TITLE:   GCN CIRCULAR
NUMBER:  11297
SUBJECT: GRB 100924A: GROND detection of an optical/NIR afterglow
DATE:    10/09/25 09:50:24 GMT
FROM:    Patricia Schady at MPE/Swift  <pschady@mpe.mpg.de>

P. Schady, T. Kruehler, and J. Greiner (all MPE Garching) report on
behalf of the GROND team:

We observed the field of GRB 100924A (Mangano et al., GCN 11294)
simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120,
405) mounted at the 2.2 m MPI/ESO telescope at La Silla Observatory (Chile).

Observations started at 04:32 UT on September 24, 0.57 hours after the
GRB and were performed under very challenging observing conditions, in
particular a full moon at close distance. A second epoch of imaging was
performed starting at 00:36 UT on September 25.

In the first epoch we detect a bright point source in all channels at:

RA = 00:02:42.26
Dec = 07:00:02.8

inside the refined BAT error circle (Barthelmy et al., GCN 11295) and
with a preliminary magnitude of r' = 17.19. Both, photometry and
astrometry have been tied to the SDSS catalog. The object faded below r'
 > 20 in the second epoch and is not present in the much deeper archival
SDSS frames. We hence conclude that this is the optical/NIR afterglow of
GRB 100924A.