Search for isotropic γ-radiation in the cosmological window between 65-tev and 200-tev

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Elsevier Science BV
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Electromagnetic energy injected into the universe above a few hundred TeV is expected to pile up as γ radiation in a relatively narrow energy interval below 100 TeV due to its interaction with the 2.7°K background radiation. We present an upper limit (90% C.L.) on the ratio of primary γ to charged cosmic rays in the energy interval 65-160 TeV (80- 200 TeV) of 10.3 . 10¯³(7.8 . 10¯³). Data from the HEGRA cosmic-ray detector complex consisting of a wide angle Cerenkov array (AIROBICC) measuring the lateral distribution of air Čerenkov light and a scintillator array, were used with a novel method to discriminate γ-ray and hadron induced air showers. If the presently unmeasured universal far infrared background radiation is not too intense, the result rules out a topological-defect origin of ultrahigh energy cosmic rays for masses of the X particle released by the defects equal to or larger than about 10_(16) GeV.
© 1995 Elsevier Science B.V. The support by the Deutsche Forschungsgemeinschaft DFG, the German Ministry for Research and Technology BMFT and the Spanish Research Council CICYT is gratefully acknowledged. We further thank the Instituto de Astrofisica de Canarias IAC and its president F. Sanchez for supplying excellent working conditions at La Palma.