The Knotty Question of the Jet of PKS B1421-490
  We report the discovery of unusually strong optical and X-ray emission associated with a knot in the radio jet of PKS B1421-490. The knot is the brightest feature observed beyond the radio band, with knot/core flux ratios \~300 and 3.7 at optical and X-ray frequencies. We interpret the extreme optical output of the knot as synchrotron emission. The nature of the X-ray emission is unclear. We consider a second synchrotron component, inverse Compton emission from a relativistic, decelerating jet, and the possibility that this feature is a chance superposition of an unusual BL Lac object. 
J. M. Gelbord (1), H. L. Marshall (1), D. M. Worrall (2 and 3), M.   Birkinshaw (2 and 3), J. E. J. Lovell (4), R. Ojha (4),...