Resum:

Active Galactic Nuclei (AGNi) are one of the most energetic phenomena in the universe, thought to be powered by a central super massive black hole (SMBH). Most of them emit synchrotron radiation from radio to gamma rays, and indeed, most of the gamma ray sources are AGN. However, due to limited resolution, we do not know where the radiation originates. The story is very different in radio VLBI observations, where we can resolve jets and their morphology and evolution. Here we present multi-frequency simultaneous radio observations of the flat spectrum radio quasar 4C 38.41 combined with additional observations in the radio, optical, X-rays, and gamma-rays carried out during the period 2012 March–2015 August. By examining a series of multi-band flares and their correlation with ejected VLBI components, we estimate that the flares appear to be associated with new components in the source originating within a particle-dominated region. Jet components in this source follow the shock-in-jet model and evolve through a semi-parabolic jet where the magnetic field and electron densities are found to fall along the jet as $B\propto r^{-1.5}$ and $n\propto r^{-1.1}$ respectively, suggesting that the magnetic configuration upstream the jet may be dominated by the poloidal component. However, as the jet evolves towards larger scales, the polarization properties are still unclear and their study may unveil more mysteries on the dynamics of this source.

 

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