SOFT VERSUS HARD X-RAY-EMISSION IN ACTIVE GALACTIC NUCLEI - PARTIAL COVERING AND WARM-PLUS-COLD ABSORBER MODELS

We analyse the ROSAT Position Sensitive Proportional Counter (PSPC) ha rdness ratio and the 0.5-2-keV to 2-10-keV flux ratio of 65 active gal actic nuclei (AGN) for which there are both ROSAT archival observation s available and 2-10-keV fluxes, mostly from the HEAO-1 MC-LASS survey . We conclude that the simplest spectral model for the AGN that can ac commodate the variety of X-ray colours obtained is a standard power la w (with energy spectral index alpha similar to 0.9) plus a similar to 0.1-keV blackbody, both of which are partially absorbed. In our sample , type 1 AGN require an absorbing column around 10(22) cm(-2) with cov ering fractions between 20 and 100 per cent, while type 2 AGN display larger columns and similar to 100 per cent coverage. This simple model also provides a good link between soft and hard AGN X-ray luminosity functions and source counts. We also consider a warm absorber as an al ternative model to partial covering and find that the presence of gas in two phases (ionized and neutral) is required.