Two kinds of Galactic source populations could explain the cosmic-ray observation up to the "knee" region

TL;DR

This paper proposes a two-component model with supernova remnants and microquasars as sources to explain cosmic-ray observations up to the PeV range, aligning with recent gamma-ray and composition data.

Contribution

It introduces a novel two-population source model for cosmic rays, incorporating recent gamma-ray detections from microquasars as PeV accelerators.

Findings

Charge-dependent cutoff explains observed spectra and composition.

Nuclei-dependent cutoff hypothesis is inconsistent with data.

Supernova remnants dominate below 100 TeV, microquasars above.

Abstract

Observations of diffuse gamma rays above hundreds of TeV from the Galactic disk provide strong evidence for the existence of PeV cosmic-ray accelerators--so-called PeVatrons--in the Galaxy. However, mounting observations have ruled out most supernova remnants as likely PeVatron candidates, suggesting instead that multiple populations of cosmic-ray sources exist in the Galaxy. Recently, the LHAASO collaboration reported the detection of ultra-high-energy gamma rays from microquasars, establishing that the black holes in these systems, which accrete matter from companion stars, are powerful PeV particle accelerators. In this work, we propose a two-component source model to explain the observed cosmic-ray spectra and composition up to the PeV range. Below approximately 100 TeV, supernova remnants serve as the dominant sources; above this energy, microquasars are considered the primary candidate population. Within this scenario, the assumption of a charge-dependent cutoff well accounts for the latest measurements, including the proton and helium spectra up to the PeV range, the energy-dependent composition, and the all-particle spectrum. In contrast, the nuclei-dependent cutoff hypothesis is ruled out by the data.