Magnetization of jets in luminous blazars

Abstract

Luminosities of many powerful blazars are strongly dominated by $γ$-rays which most likely result from Comptonization of radiation produced outside a jet. This observation sets certain constraints on composition and energetics of the jet as well as the surrounding quasar environment. We study the dependence of a Compton dominance on a jet magnetization (the magnetic-to-matter energy flux) and on the location of the 'blazar zone'. Calculations are performed for two geometries of broad-emission-line and hot-dust regions: spherical and planar. The jet magnetization corresponding to the large observed Compton dominance is found to be $\sim 0.1 (θ_{\rm j} Γ)^2$ for spherical geometries and $\sim 0.01 (θ_{\rm j} Γ)^2$ for planar geometries, where $θ_{\rm j}$ is the jet half-opening angle and $Γ$ is the jet Lorentz factor. This implies that jets in luminous blazars are matter dominated and that this domination is particularly strong for the flattened geometry of external radiation sources.