朝向银河系反中心的旋臂中宇宙射线密度的测量
Measurement of Cosmic-Ray Density in the Spiral Arms toward Galactic Anticenter
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中文总结 AI 辅助
利用Fermi-LAT近17年数据测量银河系反中心方向三个旋臂的宇宙射线密度与谱指数，发现外银河系密度更高、谱更硬，可能源于更大晕或局部加速增强。
中文摘要 AI 辅助
利用近17年的费米大面积望远镜（Fermi-LAT）数据，我们分析了银河系不同旋臂在银经$l = 105^\circ$至$145^\circ$、银纬$b = -5^\circ$至$5^\circ$范围内的弥散伽马射线发射。这些旋臂的伽马射线发射均显示出清晰的π介子鼓包特征，这可以用宇宙射线质子的幂律谱很好地解释。对应于三个不同旋臂——本地臂、英仙臂和外臂——的光谱指数分别约为$-2.75$、$-2.55$和$-2.80$。估计能量高于10 GeV的宇宙射线能量密度均约为$0.2\rm~eV~cm^{-3}$。我们进一步将我们的结果与先前的研究进行了比较，先前的研究建立了各种传播模型，预测宇宙射线密度随银心半径增加而降低，谱随之变软。我们发现外银河系中的密度高于预测值，谱指数比预测的更硬，这表明可能来自更大的晕、更慢的磁场衰减，或这些效应及其他效应的组合。特别是，在英仙臂中观测到的谱硬化可能归因于局部增强的宇宙射线加速。
英文摘要
Using nearly 17 years of Fermi-LAT data, we analyzed the diffuse gamma-ray emission associated with different spiral arms of the Milky Way in the ranges $l = 105^\circ$ to $145^\circ$ and $b = -5^\circ$ to $5^\circ$. The gamma-ray emissions from these spiral arms all exhibited clear pion-bump features, which can be well explained by a power-law spectrum of cosmic-ray protons. The spectral indices corresponding to the three distinct spiral arms -- the Local Arm, the Perseus Arm, and the Outer Arm -- are found to be approximately $-2.75$, $-2.55$, and $-2.80$, respectively. The energy densities of the cosmic rays above 10 GeV are estimated to be all around 0.2$\rm~eV~cm^{-3}$. We further compared our results with previous studies, which have established various propagation models predicting that cosmic ray density decreases and spectra soften with increasing Galactocentric radius. We found higher densities and harder spectral indices than predicted in the outer Galaxy, suggesting possible contributions from a larger halo, slower magnetic field decay, or a combination of these and other effects. In particular, the spectral hardening observed in the Perseus Arm may be attributed to locally enhanced cosmic-ray acceleration.
发表机构
- School of Astronomy, University of Science and Technology of China（中国科学技术大学天文学院）
- Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）
- TIANFU Cosmic Ray Research Center（天府宇宙线研究中心）
机构由 AI 辅助整理，请以论文原文为准。
