THE SPECTRUM OF ISOTROPIC DIFFUSE GAMMA-RAY EMISSION BETWEEN 100 MeV AND 820 GeV

Journal Article · Tue Jan 20 00:00:00 EST 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/799/1/86· OSTI ID:22364446

Ackermann, M.; Buehler, R. ^[1]; Ajello, M. ^[2]; Albert, A.; Blandford, R. D.; Bloom, E. D.; Bottacini, E.; Caliandro, G. A. ^[3]; Atwood, W. B. ^[4]; Baldini, L.; Bellazzini, R. ^[5]; Ballet, J. ^[6]; Barbiellini, G. ^[7]; Bastieri, D.; Buson, S. ^[8]; Bechtol, K. ^[9]; Bissaldi, E. ^[10]; Brandt, T. J. ^[11]; Bregeon, J. ^[12]; others, and

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1. Deutsches Elektronen Synchrotron DESY, D-15738 Zeuthen (Germany)
2. Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634-0978 (United States)
3. W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
4. Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States)
5. Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy)
6. Laboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d'Astrophysique, CEA Saclay, F-91191 Gif sur Yvette (France)
7. Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy)
8. Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy)
9. Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637 (United States)
10. Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, and Università di Trieste, I-34127 Trieste (Italy)
11. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
12. Laboratoire Univers et Particules de Montpellier, Université Montpellier 2, CNRS/IN2P3, F-34095 Montpellier (France)

The γ-ray sky can be decomposed into individually detected sources, diffuse emission attributed to the interactions of Galactic cosmic rays with gas and radiation fields, and a residual all-sky emission component commonly called the isotropic diffuse γ-ray background (IGRB). The IGRB comprises all extragalactic emissions too faint or too diffuse to be resolved in a given survey, as well as any residual Galactic foregrounds that are approximately isotropic. The first IGRB measurement with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi) used 10 months of sky-survey data and considered an energy range between 200 MeV and 100 GeV. Improvements in event selection and characterization of cosmic-ray backgrounds, better understanding of the diffuse Galactic emission (DGE), and a longer data accumulation of 50 months allow for a refinement and extension of the IGRB measurement with the LAT, now covering the energy range from 100 MeV to 820 GeV. The IGRB spectrum shows a significant high-energy cutoff feature and can be well described over nearly four decades in energy by a power law with exponential cutoff having a spectral index of 2.32 ± 0.02 and a break energy of (279 ± 52) GeV using our baseline DGE model. The total intensity attributed to the IGRB is (7.2 ± 0.6) × 10{sup –6} cm{sup –2} s{sup –1} sr{sup –1} above 100 MeV, with an additional +15%/–30% systematic uncertainty due to the Galactic diffuse foregrounds.

• OSTI ID: 22364446
• Journal Information: Astrophysical Journal, Vol. 799, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
APPROXIMATIONS
COSMIC GAMMA SOURCES
GAMMA RADIATION
GEV RANGE
INDEXES
MEV RANGE
MILKY WAY
PHOTON EMISSION
SPACE
TELESCOPES