The cosmic-ray energy spectrum observed by the Fly's Eye

We report on the cosmic-ray energy spectrum above 1017 eV as observed by the Fly's Eye detector. The detector has been operated in monocular mode (Fly's Eye I only) since 1981 and in stereo mode (both Fly's Eye I and Fly's Eye II) since 1986. This paper includes data through 1992 July. The cosmic-ray primary energy is measured by integrating over the atmospheric development curve of the extensive air shower produced by the primary particle. The differential monocular energy spectrum above 1017 eV is J(E) = 10-29.55 x (E/1018 eV)-3.07 + or -0.01/sq m/s/sr/eV. We observe a dip in the energy spectrum near 1018.5 using the higher resolution stereo data. A 3 x 1020 eV shower was detected by the monocular Fly's Eye on 1991 October 15.