Fits with two harmonics give longer bright and faint intervals in selected 2026 SMC X-1 MAXI data than in 2025

We measured time above and below a relative flux level in two selected SMC X-1 observation windows. We used public MAXI 2–20 keV daily data in MJD [60705,60865) and [61100,61334). The windows and period model come from an earlier SCI study. We fit two harmonics of the long cycle, with trend and orbital terms. The bright interval is time above the midpoint of each fitted periodic flux range. Its duration rises from 23.8 to 34.7 days. Faint duration rises from 15.2 to 23.2 days. The differences are +10.95 days [7.01,15.13] and +7.99 days [4.37,11.76]. Brackets give 95% intervals from residual resampling with eight-day blocks. The fitted bright fraction is 60.9% and 59.9%. This does not establish a constant fraction. BAT supports the early short cycle but lacks most later data. Most tested settings retain both duration increases. However, one quarter removal changes the early MAXI period to 58.29 days. The early 10–20 keV fit also gives a different duration comparison. Each window contains about four cycles, and the fixed mean model leaves excess variation. The result is a dated duration measurement under stated model and selection assumptions. The package includes frozen inputs, source addresses, hashes, code, tables, figures, and reproduction instructions.

SMC X-1 · MAXI · Swift BAT · superorbital cycle · X-ray binary · duration · public data · reproducible research