The Origins of X‐Ray Emission from the Hot Spots of FR II Radio Sources

We use new and archival Chandra data to investigate the X-ray emission from alarge sample of compact hotspots of FRII radio galaxies and quasars from the 3Ccatalogue. We find that only the most luminous hotspots tend to be in goodagreement with the predictions of a synchrotron self-Compton model withequipartition magnetic fields. At low hotspot luminosities inverse-Comptonpredictions are routinely exceeded by several orders of magnitude, but this isnever seen in more luminous hotspots. We argue that an additional synchrotroncomponent of the X-ray emission is present in low-luminosity hotspots, and thatthe hotspot luminosity controls the ability of a given hotspot to producesynchrotron X-rays, probably by determining the high-energy cutoff of theelectron energy spectrum. It remains plausible that all hotspots are close tothe equipartition condition.Comment: 49 pages, 16 figures. ApJ accepted. Revised version fixes a typo in one of the Tables and corrects a statement about 3C27