Features of the Energy Spectrum of Cosmic Rays above 2.5 ×1018 eV Using the Pierre Auger Observatory

We report a measurement of the energy spectrum of cosmic rays above 2.5 ×10¹⁸ eV based on 215 030 events. New results are presented: at about 1.3 ×10¹⁹ eV , the spectral index changes from 2.51 ±0.03 (stat ) ±0.05 (syst ) to 3.05 ±0.05 (stat ) ±0.10 (syst ) , evolving to 5.1 ±0.3 (stat ) ±0.1 (syst ) beyond 5 ×10¹⁹ 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 ×10¹⁸ eV is [5.66 ±0.03 (stat ) ±1.40 (syst ) ]×10⁵³ erg Mpc^-3 .