Fermi-LAT Study of Cosmic-rays/Diffuse Gamma-rays and Implications on Particle Physics

Abstract

The Galactic and extragalactic diffuse gamma-ray emission has been one of hot topics in high-energy astrophysics. The Galactic diffuse gamma-rays is a powerful probe to study cosmic-rays and the interstellar medium in the Milky Way. The extragalactic diffuse gamma-ray emission is composed of contributions from unresolved sources such as active galactic nuclei. They may also contain the signature of exotic physics like the annihilation of dark matter. Our knowledge of the diffuse gamma-ray emission was not good enough in the last century, however, due to the limited angular resolution, effective area and energy coverage of past instruments. The situation has been improved significantly by the advent of the Large Area Telescope (LAT) on board Fermi Gamma-ray Space Telescope launched in 2008 June. The Fermi-LAT also has a capability to measure cosmic-ray electron spectrum up to about 1TeV and may probe nearby cosmic-ray electron accelerators or dark matter signal. We review the observation and analysis of the diffuse gamma-ray emission and cosmic-ray electrons by the Fermi-LAT, and implications on astrophysics and particle physics.