The orbital period of the dipping, bursting, globular cluster x-ray source XB 1746-371 from Rossi-XTE observations

We present results from two long observations of XB 1746-371 by the Rossi X-ray Timing Explorer (RXTE) in 2002 January and May, lasting 4 and 5 d, respectively. Dips are observed in the X-ray light curves with a depth of 25 per cent, largely independent of energy within the usable band of the PCA instrument of 2.1-16.0 keV. X-ray bursting and flaring activity are also evident. The dips define the orbital period of the system, and using a power spectral analysis and a cycle counting technique, we derive an accurate period of P-orb = 5.16 +/- 0.01 h. The previously reported candidate period of 5.73 +/- 0.15 h, obtained using Ginga data, is inconsistent with our determination, perhaps owing to the weakness of the dipping and the variability of the source during that observation. The dips in the RXTE observations presented here do not align with the Ginga period; however, our improved period is consistent with a wide range of archival data.