The X-ray Baldwin effect

Using the X-ray data of active galactic nuclei (type 1 Seyfert galaxies and quasars) obtained by the X-ray satellite Ginga, we have found that the equivalent width of the Fe K emission line at 6. 4 keV, EW (Fe K), is inversely correlated with the X-ray luminosity in the 2-10 keV band. This inverse correlation is basically similar to the well-known relation known as the "Baldwin effect, " which means that the equivalent width of the C IV λ1550 emission line is inversely correlated with the UV continuum luminosity (Baldwin 1977). Hence, we may call our finding "the X-ray Baldwin effect. " The X-ray Baldwin effect is pronounced for type 1 Seyfert galaxies. The obtained correlation, EW (Fe K) is proportional to Lₓ_ (2-10 keV) ^-0. 20+/-0. 03, is quite similar to those of the original Baldwin effects for type 1 Seyfert galaxies and quasars, implying that the Fe K emission mainly comes from the broad-line regions or from the regions whose geometrical configurations are nearly the same as those of broad-line regions.