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Session 36 - Extragalactic X-Ray Sources.
Display session, Tuesday, January 14
I present spectral indices obtained from 112 X-ray-selected and fully optically-identified quasars in four sky fields in the southern hemisphere, detected by the Rosat Position Sensitive Proportional Counters. These fields were originally studied by Boyle et al. (1990) for the ultraviolet-excess properties of objects in the fields; only 47 of the quasars in the field were listed in Boyle et al.
I determine the quasars' power-law spectral index \alpha_E with three different methods: spectral ``stacking'', hardness ratios, and direct fitting. Both spectral stacking and the hardness ratio methods are used because several of the quasars were too dim to reliably calculate spectral indices individually.
The spectral stacking method, which involves co-adding quasar spectra energy bins, shows a definite change in quasar spectral index with redshift.
Program listing for Tuesday