THE UNUSUAL GALAXY J2310-43 - AN ACTIVE NUCLEUS WITHOUT OPTICAL-EMISSION LINES AND WITHOUT A SUBSTANTIAL OPTICAL CONTINUUM

X-ray, optical, and radio observations show the galaxy J2310-43 (Einst ein Observatory Source Catalog number 4689, z = 0.0886) to be a very u nusual object. Our analysis of ROSAT PSPC data for 2310-43 (23(h)10(m) 41.(s)7, -43 degrees 47'38 '', J2000) indicates that the X-ray emissio n is extended spatially out to similar to 3.'5. Spectral analysis of t he PSPC data finds that a simple power-law model with line-of-sight Ga lactic absorption can fit the observed PSPC energy distribution, as ca n two-component Raymond-Smith models, and composite power-law and Raym ond-Smith models. Analysis of CCD optical images indicates that 2310-4 3 is located within a cluster that is probably Abell richness class 0, and a search of the NASA Extragalactic Database finds a 5 GHz radio s ource of 62 mJy associated with 2310-43. While the data support a vari ety of interpretations, we note that 2310-43 differs significantly fro m clusters and groups of galaxies as well as from normal elliptical ga laxies. We can interpret similar to 20% of the observed X-ray emission as an extended component emitting similar to 3.4 x 10(43) ergs s(-1) (0.1-2.4 keV), associated with the cluster around 2310-43. The bulk of the X-ray emission, corresponding to similar to 1.45 x 10(44) ergs s( -1), can then be associated with a nuclear point source consistent wit h the PSPC spatial and spectral data. However, the (B-V) color of 2310 -43 is typical of a normal elliptical galaxy, making a BL Lac interpre tation questionable, and the absence of emission lines in the optical spectrum rules out a standard quasar/Seyfert identification for the so urce. Our data show that 2310-43 is most similar to the optically dull , X-ray, and radio-loud galaxy 3C 264 (first characterized as ''optica lly dull'' by Elvis et al.). The location of these two objects in the alpha(ro)-alpha(ox), color-color diagram is at the extreme for BL Lac objects, implying a substantial deficiency in the optical continuum em ission. We assume that the nuclear emissions from 2310-43 and 3C 264 a re primarily nonthermal radiation, possibly associated with a nuclear jet. Then, we examine our observations in the context of several curre nt models with the goal of understanding how a process (such as jet-di sk symbiosis) can result in depressed optical continuum compared to mo st active galactic nuclei (AGNs) and BL Lac objects. We also discuss f uture observations (some already underway) that can shed additional li ght on these unusual sources.