TITLE: GCN CIRCULAR NUMBER: 11756 SUBJECT: GRB 110223B: GROND Detection of Optical Afterglow Candidate DATE: 11/02/24 01:49:21 GMT FROM: Felipe Olivares Estay at MPE V. Sudilovsky, J. Elliott, F. Olivares E., and J. Greiner (MPE Garching) report on behalf of the GROND team: We observed the field of GRB 110223B (Swift trigger 446677; Stamatikos et al., GCN #11754) 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 00:05 UT on February 24th, 2.7 hours after the GRB trigger, and are continuing. They were performed at an average seeing of 1.4" and at an average airmass of 1.6. We found a single point source within the 2.1" Swift/XRT error circle reported by Stamatikos et al. (GCN #11754) at  RA (J2000.0) = 10h 00m 55.98s  DEC (J2000.0) = -68d 18' 06.0" with an uncertainty of 0.3" in each coordinate. Based on 7.7 min exposure started at 00:30 UT, we estimate a preliminary r'-band magnitude of 22.1 +/- 0.1 calibrated against GROND zero points (AB system). No statements about the variability can be made at this stage. This measurement is not corrected for the considerable Galactic foreground extinction corresponding to a reddening of E(B-V)=0.226 mag in the direction of the burst (Schlegel et al. 1998).