Limits on the isotropic diffuse flux of ultrahigh energy γ radiation

M. C. Chantell, C. E. Covault, J. W. Cronin, B. E. Fick, L. F. Fortson, J. W. Fowler, K. D. Green, B. J. Newport, R. A. Ong, S. Oser, M. A. Catanese, M. A.K. Glasmacher, J. Matthews, D. F. Nitz, D. Sinclair, J. C. van der Velde, D. B. Kieda

Research output: Contribution to journalArticlepeer-review

92 Scopus citations


Diffuse ultrahigh energy γ radiation can arise from a variety of astrophysical sources, including the interaction of 1020 eV cosmic rays with the 2.7 K microwave background radiation or the collapse of topological defects created in the early Universe. We describe a sensitive search for diffuse γ rays at ultrahigh energies using the Chicago Air Shower Array-Michigan Muon Array experiment. An isotropic flux of radiation is not detected, and we place stringent upper limits on the fraction of the γ-ray component relative to cosmic rays (< 10−4) at energies from 5.7 × 1014 to 5.5 × 1016 eV. This result represents the first comprehensive constraint on the γ-ray flux at these energies.

Original languageEnglish (US)
Pages (from-to)1805-1808
Number of pages4
JournalPhysical review letters
Issue number10
StatePublished - 1997


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