The cores of the FeK lines in Seyfert 1 galaxies observed by the Chandra High Energy Grating

We report on the results of 18 observations of the core, or peak, of the Fe Kalpha emission line at similar to6.4 keV in 15 Seyfert 1 galaxies using the Chandra High Energy Grating (HEG). These data afford the highest precision measurements of the peak energy of the Fe Kalpha line and the highest spectral resolution measurements of the width of the core of the line to date. We were able to measure the peak energy in 17 data sets, and, excluding a very deep observation of NGC 3783, we obtained a weighted mean of 6: 404 +/- 0.005 keV. In all 15 sources the two-parameter, 99% confidence errors on the line peak energy do not exclude fluorescent Kalpha line emission from Fe I, although two sources (Mrk 509 and 3C 120) stand out as very likely being dominated by Kalpha emission from Fe XVII or so. We were able to measure the line core width in 14 data sets and obtained a weighted mean of 2380 +/- 760 km s(-1) FWHM ( excluding the NGC 3783 deep exposure), a little larger than the instrument resolution (similar to1860 km s(-1) FWHM). However, there is evidence of underlying broad-line emission in at least four sources. In fact, the width of the peak varies widely from source to source and may in general have a contribution from the outer parts of an accretion disk and more distant matter. For the disk contribution to also peak at 6.4 keV requires greater line emissivity at hundreds of gravitational radii than has been deduced from previous studies of the Fe Kalpha line.