Aims: We present a method that allows us to estimate the distance from the continuum source located in the center of AGN to the highly ionized gas called warm absorber.
Methods: We computed a set of constant total pressure photoionization models compatible with the warm absorber conditions, where a metal-rich gas is irradiated by a continuum in the form of a double power law. The first power law is hard up to 100 keV and represents radiation from an X-ray source, while the second power law extends up to several eVs and illustrates radiation from an accretion disk.
Results: When the ionized continuum is dominated by the soft component, the warm absorber is heated by free-free absorption, instead of Comptonization, and the transmitted spectra show different absorption line characteristics for different values of the hydrogen number density at the cloud illuminated surface.
Conclusions: This fact results in the possibility of deriving the number density on the cloud illuminated side from observations and hence the distance to the warm absorber.