Abstract
Powerful X-ray emission is a common feature of active galaxies, some of which have also been detected as γ-ray sources1–5. The observed high luminosities, coupled with reports of variability on time scales of days or less at X-ray energies6 and of 1 yr or less at γ-ray energies3, suggest that both emissions may originate in the same volume deep within the nucleus of the galaxy. Under this assumption we investigate here the attenuation of γ rays as a result of pair-production in photon–photon collisions with X rays and show that whilst Seyfert galaxies are transparent to γ radiation up to ∼1 GeV, QSOs and BL Lac objects are generally opaque about 1 MeV. However, the detection of γ rays from these latter classes of objects may be explained if beaming of the X–γ emission is assumed.
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Bassani, L., Dean, A. Absorption of γ rays in active galaxies as a test of the jet hypothesis. Nature 294, 332–333 (1981). https://doi.org/10.1038/294332a0
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DOI: https://doi.org/10.1038/294332a0
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