Single- and double-QPO fits to the HXMT/HE 50–65 keV subject band on Day 5 (MJD 59171; panels a–d) and Day 8 (MJD 59174; panels e–h), shown for the PS νP_ν and the corresponding phase-lag spectrum relative to the HXMT/LE 1–3 keV reference band. Panels (a), (c), (e), and (g): Single-QPO model (five Lorentzians; solid red curves). Panels (b), (d), (f), and (h): Double-QPO model (six Lorentzians; solid green curves). Dashed curves denote individual Lorentzian components; in the double-QPO model, the LF and HF QPO peaks are highlighted with dashed red and blue curves, respectively, consistent with Fig. 7. Residuals (Δχ) are shown beneath each spectrum.