Observing Mkn 421 with XMM-Newton: The EPIC–PN point of view M. Ravasio, G. Tagliaferri, G. Ghisellini and F. Tavecchio A&A, 424 3 (2004) 841-855 Published online: 06 September 2004 DOI: 10.1051/0004-6361:20034545