University of Hertfordshire

From the same journal

From the same journal

Fermi Large Area Telescope Constraints on the Gamma-ray

Research output: Contribution to journalArticlepeer-review


  • A.A. Abdo
  • M. Ackermann
  • M. Ajello
  • A. Allafort
  • W.B. Atwood
  • L. Baldini
  • J. Ballet
  • J. Granot
  • M. Ziegler
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Original languageEnglish
Pages (from-to)1082-1096
JournalThe Astrophysical Journal
Publication statusPublished - 2010


The Extragalactic Background Light (EBL) includes photons with wavelengths from ultraviolet to infrared, which are effective at attenuating gamma rays with energy above ~10 GeV during propagation from sources at cosmological distances. This results in a redshift- and energy-dependent attenuation of the gamma-ray flux of extragalactic sources such as blazars and Gamma-Ray Bursts (GRBs). The Large Area Telescope onboard Fermi detects a sample of gamma-ray blazars with redshift up to z~3, and GRBs with redshift up to z~4.3. Using photons above 10 GeV collected by Fermi over more than one year of observations for these sources, we investigate the effect of gamma-ray flux attenuation by the EBL. We place upper limits on the gamma-ray opacity of the Universe at various energies and redshifts, and compare this with predictions from well-known EBL models. We find that an EBL intensity in the optical-ultraviolet wavelengths as great as predicted by the "baseline" model of Stecker et al. (2006) can be ruled out with high confidence.


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