Colored lines are the photoionization stability curves during the hard-to-soft transition (see Fig. 2 for the meaning of the blue and gray segments). The black dashed lines (squares and dashed line; star and dashed line) correspond to different paths with constant nr². The red lines are the paths followed by the wind assuming an increase (red dotted path) or decrease (red dashed path) in the wind density by a factor of 3 between MJD 55295 and MJD 55296. See Sect. 4.1.1 for the small temperature domain underlined in red on the stability curve of MJD 55294. The arrows indicate the time evolution.