The Cosmic-ray Knee as a Local Signature of Nearby PeVatrons

Abstract

A "knee" in the cosmic-ray spectrum, characterized by a sudden steepening of the spectral shape at $\sim 4$ PeV, may be interpreted either as a global feature of Galactic cosmic rays or as a local signature. In the former scenario, cosmic-ray spectra throughout the Galaxy would be similar to that observed in the solar neighborhood, and the knee would be a common feature of the cosmic-ray sea. In the latter scenario, the PeV cosmic-ray flux varies across the Galactic disk, and the knee is dominantly contributed by a small number of nearby sources. By simulating cosmic-ray propagation in the Galactic magnetic field and interstellar medium, we show that the two scenarios correspond to different regimes of the birth rate of PeV proton accelerators and depend on the presence of powerful nearby sources. By comparison with both cosmic-ray and gamma-ray observations, we find that a local knee would be best explained by sources located at distances of order $\sim 1$ kpc and with ages in the range 0.1-1 Myr, with the Cygnus Cocoon being a particularly promising candidate.

12 pages, 7 figures, to appear in ApJL

References in corpus (18)

• The First LHAASO Catalog of Gamma-Ray Sources
• Measurement of ultra-high-energy diffuse gamma-ray emission of the Galactic plane from 10 TeV to 1 PeV with LHAASO-KM2A
• CRPropa 3.2 -- an advanced framework for high-energy particle propagation in extragalactic and galactic spaces
• Potential PeVatron supernova remnant G106.3+2.7 seen in the highest-energy gamma rays
• An Ultrahigh-energy $\gamma$-ray Bubble Powered by a Super PeVatron
• The low rate of Galactic pevatrons
• Ultra-High-Energy Gamma-Ray Bubble around Microquasar V4641 Sgr
• Simulating the Galactic Multi-messenger Emissions with HERMES
• Spectroscopic characterization of the known O-star population in Cygnus OB2. Evidence of multiple star-forming bursts
• Evidence for PeV Proton Acceleration from Fermi-LAT Observations of SNR G106.3+2.7
• Milky Way as a Neutrino Desert Revealed by IceCube Galactic Plane Observation
• Multiple emission components in the Cygnus cocoon detected from Fermi-LAT observations
• Precise measurements of the cosmic ray proton energy spectrum in the "knee'' region
• Astroparticles from X-ray Binary Coronae
• Observation of Cosmic-Ray Anisotropy in the Southern Hemisphere with 12 yr of Data Collected by the IceCube Neutrino Observatory
• Imprints of PeV cosmic-ray sources on the diffuse gamma-ray emission
• LHAASO protons versus LHAASO diffuse gamma-rays: a consistency check
• Limits on Leptonic TeV Emission from the Cygnus Cocoon with Swift-XRT