[vsnet-grb-info 12616] GRB 121117A: GROND confirmation of the UVOT afterglow candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13976
SUBJECT: GRB 121117A: GROND confirmation of the UVOT afterglow candidate
DATE:    12/11/19 22:35:54 GMT
FROM:    Sylvio Klose at TLS Tautenburg  <klose at tls-tautenburg.de>

A. Nicuesa Guelbenzu, S. Klose (both TLS Tautenburg), M. Nardini 
(Universita degli studi di Milano-Bicocca), and J.Greiner (MPE Garching) 
report on behalf of the GROND team:

We observed the field of GRB 121117A (Swift trigger 538696, Cummings et 
al., GCN #13967) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 
2008, PASP 120, 405) mounted at the 2.2m MPG/ESO telescope at La Silla 
Observatory (Chile).

First-epoch observations started on November 18, 2012, at 00:16 UT, about 
15.5 hrs after the GRB trigger. Second-epoch observations were performed 
the following night. On the first-epoch images we find a faint source 
within the r=1.7 arcsec XRT error circle (Beardmore et al., GCN 13972) at 
coordinates RA(J2000) = 02:06:26.58, Dec. = 07:25:10.2 (+/- 0".3). Within 
the astrometric error this is consistent with the object seen by UVOT in 
the white band during the first 200 seconds after the GRB trigger (Oates 
et al., GCN 13973). For this source we measure the following preliminary 
AB magnitudes:

g' > 24.0,
r' = 23.6 +/- 0.2,
i' = 23.0 +/- 0.2,
z' > 23.1,
J > 21.3,
H > 20.8,
K > 19.5,

calibrated against SDSS and 2MASS field stars. On the second-epoch images 
the object had faded to r'=24.5 +/- 0.2 and i'>24.3, implying that this 
was the GRB afterglow.