Modelling Optical Emission and Polarization of Relativistic AGN Jets Using RMHD Simulations.

Abstract

Radio-loud Active Galactic Nuclei (AGN) exhibit non-thermal emission observed to span the entire electromagnetic spectrum. The majority of the emission at lower energies (from radio to soft X-rays) is produced by synchrotron emission of non-thermal electrons within a relativistic jet. The structure and kinematics of these relativistic jets can be simulated using relativistic magneto-hydrodynamic (RMHD) simulations. A 3D RMHD simulation was set up with the PLUTO code that consisted of a uniform background medium with a less dense jet. A domain size of $5$ pc was used to model the sub-parsec region. The jet was separated into two regions, namely the spine (the inner region of the jet) and the sheath (the outer region of the jet). The spine had a radius of $0.033$ pc and a maximum bulk Lorentz factor of $\Gamma_{\text{max}} = 10$, while the sheath had a radius of $0.1$ pc and a maximum bulk Lorentz factor of $\Gamma_{\text{max}}=3$. A helical magnetic field orientation was utilized where the spine and sheath had a maximum magnetic field magnitude of $B=50$ mG and $B=5$ mG, respectively. Lagrangian particles were injected at the base of the jet with an initial power-law distribution, and were allowed to evolve with time. The synchrotron and linear polarization emission coefficients were then integrated along a user defined line of sight to produce the $I$, $Q$ and $U$ Stokes parameters. We present the initial results from this study showing the spectral energy distribution (SED) and wavelength dependent polarization.