A sketch of the accretion flow geometry in the inner region of the galaxy Mrk 509. The hot corona, producing the hard X-ray emission, has a temperature of  ~100 keV and optical depth  ~0.5. It is localized in the inner part of the accretion flow (R < R_in) and illuminates the accretion disk beyond R_in, helping to form a warm layer at the disk surface. This warm component has a temperature of  ~1 keV and an optical depth  ~15 and produces the optical-UV up to soft X-ray emission. It extends over a large part of the accretion flow, heating the deeper layers and comptonizing their optical-UV emission. In return, part of this emission enters and cools the hot corona.