Astrophysical interpretation of Pierre Auger Observatory measurements of the UHECR energy spectrum and mass composition

¹ INFN and Department of Physical and Chemical Sciences, University of L’Aquila, L’Aquila, Italy
² Observatorio Pierre Auger, Av. San Martín Norte 304, 5613 Malargüe, Argentina

^a e-mail: armando.dimatteo@aquila.infn.it
^b Now at Service de Physique Théorique, Université Libre de Bruxelles, Brussels, Belgium
^c e-mail: auger_spokespersons@fnal.gov
^d Full author list: http://www.auger.org/archive/authors_2016_06.html

Published online: 23 March 2017

Abstract

We present a combined fit of a simple astrophysical model of UHECR sources to both the energy spectrum and mass composition data measured by the Pierre Auger Observatory. The fit has been performed for energies above 5 EeV, i.e. the region of the all-particle spectrum above the so-called “ankle”’ feature. The astrophysical model we adopted consists of identical sources uniformly distributed in a comoving volume, where nuclei are accelerated with a rigidity-dependent mechanism. The fit results suggest sources characterized by relatively low maximum injection energies and hard spectral indices. The impact of various systematic uncertainties on the above result is discussed.