Two published orbits change the estimated 18-day spin gain of 2S 1417−624 in 2025 by 24%

We tested whether the spin gain of the X-ray pulsar 2S 1417−624 follows the same relation to hard X-ray rate in three outbursts. We used public Fermi GBM frequencies and Swift BAT daily rates. The four GBM detections from MJD 60815.595 to 60833.485 give a gain of 21.90 microhertz with the monitor orbit. Replacing that orbit with the central 2021 orbit of Liu and coauthors gives an estimated gain of 16.65 microhertz. The decrease is 24.0%. The same replacement changes the much larger 2018 and 2020–21 gains by less than 1.4%. A rule with exponent 6/7, set by the 2018 and 2020–21 data, predicts a 2025 gain of 21.37 microhertz. The monitor result is 2.5% above this prediction. The second orbit puts the central gain 22% below its prediction. Neither comparison rejects the rule under the tested noise models. A claim of agreement within a few percent therefore depends on the orbit correction. The orbit calculation is a sensitivity estimate from short frequency measurements. It does not select the correct orbit, measure an orbit change, or refit photon arrival times. We preserve both monitor formats, the BAT data, source hashes, all code, conditional noise estimates, numerical checks, and figures.

2S 1417-624 · accreting pulsar · binary orbit · Fermi GBM · Swift BAT · spin gain · torque