This model uses a grid of XSTAR photionized absorption models (calculated assuming a microturbulent velocity of 200km/s) for the absorption, then assumes that this only covers some fraction f of the source, while the remaining (1-f) of the spectrum is seen directly. This is the model used by Reeves et al (2008) 'On why the iron K-shell absorption in AGN is not the signature of the local warm-hot intergalactic medium', and may also be more generally applicable to the spectral complexity seen in Narrow Line Seyfert 1 AGN (Miller et al 2007, A&A, 463, 13).

par1 = column density (10^{22} cm^{-2})

par2 = log(xi) where xi=L/nr^{2}

par3 = covering fraction

par4 = redshift