Discovery of periodic dips in the light curve of GX 13+1: the X-ray orbital ephemeris of the sourceR. Iaria, T. Di Salvo, L. Burderi, A. Riggio, A. D’Aì and N. R. RobbaA&A, 561 (2014) A99DOI: https://doi.org/10.1051/0004-6361/201322328
