Regular Article - Theoretical Physics
Modeling the spectrum and composition of ultrahigh-energy cosmic rays with two populations of extragalactic sources
Astronomy and Astrophysics Group, Raman Research Institute, 560080, Bengaluru, India
2 Centre for Astro-Particle Physics (CAPP) and Department of Physics, University of Johannesburg, PO Box 524, 2006, Auckland Park, South Africa
Accepted: 13 January 2021
Published online: 20 January 2021
We fit the ultrahigh-energy cosmic-ray (UHECR, EeV) spectrum and composition data from the Pierre Auger Observatory at energies eV, i.e., beyond the ankle using two populations of astrophysical sources. One population, accelerating dominantly protons (H), extends up to the highest observed energies with maximum energy close to the GZK cutoff and injection spectral index near the Fermi acceleration model; while another population accelerates light-to-heavy nuclei (He, N, Si, Fe) with a relatively low rigidity cutoff and hard injection spectrum. A significant improvement in the combined fit is noted as we go from a one-population to two-population model. For the latter, we constrain the maximum allowed proton fraction at the highest-energy bin within 3.5 statistical significance. In the single-population model, low-luminosity gamma-ray bursts turn out to match the best-fit evolution parameter. In the two-population model, the active galactic nuclei is consistent with the best-fit redshift evolution parameter of the pure proton-emitting sources, while the tidal disruption events could be responsible for emitting heavier nuclei. We also compute expected cosmogenic neutrino flux in such a hybrid source population scenario and discuss possibilities to detect these neutrinos by upcoming detectors to shed light on the sources of UHECRs.
© The Author(s) 2021
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