ARE COSMIC RAYS MODULATED BEYOND THE HELIOPAUSE?
ARE COSMIC RAYS MODULATED BEYOND THE HELIOPAUSE?
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DOI：
10.1088/0004-637x/782/1/24
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发表时间：
2014-01
期刊：
影响因子：
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通讯作者：
J. Kóta;J. Jokipii
中科院分区：
文献类型：
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作者：
J. Kóta;J. Jokipii
我们讨论银河系和异常宇宙线（GCR 和 ACR）在日球层顶（HP）及其之后可能的空间变化。在帕克输运方程的框架内，并假设日鞘中存在不可压缩等离子体，我们考虑高度理想化的简单流模型，并将我们的 GCR 结果与 Scherer 等人最近发表的论文进行比较。和施特劳斯等人。首先，我们讨论一个数量级估计和一个简单的球形模型，以证明如果 HP 之外的扩散系数大于 ≈1026 cm2 s−1（该值比根据 GCR 成分观测确定的 1028 cm2 s−1 的值小两个数量级），则 HP 之外的 GCR 的调制一定非常小。其次，我们构建了一个非球形模型，该模型允许流动的横向偏转并使用平行和垂直于磁场的不同扩散系数。我们发现，只要平行扩散足够快，即使 HP 之外的垂直扩散系数非常小（约 1022 cm2 s−1），HP 之外的 GCR 调制仍然很小。我们还考虑了超出 HP 的平行扩散速度很快，但垂直扩散小至 ≈1020 cm2 s−1 的情况；这导致 HP 处 GCR 通量急剧、几乎呈阶梯状增加（以及 ACR 减少）。简要讨论了可能的影响。我们进一步提出这样一种可能性：在 HP 处观察到的 GCR 的急剧梯度可能会使 HP 比之前想象的更接近太阳。
We discuss the possible spatial variation of Galactic and anomalous cosmic rays (GCRs and ACRs) at and beyond the heliopause (HP). Remaining within the framework of the Parker transport equation and assuming incompressible plasma in the heliosheath, we consider highly idealized simple-flow models and compare our GCR results with recent publications of Scherer et al. and Strauss et al. First, we discuss an order-of-magnitude estimate and a simple spherical model to demonstrate that the modulation of GCRs beyond the HP must be quite small if the diffusion coefficient beyond the HP is greater than ≈1026 cm2 s−1, a value that is two orders of magnitude smaller than the value of 1028 cm2 s−1 determined from observations of GCR composition. Second, we construct a non-spherical model, which allows lateral deflection of the flow and uses different diffusion coefficients parallel and perpendicular to the magnetic field. We find that modulation of GCRs beyond the HP remains small even if the perpendicular diffusion coefficient beyond the HP is quite small (≈1022 cm2 s−1) as long as the parallel diffusion is sufficiently fast. We also consider the case when the parallel diffusion beyond the HP is fast, but the perpendicular diffusion is as small as ≈1020 cm2 s−1; this results in a sharp, almost step-like increase of GCR flux (and decrease of ACRs) at the HP. Possible implications are briefly discussed. We further suggest the possibility that the observed sharp gradient of GCRs at the HP might push the HP closer to the Sun than previously thought.