TITLE: GCN CIRCULAR NUMBER: 11176 SUBJECT: Swift/UVOT Observations of GRB100901A DATE: 10/09/02 13:40:17 GMT FROM: Tyler Pritchard at PSU T. A. Pritchard (PSU) and Immler (CRESST/GSFC/UMD) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 100901A 147 s after the BAT trigger (Immler et al., GCN Circ. 11159). We detect an object not present in the DSS in all filters within 0.1 arcsec of the Enhanced Swift-XRT position (Osborne et al., GCN Circ. 11169) Preliminary magnitudes and 3-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) 147 297 147 19.55 ± 0.19 u (FC) 305 555 246 17.52 ± 0.10 white 585 605 20 18.58 ± 0.32 white 4849 5051 198 18.66 ± 0.07 b 561 581 19 17.85 ± 0.30 b 4644 4844 197 18.69 ± 0.11 u 305 555 246 17.52 ± 0.10 u 4439 4639 197 18.08 ± 0.10 v 129 139 10 >17.21 v 3824 4024 197 18.50 ± 0.21 w1 4234 4434 197 18.53 ± 0.16 m2 4029 4229 197 19.22 ± 0.32 w2 611 626 15 >17.6 w2 5055 5255 197 >20.04 w2 9620 10520 885 20.73 ± 0.32 The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.10 in the direction of the burst (Schlegel et al. 1998).