Cosmic Ray Studies with the Fermi Gamma-ray Space Telescope Large Area Telescope

TL;DR

The Fermi LAT provides detailed measurements of cosmic rays, revealing insights into their sources, distribution, and interactions in the galaxy, challenging existing models of cosmic-ray propagation.

Contribution

This paper presents new gamma-ray observations that constrain cosmic-ray models, suggesting more sources in the outer galaxy and larger diffusion halo than previously thought.

Findings

Cosmic-ray sources may be more abundant in the outer galaxy.

The scale height of the cosmic-ray diffusive halo may be larger than conventional models.

Gamma-ray observations support cosmic-ray production in supernova remnants.

Abstract

The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope provides both direct and indirect measurements of Galactic cosmic rays (CR). The LAT high-statistics observations of the 7 GeV - 1 TeV electron plus positron spectrum and limits on spatial anisotropy constrain models for this cosmic-ray component. On a Galactic scale, the LAT observations indicate that cosmic- ray sources may be more plentiful in the outer Galaxy than expected or that the scale height of the cosmic-ray diffusive halo is larger than conventional models. Production of cosmic rays in supernova remnants (SNR) is supported by the LAT gamma-ray studies of several of these, both young SNR and those interacting with molecular clouds.