Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory

Abstract

We present a combined fit of a simple astrophysical model of UHECR sources toboth the energy spectrum and mass composition data measured by the Pierre AugerObservatory. The fit has been performed for energies above $5 \cdot 10^{18}$eV, i.e.~the region of the all-particle spectrum above the so-called "ankle"feature. The astrophysical model we adopted consists of identical sourcesuniformly distributed in a comoving volume, where nuclei are acceleratedthrough a rigidity-dependent mechanism. The fit results suggest sourcescharacterized by relatively low maximum injection energies, hard spectra andheavy chemical composition. We also show that uncertainties about physicalquantities relevant to UHECR propagation and shower development have anon-negligible impact on the fit results