GCN Circular 9469
P. Schady (MSSL-UCL) and J. R. Cummings (NASA/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT observed the field of GRB 090531B starting 3924 s after the BAT trigger (Cummings et al., GCN Circ. 9461), once the GRB came out of Earth limb observing constraint. No optical afterglow is detected in any of the UVOT exposures at the position of the X-ray afterglow (Sbarufatti et al., GCN Circ. 9463), with the following three-sigma upper limits: Filter T_mid(s) Exp(s) 3-sig Mag UL white 3934 74 > 20.52 v 4105 98 > 19.08 b 4926 98 > 20.06 u 4721 98 > 19.74 uvw1 4515 98 > 19.65 uvm2 4310 98 > 19.32 uvw2 5336 98 > 19.61 The values quoted above are not corrected for the large Galactic extinction due to the reddening of E(B-V)=1.12 in the direction of the burst (Schlegel et al. 1998). The photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383, 627).