Extreme ion acceleration at extragalactic jet termination shocks

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
e-mail: benoit.cerutti@univ-grenoble-alpes.fr
² Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shanghai 201210, PR China
³ School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, PR China
e-mail: gwenael.giacinti@sjtu.edu.cn

Received: 22 March 2023
Accepted: 15 May 2023

Abstract

Context. Extragalactic plasma jets are some of the few astrophysical environments able to confine ultra-high-energy cosmic rays, but whether they are capable of accelerating these particles is unknown.

Aims. In this work, we revisit particle acceleration at relativistic magnetized shocks beyond the local uniform field approximation by considering the global transverse structure of the jet.

Methods. Using large two-dimensional particle-in-cell simulations of a relativistic electron-ion plasma jet, we show that the termination shock forming at the interface with the ambient medium accelerates particles up to the confinement limit.

Results. The radial structure of the jet magnetic field leads to a relativistic velocity shear that excites a von Kármán vortex street in the downstream medium trailing behind an over-pressured bubble filled with cosmic rays. Particles are efficiently accelerated at each crossing of the shear flow boundary layers.

Conclusions. These findings support the idea that extragalactic plasma jets may be capable of producing ultra-high-energy cosmic rays. This extreme particle acceleration mechanism may also apply to microquasar jets.