Cosmic ray signatures of a 2-3 Myr old local supernova

TL;DR

A 2-3 million-year-old local supernova likely contributed cosmic rays that explain observed anomalies in positron and antiproton fluxes, and influence cosmic ray spectra and composition measurements.

Contribution

Proposes that a local supernova event explains cosmic ray spectral features and composition anomalies, providing testable predictions for future experiments.

Findings

Local supernova explains positron and antiproton flux anomalies.

Antiproton spectrum extends as a power law into TeV energies.

Boron-to-carbon ratio may show a plateau at high energies.

Abstract

The supernova explosion which deposited $^{60}$Fe isotopes on Earth 2-3 million years ago should have also produced cosmic rays which contribute to the locally observed cosmic ray flux. We show that the contribution of this "local source" explains the "anomalies" observed in the positron and antiproton fluxes and explains why their spectral shape agrees with that of the proton flux. At the same time, this local source component accounts for the difference in the slopes of the spectra of cosmic ray nuclei as the result of the slightly varying relative importance of the "local" and the average component for distinct CR nuclei. Such a "local supernova" model for the spectra of nuclei can be tested via a combined measurement of the energy dependence of the boron-to-carbon (primary-to-secondary cosmic rays) ratio and of the antiproton spectrum: While the antiproton spectrum is predicted to extend approximately as a power law into the TeV range without any softening break, the B/C ratio is expected to show a "plateau" at a level fixed by the observed positron excess in the 30-300 GeV range. We discuss the observability of such a plateau with dedicated experiments for the measurement of the cosmic ray composition in 10 TeV energy range (NUCLEON, ISS-CREAM).