X-ray reflection spectra from photoionized accretion discs in active galaxies are presented for a wide range of illumination conditions .
The energy , equivalent width ( EW ) and flux of the Fe K \alpha line are shown to depend strongly on the ratio of illuminating flux to disc flux , F _ { x } / F _ { \mathrm { disc } } , the photon index of the irradiating power-law , \Gamma , and the incidence angle of the radiation , i .
When F _ { x } / F _ { \mathrm { disc } } \leq 2 a neutral Fe K \alpha line is prominent for all but the largest values of \Gamma .
At higher illuminating fluxes a He-like Fe K \alpha line at 6.7 keV dominates the line complex .
With a high-energy cutoff of 100 keV , the thermal ionization instability seems to suppress the ionized Fe K \alpha line when \Gamma \leq 1.6 .
The Fe K \alpha line flux correlates with F _ { x } / F _ { \mathrm { disc } } , but the dependence weakens as iron becomes fully ionized .
The EW is roughly constant when F _ { x } / F _ { \mathrm { disc } } is low and a neutral line dominates , but then declines as the line progresses through higher ionization stages .
There is a strong positive correlation between the Fe K \alpha EW and \Gamma when the line energy is at 6.7 keV , and a slight negative one when it is at 6.4 keV .
This is a potential observational diagnostic of the ionization state of the disc .
Observations of the broad Fe K \alpha line which take into account any narrow component would be able to test these predictions .
Ionized Fe K \alpha lines at 6.7 keV are predicted to be common in a simple magnetic flare geometry .
A model which includes multiple ionization gradients on the disc is postulated to reconcile the results with observations .