Orbital Parameters for the X‐Ray Pulsar IGR J16393−4643

Abstract

With recent and archival Rossi X-Ray Timing Explorer (RXTE) X-ray measurements of the heavily obscured X-ray pulsar IGR J16393À4643, we carried out a pulse timing analysis to determine the orbital parameters. Assuming a circular orbit, we phase-connected data spanning over 1.5 yr. The most likely orbital solution has a projected semima-jor axis of 43 AE 2 lt-s and an orbital period of 3:6875 AE 0:0006 days. This implies a mass function of 6:5 AE 1:1 M and confirms that this INTEGRAL source is a high-mass X-ray binary (HMXB) system. By including eccentricity in the orbital model, we find e < 0:25 at the 2 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 solution is the most likely one, we cannot completely rule out two other solutions with orbital periods of 50.2 and 8.