Diffusive Shock Acceleration: Breakdown of Spatial Diffusion and Isotropy
Diffusive Shock Acceleration: Breakdown of Spatial Diffusion and Isotropy
复制标题
扩散激波加速：空间扩散和各向同性的分解
DOI：
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发表时间：
2019
影响因子：
4.9
通讯作者：
Y. Lyubarski
中科院分区：
文献类型：
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作者：
U. Keshet;Ofir Arad;Y. Lyubarski
我们指出，在压缩比为r的非相对论激波中加速的粒子不一定达到标准的谱指数p = (r + 2)/(r−1)。以前的光谱推导，基于近似的空间扩散或可忽略的各向异性，被证明依赖于不合理的隐含假设。我们分析地证明了标准结果在各向同性介质的极限下仍然是有效的。对于各向异性介质，问题通常需要数值处理；只要各向异性不太强，标准结果仍然有效，但即使在小角度散射极限下，p也会大大偏离标准结果。讨论了额外的光谱修正，例如，在激波的中间光学深度处散射模式的运动。
We point out that particles accelerated in a nonrelativistic shock of compression ratio r do not necessarily attain the standard, p = (r + 2)/(r − 1) spectral index. Previous derivations of the spectrum, based on the approximations of spatial diffusion or negligible anisotropy, are shown to rely on unjustified implicit assumptions. We prove analytically that the standard result is nevertheless valid in the limit of an isotropic medium. For an anisotropic medium, the problem generally requires a numerical treatment; the standard result remains valid as long as the anisotropy is not too strong, but p can substantially deviate from the standard result for sufficiently anisotropic scattering, even in the small-angle scattering limit. Additional spectral modifications, for example, by motions of scattering modes at intermediate optical depths from the shock, are discussed.