Spectroscopic signatures of conduction-mediated transition layers above an X-ray-illuminated disk

We derive a semianalytic solution for the structure of conduction-mediated transition layers above an X-ray-illuminated accretion disk and calculate explicitly the X-ray line radiation resulting from both resonance-line scattering and radiative recombination in these layers. The vertical thermal structure of the illuminated disk is found to depend on the illuminating continuum: for a hard power-law continuum, there are two stable phases connected by a single transition layer, while for a softer continuum, there may exist three stable phases connected by two separate transition layers, with an intermediate stable layer in between. We show that the structure can be written as a function of the electron scattering optical depth through these layers, which leads to unique predictions of the equivalent width of the resulting line radiation from both recombination cascades and resonance-line scattering. We find that resonance-line scattering plays an important role, especially for the case in which there is no intermediate stable layer.