Signatures of the transition from Galactic to extragalactic cosmic raysстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:We discuss the signatures of the transition from galactic to extragalactic cosmic rays in different
scenarios, giving most attention to the dip scenario. The dip is a feature in the diffuse spectrum of
ultra-high energy (UHE) protons in the energy range 1 × 1018 − 4 × 1019 eV, which is caused by
electron-positron pair production on the cosmic microwave background (CMB) radiation. The dip
scenario provides a simple physical description of the transition from galactic to extragalactic cosmic
rays. Here we summarize the signatures of the pair production dip model for the transition, most
notably the spectrum, the anisotropy and the chemical composition. The main focus of our work is
however on the description of the features that arise in the elongation rate and in the distribution
of the depths of shower maximum Xmax in the dip scenario. We find that the curve for Xmax (E)
shows a sharp increase with energy, which reflects a sharp transition from an iron dominated flux at
low energies to a proton dominated flux at E ∼ 1018 eV. We also discuss in detail the shape of the
Xmax distributions for cosmic rays of given energy and demonstrate that this represents a powerful
tool to discriminate between the dip scenario and other possible models of the transition.