Constraining the sources of ultra-high-energy cosmic rays across and above the ankle with the spectrum and composition data measured at the Pierre Auger Observatory

THE PIERRE AUGER COLLABORATION, INCLUYE S MOLLERACH

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS

IOP PUBLISHING LTD

Año: 2023 vol. 2023

1475-7516

n this work we present the interpretation of the energy spectrum and masscomposition data as measured by the Pierre Auger Collaboration above 6×1017 eV. We usean astrophysical model with two extragalactic source populations to model the hardeningof the cosmic-ray flux at around 5×1018 eV (the so-called “ankle” feature) as a transitionbetween these two components. We find our data to be well reproduced if sources abovethe ankle emit a mixed composition with a hard spectrum and a low rigidity cutoff. Thecomponent below the ankle is required to have a very soft spectrum and a mix of protonsand intermediate-mass nuclei. The origin of this intermediate-mass component is not wellconstrained and it could originate from either Galactic or extragalactic sources. To theaim of evaluating our capability to constrain astrophysical models, we discuss the impacton the fit results of the main experimental systematic uncertainties and of the assumptionsabout quantities affecting the air shower development as well as the propagation and redshiftdistribution of injected ultra-high-energy cosmic rays (UHECRs).