ACTIVE GALACTIC NUCLEI WITH ULTRASOFT X-RAY-EMISSION

In the course of selecting ultrasoft X-ray-emitting objects from the data base of the Einstein Observatory, we have found a class of active galactic nuclei with clearly distinguishable soft X-ray components below 0.5 keV. The spectrum of the soft emission corresponds to that of a approximately 10 eV blackbody in the observer's frame of reference. These AGNs have necessarily been detected through equivalent hydrogen column densities that are less than a few times 10(20) cm-2. At least three kinds of AGNs comprise this sample: (1) low-redshift quasars and Seyfert galaxies that have only ultrasoft emission (these objects lack detectable hard X-ray emission); (2) AGNs that have both ultrasoft as well as hard X-ray components (for some of these objects multiple observations exist which suggest that the components are independently variable); and (3) high-redshift quasars whose soft emission may originate, as proposed for the lensed quasar 0957+561, in an extended source or, alternately, in a source that is luminosity-enhanced due to relativistic beaming.