GCN Circular 14091

J. Elliott (MPE Garching), S. Schmidl (TLS Tautenburg), and J.Greiner (MPE
Garching) report on behalf of the GROND team:

We observed the field of GRB 121217A (Swift trigger 542441; Siegel et al.,
GCN 14089
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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/ESO telescope at La Silla
Observatory (Chile).

Observations started on December 17, 2012, at 07:21 UT, 210 s after the
GRB trigger. They were performed at an average seeing of 1.6" and at an
average airmass of 1.2.

We found a fading point source at the border of the enhanced XRT error
circle given in Evans et al. (GCN 14090
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 )

RA (J2000.0) = 10:14:50.407
DEC (J2000.0) = -62:21:03.53

with an uncertainty of 0.5" in each coordinate.

Based on a total exposure time of 456 s in g'r'i'z' and 480 s in JHK,
at a midtime of 1882 s after the burst, we estimate preliminary
AB magnitudes of

g' = 20.3 +/- 0.1,
r' = 19.3 +/- 0.1,
i' = 18.9 +/- 0.1,
z' = 18.6 +/- 0.1,
J  = 18.1 +/- 0.1,
H  = 17.7 +/- 0.1,
K  = 17.4 +/- 0.1.

In the r' band the source faded with a decay slope of 0.7 +/- 0.1
between 2000 s and  4200 s after the trigger. The SED can be fit
with a power-law with a slope of beta = 0.8 +/- 0.1.

Given magnitudes are calibrated against GROND zeropoints as well as 2MASS
field stars and are not corrected for the Galactic foreground extinction
corresponding to a reddening of E(B-V)= 0.38 mag in the direction of the
burst (Schlegel et al. 1998).

The extinction-corrected SED suggests a photo-z of 3.0 +/- 0.2. We
caution, however, that the high Galactic extinction along the line of
sight might affect this result.