Ultrahigh-energy nuclei, photons, and magnetic fields

TL;DR

Recent cosmic-ray and gamma-ray data reveal new insights into the origins of ultrahigh-energy cosmic rays, the structure of magnetic fields, and photon backgrounds, suggesting both galactic and extragalactic sources influence observed phenomena.

Contribution

This paper synthesizes recent observational data to propose a comprehensive understanding of UHECR sources, magnetic field strengths, and photon interactions, highlighting the role of galactic sources and intergalactic magnetic fields.

Findings

Galactic sources contribute to UHECRs based on composition data.

Intergalactic magnetic fields are around a femtogauss, affecting cosmic ray propagation.

Secondary gamma rays from distant blazars match observed spectra.

Abstract

Combined recent data from cosmic-ray detectors and gamma-ray detectors have produced some surprising insights regarding the sources of ultrahigh-energy cosmic rays (UHECRs), magnetic fields inside and outside the Milky Way, and the universal photon backgrounds. The energy-dependent composition of UHECRs implies a non-negligible contribution of sources located in the Milky Way, such as past gamma-ray bursts that took place in our Galaxy. Extended halos of distant sources seen in the Fermi data imply that intergalactic magnetic fields have average strengths of the order of a femtogauss. Such relatively low magnetic fields imply that the protons from distant blazars generate a detectable flux of secondary gamma rays in their interactions with the photon background. A comparison with the data shows an excellent agreement of the secondary photons with the spectra of distant blazars observed by atmospheric Cherenkov telescopes.