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 lambda1550 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 L(X)(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.