Fermi LAT Measurements of the Diffuse Gamma-Ray Emission at Intermediate Galactic Latitudes

The diffuse Galactic γ-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory (CGRO) indicated excess γ-ray emission ≥ 1 GeV relative to diffuse Galactic γ-ray emission models consistent with directly measured CR spectra (the so-called “EGRET GeV excess”). The excess emission was observed in all directions on the sky, and a variety of explanations have been proposed, including beyond-the-Standard-Model scenarios like annihilating or decaying dark matter. The Large Area Telescope (LAT) instrument on the Fermi Gamma-ray Space Telescope has measured the diffuse γ-ray emission with unprecedented sensitivity and resolution. We report on LAT measurements of the diffuse γ-ray emission for energies 100 MeV to 10 GeV and Galactic latitudes 10◦ ≤ |b| ≤ 20. The LAT spectrum for this region of the sky is well reproduced by the diffuse Galactic γ-ray emission models mentioned above and inconsistent with the EGRET GeV excess.