Co-evolution of cosmic ray energy spectra, composition, and anisotropies

TL;DR

This paper proposes a comprehensive model explaining the features of cosmic ray spectra, composition, and anisotropies across a wide energy range, linking them to multiple source populations and their evolution.

Contribution

It introduces a four-component model that correlates spectral features with different Galactic and extragalactic sources, providing a unified explanation for cosmic ray observations.

Findings

The local source explains the spectral hardening and bump.

Galactic sources determine the knee and second knee energies.

Transition from Galactic to extragalactic origin occurs around 10^8 GeV.

Abstract

The origin of cosmic rays remains an unresolved fundamental problem in astrophysics. The synergy of multiple observational probes, including the energy spectra, the mass composition, and anisotropy is a viable way to jointly uncover this mystery. In this work, we propose that the energy-dependent of those observables in a wide energy range, from $O(10)$ GeV to ultrahigh energies of $10^{11}$ GeV, share quite a few correlated features, indicating a strong co-evolution which could be a consequence of the underlying origin of different source populations. We decipher these structures with a four-component model, i.e., the ensemble of Galactic sources, a local source close to the solar system, and the ensemble of two extra-galactic source populations. In this scenario, the $O(10^2)$ GV hardening and $O(10)$ TV bump is due to the contribution of the local source, the knee is due to the maximum acceleration energy of protons by the Galactic source population, the second knee is due to the maximum acceleration energy of iron nuclei by Galactic sources, the dip feature between the two knees is due to the appearance of the extra-galactic component, the ankle comes from the transition from one extra-galactic component to the other, and the spectral suppression at the highest energies arises from the acceleration limit of the second extra-galactic component. The transition from Galactic to extra-galactic origin of cosmic rays occurs around $O(10^8)$ GeV, which is smaller than the ankle energy.