Spin period evolution of GX 1+4 A. González-Galán, E. Kuulkers, P. Kretschmar, S. Larsson, K. Postnov, A. Kochetkova and M. H. Finger A&A, 537 (2012) A66 Published online: 10 January 2012 DOI: 10.1051/0004-6361/201117893