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Ultraheavy Ultrahigh-Energy Cosmic Rays
B Theodore Zhang1,2, Kohta Murase1,3,4,5, Nick Ekanger6
1Kyoto University, Yukawa Institute for Theoretical Physics, Center for Gravitational Physics and Quantum Information, Kyoto, Kyoto 606-8502, Japan.
Abstract:
We investigate the propagation of ultraheavy (UH) nuclei as ultrahigh-energy cosmic rays (UHECRs). We show that their energy loss lengths at ≲300 EeV are significantly longer than those of protons and intermediate-mass nuclei, and that the highest-energy cosmic rays with energies beyond ∼100 EeV, including the Amaterasu particle, may be UH-UHECRs. For the first time, we derive constraints on the contribution of UH-UHECR sources, and find that the current data are consistent with energy generation rate densities of UHECRs from collapsars and neutron star mergers. Our model predicts that the mean value of the depth of shower maximum is lower than that for iron nuclei beyond 100 EeV, which can be tested with future composition measurements, e.g., AugerPrime and the Global Cosmic Ray Observatory. In addition, the spectral tension between the Telescope Array (TA) and the Pierre Auger Observatory can be alleviated by considering the enhanced contribution of UHECRs-including UH nuclei-from a nearby transient.
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