Modeling the spectrum and composition of ultrahigh-energy cosmic rays with two populations of extragalactic sources

Abstract

We fit the ultrahigh-energy cosmic-ray (UHECR, $E\gtrsim 0.1$ EeV) spectrum and composition data from the Pierre Auger Observatory at energies $E\gtrsim 5\cdot 10^{18}$ eV, i.e., beyond the ankle using two populations of astrophysical sources. One population, accelerating dominantly protons (${}^1$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 (${}^4$He, ${}^{14}$N, ${}^{28}$Si, ${}^{56}$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$\sigma$ 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.

15 pages, 7 figures, Accepted for publication in EPJ C

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• Revisiting ultrahigh-energy constraints on decaying super-heavy dark matter
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• Probing superheavy dark matter through lunar radio observations of ultrahigh-energy neutrinos and the impacts of neutrino cascades
• The spectra and composition of Ultra High Energy Cosmic Rays and the measurement of the proton-air cross section
• Cosmic-Ray Constraints on the Flux of Ultra-High-Energy Neutrino Event KM3-230213A
• Cosmic Clues from Amaterasu: Blazar-Driven Ultrahigh-Energy Cosmic Rays?
• Acoustic Neutrino Detection In a Adriatic Multidisciplinary Observatory (ANDIAMO)
• Cosmogenic Origin of KM3-230213A: Delayed Gamma-Ray Emission from A Cosmic-Ray Transient
• Ultra-high energy cosmic rays with UFA-15 source model in Bumblebee gravity theory
• The Sensitivity of PUEO to Cosmogenic Neutrinos and Exotic Physics Scenarios