UHE nuclei propagation and the interpretation of the ankle in the cosmic-ray spectrum
May, 2005
4 pages
Published in:
- Astron.Astrophys. 443 (2005) L29-L32
e-Print:
- astro-ph/0505566 [astro-ph]
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Abstract: (arXiv)
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 \propto 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 \propto 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.- cosmic rays
- abundances
- nuclear reactions
- p: cosmic radiation
- nucleus: cosmic radiation
- cosmic radiation: diffusion
- cosmic radiation: particle source
- photon: interaction
- cosmic radiation: acceleration
- shock waves: relativistic
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