TITLE: GCN CIRCULAR NUMBER: 12648 SUBJECT: GRB 111209A: VLT/X-shooter redshift DATE: 11/12/10 06:05:55 GMT FROM: Paul Vreeswijk at U of Iceland Paul Vreeswijk (U. Iceland), Johan Fynbo (DARK), Andrea Melandri (INAF-OAB) report on behalf of the X-shooter GTO GRB afterglow collaboration: The afterglow of Swift GRB 111209A (Hoversten et al., GCN 12632, Klotz et al., GCN 12633, Fugazza et al., GCN 12634) was observed with the X-shooter spectrograph mounted at the Kueyen unit of the VLT on Cerro Paranal, Chile. Starting around 1 UT on 10 December 2011 (0.75 days after the burst), a series of four spectra of 1200s each were secured, covering the approximate wavelength range 0.3-2.5 micron. The slit width was set to 1", resulting in a resolving power range of 4500-7500. Preliminary reduction of the ultraviolet and visual parts of the spectra shows a smooth continuum with several absorption features that we can identify with resonance absorption lines of FeII, MgII, MgI, CaII H and K at a redshift of z=0.677; this is the likely redshift of GRB 111209A. We acknowledge the excellent support from the Paranal Observatory staff, in particular Willem-Jan de Wit, Dimitri Gadotti and Marcelo Lopez. We are also very grateful for the flexibility and willingness of the VLT-I visiting astronomer, Stefan Kraus, to shift his observations to the end of the night, which have made these X-shooter observations possible. [GCN OPS NOTE(10dec11): Per author's request, the last paragraph was expanded.]