TITLE: GCN CIRCULAR NUMBER: 11736 SUBJECT: GRB 110213B: Gemini South Redshift DATE: 11/02/16 04:10:22 GMT FROM: S. Bradley Cenko at Caltech S. B. Cenko (UC Berkeley), J. X. Prochaska (UC Santa Cruz / Lick Observatory), A. Cucchiara, D. A. Perley, and J. S. Bloom (UC Berkeley) report on behalf of a larger collaboration: We have obtained a spectrum of the candidate optical afterglow of GRB 110213B (Negoro et al., GCN 11716) with the Gemini Multi-Object Spectrograph mounted on the 8-m Gemini South telescope. Observations began at 00:44 UT on Feb. 16 and cover the wavelength range from 3900 - 6700 A. Superposed on a smooth continuum, we detect a series of strong, narrow absorption lines corresponding to Mg I, Mg II, Fe II, and Fe II* at a common redshift of z = 1.083. The detection of fine structure lines firmly establishes this as the redshift of the GRB host galaxy. An additional, strong Mg II absorption system is also present at z = 0.717. This may be related to the potential host candidate identified in pre-outburst SDSS Stripe 82 imaging (Cenko et al., GCN 11735). At z = 1.083, the prompt fluence measured by Konus (Golenetskii et al., GCN 11722) correponds to a prompt isotropic energy release of 5.5e52 erg (20 - 1400 keV observer-frame bandpass). We wish to thank the staff at Gemini Observatory, in particular Fredrik Rantakyro, for the prompt execution of these observations.