利用高纬度云的费米-LAT观测约束cosmic ray传播晕厚度
Constraining the cosmic ray propagation halo thickness using Fermi-LAT observations of high-latitude clouds
摘要：
作为宇宙线传播的一个基本特征，扩散晕可以促进我们对宇宙线相关研究和间接暗物质的理解。由于计算晕圈尺寸的方法存在退化问题，因而受到较大不确定性的影响。来自高纬云的扩散γ射线可能独立地揭示晕的大小。由于空间相关传播（SDP）模型与观测到的CR值有更好的一致性，与传统的传播模型相比，本文利用Fermi-LAT $\rmγ$射线观测，研究了基于SDP模型的中高速云晕厚度。因此，为了不超过高纬度云的相对$γ$射线发射率，晕的厚度应该在$\rm ~3.3\sim9~ kpc$的范围内。此外，基于SDP模型估计的不同晕厚度下的$\rmγ$射线的空间形态是不同的，这为我们提供了一个工具来确定晕的大小。我们希望我们的模型可以在未来通过多波长观测进行测试和调整。
英文摘要：
As a basic characteristic of cosmic ray (CR) propagation, the diffusive halo can advance our understanding of many CR-related studies and indirect dark matter. The method to derive the halo size usually has degeneracy problems thus affected by large uncertainties. The diffusion gamma ray from high-latitude clouds might shed light on the halo size independently. Since the spatially dependent propagation (SDP) model has a better agreement with the observed CRs, compared with conventional propagation model, in this work, we investigate the halo thickness based on SDP model with Fermi-LAT $\rmγ$-ray observation on the high- and intermediate-velocity clouds. As a result, in order not to exceed the relative $γ$-ray emissivity in the high-latitude clouds, halo thickness should be in the range of $\rm ~3.3\sim9~ kpc$. Moreover, the spatial morphology of $\rmγ$-rays estimated based on SDP model under different values of halo thickness are distinctive, which provides us a tool to determine the halo size. We hope that our model could be tested and tuned by multi-wavelength observations in the future.
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