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Orbital Parameters for the X-Ray Pulsar IGR J16393-4643

ATel #786; Tommy Thompson, John A. Tomsick, Richard Rothschild (CASS/UCSD), Jean in 't Zand (SRON), and Roland Walter (ISDC)
on 31 Mar 2006; 17:35 UT
Credential Certification: John A. Tomsick (jtomsick@ucsd.edu)

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

With recent and archival Rossi X-ray Timing Explorer (RXTE) X-ray measurements of the heavily obscured X-ray pulsar IGR J16393-4643, we carried out a pulse timing analysis to determine the orbital parameters. Assuming circular orbits, we phase-connected data spanning over 1.5 years. The most likely orbital solution has a projected semi-major axis of 43 +/- 2 lt-s and an orbital period of 3.688 +/- 0.001 days. This implies a mass function of 6.5 +/- 1.1 solar masses and confirms that this INTEGRAL source is a High-Mass X-ray Binary system. By including eccentricity in the orbital model, we find e < 0.25 at the 2-sigma level. The 3.7 day orbital period and the previously known ~910 s pulse period place the system in the region of the Corbet diagram populated by supergiant wind accretors, and the low eccentricity is also consistent with this type of system. Finally, it should be noted that although the 3.7 day orbital solution is the most likely one, we cannot completely rule out two other solutions with orbital periods of 50.2 and 8.1 days.