A Minimal Interpretation of the Galactic Cosmic-Ray Proton and Helium Spectra from GeV to PeV Energies
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2026
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| author | Aharonian, Felix Zhang, Bing Theodore |
| author_facet | Aharonian, Felix Zhang, Bing Theodore |
| contents | High-precision measurements of the cosmic-ray (CR) proton and helium spectra have revealed significant deviations from a simple power law, characterized by multiple spectral features, including a hardening above $\sim$100~GeV, a broad excess in the multi-TeV range, and a pronounced structure at PeV energies. We propose a minimal two-cosmic-ray-population framework that consistently accounts for the observed spectra of protons and helium across six decades in energy. In this scenario, the spectral complexity arises from a transition between two Galactic CR populations in the 10~TeV-1~PeV energy range. The low-energy proton population exhibits a sharp cutoff at tens of TeV, while a second, higher-energy population emerges and dominates above 100~TeV, terminating with a smooth exponential cutoff at $\sim$6.5~PeV. The same two-component model applied to CR helium, with a slightly harder first component extending effectively to several hundred TeV and a second component that scales with the proton spectrum in magnetic rigidity, provides a consistent description of both the helium spectrum and the p/He ratio. This framework reproduces the main observed spectral features of CR protons and helium without invoking contributions from nearby sources or non-standard assumptions about CR acceleration or propagation. Recent gamma-ray observations of supernova remnants, star-forming regions, and microquasars offer plausible astrophysical sites for these two CR components. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2602_08223 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | A Minimal Interpretation of the Galactic Cosmic-Ray Proton and Helium Spectra from GeV to PeV Energies Aharonian, Felix Zhang, Bing Theodore High Energy Astrophysical Phenomena Solar and Stellar Astrophysics High-precision measurements of the cosmic-ray (CR) proton and helium spectra have revealed significant deviations from a simple power law, characterized by multiple spectral features, including a hardening above $\sim$100~GeV, a broad excess in the multi-TeV range, and a pronounced structure at PeV energies. We propose a minimal two-cosmic-ray-population framework that consistently accounts for the observed spectra of protons and helium across six decades in energy. In this scenario, the spectral complexity arises from a transition between two Galactic CR populations in the 10~TeV-1~PeV energy range. The low-energy proton population exhibits a sharp cutoff at tens of TeV, while a second, higher-energy population emerges and dominates above 100~TeV, terminating with a smooth exponential cutoff at $\sim$6.5~PeV. The same two-component model applied to CR helium, with a slightly harder first component extending effectively to several hundred TeV and a second component that scales with the proton spectrum in magnetic rigidity, provides a consistent description of both the helium spectrum and the p/He ratio. This framework reproduces the main observed spectral features of CR protons and helium without invoking contributions from nearby sources or non-standard assumptions about CR acceleration or propagation. Recent gamma-ray observations of supernova remnants, star-forming regions, and microquasars offer plausible astrophysical sites for these two CR components. |
| title | A Minimal Interpretation of the Galactic Cosmic-Ray Proton and Helium Spectra from GeV to PeV Energies |
| topic | High Energy Astrophysical Phenomena Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2602.08223 |