膨胀局域星际云中multi-TeV宇宙射线的恒星各向异性
The sidereal anisotropy of multi-TeV cosmic rays in an expanding Local Interstellar Cloud
摘要：
西藏大气簇射（AS）实验观测到的银河宇宙线（GCR）强度的恒星各向异性尚待理论解释。所观察到的各向异性的全球功能，以及再现的双向和单向流动（BDF和UDF，分别）的GCR的叠加。如果推导出的BDF的方向表示局部星际磁场（LISMF）的方向，如通过将模型最佳拟合到数据所指示的，则偏离BDF方向的UDF意味着来自垂直于LISMF的流的显著贡献。这种垂直流动可能是由于漂移各向异性，因为预计垂直扩散的贡献远小于漂移效应。为UDF推导出的大振幅表明GCR密度的大空间梯度。我们认为，这样的密度梯度可以预期在日光层坐在接近本地星际云（LIC）的边界，如果LIC正在扩大。由于向内的交叉场扩散和膨胀引起的绝热冷却之间的平衡，LIC中GCR密度的空间分布达到稳态。我们推导出稳态分布的GCR密度的LIC基于径向输运的GCR在一个球形的LIC以恒定的速度膨胀。通过与Tibet实验观测结果的比较，我们估算了多TeV GCR在本星际空间的垂直扩散系数。
英文摘要：
The sidereal anisotropy of galactic cosmic ray (GCR) intensity observed with the Tibet Air Shower (AS) experiment still awaits theoretical interpretation. The observed global feature of the anisotropy is well reproduced by a superposition of the bi-directional and uni-directional flows (BDF and UDF, respectively) of GCRs. If the orientation of the deduced BDF represents the orientation of the local interstellar magnetic field (LISMF), as indicated by best-fitting a model to the data, the UDF deviating from the BDF orientation implies a significant contribution from the streaming perpendicular to the LISMF. This perpendicular streaming is probably due to the drift anisotropy, because the contribution from the perpendicular diffusion is expected to be much smaller than the drift effect. The large amplitude deduced for the UDF indicates a large spatial gradient of the GCR density. We suggest that such a density gradient can be expected at the heliosphere sitting close to the boundary of the Local Interstellar Cloud (LIC), if the LIC is expanding. The spatial distribution of GCR density in the LIC reaches a stationary state because of the balance between the inward cross-field diffusion and the adiabatic cooling due to the expansion. We derive the steady-state distribution of GCR density in the LIC based on radial transport of GCRs in a spherical LIC expanding at a constant rate. By comparing the expected gradient with the observation by Tibet experiment, we estimate the perpendicular diffusion coefficient of multi-TeV GCRs in the local interstellar space.
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