BLUE OPTICAL CONTINUUM ASSOCIATED WITH A RADIO KNOT IN 3C346

We report the discovery of extremely luminous near-UV continuum emissi on associated with a bright radio knot in the radio galaxy 3C346 (z=0. 162). Photometric measurements from U and r' band images and longslit spectra show a spectral energy distribution that steepens at higher fr equencies, with radio and optical spectral indices alpha(r)=-0.37+/-0. 02 and alpha(o)=-1.8-0.2, respectively. Based on a comparison of the o ptical properties of this knot with other known cases of optical emiss ion associated with radio structures, we conclude that the continuum e mission is optical synchrotron radiation. Our observations are consist ent with the suggestion that 3C346 is a foreshortened FR-11 radio gala xy with its radio axis oriented close to the line of sight. The optica l and radio emission from the knot appear to be associated with a hots pot (at the end of a jet) on the near side. Finally, our U and r' imag es of 3C346 provide a striking illustration that the optical morpholog ies of nearby radio galaxies also depend upon wavelength and that stud ies of these objects are relevant to the interpretation of the alignme nt effect seen in high redshift radio galaxies.