K. E. Heintz (Univ. Iceland and DARK/NBI), D. Malesani (DARK/NBI and DTU
Space), Z. Cano (IAA-CSIC), A. De Ugarte Postigo (IAA-CSIC and
DARK/NBI), G. Fedorets (NOT and Univ. Helsinki), R. Tronsgaard Rasmussen
(NOT), A. A. Djupvik (NOT), I. R. Losada (NOT and Stockholm Univ.), I.
Svardh (NOT), J. Clasen (NOT), S. Armas Perez (NOT), report on behalf of
a larger collaboration:
We observed the optical counterpart of GRB 161129A (Kocevski et al., GCN
20210; Mazaeva et al., GCN 20215) with the Nordic Optical Telescope
(NOT) equipped with the AlFOSC imager. Observations were carried out in
the R band (3x200 s), with a mid time 2016 Dec 4.83 UT (5.6 days after
the GRB). Observing conditions were good with a seeing of 0.8".
Two objects are detected within the XRT error region (Beardmore et al.
2016, GCN Circ. 20211), at the following coordinates (calibrated against
the USNO-B1.0 catalog):
source A: RA = 21:04:54.69, Dec = +32:08:04.7
source B: RA = 21:04:54.63, Dec = +32:08:05.9
A finding chart is posted at this URL:
Given their small separation (1.4"), these objects may be blended in
images with coarser spatial resolution. Source A (with a magnitude R =
21.6) is consistent in flux and position with the faint smudge visible
in the DSS red, previously noted by Mazaeva et al. (GCN 20215) and Klose
& Stecklum (GCN 20216).
Source B is extended, and is consistent with the position reported for
the optical afterglow by Kuin et al. (GCN 20217) and Kuroda et al. (GCN
20218). We propose that source B is (dominated by) the host galaxy of
GRB 161129A. We further note that the cumulative magnitude of the
complex (objects A+B) is R ~ 21.2, which is significantly fainter than
previous reports (e.g. Kuroda et al., GCN 20218; Mazaeva et al., GCN
20224), thus firmly establishing the presence of a fading optical
afterglow for GRB 161129A. Photometry was computed against the values of
the two USNO-B1.0 stars as listed by Mazaeva et al. (GCN 20215).