Cosmic rays from the knee to the ankle

The shape and composition of the primary spectrum as well as the large-scale anisotropy in the arrival direction of cosmic rays are key elements to understand the origin, acceleration and propagation of the Galactic radiation. Besides the well-known knee and ankle features, the measured energy spectrum exhibits also a less pronounced but still clear deviation from a single power law between the knee and the ankle, with a spectral hardening at ∼ 2 × 10 16   eV and a steepening at ∼ 10 17   eV . The average mass composition gets heavier after the knee till ∼ 10 17   eV , where a bending of the heavy component is observed. An indication of a hardening of the light component just above 10 17   eV has been measured as well. First indications of anisotropy of the arrival direction in the southern hemisphere have been reported at ∼ 10 15   eV .