Constraints on the gamma-ray opacity of the Universe with the Fermi-LAT instrument

Anita Reimer, A. Bouvier, A. Chen, S. Raino, S. Razzaque, L. Reyes

Research output: Contribution to journalConference articlepeer-review


The Fermi Large Area Telescope is scanning the sky for gamma-rays in the range 20 MeV to over 300 GeV, revealing a wealth of high energy sources. Gamma rays may interact with low-energy photons from the Extragalactic Background Light (EBL) through photon-photon pair production if above the energy threshold. This results in redshift- and energy-dependent attenuation features in extragalactic source spectra such as from blazars and Gamma-Ray Bursts (GRBs). Using photons above 10 GeV collected by the LAT during more than one year of observations from high-redshift blazars and GRBs, the effect of gamma-ray flux attenuation by the EBL is investigated. I present several techniques that are used to place robust upper limits on the gamma-ray opacity of the Universe at various energies and redshifts. The comparison with predictions from a range of EBL models allows then to derive high-confidence limits on EBL intensity models. In particular, the results of this analysis imply that the EBL intensity at optical/UV wavelengths must be significantly lower as that predicted by the "baseline model".

Original languageEnglish
JournalProceedings of Science
Publication statusPublished - 2010
Externally publishedYes
EventWorkshop on Cosmic Radiation Fields: Sources in the Early Universe, CRF 2010 - Hamburg, Germany
Duration: 9 Nov 201012 Nov 2010

ASJC Scopus subject areas

  • Multidisciplinary


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