PoS - Proceedings of Science
Volume 444 - 38th International Cosmic Ray Conference (ICRC2023) - Cosmic-Ray Physics (Indirect, CRI)
Prospects for ultra-high-energy particle acceleration at relativistic shocks
Z.Q. Huang
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Pre-published on: July 25, 2023
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Using test-particle Monte-Carlo simulations, we revisit the particle acceleration at ultra-relativistic shocks. The produced particle spectra are studied on the conditions of two regular field configurations: (i) uniform upstream field perpendicular to the shock normal, and (ii) upstream field with a cylindrical geometry. For uniform field configurations, particles could keep being accelerated until becoming magnetized on either side of the shock, which contradicts the widely-held belief that the maximum energy is constrained by the downstream magnetized limit. The corresponding steady-state particle distribution satisfies $dN/d\gamma \propto \gamma^{-2.2}$, similar to that predicted for the parallel shock case. For the cylindrical field configuration, the acceleration efficiency depends on the charge of the particles. Particles with a favorable charge will experience a curvature drift motion parallel to the shock velocity and hence increases the probability of downstream particles to cross the shock. Considering the non-resonant scattering model, these particles can only escape when reaching the confinement limit of the system size, and the accelerated spectrum could become even harder.
DOI: https://doi.org/10.22323/1.444.0193
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