Discovery of the 51.47 day orbital period in the supergiant fast X-ray transient XTE J1739-302 with INTEGRAL

Timing analysis of ~12.4 Ms of INTEGRAL/IBIS data has revealed a period of 51.47 +/- 0.02 days in the supergiant fast X-ray transient source XTE J1739-302/IGR J17391-3021 that can be interpreted as an orbital period. An outburst history showing 35 epochs of activity has been produced, showing X-ray outbursts throughout the orbit of XTE J1739-302. Possible indications of an enhanced equatorial density region within the supergiant stellar wind are present in the phase-folded lightcurve. It is found that many orbital configurations are possible within this system with eccentricities of up to e ~0.8 valid.