Cycle profiles and date cuts change tests of four fixed eclipse periods in 2005–2026 BAT data for 4U 1538−52
We test whether public Swift/BAT data for 4U 1538−52 distinguish a free 14.85–14.98-day cycle from 14.913416 days, exactly four fixed published eclipse periods. Quality and eclipse cuts retain 64,151 pointings from 2005–2026. A two-harmonic model with one cycle profile gives a best period of 14.90330 days and a fit gain of 15.6365. A 60-day residual block sign test gives p=0.0004 from 9,999 draws. Four interval profiles with a shared period give 14.91058 days, a gain of 0.3327, and p=0.554 from 4,999 draws. Their 30- and 120-day tests give p=0.542 and 0.6388. An added four-profile test from 2012 retains 45,171 rows and gives 14.88900 days. Its 30-, 60- and 120-day tests give p=0.0392, 0.0510 and 0.1110. The results depend on the cycle profiles, date cut and block errors. The tests assume an adequate mean and independent, approximately symmetric block errors. Flexible profiles can reduce power for a shared clock. A large p-value does not prove locking. The full record includes data with a monitor warning before 2012. This work extends SCI 57d7e0b6, which uses identical FITS bytes. There are no additional observations relative to that SCI study. The additions are calibrated four-profile tests, a separate profile after MJD 60750, more random draws, and separately written code. Exact inputs, provenance, code, results and figures are preserved.
4U 1538-52 · Swift BAT · superorbital period · eclipse clock · profile changes · block sign test · public astronomical data · reproducible analysis
References
12- usesCycle shape and noise blocks change the four-orbit period test in 2012–2026 BAT data for 4U 1538-52 sci:sha256:486c9147393d6f5e3747a040101ae47743094b63b0c205b04ad3ec090fb39f48
This earlier study tests the same broad clock question. We use it for comparison and add a four-profile date-cut test. The FITS input bytes are the same. We wrote our code separately.
- usesdoi:10.3847/1538-4357/abc477
This paper found the known 14.9-day cycle and noted the near four-to-one period ratio.
- usesdoi:10.3847/1538-4357/ae5530
This paper gives the comparison period and the first three time intervals. It already reports changes in cycle strength and phase.
- usesdoi:10.3847/1538-4357/ab03d3
This paper gives the fixed reference eclipse epoch and period. It separates the eclipse and anomalistic orbital clocks.
- usesdoi:10.1088/0067-0049/209/1/14
This paper describes the public Swift/BAT monitor that provides the data.
- usesDates are one day late in four of six tested Swift/BAT pointing tables for 2023–2025 sci:sha256:8df335c8aba52a813960ed565c10e06026b400e9f6d21ae623aefa7ad652b251
This date audit motivated checks of redundant day fields and use of continuous mission time.
- usesA constant period fits mean half-amplitude BAT eclipse centers of 4U 1538-52 from 2005 to 2026 under a ramp model sci:sha256:06a8a46afe230dd9f4cf61eafd98c39943bc152dff985db1ea721a0b06e26693
This eclipse study supplies the quality-cut and time conventions. Its eclipse fit is not used as independent orbital evidence.
- Evidence for a 15.196-day cycle in 4U 1909+07 at MJD 60671–61333 depends on the BAT noise model sci:sha256:d63843d9a6830a2b90a57810f8f3476f2853660801eccc2e1640404240957357
Its catalog abstract gives context for tests of BAT noise assumptions in a different source. It supplies no data or result for this source.
- usesdoi:10.3847/1538-4357/ac7c74
Astropy supplies FITS, time, and position tools.
- usesdoi:10.1038/s41586-020-2649-2
NumPy supplies arrays and linear algebra.
- usesdoi:10.1109/MCSE.2007.55
Matplotlib makes the figures.
- doi:10.1162/rest.90.3.414
Related work on inference with grouped errors. Its general regression results do not establish calibration of our period-search statistic.
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