No evidence for dust extinction in GRB 050904 at z ~ 6.3 T. Zafar, D. J. Watson, D. Malesani, P. M. Vreeswijk, J. P. U. Fynbo, J. Hjorth, A. J. Levan and M. J. Michałowski A&A, 515 (2010) A94 Published online: 15 June 2010 DOI: 10.1051/0004-6361/200913795