Abstract
Several low-power kiloparsec-scale jets in nearby radio galaxies are known for their synchrotron radiation extending up to optical and X-ray photon energies. Here we comment on high-energy γ-ray emission of one particular object of this kind, i.e., the kiloparsec-scale jet of the M87 radio galaxy, resulting from Comptonization of the starlight photon field of the host galaxy by the synchrotron-emitting jet electrons. In our analysis, we include the relativistic bulk velocity of the jet, as well as the Klein-Nishina effects. We show that upper limits to the kiloparsec-scale jet inverse Compton radiation imposed by the HESS and HEGRA Cerenkov Telescopes—which detected a variable source of very high energy γ-ray emission within 01 (~30 kpc) of the M87 central region—give us an important constraint on the magnetic field strength in this object, namely, that the magnetic field cannot be smaller than the equipartition value (referring solely to the radiating electrons) in the brightest knot of the jet, and most likely, is even stronger. In this context, we point out a need for the amplification of the magnetic energy flux along the M87 jet from the subparsec to kiloparsec scales, suggesting the turbulent dynamo as a plausible process responsible for the aforementioned amplification.
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