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Chandra observations of the X-ray jet in 3C66B

Our Chandra observation of the FRI radio galaxy 3C66B has resulted in the first detection of an X-ray counterpart to the previously known radio, infra-red and optical jet. The X-ray jet is detected up to 7 arcsec from the core and has a steep X-ray spectrum, alpha ~ 1.3 +/- 0.1. The overall X-ray flux density and spectrum of the jet are consistent with a synchrotron origin for the X-ray emission. However, the inner knot in the jet has a higher ratio of X-ray to radio emission than the others. This suggests that either two distinct emission processes are present or that differences in the acceleration mechanism are required; there may be a contribution to the inner knot's emission from an inverse-Compton process or it may be the site of an early strong shock in the jet. The peak of the brightest radio and X-ray knot is significantly closer to the nucleus in the X-ray than in the radio, which may suggest that the knots are privileged sites for high-energy particle acceleration. 3C66B's jet is similar both in overall spectral shape and in structural detail to those in more nearby sources such as M87 and Centaurus A.