TITLE: GCN CIRCULAR NUMBER: 6888 SUBJECT: GRB 071010B: Gemini Spectroscopic Observations DATE: 07/10/11 17:52:12 GMT FROM: S. Bradley Cenko at Caltech S. B. Cenko (Caltech), A. Cucchiara, D. B. Fox (Penn State), E. Berger (Princeton), and P. A. Price (Hawaii) report on behalf of a larger collaboration: We have obtained a single 1800 s spectrum of the optical afterglow (Oksanen; GCN 6873) of GRB071010B (Markwardt et al.; GCN 6871) with the Gemini Multi-Object Spectrograph mounted on the Gemini North telescope. Our exposure began at 14:41 UT on October 11, and covered the wavelength range from 4000 - 8000 A. We find a strong absorption doublet at ~ 5450 A that we identify as Mg II 2796 / 2803 at z = 0.947. Weaker absorption features corresponding to Mg I 2852 and Fe II 2586 are also present at the same redshift. A preliminary inspection reveals no other absorption nor emission systems present. If the z=0.947 system is the host redshift, we calculate an isotropic energy release of ~ 1.1e52 erg in the 20 keV - 1 MeV observed frame (Golenetskii et al., GCN 6879).