Particle acceleration in astrophysical jets

Abstract

In this chapter, we review some features of particle acceleration in astrophysical jets. We begin by describing four observational results relating to the topic, with particular emphasis on jets in active galactic nuclei and parallels between different sources. We then discuss the ways in which particles can be accelerated to high energies in magnetised plasmas, focusing mainly on shock acceleration, second-order Fermi and magnetic reconnection; in the process, we attempt to shed some light on the basic conditions that must be met by any mechanism for the various observational constraints to be satisfied. We describe the limiting factors for the maximum particle energy and briefly discuss multimessenger signals from neutrinos and ultrahigh energy cosmic rays, before describing the journey of jet plasma from jet launch to cocoon with reference to the different acceleration mechanisms. We conclude with some general comments on the future outlook.

Recent progress on particle acceleration and reconnection physics during magnetic reconnection in the magnetically-dominated relativistic regime

“…The energy dependence in acceleration and escape needs to be combined to give a power-law distribution. Stochastic acceleration in turbulence has considerable difficulty to produce power-law distributions, as it needs to fine tune the energy dependence to produce a power-law distribution (see discussion in e.g., Matthews et al 2020). Drury (2012) has illustrated that in a simple leaking box model, the escape term due to advection of energetic particles in the reconnection outflow can lead to escape that allows a power-law distribution.…”

“…In the magnetically dominated scenarios, magnetic reconnection is thought to be the driver for energy release and particle acceleration. To explain the high-energy emissions, it is generally expected that the accelerated particles (electrons and ions) should develop a nonthermal power-law energy distribution extending to high energy (Matthews et al 2020).…”

Particle acceleration by relativistic magnetic reconnection driven by kink instability turbulence in Poynting flux dominated jets

“…Magnetic reconnection acceleration, as in the Fermi process, predicts a dependence of the acceleration rate with reconnection velocity and the particles energy (de Gouveia Dal Pino & Kowal 2015;del Valle et al 2016;Matthews et al 2020). Similarly as in del Valle et al (2016), in order to quantify the effectiveness of the acceleration of the particles for each test particle model (Table 2), we have calculated the average time per energy interval that particles take to reach a certain energy, which gives the acceleration time as a function of the energy shown in Figure 9 (top panel) for all the models.…”

Persistent mysteries of jet engines, formation, propagation, and particle acceleration: have they been addressed experimentally?

“…Particle acceleration at collisionless shocks as a means of dissipating hydrodynamic flows has been studied for decades in relativistic and non-relativistic flows, with a variety of analytical and numerical methods (for reviews see Ref. [122,116]). Different methods have strengths and weaknesses.…”