TITLE: GCN CIRCULAR NUMBER: 18595 SUBJECT: GRB 151112A: GROND Detection of the Optical/NIR Afterglow Candidate DATE: 15/11/13 01:27:10 GMT FROM: Fabian Knust at MPE/GROND F. Knust, T.-W. Chen and J. Greiner (all MPE Garching) report on behalf of the GROND team: We observed the field of GRB 151112A (Swift trigger 663179; Malesani et al., GCN #18588) 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 the ESO La Silla Observatory (Chile). Observations started at 00:09 UT on 2015-11-13, 10.5hrs after the GRB trigger, and are continuing. They were performed at an average seeing of 1.8" and at an average airmass of 1.2. We found a single point source within the 1.4" Swift-XRT error circle reported by Osborne et al. (GCN #18592) at RA (J2000.0) = 00h 08m 12.77s DEC (J2000.0) = -61d 39' 48.4" with an uncertainty of 0.5" in each coordinate. Based on 11.50 min of total exposures in g'r'i'z' and 12.00 min in JHK, we estimate preliminary magnitudes (all in AB system) of g' > 23.9 mag, r' = 23.9 +/- 0.373 mag, i' = 22.4 +/- 0.169 mag, z' = 22.5 +/- 0.288 mag, J > 21.0 mag, H > 20.5 mag, and K > 19.0 mag. Given magnitudes are calibrated against GROND zeropoints as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.01 mag in the direction of the burst (Schlegel et al. 1998).