Twelve MAXI fits put the April 2026 GRO J1008-57 onset 1.2 to 2.4 days after a fixed phase prediction
We test the April 2026 outburst of GRO J1008-57 against the last published MAXI onset phase. The event is later than the interval in that phase fit. We fit a linear rise and an exponential decay to 232 daily measurements at 2–20 keV. The onset is MJD 61134.87, or 1.34 days after the fixed prediction. Its formal error is 0.33 day. Twelve choices of window, background and weights give offsets from 1.23 to 2.38 days. The main fit has chi-square per degree of freedom of 2.55. One of four residual-sign tests gives a range that includes the prediction. Formal errors alone thus do not describe all timing limits. BAT has no valid measurement within 40 days of the predicted peak and cannot check the onset. The result uses one monitor and a fixed orbital ephemeris. It does not establish a new phase step. The package includes frozen source tables, provenance, code, fit results and conditional uncertainty checks.
GRO J1008-57 · MAXI · Swift BAT · X-ray pulsar · Be star binary · outburst onset · orbital phase · reproducible timing
References
4- usesdoi:10.48550/arXiv.2605.19211
We extend the last MAXI onset phase in version 1 to a later event and use its rise and decay function.
- usesdoi:10.1051/0004-6361/201321203
We use its orbital ephemeris and compare peak times to its peak clock.
- usesdoi:10.1093/pasj/61.5.999
MAXI supplies the daily X-ray measurements for the onset fit.
- usesdoi:10.1088/0067-0049/209/1/14
We use the Swift BAT monitor table for the coverage check and cycle ledger.
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