The AGN Source Population in the Chandra Deep Field-North Survey:   Constraints from X-ray Spectroscopy and Variability
  We briefly report here on our ongoing X-ray spectroscopy and variability analyses of 136 faint X-ray sources discovered in the 2 Ms Chandra Deep Field North observations spanning 1.4x10-15 to 2x10-13 ergs s-1 cm-2. Most sources are adequatley fitted with a simple intrinsic absorption plus power-law model, although the resulting photon index is much lower than the canonical average unabsorbed spectral slope found locally (suggesting additional spectral complexity). Among the 136 sources, 7% show significant Fe (Ka) emission features, with equivalent widths in the range 0.1-1.3 keV. Two of these emission-line sources appear to be Compton thick. For the subset of sources with redshifts, we also find that fewer than 10% are likely to be Compton thick. Finally, ~60% of the sample show signs of long-term variability. This fraction climbs to ~90% for the bright sources (>500 cnts) or BLAGN. 
F.E. Bauer, C. Vignali, D.M. Alexander, W.N. Brandt, G.P. Garmire,   A.E. Hornschemeier, P. Broos, L. Townsley, and D.P. Sch...