Magnetic Field Strengths in the Hot Spots and Lobes of Three Powerful Fanaroff‐Riley Type II Radio Sources

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Abstract
We have made deep Chandra observations of three powerful Fanaroff-Riley type II (FR II) radio sources: two quasars (3C 263 and 3C 351) and one radio galaxy (3C 330). X-ray emission from hot spots and lobes, as well as from the active nucleus, is detected in each source. We model the hot spots' synchrotron spectra using VLA, BIMA, and Hubble Space Telescope data. In 3C 263 and 3C 330, the hot spots' X-ray emission is at a level consistent with being synchrotron self-Compton (SSC) emission, with a hot spot magnetic field close to the equipartition value. In the two hot spots of 3C 351, however, an SSC origin for the X-rays would require the magnetic field strength to be an order of magnitude below the equipartition value in our models; in addition, there are offsets between the radio, optical, and X-ray emission from the secondary hot spot that are hard to explain in a simple SSC model. We discuss the emission mechanisms that may be responsible for these observations. On our preferred model, the X-ray emission from the radio lobes of the three sources is due to inverse Compton scattering of the microwave background radiation. If this is the case, the magnetic field strengths in the lobes are typically about a factor of 2 below the equipartition values, assuming uniform lobe electron and magnetic field distributions. We detect extended X-ray emission, which we attribute to a cluster/group environment, around 3C 263 and 3C 330. This detection allows us to show that the lobes are close to pressure balance with their surroundings, as long as no nonradiating particles contribute to the internal pressure of the lobes.
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