Measurement Of The Cosmic Ray Spectrum Above 4 × 1018 Ev Using Inclined Events Detected With The Pierre Auger Observatory

A measurement of the cosmic-ray spectrum for energies exceeding 4×1018 eV is presented, which is based on the analysis of showers with zenith angles greater than 60° detected with the Pierre Auger Observatory between 1 January 2004 and 31 December 2013. The measured spectrum confirms a flux suppression at the highest energies. Above 5.3×1018 eV, the "ankle", the flux can be described by a power law E-γ with index γ=2.70 ± 0.02 (stat) ± 0.1 (sys) followed by a smooth suppression region. For the energy (Es) at which the spectral flux has fallen to one-half of its extrapolated value in the absence of suppression, we find Es=(5.12 ± 0.25 (stat)+1.0-1.2 (sys))×1019 eV. © 2015 IOP Publishing Ltd and Sissa Medialab srl.20158Abraham, J., Properties and performance of the prototype instrument for the Pierre Auger Observatory (2004) Nucl. Instrum. Meth., 523, p. 50Aab, A., The Pierre Auger cosmic ray observatory (2015) Nucl. Instrum. 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