Searching for the orbital period of the ultraluminous X-ray source NGC   1313 X-2
  We analyzed the longest phase-connected photometric dataset available for NGC 1313 X-2, looking for the ~6 day modulation reported by Liu et al. (2009). The folded B band light curve shows a 6 day periodicity with a significance slightly larger than 3 sigma. The low statistical significance of this modulation, along with the lack of detection in the V band, make its identification uncertain. 
L. Zampieri, D. Impiombato, R. Falomo, F. Gris\'e, R. Soria
astro-ph.HE