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Implication of multiple source populations of Galactic cosmic rays from proton and helium spectra

Qiang Yuan

TL;DR

This study tackles the origin of Galactic cosmic rays by addressing the complex, multi‑bump structure observed in proton and helium spectra across wide energy ranges. It combines a phenomenological three‑component fit with a physically grounded, spatially dependent propagation (SDP) model to attribute spectral features to distinct source populations and local accelerators. The results show that the data can be reproduced either by two background populations plus one local source or by one background plus two local sources, with plausible energetics (~$10^{50}$ erg) and realistic source classes such as SNRs, PWNe, and star clusters. This framework, aligned with γ‑ray observations of nearby accelerators, offers a path toward identifying the origins of Galactic CRs and motivates future γ‑ray and molecular‑cloud tests to validate the local‑source scenarios.

Abstract

Complicated hardenings and softenings of the spectra of cosmic ray protons and helium have been revealed by the newest measurements, which indicate the existence of multiple source populations of Galactic cosmic rays. We study the physical implications of these results in this work. A phenomenological fitting shows that three components can properly give the measured structures of the proton and helium spectra. The data are then accounted for in a physically motivated, spatially-dependent propagation model. It has been shown that one background source population plus two local sources, or two background source populations plus one local source can well reproduce the measurements. The spectral structures of individual species of cosmic rays are thus natural imprints of different source components of cosmic rays. Combined with ultra-high-energy $γ$-ray observations of various types of sources, the mystery about the origin of Galactic cosmic rays may be uncovered in future.

Implication of multiple source populations of Galactic cosmic rays from proton and helium spectra

TL;DR

This study tackles the origin of Galactic cosmic rays by addressing the complex, multi‑bump structure observed in proton and helium spectra across wide energy ranges. It combines a phenomenological three‑component fit with a physically grounded, spatially dependent propagation (SDP) model to attribute spectral features to distinct source populations and local accelerators. The results show that the data can be reproduced either by two background populations plus one local source or by one background plus two local sources, with plausible energetics (~ erg) and realistic source classes such as SNRs, PWNe, and star clusters. This framework, aligned with γ‑ray observations of nearby accelerators, offers a path toward identifying the origins of Galactic CRs and motivates future γ‑ray and molecular‑cloud tests to validate the local‑source scenarios.

Abstract

Complicated hardenings and softenings of the spectra of cosmic ray protons and helium have been revealed by the newest measurements, which indicate the existence of multiple source populations of Galactic cosmic rays. We study the physical implications of these results in this work. A phenomenological fitting shows that three components can properly give the measured structures of the proton and helium spectra. The data are then accounted for in a physically motivated, spatially-dependent propagation model. It has been shown that one background source population plus two local sources, or two background source populations plus one local source can well reproduce the measurements. The spectral structures of individual species of cosmic rays are thus natural imprints of different source components of cosmic rays. Combined with ultra-high-energy -ray observations of various types of sources, the mystery about the origin of Galactic cosmic rays may be uncovered in future.

Paper Structure

This paper contains 7 sections, 4 equations, 5 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Phenomenological three-component fitting of the spectra
  3. Modeling of the spectra in a physical propagation framework
  4. Propagation model
  5. Local source
  6. Results
  7. Conclusion and discussion

Figures (5)

  • Figure 1: Joint fiting results of the proton and helium spectra assuming three source components, compared with the measurement of DAMPE (FTFP_BERT model) 2019SciA....5.3793A2021PhRvL.126t1102A and LHAASO (EPOS-LHC model) 2025arXiv250514447T2025LHAASOhelium.
  • Figure 2: Fitting results of the ratios of B/C, B/O, and fluxes of carbon and oxygen in the SDP model, compared with the measurement of Voyager-1 2016ApJ...831...18C, ACE 2019SCPMA..6249511Y, AMS-02 2021PhR...894....1A, and DAMPE 2022SciBu..67.2162D. Dashed lines are the results in the local interstellar medium, and solid lines are those after solar modulation with a potential of $600$ MV.
  • Figure 3: Model results of the proton and helium spectra assuming the contribution from background sources (green short-dashed) and a local source (red long-dashed). Solid lines show the total fluxes. The solar modulation is applied with a modulation potential of 600 MV.
  • Figure 4: Model results of the proton and helium spectra assuming the contribution from background sources (green short-dashed) and two local sources (long-dashed). Solid lines show the total fluxes. The solar modulation is applied with a modulation potential of 600 MV.
  • Figure 5: Model results of the proton and helium spectra assuming the contribution from two populations of background sources (short-dashed) and one local source (red long-dashed). Solid lines show the total fluxes. The solar modulation is applied with a modulation potential of 600 MV.