Cosmic rays: the spectrum and chemical composition from $10^{10}$ to $10^{20}$ eV

Abstract

The production of energetic particles in the universe remains one of the great mysteries of modern science. The mechanisms of acceleration in astrophysical sources and the details about the propagation through the galactic and extragalactic media are still to be defined. In recent years, the cosmic ray flux has been measured with high precision in the energy range from \energy{10} to \energyEV{20.5} by several experiments using different techniques. In some energy ranges, it has been possible to determine the flux of individual elements (hydrogen to iron nuclei). This paper explores an astrophysical scenario in which only our Galaxy and the radio galaxy Cen A produce all particles measured on Earth in the energy range from \energy{10} to \energyEV{20.5}. Data from AMS-02, CREAM, KASCADE, KASCADE-Grande and the Pierre Auger Observatories are considered. The model developed here is able to describe the total and individual particle flux of all experiments considered. It is shown that the theory used here is able to describe the smooth transition from space-based to ground-based measurements. The flux of each element as determined by KASCADE and KASCADE-Grande and the mass sensitivity parameter \xmax measured by the Pierre Auger Observatory above \energyEV{18} are also explored within the framework of the model. The transition from \energy{16} to \energyEV{18} is carefully analyzed. It is shown that the data measured in this energy range suggest the existence of an extra component of cosmic rays yet to be understood.