Optical novae: the major class of supersoft X-ray sources in M 31 W. Pietsch, J. Fliri, M. J. Freyberg, J. Greiner, F. Haberl, A. Riffeser and G. Sala A&A, 442 3 (2005) 879-894 Published online: 14 October 2005 DOI: 10.1051/0004-6361:20053127