TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3937 SUBJECT: GRB 050904: Subaru Optical Spectroscopy DATE: 05/09/07 16:38:55 GMT FROM: Nobuyuki Kawai at Tokyo Tech N. Kawai (Tokyo Tech), T. Yamada (NAOJ), G. Kosugi, T. Hattori, and K. Aoki (Subaru/NAOJ) report on behalf of Subaru GRB team: "We observed the field of GRB 050904 (GCN 3910) with Faint Object Camera And Spectrograph on the Subaru 8.2m telescope atop Mauna Kea on the night of September 6, approximately 3.5 days after the burst. We obtained spectra of the afterglow candidate (Haislip et al. GCN 3913, 3922, D'Avanzo et al. GCN 3921). Based on the absorption features we measure the redshift to be z=6.29 +- 0.01, confirming the photometoric redshift reported earlier (Haislip et al. GCN 3914, 3919, Antonelli et al. GCN 3924)." This message may be cited.