EUV and Soft X-Ray Evidence for Partially Ionized Gas in Active Galactic Nuclei

J.P.D. Mittaz, R. Lieu, S. Bowyer, C.-Y. Hwang, J. Lewis

Proceedings of IAU Colloquium 152: Astrophysics in the Extreme Ultraviolet, 1996

Abstract

We present a synoptic study of active galactic nuclei (AGN) detected by EUVE. We also present complementary ROSAT PSPC spectra for these sources and for other AGN in directions of low galactic absorption. It is found that the best-fit power-law photon indices of the X-ray spectra at 0.1-2.4 keV are anti-correlated with their galactic hydrogen columns. The indices for the 0.9-2.4 keV range do not show such a correlation, and are considerably smaller (i.e. flatter). We discuss a number of possible interpretations of this correlation but only one of these, the presence of a partially ionized absorbing gas in the AGN, explains the observations satisfactorily. The ubiquity of this effect suggests that this component be may very common in AGN.

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