Constraining models for the origin of ultra-high-energy cosmic rays with a novel combined analysis of arrival directions, spectrum, and composition data measured at the Pierre Auger Observatory

THE PIERRE AUGER COLLABORATION; SILVIA MOLLERACH

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS

IOP PUBLISHING LTD

Año: 2024 vol. 2024

1475-7516

The combined fit of the measured energy spectrum and shower maximum depthdistributions of ultra-high-energy cosmic rays is known to constrain the parameters ofastrophysical models with homogeneous source distributions. Studies of the distribution ofthe cosmic-ray arrival directions show a better agreement with models in which a fraction ofthe flux is non-isotropic and associated with the nearby radio galaxy Centaurus A or withcatalogs such as that of starburst galaxies. Here, we present a novel combination of bothanalyses by a simultaneous fit of arrival directions, energy spectrum, and composition datameasured at the Pierre Auger Observatory. The model takes into account a rigidity-dependentmagnetic field blurring and an energy-dependent evolution of the catalog contribution shapedby interactions during propagation.We find that a model containing a flux contribution from the starburst galaxy catalogof around 20% at 40 EeV with a magnetic field blurring of around 20 ◦ for a rigidity of10 EV provides a fair simultaneous description of all three observables. The starburst galaxymodel is favored with a significance of 4.5σ (considering experimental systematic effects)compared to a reference model with only homogeneously distributed background sources.By investigating a scenario with Centaurus A as a single source in combination with thehomogeneous background, we confirm that this region of the sky provides the dominantcontribution to the observed anisotropy signal. Models containing a catalog of jetted activegalactic nuclei whose flux scales with the γ-ray emission are, however, disfavored as theycannot adequately describe the measured arrival directions.