BL Lac contribution to the Extragalactic Gamma-Ray Background

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dc.creatorKneiske, Tanja
dc.creatorMannheim, Karl
dc.date2004-11-05
dc.date2004-11-14
dc.date.accessioned2026-07-07T06:22:11Z
dc.date.available2026-07-07T06:22:11Z
dc.descriptionVery high energy gamma-rays(E>20GeV) from blazars traversing cosmological distances through the metagalactic radiation field can convert to electron-positron pairs in photon-photon collisions. The converted gamma-rays initiate electromagnetic cascades driven by inverse-Compton scattering off the microwave background photons. The cascades shift the injected gamma ray spectrum to MeV-GeV energies. Randomly oriented magnetic fields rapidly isotropize the secondary electron-positron beams resulting from the beamed blazar gamma ray emission, leading o faint gamma-ray halo. Using a model for the time-dependent metagalactic radiation field consistent with all currently available far-infrared-to-optical data, we compute (i) the expected gamma-ray attenuation in blazar spectra, and (ii) the cascade contribution from faint, unresolved blazars to the extragalactic gamma-ray background as measured by EGRET, assuming a generic emitted spectrum extending to an energy of 10 TeV. The latter cascade contribution to the EGRET background is fed by the assumed >20 GeV emission from the hitherto undiscovered sources, and we estimate their dN-dz distribution taking into account that the nearby (z<0.2) fraction of these sources must be consistent with the known (low) numbers of sources above 300 GeV.
dc.description6 pages, 5 figures to appear in the proceedings of the Gamma 2004 Symposium on High Energy Gamma Ray Astronomy, Heidelberg, July 2004 (AIP Proceedings Series)
dc.identifierhttps://arxiv.org/abs/astro-ph/0411146
dc.identifierhttp://arxiv.org/abs/astro-ph/0411146
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/95833
dc.subjectAstrophysics
dc.titleBL Lac contribution to the Extragalactic Gamma-Ray Background
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