Numerical study of Kelvin-Helmholtz instability and its impact on synthetic emission from magnetized jets

Abstract

Non-thermal emission from Active Galactic Nuclei (AGN) jets extends up-to large scales in-spite of them being prone to a slew of magneto-hydrodynamic instabilities. The main focus of this study is to understand the impact of MHD instabilities on the non-thermal emission from large-scale AGN jets. We perform high-resolution three-dimensional numerical magneto-hydrodynamic simulations of a plasma column to investigate the dynamical and emission properties of jet configurations at kilo-parsec scales with different magnetic field profiles, jet speeds, and density contrast. We also obtain synthetic non-thermal emission signatures for different viewing angles using an approach that assumes static particle spectra and that obtained by evolving the particle spectra using Lagrangian macro-particles incorporating the effects of shock acceleration and radiative losses. We find that the shocks due to Kelvin-Helmholtz (KH) instability in the axial magnetic field configurations can strongly affect the jet dynamics. Additionally, we also find the presence of weak biconical shocks in the under-dense jet columns. The inclusion of a helical magnetic field hinders the vortex growth at the shear surface thereby stabilizing the jet column. With the evolving particle spectra approach, the synthetic SEDs obtained for cases with strong KH instability show the presence of multiple humps ranging from radio to TeV gamma-ray band. We conclude that the high-energy electrons accelerated in the vicinity of freshly formed shocks due to KH instability, result in high X-ray emission.