UHECR composition models

Abstract

In light of the increasingly heavy UHECR composition at the highest energies, as observed by the Pierre Auger Observatory, the implications of these results on the actual source composition and spectra are investigated. Depending on the maximum energy of the particles accelerated, sources producing hard spectra and/or containing a considerably enhanced heavy component appear a necessary requirement. Consideration is made of two archetypal models compatible with these results. The secondary signatures expected , following the propagation of the nuclear species from source to Earth, are determined for these two example cases. Finally, the effect introduced by the presence of nG extragalactic magnetic fields in collaboration with a large (80 Mpc) distance to the nearest source is discussed.

Cosmic rays from the ankle to the cutoff

“…Another interpretation of the suppression region has been presented in e.g. [19,20,21,22]. In this group of models, the flux suppression is primarily caused by the limiting acceleration energy at the sources rather than by the GZK-effect.…”

“…in Refs. [22,16,24]. However, as recently discussed in [25], effects of diffusion of high energy cosmic rays in turbulent extra-galactic magnetic fields counteract the requirement of hard injection spectra (γ < 2.0) for a reasonable range of magnetic field strengths and coherence lengths.…”

“…Figure 3. Example of Xmax and RMS(Xmax) predicted by the archetypal maximum energy model of [22] in comparison to data from the Auger observatory.…”

The Physics of UHECRs: Spectra, Composition and the Transition Galactic-Extragalactic

“…Nevertheless, the anisotropy expected for a galactic light component extending up to 10 18 eV exceeds by more than one order of magnitude the upper limit measured by Auger [25]. The possible origin of the additional (light and extra-galactic) component can be modelled essentially in two ways: (i) assuming the presence of different classes of sources: one injecting also heavy nuclei with hard spectrum and the other only proton and helium nuclei with soft spectrum [26,27] or (ii) identifying a peculiar class of sources that could provide at the same time a steep light component and a flat heavy one [28][29][30].…”

Propagation of Ultra High Energy Cosmic Rays and the Production of Cosmogenic Neutrinos

“…Taking into account the sole Auger data, to reach a reasonable agreement with observations, one should consider mixed compositions. Assuming that protons give their principal contribution only at the lowest energies ≤ 3×10 19 eV [14,15], below the photo-pion production threshold ∼ 6 × 10 19 eV. In this case the flux suppression observed at the highest energies is due to the photodisintegration process suffered by heavy nuclei [14,16].…”