NASA/IPAC EXTRAGALACTIC DATABASE
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For refcode 1993MNRAS.262...63S:
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NED Abstract

Copyright by Royal Astronomical Society. 1993MNRAS.262...63S The soft X-ray excesses of high-luminosity AGN R. D. Saxton, M. J. L. Turner, O. R. Williams, G. C. Stewart, T. Ohashi and T. Kii Department of Physics and Astronomy, University of Leicester University Road, Leicester LE1 7RH Department of Physics, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113, Japan Institute of Space and Astronautical Science, 3-1-1, Yoshinodai, Sagamihara, Kanagawa 229, Japan Accepted 1992 October 16. Received 1992 October 12; in original form 1991 October 10 ABSTRACT LE and ME spectra of 12 quasars from the EXOSAT data base have been analysed in a search for soft excesses. We have been able to quantify the soft excesses more accurately by using spectral indices for the ME taken from the much more sensitive Ginga observations of the same quasars. Eight quasars show a significant soft excess and the remaining four have upper limits consistent with ubiquity of a soft excess in our sample. We establish variability of the soft excess for three quasars with time- scales consistent with the inner region of an accretion disc around a 10^8^-M_sun_ black hole. The luminosity of the soft excess correlates well with other wavebands above M_B_ = - 23, but for the most luminous objects the soft excess appears to saturate. We interpret this to indicate that, compared to lower luminosity AGN, the most luminous quasars have an accretion disc which is cooler in its inner regions due to a black hole of larger mass. Key words: accretion, accretion discs - galaxies: active - quasars: general - X-rays: galaxies.
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