SIMBAD references

The electron-scattering region (ESR) is one of the important ingredients of Seyfert nuclei because it makes it possible to observe the hidden broad-line region (HBLR) in some type 2 Seyfert nuclei (S2's). However, little is known about its physical and geometrical properties. Using the number ratio of S2's with and without HBLR, we statistically investigate where the ESR is in Seyfert nuclei. Our analysis suggests that the ESR is located at a radius between ∼0.01 and ∼0.1 pc from the central engine. We also briefly discuss a possible origin of the ESR.