Discovery of the optical counterpart to the X-ray pulsar SAX J2103.5+4545 P. Reig, I. Negueruela, J. Fabregat, R. Chato, P. Blay and F. Mavromatakis A&A, 421 2 (2004) 673-680 Published online: 22 June 2004 DOI: 10.1051/0004-6361:20035786