Simultaneous absolute timing of the Crab pulsar at radio and optical wavelengths T. Oosterbroek, I. Cognard, A. Golden, P. Verhoeve, D. D. E. Martin, C. Erd, R. Schulz, J. A. Stüwe, A. Stankov and T. Ho A&A, 488 1 (2008) 271-277 Published online: 24 June 2008 DOI: 10.1051/0004-6361:200809751