A phase-dependent absorption line in the spectrum of the X-ray pulsar RX J0720.4-3125 F. Haberl, V. E. Zavlin, J. Trümper and V. Burwitz A&A, 419 3 (2004) 1077-1085 Published online: 07 May 2004 DOI: 10.1051/0004-6361:20034129