Are Quasar Jets Dominated by Poynting Flux?

The formation of relativistic astrophysical jets is presumably mediated bymagnetic fields threading accretion disks and central, rapidly rotatingobjects. As it is accelerated by magnetic stresses, the jet's kinetic energyflux grows at the expense of its Poynting flux. However, it is unclear howefficient is the conversion from magnetic to kinetic energy and whether thereare any observational signatures of this process. We address this issue in thecontext of jets in quasars. Using data from all spatial scales, we demonstratethat in these objects the conversion from Poynting-flux-dominated tomatter-dominated jets is very likely to take place closer to the black holethan the region where most of the Doppler boosted radiation observed in blazarsis produced. We briefly discuss the possibility that blazar activity can beinduced by global MHD instabilities, e.g., via the production of localizedvelocity gradients that lead to dissipative events such as shocks or magneticreconnection, where acceleration of relativistic particles and production ofnon-thermal flares is taking place.Comment: Accepted by the Astrophysical Journa