2002ApJ...569..487Y

The ASCA calibration has evolved considerably since launch and, indeed, is still evolving. There have been concerns in the literature that changes in the ASCA calibration have resulted in the Fe K lines in active galactic nuclei (AGNs) now being systematically narrower than was originally thought. If this were true, a large body of ASCA results would be affected. In particular, it has been claimed that the broad red wing (when present) of the Fe K line has been considerably weakened by changes in the ASCA calibration. We demonstrate explicitly that changes in the ASCA calibration over a period of about 8 years have a negligible effect on the width, strength, or shape of the Fe K lines. The reduction in both width and equivalent width is only ∼8% or less. We confirm this with simulations and individual sources, as well as sample average profiles. The average profile for type 1 AGNs is still very broad, with the red wing extending down to ∼4 keV. The reason for the claimed, apparently large, discrepancies is that in some sources the Fe K line is complex, and a single-Gaussian model, being an inadequate description of the line profile, picks up different portions of the profile with different calibration. Single-Gaussian fits do not, therefore, model all of the line emission in some sources, in which case they do not compare old and current calibration, since the models do not then describe the data.