GCN Circular 28025
A. A. Breeveld (UCL-MSSL) and B. Sbarufatti (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began target-of-opportunity observations of the field of GRB 200623A 37910 s after the Guano and GBM trigger (Fermi GBM team, GCN Circ. 28011; Debaunay et al., GCN Circ. 28013). No significant new sources were found at the positions of the XRT candidate sources 1 and 3 (Tohuvavohu et al., GCN Circ. 28023). XRT source 2 was outside the field of view for all exposures. Preliminary 3-sigma upper limit using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 37910 45836 4299 >22.4 The magnitude in the table is not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.012 in the direction of the burst (Schlegel et al. 1998).