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

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 $\text{ (stat.)}$ \pm 0.05 $\text{ (sys.)}$$to$3.05 \pm 0.05 \textrm{ (stat.)}\pm 0.10$\text{ (sys.)}$$,evolvingto$5.1\pm0.3$\text{ (stat.)}$ \pm 0.1$\text{ (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 $\text{ (stat.)}$ \pm 1.40 \textrm{ (sys.)} ) {\times} 10^{53}~$ergMpc$^{-3}$.