GCN Circular 14117

K. Varela (MPE Garching), V. Sudilovsky (MPE Garching), S. Klose (TLS
Tautenburg), and J. Greiner (MPE
Garching) report on behalf of the GROND team:

We observed the field of GRB 121229A (Swift trigger 544347; Sonbas et al.,
GCN 14115
Not found
 
 
) 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 29, 2012, at 05:09 UT, 540 s after the
GRB trigger. They were performed at an average seeing of 1.0" and at an
average airmass of 1.8.

We find a point source at the border of the XRT error
circle at a position

RA (J2000.0) = 12:40:24.29
DEC (J2000.0) = -50:35:39.48

with an uncertainty of 0.5" in each coordinate.

Based on a total exposure time of 1500 s in g'r'i'z' and 1200 s in JHK,
at a midtime of 3840s after the burst, we estimate preliminary
AB magnitudes of

g' = 22.2 +/- 0.2,
r' = 21.5 +/- 0.1,
i' = 21.3 +/- 0.1,
z' = 21.1 +/- 0.1,
J  = 20.9 +/- 0.1,
H  = 20.2 +/- 0.1, and
K  > 19.7.

This source's spectral energy distribution is best fit with a power-law of
slope beta = 0.8 +/- 0.2.
We suggest that this source is the afterglow of GRB 121229A.

Given magnitudes are calibrated against GROND zeropoints in g'r'i'z' and
2MASS
field stars in JHK, and are not corrected for the Galactic foreground
extinction
corresponding to a reddening of E(B-V)= 0.16 mag in the direction of the
burst (Schlegel et al. 1998).