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

We report on the cosmic-ray energy spectrum above 10<SUP>17</SUP> 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 10<SUP>17</SUP> eV is J(E) = 10<SUP>-29.55</SUP> x (E/10<SUP>18</SUP> eV)<SUP>-3.07 + or -0.01</SUP>/sq m/s/sr/eV. We observe a dip in the energy spectrum near 10<SUP>18.5</SUP> using the higher resolution stereo data. A 3 x 10<SUP>20</SUP> eV shower was detected by the monocular Fly's Eye on 1991 October 15.