The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV

Collaboration
Oct 14, 2014
61 pages
Published in:
  • Astrophys.J. 799 (2015) 86
  • Published: Jan 19, 2015
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Abstract: (IOP)
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(–)(6) cm(–)(2) s(–)(1) sr(–)(1) above 100 MeV, with an additional +15%/–30% systematic uncertainty due to the Galactic diffuse foregrounds.
Note:
  • Accepted by The Astrophysical Journal
  • gamma rays: diffuse background
  • diffuse radiation
  • gamma ray: energy spectrum
  • gamma ray: background
  • cosmic radiation: galaxy
  • gamma ray: VHE
  • GLAST
  • direct detection
  • cosmic background radiation
  • gamma ray: emission