TITLE:   GCN CIRCULAR
NUMBER:  12366
SUBJECT: GRB 110918A: GROND detection of the afterglow candidate
DATE:    11/09/20 14:54:05 GMT
FROM:    Arne Rau at MPE  <arau@mpe.mpg.de>

J. Elliott (MPE Garching), T. Kruehler (DARK/NBI), S. Klose, D. A. Kann 
(both TLS Tautenburg), A. Rau and J. Greiner (both MPE Garching) report 
on behalf of the GROND team:

We observed the field of the IPN GRB 110918A (Hurley et al., GCN 12357) 
simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 
405) mounted at the 2.2m MPI/ESO telescope at La Silla Observatory (Chile).

Observations started at September 20, 2011, 02:37 which is roughly 29.2 
hr after the trigger. They consisted of a dithered mosaic of 5 tiles 
covering the full IPN error box. The X-ray and optical afterglow 
candidate reported by Mangano et al. (GCN #12364) and Tanvir et al. (GCN 
#12365) however is only covered by the larger field of view of the NIR 
channels.

We confirm the presence of a bright NIR source, and estimate a 
preliminary AB magnitude of J = 18.7 +/- 0.1 at a midtime of 08:04 UT, 
which has been derived by calibrating the field against stars from the 
2MASS catalog.