The 54-day orbital period of AX J1820.5–1434 unveiled by Swift A. Segreto, V. La Parola, G. Cusumano, A. D’Aì, N. Masetti and S. Campana A&A, 558 (2013) A99 Published online: 10 October 2013 DOI: 10.1051/0004-6361/201321892