2015/05/31 by Andrew M. Taylor, Markus Ahlers, M. Ahlers +1 · 2 citations
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #COSMIC cancer database #Cosmic microwave background #Cosmic ray #Dark Matter and Cosmic Phenomena #Electron #Energy spectrum #Fermi Gamma-ray Space Telescope #Fermi acceleration #Galaxy #Gamma-ray bursts and supernovae #Nuclear physics #Optics #Particle acceleration #Physics #Redshift #Spectral index #Spectral line #Universe #astro-ph.HE
paper · pdf · doi:10.1103/physrevd.92.063011
published as Phys. Rev. D 92, 063011 (2015) · 9 pages, 4 figures
arxiv created 2015/09/10 · openalex publication_date 2015/09/14 · arxiv updated 2015/09/23 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
Using recent measurements of the spectrum and chemical composition of the highest energy cosmic rays, we consider the sources of these particles. We find that these data strongly prefer models in which the sources of the ultra-high-energy cosmic rays inject predominantly intermediate mass nuclei, with comparatively few protons or heavy nuclei, such as iron or silicon. If the number density of sources per comoving volume does not evolve with redshift, the injected spectrum must be very hard (\ensuremathα\ensuremath≃1) in order to fit the spectrum observed from Earth. Such a hard spectral index would be surprising and difficult to accommodate theoretically. In contrast, much softer spectral indices, consistent with the predictions of Fermi acceleration (\ensuremathα\ensuremath≃2), are favored in models with negative source evolution. With this theoretical bias, these observations thus favor models in which the sources of the highest energy cosmic rays are preferentially located within the low-redshift universe.