Reconciling models of luminous blazars with magnetic fluxes determined by radio core shift measurements

TL;DR

This paper examines the apparent contradiction between magnetic flux estimates in blazar jets and their spectral energy distributions, proposing scenarios to reconcile magnetic flux measurements with observed high-energy emissions.

Contribution

It introduces models that reconcile magnetic flux measurements with the high Compton dominance observed in powerful blazars, considering jet geometry and emission regions.

Findings

Magnetic flux estimates align with MAD scenario predictions.

High-energy emission likely originates from low-magnetization regions.

External radiation source geometry impacts observed blazar spectra.

Abstract

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.