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

We have made deep Chandra observations of three powerful FRII radio sources:two quasars (3C263 and 3C351) and one radio galaxy (3C330). X-ray emission fromhotspots and lobes, as well as from the active nucleus, is detected in eachsource. We model the hotspots' synchrotron spectra using VLA, BIMA and HST data. In3C263 and 3C330, the hotspots' X-ray emission is at a level consistent withbeing synchrotron self-Compton (SSC) emission, with a hotspot magnetic fieldclose to the equipartition value. In the two hotspots of 3C351, however, an SSCorigin for the X-rays would require the magnetic field strength to be an orderof magnitude below the equipartition value in our models: in addition, thereare offsets between the radio, optical and X-ray emission from the secondaryhotspot which are hard to explain in a simple SSC model. We discuss theemission mechanisms that may be responsible for these observations. On our preferred model, the X-ray emission from the radio lobes of the threesources is due to inverse-Compton scattering of the microwave backgroundradiation. If this is the case, the magnetic field strengths in the lobes aretypically about a factor 2 below the equipartition values, assuming uniformlobe electron and magnetic field distributions. We detect extended X-ray emission, which we attribute to a cluster/groupenvironment, around 3C263 and 3C330. This detection allows us to show that thelobes are close to pressure balance with their surroundings, as long as nonon-radiating particles contribute to the internal pressure of the lobes.