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Fermi/GBM Update on the Orbital Ephemeris of Swift J0243.6+6124

ATel #11280; P. jenke (UAH-SPA/CSPAR), C. A. Wilson-Hodge (NASA/MSFC), C. Malacaria (NASA/MSFC-USRA)
on 9 Feb 2018; 17:47 UT
Credential Certification: Peter Jenke (peter.a.jenke@nasa.gov)

Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar

Using Fermi/GBM data between MJD 58098 and 58154 (2017 December 11 to 2018 February 5) in the 12-50 keV range, we determine a new orbital ephemeris for the newly discovered (ATEL #10809) Be X-ray binary Swift J0243.6+6124. Pulsed searches using the ephemeris from M. Ge et al. (ATEL #10907) and V. Doroshenko et al. 2017 resulted in superfluous structure to the torque model that was correlated with the orbital period likely related to a residual orbital signature. This new orbital ephemeris results in orbit corrected frequency derivatives that correlate well with corrected Swift/BAT rates and Fermi/GBM pulsed flux. The Fermi/GBM pulsed flux and frequency history may be viewed at: https://gammaray.msfc.nasa.gov/gbm/science/pulsars/lightcurves/swiftj0243.html.

We obtain the following orbital parameters: orbital period ~ (27.587 +/- 0.017) days, semi-major axis ~ (115.84 +/- 0.32) light-seconds, eccentricity ~ (0.09848 +/- 0.00042), longitude of periastron ~ (-73.56 +/- 0.16) degrees, and periastron epoch (JD) ~ (2458103.629 +/- 0.017).

Fermi/GBM Accreting Pulsar Histories