Efficient non-thermal particle acceleration mediated by the current-driven kink instability in jets

Astrophysical jets shine across the entire electromagnetic spectrum and are among the most powerful particle accelerators in the universe. Yet, the dominant mechanisms underlying their particle acceleration are not well understood. Global magnetohydrodynamic simulations suggest that the development of the current-driven kink instability (KI) can play an important role in the dissipation of the jet’s internal magnetic field near recollimation regions, but it remains unclear if such process could lead to efficient non-thermal particle acceleration. We have performed large-scale 3D particle-in-cell simulations to investigate the self-consistent particle acceleration associated with the development of the KI in conditions relevant to magnetized relativistic jets. We find that the development of the KI mediates the efficient dissipation of the magnetic field into high-energy particles. Interestingly, we find that efficient acceleration is achieved via a new acceleration mechanism, that is distinct from the commonly invoked shock and magnetic reconnection mechanisms. Non-thermal particles are accelerated by the combination of a coherent large-scale inductive electric field, that develops throughout the unstable region during the nonlinear stage of the KI, and efficient scattering in the highly tangled magnetic fields. This results in the development of a power-law energy tail that contains 50% of the initial magnetic energy and is robust for a large range of initial conditions and system sizes. In the context of the bright knots in AGN jets, such as HST-1 and Knot A in M87, we show that this mechanism can account for the spectrum of synchrotron radiating particles, and offers a viable means for accelerating ultra-high energy cosmic rays.