Synchrotron Radiation of Self-Collimating Relativistic Magnetohydrodynamic Jets

Abstract

The goal of this paper is to derive signatures of synchrotron radiation from state-of-the-art simulation models of collimating relativistic magnetohydrodynamic (MHD) jets featuring a large-scale helical magnetic field. We perform axisymmetric special relativistic MHD simulations of the jet acceleration region using the PLUTO code. The computational domain extends from the slow magnetosonic launching surface of the disk up to 6000 2 Schwarzschild radii allowing to reach highly relativistic Lorentz factors. The Poynting dominated disk wind develops into a jet with Lorentz factors of Γ 8 and is collimated to 1 • . In addition to the disk jet, we evolve a thermally driven spine jet, emanating from a hypothetical black hole corona. Solving the linearly polarized synchrotron radiation transport within the jet, we derive VLBI radio and (sub-) mm diagnostics such as core shift, polarization structure, intensity maps, spectra and Faraday rotation measure (RM), directly from the Stokes parameters. We also investigate depolarization and the detectability of a λ 2 -law RM depending on beam resolution and observing frequency. We find non-monotonic intrinsic RM profiles which could be detected at a resolution of 100 Schwarzschild radii. In our collimating jet geometry, the strict bi-modality in polarization direction (as predicted by Pariev et al.) can be circumvented. Due to relativistic aberration, asymmetries in the polarization vectors across the jet can hint to the spindirection of the central engine.

PROBING THE INNERMOST REGIONS OF AGN JETS AND THEIR MAGNETIC FIELDS WITH RADIOASTRON. I. IMAGING BL LACERTAE AT 21 μas RESOLUTION

“…As discussed in Zamaninasab et al (2013), Broderick & McKinney (2010), and Porth et al (2011), a large-scale helical magnetic field would lead to similar point symmetric structures around the centroid of the core of both RM and 0 c as found in Figures 9 and 10. This suggests that the core region in BLLac is threaded by a large-scale helical magnetic field.…”

“…Due to the np ambiguity in the EVPAs, we have developed an IDL routine that searches for possible np rotations, finding that no wraps higher than p  were required to fit the data. When performing the RM analysis of the core area, it is also important to pay special attention to possible 2 p rotations due to opacity (e.g., Gómez et al 1994;Gabuzda & Gómez 2001;Porth et al 2011). We have checked for these by first computing the spectral index maps between each pair of frequencies.…”

Radiative Signatures of Parsec-Scale Magnetised Jets

“…By performing multi-frequency VLBI observations, estimates of the magnetic field can be extracted by computing the core-shift (i.e., the frequency-dependent position of the VLBI core-the observed apex of the jet), or by extracting the turnover frequency, ν m , and turnover flux density, S m (e.g., [1][2][3]). To probe the effects of different jet configurations on the observed emission, special-relativistic magneto-hydrodynamical (SRMHD) simulations together with radiative transfer calculations can be used (e.g., [4][5][6]). The simulated radiative signatures can be employed to explain and interpret observed features in the VLBI images and single-dish spectra (see for example [7] for a case of shock-shock interaction in jets).…”

A Numerical Model of Parsec-Scale SSC Morphologies and Their Radio Emission

“…Kellermann & Moran 2001). Models of the jet morphology on larger scales are based on (general relativistic) magnetohydrodynamic (MHD) methods, but those models can only produce synthetic spectra (Gracia et al 2009;Porth et al 2011). Furthermore they are scale invariant and can not explain the necessary and observed length scales, respectively.…”