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Editor: S. DodelsonWe report a measurement of the flux of cosmic rays with unprecedented precision and statistics using the Pierre Auger Observatory. Based on fluorescence observations in coincidence with at least one surface detector we derive a spectrum for energies above 10 18 eV. We also update the previously published energy spectrum obtained with the surface detector array. The two spectra are combined addressing the systematic uncertainties and, in particular, the influence of the energy resolution on the spectral shape. 242Pierre Auger Collaboration / Physics Letters B 685 (2010) The spectrum can be described by a broken power law E −γ with index γ = 3.3 below the ankle which is measured at log 10 (E ankle /eV) = 18.6. Above the ankle the spectrum is described by a power law with index 2.6 followed by a flux suppression, above about log 10 (E/eV) = 19.5, detected with high statistical significance.

We report a study of the distributions of the depth of maximum, Xmax, of extensive air-shower profiles with energies above 10 17.8 eV as observed with the fluorescence telescopes of the Pierre Auger Observatory. The analysis method for selecting a data sample with minimal sampling bias is described in detail as well as the experimental cross-checks and systematic uncertainties. Furthermore, we discuss the detector acceptance and the resolution of the Xmax measurement and provide parameterizations thereof as a function of energy. The energy dependence of the mean and standard 4 deviation of the Xmax-distributions are compared to air-shower simulations for different nuclear primaries and interpreted in terms of the mean and variance of the logarithmic mass distribution at the top of the atmosphere.

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