Folding energy (E_fold) as a function of the 3–79 keV luminosity based on our orbit-by-orbit and pulse-by-pulse spectroscopy results. Dark blue diamonds are the results of the orbit-by-orbit analysis for observation I, light blue diamonds are the results of the pulse-by-pulse spectroscopy for observation I, bright red stars are the results of the orbit-by-orbit spectroscopy for observation IIa, pink stars are the results of the pulse-by-pulse spectroscopy for observation IIa, dark red stars are the results of the orbit-by-orbit spectroscopy for observation IIb, and lavender stars are the results of the pulse-by-pulse spectroscopy for observation IIb.