Chandra Grating Observations of AGN
  The highest spectral resolution data for the Fe-K lines in type I AGN, as observed with the Chandra High Energy Grating (HEG), reveal a variety of line shapes. However, the energies of the most prominent peak are all clustered tightly around 6.4 keV (weighted mean $6.403 \pm 0.062$ keV). If all the peaks were part of single, relativistically broadened disk line, this would require unrealistically fine tuning. Thus, some of the cores must originate in distant matter (e.g. BLR, NLR, torus). On the other hand, in at least two AGN, the emission at 6.4 keV has been seen to vanish on short timescales, indicating an origin close to the central engine. For one of these (Mrk 509) this is puzzling because the HEG and simultaneous RXTE time-averaged spectra indicate only a narrow line was present at that time. Simultaneous HEG/RXTE observations for NGC 4593 indicate a broad and narrow Fe-K complex, all originating in neutral Fe, and for F9 show a narrow, neutral Fe-K component plus a broad, He-like component. The latter signature has been observed in three other AGN by XMM and may be quite common. 
T. Yaqoob (Johns Hopkins U., LHEA/GSFC), U. Padmanabhan (Johns Hopkins   U.)