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        Fermi Large Area Telescope Constraints on the Gamma-ray

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        905132.pdf (PDF, 497Kb)
        Author
        Abdo, A.A.
        Ackermann, M.
        Ajello, M.
        Allafort, A.
        Atwood, W.B.
        Baldini, L.
        Ballet, J.
        Granot, J.
        Ziegler, M.
        Attention
        2299/5494
        Abstract
        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.
        Publication date
        2010
        Published in
        The Astrophysical Journal
        Other links
        http://hdl.handle.net/2299/5494
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