zxipab: power-law distribution of ionized absorbers

This is an extension of the pwab model in which the complex absorption is modelled as a power-law distribution of covering fraction and column of ionised absorbers. Unlike pwab, which is based on neutral absorbers, zxipab utilizes pre-calculated grid of XSTAR photo-ionisation model also used by zxipcf model, with ionising parameter log (xi). See Islam & Mukai (2021) for details.

par1 nHmin: minimum equivalent hydrogen column density ($10^{22}$cm$^{-2}$)
par2 nHmax: maximum equivalent hydrogen column density ($10^{22}$cm$^{-2}$)
par3 beta: power law index for covering fraction
par4 logxi: ionizing parameter $\log\xi$
par5 redshift