Features of the energy spectrum of cosmic rays above $2.5{\times} 10^{18}$ eV using the Pierre Auger Observatory

TL;DR

This paper presents a detailed measurement of the cosmic ray energy spectrum above 2.5×10^18 eV, revealing spectral index changes and their consistency with energy-dependent composition models, based on data from the Pierre Auger Observatory.

Contribution

It provides new high-precision measurements of the cosmic ray spectrum and spectral features above 2.5×10^18 eV, with implications for understanding cosmic ray origins and composition.

Findings

Spectral index changes at about 1.3×10^19 eV

Spectral steepening beyond 5×10^19 eV

Spectrum consistent with energy-dependent mass composition models

Abstract

We report a measurement of the energy spectrum of cosmic rays above $2.5{\times} 10^{18}$ eV based on $215,030$ events. New results are presented: at about $1.3{\times} 10^{19}$ eV, the spectral index changes from $2.51 \pm 0.03 \textrm{ (stat.)} \pm 0.05 \textrm{ (sys.)}$ to $3.05 \pm 0.05 \textrm{ (stat.)}\pm 0.10\textrm{ (sys.)}$, evolving to $5.1\pm0.3\textrm{ (stat.)} \pm 0.1\textrm{ (sys.)}$ beyond $5{\times} 10^{19}$ eV, while no significant dependence of spectral features on the declination is seen in the accessible range. These features of the spectrum can be reproduced in models with energy-dependent mass composition. The energy density in cosmic rays above $5{\times} 10^{18}$ eV is $(5.66 \pm 0.03 \textrm{ (stat.)} \pm 1.40 \textrm{ (sys.)} ) {\times} 10^{53}~$erg Mpc$^{-3}$.