Impact of Fermi-LAT and AMS-02 results on cosmic-ray astrophysics

TL;DR

This paper reviews recent AMS-02 and Fermi-LAT data on cosmic rays and gamma-ray emissivity, analyzing their implications for cosmic-ray spectra, origins of spectral hardening, and nuclear enhancement factors in Galactic astrophysics.

Contribution

It provides a comprehensive analysis of recent cosmic-ray and gamma-ray data, exploring spectral features and nuclear corrections relevant to Galactic cosmic-ray models.

Findings

Cosmic-ray proton spectra can be modeled with or without a spectral hardening at >300 GV.

Gamma-ray emissivity data alone cannot distinguish between a simple power-law and a hardened spectrum.

Nuclear enhancement factors are estimated to range from 1.52 to 1.92.

Abstract

This article reviews a few topics relevant to Galactic cosmic-ray astrophysics, focusing on the recent AMS-02 data release and Fermi Large Area Telescope data on the diffuse Galactic gamma-ray emissivity. Calculations are made of the diffuse cosmic-ray induced p+p --> pi^0 --> 2 gamma spectra, normalized to the AMS-02 cosmic-ray proton spectrum at ~ 10 - 100 GV, with and without a hardening in the cosmic-ray proton spectrum at rigidities R >~ 300 GV. A single power-law momentum "shock" spectrum for the local interstellar medium cosmic-ray proton spectrum cannot be ruled out from the gamma-ray emissivity data alone without considering the additional contribution of electron bremsstrahlung. Metallicity corrections are discussed, and a maximal range of nuclear enhancement factors from 1.52 to 1.92 is estimated.Origins of the 300 GV cosmic-ray proton and alpha-particle hardening are discussed.