Journal
ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES
Volume 223, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.3847/0067-0049/223/2/26
Keywords
gamma rays: diffuse background; gamma rays: general; gamma rays: ISM
Categories
Funding
- National Aeronautics and Space Administration in the United States
- Department of Energy in the United States
- Commissariat a l'Energie Atomique in France
- Centre National de la Recherche Scientifique/Institut National de Physique Nucleaire et de Physique des Particules in France
- Agenzia Spaziale Italiana in Italy
- Istituto Nazionale di Fisica Nucleare in Italy
- Ministry of Education, Culture, Sports, Science and Technology (MEXT) in Japan
- High Energy Accelerator Research Organization (KEK) in Japan
- Japan Aerospace Exploration Agency (JAXA) in Japan
- KA Wallenberg Foundation in Sweden
- Swedish Research Council in Sweden
- Swedish National Space Board in Sweden
- Istituto Nazionale di Astrofisica in Italy
- Centre National d'Etudes Spatiales in France
- Grants-in-Aid for Scientific Research [15H02086, 26800160] Funding Source: KAKEN
- ICREA Funding Source: Custom
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Most of the celestial. rays detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope originate from the interstellar medium when energetic cosmic rays interact with interstellar nucleons and photons. Conventional point-source and extended-source studies rely on the modeling of this diffuse emission for accurate characterization. Here, we describe the development of the Galactic Interstellar Emission Model (GIEM), which is the standard adopted by the LAT Collaboration and is publicly available. This 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. In the GIEM, we also include large-scale structures like Loop. I and the Fermi bubbles. The measured gas emissivity spectra confirm that the cosmic-ray proton density decreases with Galactocentric distance beyond 5 kpc from the Galactic Center. The measurements also suggest a softening of the proton spectrum with Galactocentric distance. We observe that the Fermi bubbles have boundaries with a shape similar to a catenary at latitudes below 20 degrees and we observe an enhanced emission toward their base extending in the north and south Galactic directions and located within similar to 4 degrees of the Galactic Center.
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