Gelbord, J. M.Marshall, H. L.Worrall, D. M.Birkinshaw, M.Lovell, J. E. J.Ojha, R.Godfrey, L.Schwartz, D. A.Perlman, E. S.Georganopoulos, M.Murphy, D. W.Jauncey, D. L.2020-05-042020-05-042005-10-04J. M. Gelbord, H. L. Marshall, D. M. Worrall, M. Birkinshaw, J. E. J. Lovell, R. Ojha, L. Godfrey, D. A. Schwartz, E. S. Perlman, M. Georganopoulos, D. W. Murphy, and D. L. Jauncey, The Knotty Question of the Jet of PKS B1421–490,The Astrophysical Journal Letters, Volume 632, Number 2,https://doi.org/10.1086%2F497823https://doi.org/10.1086%2F497823http://hdl.handle.net/11603/18481http://simbad.u-strasbg.fr/simbad/sim-ref?querymethod=bib&simbo=on&submit=submit+bibcode&bibcode=2005ApJ...632L..75Ghttps://ned.ipac.caltech.edu/cgi-bin/objsearch?search_type=Search&refcode=2005ApJ...632L..75Ghttps://ui.adsabs.harvard.edu/link_gateway/2005ApJ...632L..75G/ChandraWe 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, respectively. 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.4 pagesen-USThis item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author.© 2005. The American Astronomical Society. All rights reserved.Text