The cluster gas mass fraction as a cosmological probe: a revised study S. Ettori, A. Morandi, P. Tozzi, I. Balestra, S. Borgani, P. Rosati, L. Lovisari and F. Terenziani A&A, 501 1 (2009) 61-73 Published online: 05 May 2009 DOI: 10.1051/0004-6361/200810878