TITLE: GCN CIRCULAR NUMBER: 14225 SUBJECT: GRB 120118B: host observations and redshift determination DATE: 13/02/17 01:46:52 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst Daniele Malesani, Thomas Kruehler (DARK/NBI), Daniel Perley (Caltech), Johan P. U. Fynbo, Dong Xu, Bo Milvang-Jensen (DARK/NBI), Paolo Goldoni (APC, CEA/Irfu), Steve Schulze (PUC and MCSS), report on behalf of the X-shooter GTO GRB collaboration: We observed the field of GRB 120118B (Littlejohns et al., GCN 12852) with the Keck I telescope located on Mauna Kea. Observations were carried out on 2013 Feb 10 (389 days after the GRB), using the LRIS instrument, simultaneously in the g and I bands, for a total exposure time of 750 and 720 s, respectively. Consistent with the latest XRT position (Osborne et al. GCN 12857; see also http://www.swift.ac.uk/xrt_positions/), we detect a bright, slightly extended object (I = 23.8, Vega), which we consider to be the GRB host galaxy. Its coordinates are (J2000): RA = 08:19:29.047 Dec = -07:11:05.14 This position is consistent with that of the tentative near-infrared counterpart reported by D'Avanzo & Palazzi (GCN 12870). A spectrum of this source was taken on 2013 Feb 13 with the ESO VLT equipped with the X-shooter spectrograph, covering the wavelength range 3000-20500 AA. The seeing was 0.6". In the NIR arm, we detect several emission lines, interpreted as [O III] (5007), [Ne III] (3869), and hints for [O III] (4959) and [O II] (3727) at a common redshift z = 2.943. The weakness/lack of other prominent lines usually seen in GRB host spectra is readily explained by their location in non-favorable parts of the spectrum. In the UVB arm, the host continuum is detected down to ~4750 AA, which corresponds to the onset of the Lyman alpha forest at z = 2.943. At z = 2.94 the host is a fairly luminous galaxy at 2000 Å rest-frame, roughly 0.5 mag brighter than L* at that redshift (e.g. Gabasch et al. 2004, A&A, 421, 41). The properties of this object are akin to those of Lyman-break galaxies. We acknowledge excellent support from the observing staff at Mauna Kea and Paranal, in particular Cedric Ledoux and Andrea Mehner.