Interpretation of the cosmic ray positron and antiproton fluxes

摘要

The spectral shape of cosmic ray positrons and antiprotons has been accurately measured in the broad kinetic energy range 1–350 GeV. In the higher part of this range (E approx> 30 GeV), the e~+ and p are both well described by power laws with spectral indices γ_e~+ - 2.77 ± 0.02 and γ_p approx= 2.78 ± 0.04 that are approximately equal to each other and to the spectral index of protons. In the same energy range, the positron-antiproton flux ratio has the approximately constant value 2.04 ± 0.04, that is consistent with being equal to the ratio e~+/p calculated for the conventional mechanism of production, where the antiparticles are created as secondaries in the inelastic interactions of primary cosmic rays with interstellar gas. The positron-antiproton ratio at lower energy is significantly higher (reaching a value e~+/p ≈ 100 for E ≈ 1 GeV), but, in the entire energy range 1–350 GeV, the flux ratio is consistent with being equal to the ratio of the production rates in the conventional mechanism, as the production of low-energy antiprotons is kinematically suppressed in collisions with a target at rest. These results strongly suggest that cosmic ray positrons and antiprotons have a common origin as secondaries in hadronic interactions. This conclusion has broad implications for the astrophysics of cosmic rays in the Galaxy.