Kinetic Simulations of Cosmic-Ray-Modified Shocks II: Particle Spectra

Damiano Caprioli, Colby C. Haggerty, Pasquale Blasi

Published 2020-08-31Version 1

Diffusive shock acceleration is a prominent mechanism for producing energetic particles in space and in astrophysical systems. Such energetic particles have long been predicted to affect the hydrodynamic structure of the shock, in turn leading to CR spectra flatter than the test-particle prediction. However, in this work along with a companion paper, C. C. Haggerty and D. Caprioli, 2020, arXiv:2008.12308 [astro-ph.HE], we use self-consistent hybrid (kinetic ions-fluid electrons) simulations to show for the first time how CR-modified shocks actually produce steeper spectra. The steepening is driven by the enhanced advection of CRs embedded in magnetic turbulence downstream of the shock, in what we call the "postcursor". These results are consistent with multi-wavelength observations of supernovae and supernova remnants and have significant phenomenological implications for space/astrophysical shocks in general.