a Statistical X-Ray Osos Classification

A sample of 40 X-ray-emitting QSOs observed by the Einstein Observatory (Tananbaum et al., 1979) is characterized statistically using the G-mode method (Giovannelli et al., 1981) without a priori knowledge of taxonomic units. Parameters used in the classification (into nine classes forming two distinct clusters of four classes each with one intermediate class) include redshift, net counts, X-ray luminosity, and the X-ray/optical luminosity ratio. The characteristic parameter of the clusters is the 5-GHz radio flux, -32.655 dex in the first cluster, -33.73 dex in the intermediate class, and -34.715 dex in the second cluster. The variation of f2500 in the clusters is found to be proportional to the inverse square of the redshift, as predicted by the Hubble law without evolution of luminosity.