Numerical Investigation of Instabilities in Over-pressured Magnetized Relativistic Jets

TL;DR

This study uses 3D relativistic magnetohydrodynamic simulations to analyze how magnetic pitch influences instabilities in over-pressured relativistic jets, revealing the interplay between RTI and kink instabilities and their observational implications.

Contribution

It provides new insights into the role of magnetic pitch in the development of instabilities in relativistic jets through detailed numerical simulations.

Findings

RTI triggered at jet-ambient interface in recollimation zones

Decreased magnetic pitch weakens RTI growth but excites kink instability

Kink instability may explain observed quasi-periodic oscillations in BL Lac

Abstract

Context. Relativistic jets from Active Galactic Nuclei are observed to be collimated on the parsec scale. When the pressure between the jet and the ambient medium is mismatched, recollimation shocks and rarefaction shocks are formed. Previous numerical simulations have shown that instabilities can destroy the recollimation structure of jets. Aims. In this study, we aim to study the instabilities of non-equilibrium over-pressured relativistic jets with helical magnetic fields. Especially, we investigate how the magnetic pitch affects the development of instabilities. Methods. We perform three-dimensional relativistic magnetohydrodynamic simulations for different magnetic pitches, as well as a two-dimension simulation and a relativistic hydrodynamic simulation served as comparison groups Results. In our simulations, Rayleigh-Taylor Instability (RTI) is triggered at the interface between the jet and ambient medium in the recollimation structure of the jet. We found that when the magnetic pitch decreases the growth of RTI becomes weak but interestingly, another instability, the CD kink instability is excited. The excitement of CD kink instability after passing the recollimation shocks can match the explanation of the quasi-periodic oscillations observed in BL Lac qualitatively.