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Development of the Model of Galactic Interstellar Emission for Standard Point-Source Analysis of Fermi Large Area Telescope DataMost of the celestial gamma 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 20deg and we observe an enhanced emission toward their base extending in the north and south Galactic directions and located within approximately 4deg of the Galactic Center.
Document ID
20170003792
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Acero, F.
(Universite Paris Diderot Paris, France)
Ackermann, M.
(Deutsches Elektronen-Synchrotron Zeuthen, Germany)
Ajello, M.
(Clemson Univ. SC, United States)
Albert, A.
(Kavli Inst. for Particle Astrophysics and Cosmology Stanford, CA, United States)
Baldini, L.
(Kavli Inst. for Particle Astrophysics and Cosmology Stanford, CA, United States)
Ballet, J.
(Universite Paris Diderot Paris, France)
Barbiellini, G.
(Istituto Nazionale di Fisica Nucleare Pisa, Italy)
Bastieri, D.
(Istituto Nazionale di Fisica Nucleare Padova, Italy)
Bellazzini, R.
(Istituto Nazionale di Fisica Nucleare Pisa, Italy)
Brandt, T. J.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Ferrara, E. C.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Harding, A. K.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Hays, E.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
McEnery, J. E.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Thompson, D. J.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Date Acquired
April 20, 2017
Publication Date
April 22, 2016
Publication Information
Publication: The Astrophysical Journal, Supplement Series
Publisher: The American Astromical Society
Volume: 223
Issue: 2
ISSN: 0067-0049
e-ISSN: 1538-4365
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN41896
Distribution Limits
Public
Copyright
Other
Keywords
gamma rays: diffuse background – gamma rays: general – gamma rays: ISM

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