Challenging Cosmic‐Ray Propagation with Antiprotons: Evidence for a “Fresh” Nuclei Component?

Recent measurements of the cosmic-ray (CR) antiproton flux have been shown to challenge existing CR propagation models. It was shown that the reacceleration models designed to match secondary/primary nuclei ratios (e.g., boron/carbon) produce too few antiprotons. Matching both the secondary/primary nuclei ratio and the antiproton flux requires artificial breaks in the diffusion coefficient and the primary injection spectrum, suggesting the need for other approaches. In the present paper we discuss one possibility to overcome these difficulties. Using the measured antiproton flux and B/C ratio to fix the diffusion coefficient, we show that the spectra of primary nuclei as measured in the heliosphere may contain a fresh, local, "unprocessed" component at low energies, perhaps associated with the Local Bubble, thus decreasing the measured secondary/primary nuclei ratio. The independent evidence for supernova activity in the solar vicinity in the last few Myr supports this idea. The model reproduces antiprotons, B/C ratio, and elemental abundances up to Ni ( Z ≤ 28). Calculated isotopic distributions of Be and B are in perfect agreement with CR data. The abundances of three "radioactive clock" isotopes in CRs, 10 Be, 26 Al, and 36 Cl, are all consistent and indicate a halo size z h ~ 4 kpc, based on the most accurate data taken by the ACE spacecraft.