TITLE: GCN CIRCULAR NUMBER: 30180 SUBJECT: GRB210610B: MeerLICHT multi-colour photometry DATE: 21/06/10 22:52:22 GMT FROM: Paul Vreeswijk at Radboud U/Nijmegen S. de Wet (UCT), P.J. Groot (Radboud/UCT/SAAO), A.J. Levan and P.M. Vreeswijk (Radboud) report on behalf of the MeerLICHT consortium: "Following the detection of GRB210610B by Swift and its optical counterpart (Page et al., GCN 30170), the 0.6m MeerLICHT telescope, located at Sutherland, South Africa began observations of the field at 2021-06-10, 21:00:54 UT (1h9m after burst) with a repeating sequence of optical filters: q,u,q,g,q,r,q,i,q,z, at 60s integration time each. The q-band wavelength limits are 440-720nm. First detections are: q_AB = 17.25 +/- 0.01 +/- 0.02 at 21:00:54 UT u_AB = 17.48 +/- 0.05 +/- 0.05 at 21:02:18 UT g_AB = 17.39 +/- 0.02 +/- 0.03 at 21:05:27 UT i_AB = 17.12 +/- 0.03 +/- 0.01 at 21:11:25 UT z_AB = 17.10 +/- 0.07 +/- 0.02 at 21:14:26 UT r_AB = 17.37 +/- 0.02 +/- 0.02 at 21:23:29 UT where the first uncertainty on the magnitude is the statistical uncertainty and the second is the uncertainty on the photometric calibration. No correction for Galactic extinction has been made. Inspection of DECaLS/DR3 data (Dey et al., 2019, AJ 157, 168) shows an underlying blue galaxy, centered on RA,Dec (J2000) = 243.91823, +14.39901, with magnitude g=22.97, r=22.87 and z=22.57. Further monitoring is continuing. MeerLICHT is built and run by a consortium consisting of Radboud University, University of Cape Town, the South African Astronomical Observatory, the University of Oxford, the University of Manchester and the University of Amsterdam."