TITLE: GCN CIRCULAR NUMBER: 6928 SUBJECT: GRB 071010B: Keck/DEIMOS emission-line redshift DATE: 07/10/17 04:47:44 GMT FROM: Daniel Perley at U.C. Berkeley D. Stern (JPL), D. A. Perley (UC Berkeley), N. Reddy (NOAO), J. X. Prochaska (UCSC), H. Spinrad (UCB) and M. Dickinson (NOAO) report: On the night of 2007 Oct. 11 we observed the afterglow of GRB 071010B (GCN 6871, Markwardt et al.; GCN 6873, Okansen et al.) with the Keck II 10m telescope + DEIMOS, for a total integration time of 1260 seconds, starting at 14:41 UT. The wavelength coverage was between 5230 and 10480 Angstroms. The detection of MgII previously reported by Cenko et al. (GCN 6888) and Prochaska et al. (GCN 6890) at a redshift of 0.947 is further confirmed, as is a weak detection of MgI 2852. In addition, the [OII] 3727 doublet emission feature is well-detected at the same redshift, superimposed on the continuum. [OIII] 5008 is also detected, as is (marginally) [OIII] 4960. These results strongly suggest that the redshift of GRB 071010B and its host galaxy is most likely 0.947.