobue Shimada, Masahiro Hoshino, Takanobu Amano

摘要:

利用数值模拟方法,报道了一个超新星激波过渡区(STR)内新的快速湍流过程。尽管作为主要耗散区的短轴反应区的规模只有几十万公里,但发现了一些与高能粒子根的产生有关的有趣结构。等离子体不稳定性的非线性演化导致了离子相空间分布的动态变化,这种动态变化与场性质的变化有关。结果,出现了不同类型的大振幅场结构。一个是主导的波包,另一个是一系列的磁孤立峰。每个场结构都有一个微观尺度(~离子惯性长度)。通过这些大振幅场结构之间的多重非线性散射,电子被直接加速。在STR中,快速热化实现了离子和电子之间的能量均分,热电子在保持这些大振幅场结构在离子声学模式上起着重要作用。超热电子呈现非麦克斯韦分布,可能是进一步非热布居的种子。“冲击系统”,新鲜的传入和反射的离子不断提供,在我们的结果中发挥了至关重要的作用。在垂直激波几何条件下,通过将STR的宽度等于高能电子的Larmor半径的长度来估算电子的最大能量,在MA = 170,ω pe/Ω ce = 120的实际条件下,估算出仅在STR内瞬时最大能量约为10 MeV。

英文摘要:

A new rapid energization process within a supernova shock transition region (STR) is reported by utilizing numerical simulation. Although the scale of a STR as a main dissipation region is only several hundreds of thousands km, several interesting structures are found relating to generation of a root of the energetic particles. The nonlinear evolution of plasma instabilities lead to a dynamical change in the ion phase space distribution which associates with change of the field properties. As a result, different types of large-amplitude field structures appear. One is the leading wave packet and another is a series of magnetic solitary humps. Each field structure has a microscopic scale (~ the ion inertia length). Through the multiple nonlinear scattering between these large-amplitude field structures, electrons are accelerated directly. Within a STR, quick thermalization realizes energy equipartition between the ion and electron, hot electrons play an important role in keeping these large-amplitude field structures on the ion-acoustic mode. The hot electron shows non-Maxwellian distribution and could be the seed of further non-thermal population. The "shock system", where fresh incoming and reflected ions are supplied constantly, play an essential role in our result. With a perpendicular shock geometry, the maximum energy of the electron is estimated by equating a width of the STR to a length of the Larmor radius of the energetic electron. Under some realistic condition of M_A = 170 and ω_{pe}/Ω_{ce} = 120, maximum energy is estimated to ~ 10 MeV at an instant only within the STR.

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