Development of the Model of Galactic Interstellar Emission for Standard Point-Source Analysis of Fermi Large Area Telescope Data

Understand

Most of the celestial gamma rays detected by the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope originate from the interstellar medium when energetic cosmic rays interact with interstellar nucleons and photons.

• Conventional point and extended source studies rely on the modeling of this diffuse emission for accurate characterization.
• We describe here the development of the Galactic Interstellar Emission Model (GIEM) that is the standard adopted by the LAT Collaboration and is publicly available.
• The model is based on a linear combination of maps for interstellar gas column density in Galactocentric annuli and for the inverse Compton emission produced in the Galaxy.