GCN Circular 14286

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
Not found
 
 
) 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
Not found
 
 
), 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.