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[74.01] The Sources Comprising the X-ray Background in the HDF_N Region observed by the Chandra X-ray Observatory

G. P. Garmire, N. W. Brandt, A. E. Hornschemeier, D. P. Schneider, P. S. Broos, L. K. Townsley, D. N. Burrows, G. Chartas, E. D. Feigelson, J. A. Nousek, L. W. Ramsey (Penn State University), A. J. Barger (U. Wisc and U. Hawaii), L. L. Cowie (U. Hawaii), M. W. Bautz (CSR MIT), R. Griffiths (CMU), D. Lumb (ESTEC), W. L. W. Sargent (Caltech)

The Chandra X-ray Observatory (CXC) has observed the HDF-N region (a ~17' by 19' area including the HDF-N) for 224.7 ks as of this writing. Another 775 ks will be devoted to this region in the next six months. A total of about 200 sources have been detected in the 0.5 - 8.0 keV energy band. The 2.0 - 8.0 keV Log N(>S) vs Log S plot, where N is the areal density of sources and S the flux, reveals that the bulk of the sky flux comes from sources brighter than ~ 10^-14 ergs/cm²/s. The majority of these sources lies closer than a redshift of 1, based on 51 redshifts measured thus far. The X-ray spectra of the sources show a gradual hardening with decreasing source intensity, with the fainter sources (3 x 10^-15 ergs/cm²/s in the 0.5 - 10.0 keV band) exhibiting a photon number spectral slope of 1.35+/-0.2.

This work is supported in part by NASA grant NAS 8-38252(GPG PI), NASA GSRP grant NGT5-50247 (AEH), NSF CAREER award AST-9983783 and the Alfred P. Sloan Foundation (WNB), and NSF grant AST99-00703 (DPS).

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