Injection spectra of different species of cosmic rays from AMS-02, ACE-CRIS and Voyager-1

Abstract

Precise measurements of energy spectra of different cosmic ray species were obtained in recent years, by particularly the AMS-02 experiment on the International Space Station. It has been shown that apparent differences exist in different groups of the primary cosmic rays. However, it is not straightforward to conclude that the source spectra of different particle groups are different since they will experience different propagation processes (e.g., energy losses and fragmentations) either. In this work, we study the injection spectra of different nuclear species using the measurements from Voyager-1 outside the solar system, and ACR-CRIS and AMS-02 on top of atmosphere, in a physical framework of cosmic ray transportation. Two types of injection spectra are assumed, the broken power-law and the non-parametric spline interpolation form. The non-parametric form fits the data better than the broken power-law form, implying that potential structures beyond the constrained spectral shape of broken power-law may exist. For different nuclei the injection spectra are overall similar in shape but do show some differences among each other. For the non-parametric spectral form, the helium injection spectrum is the softest at low energies and the hardest at high energies. For both spectral shapes, the low-energy injection spectrum of neon is the hardest among all these species, and the carbon and oxygen spectra have more prominent bumps in 1-10 GV in the R2dN/dR presentation. Such differences suggest the existence of differences in the sources or acceleration processes of various nuclei of cosmic rays.