The unreasonable weakness of r-process cosmic rays in the neutron-star-merger nucleosynthesis scenario

Abstract

We reach the robust conclusion that, by combining the observed cosmic rays of r-process elements with the fact that the velocity of the neutron-star-merger ejecta is much higher than that of the supernova ejecta, either (1) the reverse shock in the neutron-star-merger ejecta is a very inefficient accelerator that converts less than 0.003% of the ejecta kinetic energy to the cosmic-ray energy or (2) the neutron star merger is not the origin of the Galactic r-process elements. We also find that the acceleration efficiency should be less than 0.1% for the reverse shock of the supernova ejecta with the observed cosmic rays lighter than the iron.

5 pages, 1 figure

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• Horizons: Nuclear Astrophysics in the 2020s and Beyond
• r-Process Radioisotopes from Near-Earth Supernovae and Kilonovae
• Super-Knee Cosmic Rays from Galactic Neutron Star Merger Remnants
• Systematic exploration of heavy element nucleosynthesis in protomagnetar outflows
• R-process Element Cosmic Rays from Neutron Star Mergers
• Ultraheavy Ultrahigh-Energy Cosmic Rays
• Neutrinos and Heavy Element Nucleosynthesis