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

The supernova explosion which deposited Fe-60 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 causes the anomalies observed in the positron and antiproton fluxes and explains why their spectral shapes agree 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 the 10 TeV energy range (NUCLEON, ISS-CREAM).