Measurement of the cosmic ray spectrum above 4 × 10 < sup> 18 eV using inclined events detected with the Pierre Auger Observatory

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© 2015 IOP Publishing Ltd and Sissa Medialab srl. 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.

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Journal of Cosmology and Astroparticle Physics