S. de Wet (UCT), P.J. Groot (Radboud/UCT/SAAO) and P.M. Vreeswijk (Radboud) report on behalf of the MeerLICHT consortium:
The 0.6 m wide-field MeerLICHT optical telescope located in Sutherland, South Africa, obtained a repeated series of 60 s exposures in the q,u,g,r,i,z bands of GRB 231118A following the Swift detection (Laha et al., GCN 35101). Observations started at 18:58:24 UT on 2023 November 18 (1.7 hours post-trigger) and continued until 21:46:37 UT, following the filter sequence quqgqrqiqz.
We detect the optical afterglow first reported by Dutton et al. (GCN 35103) with the following AB magnitudes:
q = 17.65 +/- 0.05 at 18:58:56 UT
u = 18.39 +/- 0.20 at 19:00:35 UT
g = 18.03 +/- 0.09 at 19:04:08 UT
r = 17.40 +/- 0.12 at 19:07:43 UT
i = 17.24 +/- 0.11 at 19:28:53 UT
z = 17.72 +/- 0.17 at 19:50:19 UT
Our high cadence q-band observations show a power-law decline with temporal index of -1.63, consistent with the decay reported by Dutton et al. (GCN 35108).
MeerLICHT is built and run by a consortium consisting of Radboud University, the University of Cape Town, the South African Astronomical Observatory, the University of Oxford, the University of Manchester and the University of Amsterdam.