Under a fixed clock and error weights, the BAT rate in phase 0.10–0.30 exceeds that in phase 0.70–0.90 for IGR J18027–2016 in 2019–2026

We tested public Swift/BAT data for IGR J18027–2016 after the 2019-02-14 cutoff of an earlier eclipse study. We used the published linear clock with period 4.56993 days and reference time 55083.82 BMJD. In 21,977 valid pointings from 2019-02-15 to 2026-10-20, the rate in phase 0.10–0.30 exceeded the rate in phase 0.70–0.90 by 3.39 mCrab. The 95% interval from resampling ten-cycle blocks is 1.64 to 5.03 mCrab. A separate mean level in each block controls slow rate changes. With equal block weights, the interval includes zero. The change from a 2012–2019 reference is 0.94 [-1.01, 2.81] mCrab and is not resolved. A date audit found 4,304 pointing rows with a listed MJD one day too late; mission seconds and calendar fields agree. We used mission seconds. The later rate contrast agrees with the direction of the known eclipse asymmetry under the fixed clock. It does not identify a unique gas structure or show that the contrast exists in each orbit. The analysis is exploratory. The package contains frozen data, code, figures, date records, checks, and offline instructions.

IGR J18027-2016 · Swift BAT · X-ray binary · eclipse · stellar wind · block bootstrap · data quality