TITLE: GCN CIRCULAR NUMBER: 15652 SUBJECT: GRB 131231A: Gemini-South Redshift DATE: 14/01/02 21:09:59 GMT FROM: Antonino Cucchiara at NASA/GSFC A. Cucchiara (ORAU/NASA-GSFC) reports on behalf of a larger collaboration: "On January 1.09 UT (~21.5 hours after the trigger) we observed the afterglow of GRB 131231A (Sombas et al. GCN 15640, Xu et al. GCN 15641, Malesani et al. 15642, Singer et al. GCN 15643) with the Gemini South telescope equipped with the GMOS camera. A series of spectroscopic observations in Nod & Shuffle more, was carried out using the R400 grating covering the 6000-10000 A wavelength range at an average airmass of 2.1. The resulting spectra show absorption features from CaH+K, as well as emission lines from forbidden [OII]3727 and [OIII]4959,5007 transitions at the common redshift of z=0.6439, consistent with the one reported by Xu et al. (GCN 15645). We thank the Gemini staff for performing these observations, in particular E. Marin and E. Wenderoth."