[P-EM16] 太陽圏・惑星間空間

[PEM16-09] 銀河宇宙線異方性とそのrigidity依存性のベイズ推定

*小財 正義¹、宗像 一起²、加藤 千尋²、林 優希²、片岡 龍峰³、三宅 晶子⁴、門倉 昭¹ (1.情報・システム研究機構　データサイエンス共同利用基盤施設、2.信州大学、3.国立極地研究所、4.岐阜高専)

キーワード：銀河宇宙線、異方性、ミューオン、太陽変調

Anisotropy of galactic cosmic-rays (GCRs) represents their momentum-space distribution in the interplanetary plasma, playing a key role in revealing the GCR propagation and space environment. The ground-based muon detector network has been a unique means to observe the anisotropy, thanks to its excellent angular resolution, angular acceptance, and statistics. However, quantitative analysis of rigidity dependence of the anisotropy has been difficult because of poor energy resolutions of ground-based muon or neutron detectors. To overcome this situation and derive the rigidity dependence from differences in geomagnetic and atmospheric effects in the network, we are developing a new analysis method utilizing the Bayesian estimation approach. The Gaussian process is introduced as a prior distribution of the Bayesian estimation. It allows us to confine the smoothness of the rigidity spectrum, which is required to derive the spectrum from broad rigidity responses of ground-based observations, while being tolerant of spectrum shapes without assuming any analytical function. A focused analysis of the North-South (NS) anisotropy demonstrates the usefulness of this new method (https://doi.org/10.3847/1538-4357/ad8577). It reveals solar cycle variations of the NS anisotropy and, moreover, the diffusion coefficient or mean-free-path length of GCRs (attached figure) based on the GCR propagation theory. We are attempting to generalize this Bayesian estimation approach to three-dimensional anisotropy and will report on its application to short-term events, such as interplanetary shocks.