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F.E. Bauer (Columbia), D.M Alexander (IoA), G.T. Richards (JHU), D. Stern (JPL), W.N. Brandt (PSU), S.C. Gallagher (UCLA), A.E. Hornschemeier, R. Mushotzky (GSFC)
The deepest Chandra and XMM-Newton surveys have directly resolved ~90% of the 0.5--6 keV CXRB and ~50% of the 6--12 keV CXRB (Worsley et al. 2005), uncovering an order of magnitude higher AGN source density than found at optical wavelengths (e.g., ~7200/sq.deg; Bauer et al. 2004). The deepest >10 keV observations of the Universe have only resolved ~3% of the CXRB at its ~20--50 keV peak (Krivonos et al. 2004). These sources are so X-ray faint, that in general there is very little we can do with the current generation of X-ray telescopes to characterize them spectroscopically (and thus ascertain their true astrophysical nature). However, Constellation-X, with its large gain in collecting area and spectroscopic capability, will enable both source classifications and redshifts.
Beyond the iron K alpha emission line and the reflection component (which peaks at 20--30 keV) the hard X-ray spectra of AGN are dominated by the Compton upscattered component. Since there are currently no reliable measures of the high-energy Compton cutoff in quasars, the sensitive 10--40 keV hard energy coverage of Constellation-X will provide new insights into our understanding of the state and structure of X-ray emitting accretion-disk coronae (e.g., Sobolewska, Siemiginowska, & Zycki 2004; Zdziarski & Gierlinski 2004). For high-redshift quasars where we can probe rest-frame energies of 100--300 keV (and perhaps as high as 600 keV), we can expect to see the high-energy cutoff (50--200 keV) in some cases, thus allowing a determination of the electron temperature and optical depth of the Comptonizing plasma.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.