Talk Title: Are Quasar jets matter or Poynting flux dominated?
Abstract: If quasar jets are accelerated by magnetic fields but terminate as matter dominated, where and how does the conversion take place from Poynting to kinetic flux? To address this question, we study constraints which are imposed on jet structure by observations at different spacial scales. In particular, using high energy spectra of blazars, we derive the number flux of electrons and positrons. This flux is consistent with the rate of creation of pairs in the accretion disk corona and, therefore, there is no need for pair production in the jet. However, the momentum of the leptonic flux is too small to power radio lobes and, therefore, the energy flux of quasar jets must be dominated by magnetic fields and/or protons. We demonstrate that available observational data are consistent with a scenario, according to which acceleration of a jet is accomplished within $10^{3-4} R_g$. In this picture, non-thermal flares --- an attribute of the blazar phenomenon --- are produced by strong shocks, formed in the region where the jet inertia is already dominated by protons. The shocks are formed due to collisions between portions of the jet accelerated to different velocities, and the differential acceleration is very likely related to global MHD instabilities.
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