The afterglow of GRB 021004: Surfing on density waves D. Lazzati, E. Rossi, S. Covino, G. Ghisellini and D. Malesani A&A, 396 2 (2002) L5-L9 Published online: 03 December 2002 DOI: 10.1051/0004-6361:20021618