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Description
We survey the broadband spectral properties of ~500 X-ray-selected active galactic nuclei (AGNs) observed with the Einstein Observatory. Included in this survey are the ~450 AGNs in the Extended Medium Sensitivity Survey of Gioia et al. (1990ApJS...72..567G) and the ~50 AGNs in the Ultrasoft Survey of Cordova et al. (1992ApJS...81..661C). We present a revised version of the latter sample, based on the post publication discovery of a software error in the Einstein Rev-1b processing. We find that the mean spectral index of the AGNs between 0.1 and 0.6keV is softer, and the distribution of indices wider, than previous estimates based on analyses of the X-ray spectra of optically selected AGNs. A subset of these AGNs exhibit flux variability, some on timescales as short as 0.05-days. A correlation between radio and hard X-ray luminosity is confirmed, but the data do not support a correlation between the radio and soft X-ray luminosities, or between radio loudness and soft X-ray spectral slope. Evidence for physically distinct soft and hard X-ray components is found, along with the possibility of a bias in previous optically selected samples toward selection of AGNs with flatter X-ray spectra.
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