ROSAT Spectra of QSOs in the Large Bright Quasar Survey
Session 24 -- AGNs/QSOs - High Luminosity
Display presentation, Tuesday, June 13, 1995, 9:20am - 6:30pm

## [24.01] ROSAT Spectra of QSOs in the Large Bright Quasar Survey

Paul J. Green (SAO), Norbert Schartel (MPE), Scott F. Anderson (UWa), Paul C. Hewett (IoA), Craig B. Foltz (UAz), Bruce Margon (UWa), Wolfgang Brinkmann, Henner Fink, and Joachim Tr\"umper (MPE)

We study the X-ray spectral properties of 908 QSOs in the Large Bright Quasar Survey (LBQS) that were observed during the soft X-ray ROSAT All-Sky Survey (RASS). X-ray spectral model fits for individual QSOs are precluded by poor photon statistics. We present a novel approach to co-adding X-ray spectra which obviates both the distinction between detections and non-detections, and the need to sum only those QSO spectra with similar Galactic column densities $N_H$. We thus obtain effectively much more sensitive X-ray observations for an {\em average} QSO in bins of redshift or luminosity, and for several classes of QSOs. We marginally confirm a flattening of the X-ray spectral index toward higher redshifts. Radio-loud QSOs show flatter X-ray photon indices, in agreement with previous work. We show that the apparent flattening of the photon index with redshift is not due to an increasing fractional contribution from the radio-loud class of QSOs.