GRB 210218A: Swift/UVOT observations

The Swift/UVOT began settled observations of the field of GRB 210218A approximately 170 ks after the BAT trigger (B. Sbarufatti et al., GCN 29529) due to a Moon constraint. No optical afterglow consistent with the XRT candidate position is detected (Osborne et al., GCN 29542). Preliminary 3-sigma upper limit using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first exposure is: Filter T_start(s) T_stop(s) Exp(s) Mag wh 170031 188263 1665 >21.65 The magnitude in the table is not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.19 in the direction of the burst (Schlegel et al. 1998).