Particles in Relativistic MHD Jets II: Bridging Jet Dynamics with Multi-waveband Non-Thermal Emission Signatures

TL;DR

This paper presents synthetic multi-wavelength emission signatures from 3D relativistic MHD simulations of AGN jets, linking jet dynamics, shock acceleration, and non-thermal radiation to explain observed jet features and variability.

Contribution

It develops a novel connection between jet dynamics, particle acceleration, and non-thermal emission in relativistic jets, incorporating shock re-acceleration and cooling effects.

Findings

Jets exhibit localized emission patterns called knots that can fade or flare.

Knots can have superluminal pattern speeds up to ~5c.

Precessing jets produce the most powerful and flatter spectra.

Abstract

Relativistic magnetized jets, originating near black holes, are observed to exhibit sub-structured flows. In this study, we present synthetic synchrotron emission signatures for different lines of sight and frequencies, derived from three-dimensional relativistic magneto-hydrodynamic simulations of pc-scale AGN jets. These simulations apply different injection nozzles, injecting steady, variable, and precessing jets. Extending our previous study, here, we have developed a bridge to connect jet dynamics and particle acceleration within relativistic shocks with non-thermal radiation dominant in jets. The emission is derived from Lagrangian particles - injected into the jet and following the fluid - accelerated through diffusive shock acceleration and subsequently cooled by emitting energy via synchrotron and inverse-Compton processes. Overall, the different shocks structures lead to the formation of numerous localized emission patterns - interpreted as jet knots. These knot patterns can fade or flare, also as a consequence of merging or Doppler boosting, leading to jet variability. We find knots with high-enough pattern speed supposed to be visible as superluminal motion <~5c. Synchrotron spectra of all jets reveal double-humped structures, reflecting multiple electron populations characterized by the nature of underlying shock and their age. The precessing jet is the most powerful emitter, featuring a spectrum flatter than the steady and the variable jet. The emission, although essentially governed by the acceleration through shocks, depends on the cooling history of the particle as well. Overall, the continuous re-acceleration of electrons through shocks along the jet we found, is an essential prerequisite for observing extended jet emission over large time-scales and length-scales.