TITLE: GCN CIRCULAR NUMBER: 10100 SUBJECT: GRB 091029: Gemini-South Redshift DATE: 09/10/29 07:49:19 GMT FROM: Ryan Chornock at UC Berkeley R. Chornock, D. A. Perley, and B. E. Cobb (UC Berkeley) report on behalf of a larger collaboration: We obtained optical spectra of the afterglow of GRB 091029 (Grupe et al., GCN 10097; Filgas et al., GCN 10098; LaCluyze et al., GCN 10099) using GMOS on Gemini-South. Our spectra cover the wavelength range of 3900-8100 angstroms with the R400 grating. Our first 600s exposure, starting at 06:06 UT on Oct. 29 (2.2 hr after the BAT trigger) reveals absorption lines from Lyman-alpha, C II, C IV, Si II, and Si IV at a common redshift of 2.752, which we identify as the redshift of the GRB. The afterglow is still quite bright (R~17.8 mag at t=2.02 hr) in the acquisition image. We would like to thank German Gimeno and the Gemini staff for their assistance.