Results of the search for periodicity in the Swift/BAT data obtained with the technique described by D’Aì et al. (2011). The upper panel shows the χ² computed from the Swift/BAT lightcurve folded at different periods in the range 15–600 days. The most prominent peak is at 116.2 ± 0.6 days. To estimate the significance of this peak, we followed the procedure described in D’Aì et al. (2011), and report the histogram of the detrended χ² values in the middle panel. We show in the bottom panel the Swift/BAT lightcurve (15–50 keV) of the source folded at the best determined orbital period (116.2 ± 0.6 days). The reference time used is 54 877.3957 MJD. Each phase bin in the plot corresponds to an integration time of three days.