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galaxies: jetsmagnetic fieldsradiation mechanisms: nonthermalradio continuum: galaxies
Abstract:
We examine a systematic comparison of jet knots, hot spots, and radio lobes recently observed with Chandra and ASCA. This report discusses the origin of their X-ray emissions and investigates the dynamics of the jets. The data were compiled at well-sampled radio (5 GHz) and X-ray (1 keV) frequencies for more than 40 radio galaxies. We examine three models for the X-ray production: synchrotron (SYN), synchrotron self-Compton (SSC), and external Compton (EC) on cosmic microwave background (CMB) photons. For the SYN sourcesmostly jet knots in nearby low-luminosity radio galaxiesX-ray photons are produced by ultrarelativistic electrons with energies 10100 TeV that must be accelerated in situ. For the other objects, conservatively classified as SSC or EC sources, a simple formulation of calculating the "expected" X-ray fluxes under an equipartition hypothesis is presented. We confirm that the observed X-ray fluxes are close to the expected ones for nonrelativistic emitting plasma velocities in the case of radio lobes and the majority of hot spots, whereas a considerable fraction of jet knots are too bright in X-rays to be explained in this way. We examine two possibilities to account for the discrepancy in a framework of the inverse Compton model: (1) the magnetic field is much smaller than the equipartition value, and (2) the jets are highly relativistic on kiloparsec and megaparsec scales. We conclude that if the inverse Compton model is the case, the X-raybright jet knots are most likely far from the minimum-power condition. We also briefly discuss the other possibility, namely, that the observed X-ray emission from all the jet knots is synchrotron in origin.
