PKS 0537-441: Extended [O II] emission and a binary QSO? J. Heidt, K. Jäger, K. Nilsson, U. Hopp, J. W. Fried and E. Sutorius A&A, 406 2 (2003) 565-577 Published online: 17 November 2003 DOI: 10.1051/0004-6361:20030804