2005/05/31 by D. Allard, E. Parizot, E. Khan +2 · 1 citation
Physics and Astronomy · #astro-ph
paper · pdf · doi:10.1051/0004-6361:200500199
published as Astron.Astrophys.443:L29-L32,2005 · 4 pages, 4 figures, submitted to A&A Letters (minor changes, two figures replaced, two references added)
arxiv created 2005/06/04 · arxiv updated 2011/05/12
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 case 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 (GCRs), 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.