We interpret the Pierre Auger Observatory's measurement of the energy spectrum and mass composition of cosmic rays with energies above 1017.8 eV as coming from two extragalactic source populations, one dominating the flux below a few EeV and the other above. Fitting the data neglecting magnetic fields, we find that the high-energy population is required to have a very hard injection spectrum, incompatible with the expectations from diffusive shock acceleration (E−2). Turbulent magnetic fields between us and the closest sources can suppress the flux of low-rigidity particles, modifying the cosmic-ray spectrum at Earth. We include the effect of magnetic fields in the fit to the Auger data, which results in softer high-energy injection spectra.
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