A HIGH-REDSHIFT, ULTRASOFT X-RAY AGN

We present ROSAT data for the quasar E1346 + 266, an AGN identified as part of the Einstein Ultra-Soft Survey, and two other AGN nearby, EXO 1346.4 + 2637 and EXO 1346.2 + 2645. E1346 + 266 has an unusually high redshift (0.92) for a quasar with a strong, ultrasoft X-ray (similar to 0.25 keV) excess. Consequently, the effective rest-frame temperature of the soft component in E1346 + 266 is high (blackbody kT(eff) similar to 120 eV), and its soft-component luminosity may be the strongest identified in any soft-excess AGN to date. We find that the temperatures and luminosities of bare accretion disc spectra are too low to account for this soft X-ray excess. The addition of a hot, optically thin corona around a geometrically thick disc gives a better agreement with the X-ray data; reprocessing in cool dense clouds is an alternative. However, published spectra for both models predict an excess of flux in the optical/IR relative to the X-rays.