Cosmological constraints with GRBs: homogeneous medium vs. wind density profile G. Ghirlanda, G. Ghisellini, C. Firmani, L. Nava, F. Tavecchio and D. Lazzati A&A, 452 3 (2006) 839-844 Published online: 06 June 2006 DOI: 10.1051/0004-6361:20054544