SED (left) and corresponding photoionization stability curves (right) between MJD 55208 and 55293 (hard state, a and b), MJD 55294 and 55303 (hard-to-soft transition, c and d), MJD 55304 and 55592 (soft state, e and f) and MJD 55593 and 55606 (soft-to-hard transition, g and h). The stability curves are labeled with their corresponding MJD. The highlighted (blue and gray) areas on each curve correspond to the range of the ionization parameter consistent with Fe XXV and Fe XXVI. They are colored in blue (resp. gray) if they are located on a stable (resp. unstable) part of the stability curve.