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

• Published in: The European physical journal. C, Particles and fields Particles and fields, 2021, Vol.81 (1), p.1-15, Article 59
• Main Authors: Das, Saikat, Razzaque, Soebur, Gupta, Nayantara
• Format: Article
• Language: English
• Subjects: Active galactic nuclei; Astronomy; Astrophysics and Cosmology; Augers; Composition; Cosmic rays; Elementary Particles; Galactic evolution; Gamma ray bursts; Hadrons; Heavy Ions; Heavy nuclei; High energy astronomy; Iron isotopes; Luminosity; Mathematical models; Measurement Science and Instrumentation; Neutrinos; Nuclear Energy; Nuclear Physics; Parameters; Physics; Physics and Astronomy; Population; Population (statistical); Protons; Quantum Field Theories; Quantum Field Theory; Red shift; Regular Article - Theoretical Physics; String Theory
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s10052-021-08885-4

We fit the ultrahigh-energy cosmic-ray (UHECR, E ≳ 0.1 EeV) spectrum and composition data from the Pierre Auger Observatory at energies E ≳ 5 · 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 σ 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.