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We present an analysis of the narrow Fe K-alpha line in Chandra/HETGSobservations of the Seyfert AGN, NGC 4151. The sensitivity and resolutionafforded by the gratings reveal asymmetry in this line. Models including weakDoppler boosting, gravitational red-shifts, and scattering are generallypreferred over Gaussians at the 5 sigma level of confidence, and generallymeasure radii consistent with R ~ 500-1000 GM/c^2. Separate fits to"high/unobscured" and "low/obscured" phases reveal that the line originates atsmaller radii in high flux states; model-independent tests indicate that thiseffect is significant at the 4-5 sigma level. Some models and Delta t ~ 2 E+4 svariations in line flux suggest that the narrow Fe K-alpha line may originateat radii as small as R ~ 50-130 GM/c^2 in high flux states. These resultsindicate that the narrow Fe K-alpha line in NGC 4151 is primarily excited inthe innermost part of the optical broad line region (BLR), or X-ray BLR.Alternatively, a warp could provide the solid angle needed to enhance FeK-alpha line emission from intermediate radii, and might resolve an apparentdiscrepancy in the inclination of the innermost and outer disk in NGC 4151.Both warps and the BLR may originate through radiation pressure, so theseexplanations may be linked. We discuss our results in detail, and consider thepotential for future observations with Chandra, XARM, and ATHENA to measureblack hole masses and to study the intermediate disk in AGN using narrow FeK-alpha emission lines.

X-ray Structure between the Innermost Disk and Optical Broad Line Region in NGC 4151