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 4x10(18) eV is presented, which is based on the analysis of showers with zenith angles greater than 60 degrees 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 5.3x10(18) eV, the "ankle", the flux can be described by a power law E-gamma with index gamma = 2.70 +/- 0.02 (stat) +/- 0.1 (sys) followed by a smooth suppression region. For the energy (E-s) at which the spectral flux has fallen to one-half of its extrapolated value in the absence of suppression, we find E-s = (5.12 +/- 0.25 (stat)(-1.2)(+1.0) (sys)) x10(19) eV.