Determination of a magnetization parameter of the parsec-scale AGN jets
  The observed shift of the core of the relativistic AGN jets as a function of frequency allows us to evaluate the number density of outflowing plasma and, hence, the magnetization parameter. New analysis of more than 20 sources shows that for most of jets the magnetization parameter ~ 10 - 100. Since the magnetization parameter is the maximum possible bulk Lorentz-factor of the relativistic flow, this estimate is consistent with the observed superluminal motion. 
V. S. Beskin, Y. Y. Kovalev and E. E. Nokhrina
astro-ph.HE astro-ph.CO