Long-term X-ray properties of ULX-3. (a) L_X light curve in the 0.3–10 keV band, with the inset showing a zoomed-in view for clarity (MJD 56134-56322). (b) Hardness–intensity diagram, where the count rate in the 0.3–10 keV band is plotted against the hardness ratio HR_{1.5 − 10 keV/0.3 − 1.5 keV}. (c) Temporal evolution of the hardness ratio HR_{3.5 − 10 keV/2 − 3.5 keV} as a function of time (MJD), with the dashed red line marking the reference level. Swift/XRT, XMM-Newton, and Chandra observations are shown with filled black and red circles and blue triangles, respectively.