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UHE nuclei propagation and the interpretation of the ankle in the cosmic-ray spectrum

par Allard, D.;Parizot, Etienne;Khan, Elias;Goriely, Stéphane ;Olinto, Angela V.
Référence Astronomy & astrophysics, 443, 3, page (29-32)
Publication Publié, 2005

Article révisé par les pairs

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Résumé :

We consider the stochastic propagation of high-energy protons and nuclei in the cosmological microwave and infrared backgrounds, using revised photonuclear cross-sections and following primary and secondary nuclei in the full 2D nuclear chart. We confirm earlier results showing that the high-energy data can be fit with a pure proton extragalactic cosmic ray (EGCR) component if the source spectrum is ∝E-2.6. In this caset the ankle in the CR spectrum may be interpreted as a pair-production dip associated with the propagation. We show that when heavier nuclei are included in the source with a composition similar to that of Galactic cosmic-rays (OCRs), the pair-production dip is not present unless the proton fraction is higher than 85%. In the mixed composition case, the ankle recovers the past interpretation as the transition from GCRs to EGCRs and the highest energy data can be explained by a harder source spectrum ∝E-2.2-E-2.3, reminiscent of relativistic shock acceleration predictions, and in good agreement with the GCR data at low-energy and holistic scenarios. © ESO 2005.