GCN Circular 29679
M.. H. Siegel (PSU) and S. Dichiara (NASA/GSFC/UMCP) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 210321A 2735 s after the BAT trigger (Dichiara et al., GCN Circ. 29677). A source consistent with the XRT position (Perri et al., GCN Circ. 29678) is detected in the initial UVOT exposures. Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 2735 2837 100 18.76 +/- 0.11 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.116 in the direction of the burst (Schlegel et al. 1998).