GCN Circular 17212

GRB 141221A: GROND Detection of the Optical/NIR Afterglow

T. Schweyer, P. Wiseman, P. Schady and J. Greiner (all MPE Garching),
report on behalf of the GROND team:

We observed the field of GRB 141221A (Swift trigger 622006; Sonbas et al.,
GCN #17206
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 telescope at ESO La Silla
Observatory (Chile).

Observations started at 08:09:33 UT on 21/12/2014, 142 seconds after the
GRB trigger, and continued in all bands for ~18 minutes of exposures until
the beginning of twilight, and in NIR for another 4 minute exposure. They
were performed at an average seeing of 1.7" and at an average airmass of
2.1.

We find a single point source, consistent with the enhanced SWIFT-XRT
position of Beardmore et al. (GCN #17211
Not found
 
 
) and that reported by e.g. Covino
(GCN 17208
Not found
 
 
), Trotter et al. (GCN #17210
Not found
 
 
),  at:

RA (J2000.0) = 13h 13m 08.80s

DEC (J2000.0) = + 08d 12' 18.9"

with an uncertainty of 0.2" in both co-ordinates.

There were problems with telescope pointing throughout the observations,
Based on our first short exposures in grizJHK, we estimate preliminary
magnitudes (all in AB system) of

g' = 17.1 +/- 0.1 mag,
r' = 16.6 +/- 0.1 mag,
i' = 16.4 +/- 0.1 mag,
z' = 16.1 +/- 0.1 mag,
J = 15.7 +/- 0.1 mag,
H = 15.4 +/- 0.1 mag, and
K = 15.3 +/- 0.1 mag.

The best-fit SED has a spectral index beta = 1.0 +/- 0.1.

Given magnitudes are not corrected for the expected Galactic foreground
extinction corresponding to a reddening of E_(B-V)=0.024 mag in the
direction of the burst (Schlegel et al. 1998).