TITLE: GCN CIRCULAR NUMBER: 23422 SUBJECT: GROND observations of GRB181110A DATE: 18/11/11 13:17:04 GMT FROM: Jan Bolmer at MPE/Garching J. Bolmer (MPE, Garching) and P. Schady (Univ. of Bath) report: We observed the field of GRB 181110A (Swift trigger 871316; Evans et al., GCN #23413) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile). Observations started at 00:01 UT, 15.5 hrs after the GRB trigger, and were performed under poor seeing conditions, 4.1“, and at an average airmass of 1.2. We detect a source at a position consistent with the X-ray and optical afterglow (Evans et al., GCN #23413; Kuin et al., GCN #23419). Based on the first 17 min of total exposures in g'r'i'z' and 20 min in JHK, we measure the following preliminary AB magnitudes: g' = 21.25 +/- 0.06 mag r' = 20.58 +/- 0.05 mag i' = 19.91 +/- 0.08 mag z' = 20.08 +/- 0.09 mag J = 20.16 +/- 0.20 mag H = 19.76 +/- 0.18 mag K = 19.27 +/- 0.18 mag Given magnitudes are calibrated against USNO and 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.06 in the direction of the burst (Schlafly & Finkbeiner 2011).