GCN Circular 17078

M. Tanga (MPE Garching), D. A. Kann (TLS Tautenburg), and J. Greiner (MPE
Garching) report on behalf of the GROND team:

We observed the field of GRB 141121A (Swift trigger 619182; A. Y. Lien et
al., GCN 17075
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 ) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla
Observatory (Chile).

Observations started at 05:52 UT on November 21, 2014, 2.02 hours after
the GRB trigger. They were performed at an average seeing of 1".4 and at
an average airmass of 2.3.

Within the XRT error circle reported by Lien et al., we detect a bright
source in all bands. This source is not detected in the SDSS, therefore we
consider it to be the afterglow of GRB 141121A. The source lies at:

RA (J2000) = 08:10:40.62
Dec. (J2000) = +22:13:01.8

with an error of 0".3 in each coordinate.

Based on total exposures of 7.7 minutes in g'r'i'z' and 8.0 minutes in
JHK, at a midtime of 2.34 hrs after the burst, we measure the following
preliminary magnitudes (AB magnitude system):

g' = 20.0 +/- 0.1 mag,
r' = 19.8 +/- 0.1 mag,
i' = 19.6 +/- 0.1 mag,
z' = 19.4 +/- 0.1 mag,
J = 19.4 +/- 0.2 mag, and
H = 19.2 +/- 0.2 mag.

The magnitudes are calibrated against SDSS and 2MASS field stars and are
not corrected for the Galactic foreground extinction corresponding to a
reddening of E_(B-V)= 0.05 in the direction of the burst (Schlegel et al.
1998).