Volume 501 - 39th International Cosmic Ray Conference (ICRC2025) - Cosmic-Ray Indirect
Ultraheavy Nuclei as Ultrahigh-Energy Cosmic Rays: Constraints from Collapsars and neutron star mergers
B.T. Zhang*, K. Murase, N. Ekanger, M. Bhattacharya and S. Horiuchi
*: corresponding author
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Pre-published on: September 24, 2025
Published on:
Abstract
We investigate the propagation of ultraheavy (UH) nuclei as ultrahigh-energy cosmic rays (UHECRs). We show that their energy loss lengths at $\lesssim300$~EeV are significantly longer than those of protons and intermediate-mass nuclei, and that the highest-energy cosmic rays with energies beyond $\sim100$~EeV, may originate from such UH-UHECRs. We derive constraints on the contribution of UH-UHECR sources, and the allowed energy generation rate densities are consistent with those of collapsars and compact binary mergers. A nearby transient, e.g., a low-luminosity gamma-ray burst (LL GRB), may give a special contribution to the observed UHECR flux, and we explore the possibility of simultaneously explaining both the Auger and TA spectra. These models predict a measurable shift toward heavier compositions above 100~EeV, testable with next-generation UHECR observatories.
DOI: https://doi.org/10.22323/1.501.0445
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