The Electron Scattering Region in Seyfert Nuclei

The electron scattering region (ESR) is one of important ingredients in Seyfert nuclei because it makes possible to observe the hidden broad line region (hereafter HBLR) in some type 2 Seyfert nuclei (hereafter S2s). However, little is known about its physical and geometrical properties. Using the number ratio of S2s with and without HBLR, we investigate statistically where the ESR is in Seyfert nuclei. Our analysis suggests that the ESR is located at radius between $\sim$ 0.01 pc and $\sim$ 0.1 pc from the central engine. We also discuss a possible origin of the ESR briefly.