Super-knee Cosmic Rays from Galactic Neutron Star Merger Remnants

Abstract

The detection of gravitational waves and electromagnetic counterparts from a binary neutron star merger confirmed that it is accompanied by the launch of fast merger ejecta. Analogous to supernova remnants, forward shocks formed by the interaction of the ejecta with interstellar material will produce high-energy cosmic rays. We investigate the possibility that Galactic neutron star merger remnants (NSMRs) significantly contribute to the observed cosmic rays in the energy range between the knee and the ankle. Using typical parameters obtained by the modeling of GW170817, we find that NSMRs can accelerate iron nuclei up to ∼500 PeV. We calculate the cosmic-ray (CR) spectrum and composition observed on Earth, and show that the Galactic NSMR scenario can account for the experimental CR data in the 20–1000 PeV range. Our model can naturally explain the hardening feature around 20 PeV for the total CR spectrum, which has been observed by the Telescope Array Low Energy extension and the IceTop air-shower array.