Combined fit of UHECR spectrum and composition with two extragalactic source populations

Saikat Das, Soebur Razzaque, Nayantara Gupta

Research output: Contribution to journalConference articlepeer-review


A mixed composition of light-to-heavy nuclei elements (1H, 4He, 14N, 28Si, 56Fe) at injection fits the ultrahigh-energy cosmic ray (UHECR; E > 1017 eV) spectrum data measured by the Pierre Auger Observatory, beyond the ankle, i.e., E & 5 × 1018 eV. However, the composition fit can be further improved by the addition of light nuclei at the highest energies. We consider the light nuclei to originate from a discrete source population consisting of protons (1H). We constrain the maximum allowed proton fraction at the highest-energy bin at 3.5σ statistical significance. Including the redshift evolution of sources as a free parameter further improves the composition fit. We find that low-luminosity gamma-ray bursts match the best-fit evolution index in the case of the one-population model. Active galactic nuclei are the plausible candidates for light nuclei injection in the two-population model, whereas tidal disruption events can inject heavy nuclei composition. We also present the secondary neutrino flux in one- and two-population models, constraining the composition at highest energies.

Original languageEnglish
Article number460
JournalProceedings of Science
Publication statusPublished - 18 Mar 2022
Event37th International Cosmic Ray Conference, ICRC 2021 - Virtual, Berlin, Germany
Duration: 12 Jul 202123 Jul 2021

ASJC Scopus subject areas

  • Multidisciplinary


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