A NONTHERMAL RADIO/OPTICAL/X-RAY SOURCE IN PKS 2316-423

We report observations of PKS 2316 - 423 in the ultraviolet and with the ROSAT HRI, where it appears as a bright point source. Optical spectroscopy reveals weak emission lines and a strong, excess blue continuum that is centrally concentrated. The combined optical-ultraviolet continuum spectrum cannot be fitted by any simple combination of a main-sequence stellar spectrum and a late-type elliptical galaxy spectrum, even allowing for intrinsic reddening. A non-thermal, power-law spectrum reddened by less than 0.5 mag fits the optical-ultraviolet spectrum very well, and extrapolates to match both the radio and X-ray fluxes. We suggest that this continuum emission is probably due to a non-thermal source, such as an active nucleus with an optical synchrotron jet. A second weak X-ray source 10 arcsec south of the nucleus may be related to the central source. PKS 2316 - 423 is probably a BL Lac object, orientated at an intermediate angle to our line of sight.