A minimal model for understanding secondary cosmic rays

We take a phenomenological approach in a minimal model to understand the spectral intensity of secondary cosmic-ray particles like positrons, antiprotons, Lithium, Beryllium and Boron. Our analysis shows that cosmic rays at GeV energies pass through a significant amount of matter in regions surrounding the sources. This grammage decreases with increasing cosmic-ray energy and becomes negligible beyond 100 GeV. During the subsequent propagation in the interstellar medium cosmic rays of all energies up to 105 GeV/n pass through about 1-2 g cm -2 of matter before leaking into the intergalactic medium. It is in the interstellar medium that the bulk of the positrons and antiprotons are generated. Also cosmic-ray nuclei like C, N, and O at all energies generate additional amounts of Li, Be and B nuclei with a spectrum similar to those of C, O etc. The implications of these findings of the minimal model to the observations of gamma rays and also the importance of spatial and temporal discreteness of cosmic-ray sources for modeling cosmic-ray propagation are briefly pointed out.(c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.

Automated summary

We use a phenomenological approach in a minimal model to study the spectral intensity of secondary cosmic-ray particles such as positrons, antiprotons, Lithium, Beryllium, and Boron. Our analysis shows that at GeV energies, cosmic rays traverse a significant amount of matter in the regions surrounding their sources. This amount decreases with increasing cosmic-ray energy and becomes negligible beyond 100 GeV. In the interstellar medium, cosmic rays of all energies up to 105 GeV/n pass through approximately 1-2 g/cm2 of matter before entering the intergalactic medium. The bulk of positrons and antiprotons are generated in the interstellar medium. Additionally, cosmic-ray nuclei like C, N, and O produce additional amounts of Li, Be, and B nuclei with spectra similar to those of C, O, etc. The implications of these minimal model findings for gamma-ray observations and the importance of spatial and temporal discreteness of cosmic-ray sources for modeling cosmic-ray propagation are briefly discussed.