Possible Evidence for the Stochastic Acceleration of Secondary Antiprotons by Supernova Remnants

TL;DR

This paper investigates whether secondary antiprotons produced and accelerated in supernova remnants can explain the observed increase in the cosmic-ray antiproton-to-proton ratio at high energies, challenging conventional models.

Contribution

It provides evidence supporting the stochastic acceleration of secondary antiprotons in supernova remnants as a significant factor in cosmic-ray spectra, which was not fully considered before.

Findings

The observed antiproton-to-proton ratio increase above 100 GV cannot be explained by standard propagation models.

Secondary antiprotons accelerated in supernova remnants can account for the high-energy ratio rise.

This process also likely contributes to the cosmic-ray positron excess.

Abstract

The antiproton-to-proton ratio in the cosmic-ray spectrum is a sensitive probe of new physics. Using recent measurements of the cosmic-ray antiproton and proton fluxes in the energy range of 1-1000 GeV, we study the contribution to the $\bar{p}/p$ ratio from secondary antiprotons that are produced and subsequently accelerated within individual supernova remnants. We consider several well-motivated models for cosmic-ray propagation in the interstellar medium and marginalize our results over the uncertainties related to the antiproton production cross section and the time-, charge-, and energy-dependent effects of solar modulation. We find that the increase in the $\bar{p}/p$ ratio observed at rigidities above $\sim$ 100 GV cannot be accounted for within the context of conventional cosmic-ray propagation models, but is consistent with scenarios in which cosmic-ray antiprotons are produced and subsequently accelerated by shocks within a given supernova remnant. In light of this, the acceleration of secondary cosmic rays in supernova remnants is predicted to substantially contribute to the cosmic-ray positron spectrum, accounting for a significant fraction of the observed positron excess.