XMM-Newton observations of Markarian 421 W. Brinkmann, S. Sembay, R. G. Griffiths, G. Branduardi-Raymont, M. Gliozzi, Th. Boller, A. Tiengo, S. Molendi and S. Zane A&A, 365 1 (2001) L162-L167 Published online: 15 January 2001 DOI: 10.1051/0004-6361:20000084