LIMITS ON THE ISOTROPIC DIFFUSE FLUX OF ULTRAHIGH-ENERGY GAMMA-RADIATION

Diffuse ultrahigh energy gamma radiation can arise from a variety of a strophysical sources, including the interaction of 10(20) eV cosmic ra ys with the 2.7 K microwave background radiation or the collapse of to pological defects created in the early Universe. We describe a sensiti ve search for diffuse gamma rays at ultrahigh energies using the Chica go Air Shower Array-Michigan Muon Array experiment. An isotropic flux of radiation is not detected, and we place stringent upper limits on t he fraction of the gamma-ray component relative to cosmic rays (<10(-4 )) at energies from 5.7 x 10(14) to 5.5 X 10(16) eV. This result repre sents the first comprehensive constraint on the gamma-ray flux at thes e energies.