TITLE: GCN CIRCULAR NUMBER: 11123 SUBJECT: GRB 100816A: VLT and Gemini-N revised redshift DATE: 10/08/17 12:56:20 GMT FROM: Nial Tanvir at U.Leicester N. R. Tanvir (U. Leicester), S. Vergani (GEPI/Obs. Paris and APC/Univ. Paris 7), J. Hjorth, J. P. U. Fynbo, B. Milvang-Jensen, D. Malesani (DARK), K. Wiersema (U. Leicester),  P. Vreeswijk (Reykjavik), A. J. Levan (U. Warwick) P. Goldoni (APC/Univ. Paris 7 and SAp/CEA), S. Covino (INAF/Brera), & L. A. Antonelli (INAF/Roma) report on behalf of a larger collaboration: We observed the location of possible short-hard GRB 100816A (Oates et al. GCN 11102; Markwardt et al. GCN 11111; Norris et al. GCN 11116) with VLT/X-Shooter on 2010 Aug 17 beginning 04:20 (UT).  We clearly detect the putative host galaxy of the burst, and identify lines of Halpha, Hbeta,  OII (3727), NII (6548/6583) and OIII (5007) in emission and CaII H&K in absorption.  In fact, the system splits (spectrally and spatially) into two components at redshifts z=0.8034 and z=0.8049 (based on a provisional wavelength calibration), possibly indicating an interacting system or reflecting internal velocity components within a single galaxy.  This redshift is inconsistent with the tentative redshift for this galaxy suggested by Tanvir et al. (GCN 11116). We have also re-analysed the Gemini-N GMOS afterglow spectroscopy initially reported in GCN 11116.  The trace shows faint absorption features consistent with MgII (2797/2803A) doublet and FeII (2600A) at a redshift of z=0.8035. The agreement of this redshift with that obtained for the galaxy from the X-shooter data, strongly suggests that it is the host.  We note that none of the emission lines seen in the X-Shooter spectrum are within the spectral range of the GMOS data. We acknowledge the support of the VLT staff, in particular Giovanni Carraro. [GCN OPS NOTE(19aug10): Per author's request, LAT was added to the author list.]