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Very high energy gamma rays from active galactic nuclei: Cascading on the cosmic background radiation fields and the formation of pair halosRecent high-energy gamma-ray observations (E(sub gamma) greater than 100 MeV) of blazar Active Galactic Nuclei (AGNs) show emission spectra with no clear upper energy cutoff. AGNs, considered to be possible sources for the observed flux of cosmic rays beyond 10(exp 19) eV, may well have emission extending into the very high energy (VHE), (E(sub gamma) greater than 100 GeV) domain. Because VHE gamma-rays are absorbed by pair production on the intergalactic background radiation fields, much of this emission may not be directly visible. The electromagnetic cascades initiated by absorbed VHE gamma-rays, however, may be observable. Since, most probably, the velocities of (e(+), e(-)) pairs produced in a cascade are quickly isotropized by an ambient random magnetic field, extended 'halos' (R greater than 1 Mpc) of pairs will be formed around AGNs with VHE emission. The cascade radiation from these pair halos is emitted isotropically and should be observable at energies below a few TeV. The halo radiation can be distinguished by its characteristic variation in spectrum and intensity with angular distance from the central source. This variation depends weakly on the details of the central source model, e.g., the orientation and beaming/opening angle of an emitting jet. Limiting or determining the intensity of the pair halo can thus serve as a model-independent bound on or measure of the VHE power of AGNs. Next-generation Cherenkov telescopes may be able to image a pair halo.
Document ID
19950033063
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Aharonian, F. A.
(Max-Planck-Institut fuer Kernphysik Heidelberg, Germany)
Coppi, P. S.
(Univ. of Chicago, Chicago, IL United States)
Voelk, H. J.
(Max-Planck-Institut fuer Kernphysik Heidelberg, Germany)
Date Acquired
August 16, 2013
Publication Date
March 1, 1994
Publication Information
Publication: Astrophysical Journal, Part 2 - Letters
Volume: 423
Issue: 1
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
95A64662
Funding Number(s)
CONTRACT_GRANT: NAGW-1636
CONTRACT_GRANT: NAGW-830
CONTRACT_GRANT: NAGW-1284
Distribution Limits
Public
Copyright
Other

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