Analyzing Cosmic Ray Spectral Features: A Numerical Investigation

Abstract

Recent cosmic ray space-based and balloon-borne experiments have revealed various spectral features. Spectral hardening around ~200 GV has been seen in primary nuclei as well as secondaries produced during propagation. Proton spectrum softening at ~10 TV and helium spectrum softening at a few tens TV has also been seen. Additionally, a positron excess has been observed above ~25 GeV. The cosmic ray propagation code, GALPROP v57, was utilized to investigate the cause behind these features. A diffusion model with reacceleration and convection effects was used as a baseline. To find the best fit to the experimental data, GALPROP v57's parameter optimization module, utilizing the external numerical minimization software MINUIT2, was used. For the hardening, three scenarios were studied: (1) a diffusion coefficient break, (2) injection spectra breaks, and (3) a combination of both breaks. An additional injection spectrum break was considered to fit the softening of the proton and helium spectra. An additional positron source was introduced for the positron excess. The resulting elemental spectra and ratios, along with the all-particle spectrum, are compared to compiled cosmic ray data. Implications of these spectral features are also discussed.