The energy spectrum and arrival direction distribution of cosmic rays with energies above 10 to the 19th electrovolts

Results from three experiments provide evidence that the cosmic-ray energy spectrum flattens above 10 to the 19th eV; no 'cutoff' in the spectrum is observed to at least 1.6 x 10 to the 20th eV. Below 10 to the 19th eV the differential slope of the power-law spectrum is -3.09 + or - 0.02 while at higher energies it is -2.31 + or - 0.10. An analysis of the arrival direction distribution of over 4700 primaries above 10 to the 18th eV and 142 above 10 to the 19th eV recorded at Haverah Park suggests that the mean galactic latitude of these events increases beyond the energy at which the spectrum flattens. The implications of these results for theories of the origin of the highest-energy cosmic rays are discussed.