Reconciling models of luminous blazars with magnetic fluxes determined   by radio core shift measurements
  Estimates of magnetic field strength in relativistic jets of active galactic nuclei (AGN), obtained by measuring the frequency-dependent radio core location, imply that the total magnetic fluxes in those jets are consistent with the predictions of the magnetically-arrested disk (MAD) scenario of jet formation. On the other hand, the magnetic field strength determines the luminosity of the synchrotron radiation, which forms the low-energy bump of the observed blazar spectral energy distribution (SED). The SEDs of the most powerful blazars are strongly dominated by the high-energy bump, which is most likely due to the external radiation Compton (ERC) mechanism. This high Compton dominance may be difficult to reconcile with the MAD scenario, unless 1) the geometry of external radiation sources (broad-line region, hot-dust torus) is quasi-spherical rather than flat, or 2) most gamma-ray radiation is produced in jet regions of low magnetization, e.g., in magnetic reconnection layers or in fast jet spines. 
Krzysztof Nalewajko, Marek Sikora, Mitchell C. Begelman
astro-ph.HE astro-ph.GA