GCN Circular 9774
P. Schady (MSSL-UCL) and M. Stamatikos (NASA/ORAU) report on behalf of the Swift UVOT team: The Swift/UVOT began settled observations of the field of GRB 090812 86s after the BAT trigger (Stamatikos et al., GCN Circ. 9768). An uncatalogued, fading source is detected in the UVOT white, v, b and u band filters at the position reported in Stamatikos et al. (GCN Circ. 9768), consistent with the refined XRT error circle (Goad et al., GCN Circ. 9772). The detection of the afterglow in the white, v, b and u filters is consistent with the spectroscopic redshift of z=2.452 reported by Ugarte Postigo et al. (GCN Circ. 9771). Early time UVOT obserations indicate a decay rate of alpha~1.5. The magnitudes and 3-sigma upper limits for the UVOT observations of GRB 090812 in each filter are as follows: Filter T_start(s) T_stop(s) Exp(s) Mag/3-sig UL white 86 235 146 17.35+/-0.03 v 628 647 19 18.17+/-0.41 b 554 573 19 18.62+/-0.28 u 299 548 246 18.65+/-0.11 uvw1 677 1124 58 > 19.20 uvm2 652 1099 58 > 18.72 uvw2 603 1050 58 > 19.13 The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.02 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).