TITLE: GCN CIRCULAR NUMBER: 22819 SUBJECT: GROND observations of GRB 180620B DATE: 18/06/21 11:18:56 GMT FROM: Patricia Schady at MPE/Swift Tassilo Schweyer and Patricia Schady (MPE Garching) report: We observed the field of GRB 180620B (Swift trigger 843211; Evans et al., GCN #22807) 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 05:06 UT on 2018-06-21, 13.3 hours after the GRB trigger. They were performed at an average seeing of 1.6" and at an average airmass of 1.5. We found a single, bright point source within the 1.4" Swift-XRT enhanced error circle reported by Beardmore et al. (GCN #22814) at RA (J2000.0) = 23:50:05.088 Dec (J2000.0) = -57:57:43.88 with an uncertainty of 0.14" in each coordinate. Based on a total exposure time of around 30mins we estimate the following AB magnitudes: g' = 21.3 +/- 0.1 mag r' = 20.8 +/- 0.1 mag i' = 20.4 +/- 0.1 mag z' = 20.3 +/- 0.1 mag J = 19.7 +/- 0.1 mag H = 19.6 +/- 0.2 mag K = 19.1 +/- 0.4 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 in the direction of the burst (Schlafly & Finkbeiner 2011). We thank Markus Rabus for the excellent support from La Silla.