The variable cyclotron line in GX 301-2 I. Kreykenbohm, J. Wilms, W. Coburn, M. Kuster, R. E. Rothschild, W. A. Heindl, P. Kretschmar and R. Staubert A&A, 427 3 (2004) 975-986 Published online: 16 November 2004 DOI: 10.1051/0004-6361:20035836