The Swift-BAT survey reveals the orbital period of three high-mass X-ray binaries A. D’Aì, V. La Parola, G. Cusumano, A. Segreto, P. Romano, S. Vercellone and N. R. Robba A&A, 529 (2011) A30 Published online: 25 March 2011 DOI: 10.1051/0004-6361/201016401