TITLE:   GCN CIRCULAR
NUMBER:  8849
SUBJECT: GRB 090123: GROND detection
DATE:    09/01/24 11:09:19 GMT
FROM:    Jochen Greiner at MPI  <jcg@mpe.mpg.de>

A. Rossi (Tautenburg Obs.) and J. Greiner (MPE Garching) report on behalf 
of the GROND team:

GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m ESO/MPI
telescope at La Silla Observatory (Chile) imaged the field of GRB 090123
(Swift trigger 340895, Grupe et al. 2009, GCN #8842) simultaneously in
g'r'i'z'JHK. Observation started on 2009-01-24 at 01:22 UTC, about 17 hours 
after the burst. The total exposure time was 25 minutes, the average seeing 
1.3 at airmass 2.5.

We detect the afterglow at the position reported by SWIFT UVOT (Marshall 
et al 2009, GCN #8846) in g'r'i'z', but not in JHK. We estimate the following 
observed magnitudes and upper limits (all in AB system):

g' = 22.77 +- 0.05
r' = 22.45 +- 0.05
i' = 21.95 +- 0.08
z' = 22.09 +- 0.12
J > 21.5
H > 21.0
K > 20.5

calibrated against GROND zeropoints and 2MASS field stars.