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arXiv · 2601.17851

Joint constraint on the propagation origin of the cosmic-ray spectral knee from energy spectrum and anisotropy observations

Hua Yue·Lin Nie·Yi-Qing Guo·Hong-Bo Hu
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Abstract

The origin mechanism of the cosmic-ray knee region remains an unresolved mystery, with acceleration, interaction, and propagation models drawing significant attention. The latest experimental observations of the PeV total spectrum, composition energy spectrum, and anisotropy-particularly the precise measurements of the proton spectrum by the LHAASO experiment-have provided crucial breakthroughs in uncovering its origin. Based on the latest LHAASO measurements of the proton energy spectrum, combined with cosmic-ray spectral and anisotropy data, this study proposes that the spectral index variation in the knee region arises from changes in the propagation coefficient. By introducing a knee position $\rm \mathcal{R}_{knee}$ and an index variation $\rm \delta_{knee}$, we construct a rigidity-dependent double-power-law diffusion model to reproduce the knee-region spectral structure. Through modifications to the diffusion coefficient, we successfully replicate the observed knee-region spectral structure in the LHAASO proton spectrum and calculate the corresponding anisotropy. Under current data and model dependencies, a joint analysis of the energy spectrum and anisotropy does not support the propagation origin model of the cosmic-ray knee at a 95\% confidence level. We hope that future LHAASO experiments will provide precise measurements of the energy spectra and anisotropies of various nuclei in the knee region, thereby offering a definitive test of the propagation model as the origin mechanism of the knee-region spectral structure.

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Hua Yue, Lin Nie, Yi-Qing Guo, Hong-Bo Hu. 2026-01-25. Joint constraint on the propagation origin of the cosmic-ray spectral knee from energy spectrum and anisotropy observations. https://doi.org/10.3847/1538-4357%2Fae3d2d

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