Broad–band spectral evolution of GRB afterglows N. Masetti, E. Pian, E. Palazzi, L. Amati, T. J. Galama, L. Nicastro, P. M. Vreeswijk, F. Frontera and J. van Paradijs Astron. Astrophys. Suppl. Ser., 138 3 (1999) 453-454 Published online: 15 September 1999 DOI: 10.1051/aas:1999305