Joint fit to the NICER data of 1A 0535+262 from Day 1. (a) PS of the reference (0.2–2 keV; blue) and subject (8–12 keV; red) bands. (b) 45°-rotated CS: Re^rot (blue) and Im^rot (red; QPO Re^rot sign-flipped; see Fig. A.2a). In (a) and (b), solid and dashed curves show the total five-Lorentzian model and individual components. (c) Coherence and (d) phase lags, with models including (solid) and excluding (dashed) the QPO. Dash-dotted yellow line marks the QPO centroid frequency, which coincides with a coherence dip and phase-lag rise. Data above ∼1 Hz are logarithmically re-binned with a factor of exp(1/10). Bottom sub-panels: Residuals, Δχ = (data − model)/error.