GCN Circular 9786
P. Schady (MSSL-UCL) and J.R. Cummings (NASA/UMBC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 090813 88s after the BAT trigger (Cummings et al., GCN Circ 9781). No new source is detected within the XRT error circle or at the optical position reported by Cenko (GCN Circ. 9783) in any of the individual or combined UVOT filters. The 3-sigma upper limits of detected a source at the position of the optical afterglow reported by Cenko (GCN Circ. 9783) in the first white band finding chart (fc) observation, and in consecutive coadded observations for each of the UVOT filters are as follows: Filter T_start(s) T_stop(s) Exp(s) Mag 3-sig UL wh (fc) 88 237 147 > 20.55 wh 581 1894 264 > 21.35 vv 631 1943 156 > 19.39 bb 556 1869 136 > 20.29 uu 300 2017 382 > 20.44 w1 681 1992 156 > 19.73 m2 656 1967 156 > 19.41 w2 607 1919 156 > 19.83 The values quoted above are not corrected for the Galactic extinction due to the large reddening of E(B-V) = 0.17 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).