Search for isotropic #gamma# radiation of cosmological origin between 65 and 200 TeV

Electromagnetic energy injected into the universe above a few hundred TeV is expected to pile up as #gamma# radiation in the energy range between about 65 and 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 #gamma# 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 Cerenkov light and a scintillator array, were used with a novel method to discriminate #gamma#-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"1"6 GeV. (orig.)Available from TIB Hannover: RR 2916(94-28) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman