TITLE:   GCN CIRCULAR
NUMBER:  20245
SUBJECT: GRB 161129A: GTC redshift of the likely host galaxy
DATE:    16/12/09 15:31:37 GMT
FROM:    Zach Cano at U of Iceland  <zewcano@gmail.com>

​Z. Cano (IAA-CSIC), D. Malesani (DARK/NBI and DTU Space), A. de Ugarte
Postigo (IAA-CSIC, DARK/NBI), L. Izzo, C. C. Thoene (IAA-CSIC) and N.
Castro-Rodriguez (GRANTECAN/IAC/Universidad de La Laguna) report:

We observed the field of GRB 161129A (Kocevski et al., GCN Circ. 20210)
with OSIRIS on the 10.4 m GTC telescope on La Palma (Spain).  The
observations started at 19:46:40.9 UT on 05-December-2016 (6.52 days after
the burst), which consisted of 4 x 1200 s spectra using grism R1000B, which
covers the wavelength range 3700-7800 angstroms, with a resolution of
R~1000.

Within the enhanced XRT error region (Beardmore et al. 2016, GCN Circ.
20211) we note the presence of sources A & B detected by Heintz et al. (GCN
Circ. 20244).  The spectrum of the extended object (source B) shows a
continuum with a strong emission line that we attribute to the [OII]
3727/3729 doublet at z=0.645, as well as weaker emission lines consistent
with being H-gamma and H-delta at the same redshift. We propose this
star-forming galaxy to be the host of GRB 161129A. The spectrum of source A
displays absorption features of Ca II K and H, Mg I and MgH at z~0,
confirming it is a foreground star and not related to GRB 161129A.