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GCN Circular 20244

GRB 161129A: NOT optical observations and candidate host galaxy
2016-12-09T14:58:08Z (7 years ago)
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <>
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).
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