[vsnet-grb-info 14322] GRB 131229A: GROND observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15636
SUBJECT: GRB 131229A: GROND observations
DATE:    13/12/29 19:23:16 GMT
FROM:    Patricia Schady at MPE/Swift  <pschady at mpe.mpg.de>

J. F. Graham, P. Schady, D. A. Kann and J. Greiner (all MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 131229A (Page et al., GCN #15627) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at La Silla Observatory (Chile). 

Observations started at 07:02 UT on 29th December, 23 mins after the GRB trigger. They were performed at an average seeing of 1.7" and at high airmass.

Source B from Perley et al. (GCN #15630) is clearly detected within a 1440s exposure stacked H-band image (mid-time 07:45UT) with an AB magnitude of 20.1+/-0.2, and marginally detected in z' and J. However, we note that this source lies 1.5" outside the refined XRT position. 

In 3x8min stacked images centred 53 mins after the trigger, we do not detect a source within the refined Swift-XRT error circle down to the following upper limits (AB magnitudes):
g' > 24.2,
r' > 24.0,
i' > 23.4,
z' > 23.2,
J > 21.3,
H > 20.7, and
K > 19.4.

The given optical and NIR limits are calibrated against GROND zeropoints and 2MASS field stars in g'r'i'z and JHK respectively, and are not corrected for the Galactic foreground extinction corresponding to a reddening of E(B-V)=0.29 in the direction of the burst (Schlegel et al. 1998).