[vsnet-grb-info 11363] GRB 111229A: GROND afterglow candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12775
SUBJECT: GRB 111229A: GROND afterglow candidate
DATE:    11/12/30 01:57:34 GMT
FROM:    Sylvio Klose at TLS Tautenburg  <klose at tls-tautenburg.de>

A. Nicuesa Guelbenzu, S. Klose, D. A. Kann (all TLS Tautenburg), and J.
Greiner (MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 111229A (Lien et al., GCN 12774) 
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 on La Silla.

Observations started in twilight, at 00:45 UT on December 30, 2.12 hr 
after the burst. In the refined XRT error circle (Lien et al., GCN 12774), 
we detect a new source in all bands which is significantly brighter than 
the DSS2 limit at RA, DEC (J2000) = 05:05:08.84, -84:42:38.7. At a mean 
time of December 30, 00:51 UT, in an 8min exposure, we measure the 
following preliminary magnitudes (AB system):

     g' = 20.50  +/- 0.04,
     r' = 19.96  +/- 0.03,
     i' = 19.74  +/- 0.03,
     z' = 19.58  +/- 0.03,
     J  = 19.01  +/- 0.11.

We propose this source to be the afterglow of GRB 111229A, implying a 
redshift of less than 3.5.

After correcting for a Galactic reddening of 0.18 mag, the SED is best fit 
with a spectral slope of 0.72 +/- 0.06.

Optical data are calibrated against GROND zero points and NIR data against 
2MASS field stars. Observations are continuing.