TITLE: GCN CIRCULAR NUMBER: 14286 SUBJECT: GRB 130131B: host detection and redshift DATE: 13/03/11 14:20:28 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst Johan P. U. Fynbo, Dong Xu, Daniele Malesani, Thomas Kruehler (DARK/NBI), Dan A. Perley (Caltech), Valerio D'Elia (ASDC, INAF), report on behalf of the X-shooter GTO GRB collaboration: We observed the field of GRB 130131B (Siegel et al., GCN 14159) using the Keck-I telescope equipped with the LRIS instrument. Observations were carried out on 2013 February 10 (9.62 days after the burst), simultaneously in the g and I bands, for a total exposure time of 750 and 720 s, respectively. A source with g = 25.7 (AB) and I = 24.9 (Vega) is detected inside the enhanced XRT error circle (which has a radius of 1.8"; Goad et al., GCN 14165), at coordinates: R.A.(J2000) = 11:35:49.31 Dec.(J2000) = +15:02:18.0 We consider this object to be the likely host galaxy of GRB 130131B. A spectrum of this source was taken on 2013 March 9 with the ESO VLT equipped with the X-shooter spectrograph, covering the wavelength range 3000-20000 AA. The exposure time was 8x900 s. In the NIR arm, we detect three emission lines, interpreted as [O III] (4960, 5007) and [O II] (3727), all at a common redshift z = 2.539. In the UVB arm, the host continuum is detected down to ~4400 AA, which corresponds to the onset of the Lyman alpha forest at the proposed redshift. We acknowledge excellent support from the observing staff at Mauna Kea and Paranal, in particular Emanuela Pompei, Claudio Melo, and Thomas Rivinius.