Residual of spectral fitting with different models. The residual (D-M)/E stands for (data–model)/error. Top panel: Spectral fitting with only continuum models and the Galactic absorptions. Middle panel: Spectral fitting after adding the first pion model on the models shown in the top panel. This pion model is used to model the high-ionization warm absorber. The ΔC here means the C-stat differential between the spectral fitting results in the top and middle panels. Bottom panel: Spectral fitting after adding the second pion model on the models shown in the middle panel. This pion model is used to model the low-ionization warm absorber. The ΔC here means the C-stat differential between the spectral fitting results in the middle and bottom panels.