TITLE: GCN CIRCULAR NUMBER: 8962 SUBJECT: GRB 090308: Swift/UVOT Upper Limits DATE: 09/03/09 18:31:52 GMT FROM: Frank Marshall at GSFC F.E. Marshall (NASA/GSFC) and P. Evans (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT observed the field of GRB 0900308 starting 132 s after the BAT trigger (Evans et al., GCN Circ. 8948). No optical afterglow is detected in the initial UVOT exposures at the position of the X-ray afterglow (Evans and Page, GCN Circ. 8956). Three-sigma upper limits using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white (FC) 132 282 147 >21.1 white 570 11390 1102 >22.2 v 620 17423 1101 >20.6 b 545 6455 382 >20.8 u 290 6281 639 >20.7 uvw1 669 6077 399 >20.6 uvm2 644 18019 798 >20.8 uvw2 595 12237 1044 >21.2 The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.11 in the direction of the burst (Schlegel et al. 1998).