TITLE:   GCN CIRCULAR
NUMBER:  18585
SUBJECT: GRB 151111A: GROND marginal detection of a afterglow candidate
DATE:    15/11/12 04:42:46 GMT
FROM:    John Graham at MPE/Garching  <graham@mpe.mpg.de>

J. F. Graham, T. Schweyer, and J. Greiner (all MPE Garching) report:

We observed the field of GRB 151111A (Swift trigger 663074; Page et al., GCN 18578) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at ESO La Silla Observatory (Chile).

Observations started at 00:08:05 UT on November 12, about 16 hours after the GRB trigger. Consistent with the enhanced X-ray error circle (Evans et al., GCN 18579) and the LCOGT-FTS possible source (Dichiara et al., GCN 18581) we detect a faint source at coordinates RA, DEC (J2000) = 03:47:22.73, -44:09:43.3 with an error of 2".

Due to high winds we were able to observe the target for only a limited period in conditions of extremity poor seeing (~3") and thick cirrus.  We thus give the following preliminary AB magnitudes with statistical and estimated systematic errors.

g: 23.25 ± 0.21 ± 1.0
r: 22.16 ± 0.14 ± 0.5
i: 20.89 ± 0.15 ± 0.5

At present we cannot decide if this is the afterglow.  Further observations are currently precluded by high winds.  We encourage additional observations from locations with better observing conditions.

Magnitudes are calibrated against the USNO-B1.0 catalog and are not corrected for the Galactic extinction in the direction of the burst.