An extragalactic ``flux trapping'' origin of the dominant part of hadronic cosmic rays?

TL;DR

This paper proposes that extragalactic cosmic rays are trapped in the Galaxy's magnetic fields, explaining their observed spectrum and the cosmic-ray ankle, and suggests a dual origin for cosmic rays involving both extragalactic and Galactic sources.

Contribution

It introduces a flux trapping hypothesis for extragalactic cosmic rays, reconciling their energy spectrum with Galactic propagation models and explaining the cosmic-ray ankle.

Findings

Extragalactic cosmic-ray density matches local observations.

The cosmic-ray ankle naturally arises from the flux trapping scenario.

Magellanic clouds' gamma-ray flux does not test the extragalactic origin hypothesis.

Abstract

An extragalactic origin of the dominant part of all extrasolar hadronic cosmic rays above about 10 MeV/nucleon has long been considered unlikely due to energy considerations. In order to circumvent such arguments, the hypothesis that ``flux trapping'' of extragalactic cosmic rays occurs in the Galactic confinement volume is advanced in this paper. This hypothesis is based on a number of speculative assumptions about the properties of Galactic and intergalactic magnetic fields. The intergalactic cosmic-ray density expected under conservative assumptions about its extragalactic origins is then shown to be of the right order of magnitude to account for the locally observed cosmic radiation. It is demonstrated that an extragalactic scenario of cosmic-ray origin that is consistent with the observed cosmic-ray energy spectrum and preserves the successes of Galactic propagation theory can be constructed. The position of the ``ankle'' in the cosmic-ray energy spectrum follows as a natural consequence from this explanation. The $\gamma$-ray flux from the Magellanic clouds is shown to provide no suitable testing ground for the decision for or against an extragalactical origin in this scenario. It is argued that recent observational evidence seems to be in favour of a dual origin of cosmic-rays. The hadronic component is mainly extragalactic while the electrons are accelerated in Galactic supernova remnants.