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R. Scarpa, C. M. Urry (Space Telescope Science Institute)
We discuss the energy budget of AGN jets, based on available data for all 14 having detected optical synchrotron emission. Assuming equipartition between magnetic field and particle energy, these jets transport enough kinetic energy to power a typical extended radio lobe only if the bulk motion of the jet plasma is at least moderately relativistic (v>0.75c). This suggests that, like the M87 jet, all optical jets could be be relativistic on kiloparsec scales, generalizing what has already been found for parsec scales based on radio data alone. In several cases, the jets are longer, by up to two orders of magnitude, than implied by electron lifetimes, unless there is particle reacceleration along the jet. Alternatively, if the magnetic field strength is an order of magnitude below the equipartition value, and the jets are still moderately relativistic, their lengths are commensurate with the intrinsic radiative lifetimes of the electrons. In this case, relativistic particles carrying most of the energy, roughly 103-104 times the energy density of the magnetic field. These optical data, though sparse, greatly improve constraints on the intrinsic physical conditions in jets.
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