F. Knust (MPE Garching), S. Klose, A. Nicuesa Guelbenzu (both TLS
Tautenburg), and J. Greiner (MPE Garching) report on behalf of the GROND
We observed the field of GRB 120923A (Swift trigger 534402; Yershov et
al., GCN 13796) 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
Observations started at 00:10 UT on Sep 24, 19 hrs after the GRB trigger,
and are continuing. In a first 30 min exposure, at a mid time 00:35 UT, we
do not detect any source at the position of the NIR transient reported by
Levan et al. (GCN 13802) down to (AB mags, 3 sigma)
g' > 23.5,
r' > 23.7,
i' > 23.0,
z' > 23.0,
J > 21.0,
H > 20.4.
These uper limits are derived based on calibrating the images against
GROND zeropoints and 2MASS field stars and are not corrected for the
Galactic foreground extinction corresponding to a reddening of E_(B-V)=
0.15 mag in the direction of the burst (Schlegel et al. 1998).