TITLE:   GCN CIRCULAR
NUMBER:  13811
SUBJECT: GRB 120923A: GROND Upper limits
DATE:    12/09/24 03:01:34 GMT
FROM:    Sylvio Klose at TLS Tautenburg  <klose@tls-tautenburg.de>

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

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 
Observatory (Chile).

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).