The warm absorber in NGC 5548 - The lean years R. G. Detmers, J. S. Kaastra, E. Costantini, I. M. McHardy and F. Verbunt A&A, 488 1 (2008) 67-72 Published online: 16 June 2008 DOI: 10.1051/0004-6361:200809862