TITLE: GCN CIRCULAR NUMBER: 10143 SUBJECT: GRB 091109: Swift/UVOT observations DATE: 09/11/09 12:24:27 GMT FROM: Samantha Oates at MSSL S. R. Oates (MSSL-UCL) reports on behalf of the Swift/UVOT team: The Swift/UVOT began observerving the field of GRB 091109 156s after the BAT trigger (Oates et al., GCN Circ. 10138). We detect the optical afterglow in the white filter only, which faded rapidly. The refined UVOT position is: RA (J2000) 20:37:01.80 Dec (J2000) -44: 9:29.6 with an estimated uncertainty of 0.7 arcsec (radius, 90% confidence). This position is consistent with the XRT refined position (Beardmore et al., GCN Circ 10140). Preliminary magnitudes and the 3 sigma upper limits are reported below. Filter T_start(s) T_stop(s) Exposure Mag Err ########################################################### white 156 306 147 19.88 +\- 0.14 white 5371 5571 197 > 21.26 v 4345 5981 393 > 19.94 b 5166 5365 197 > 20.49 u 314 6572 615 > 20.97 uvw1 4755 6392 393 > 20.59 uvm2 4550 6186 393 > 20.46 uvw2 4140 5777 393 > 20.68 ########################################################### The above magnitudes are not corrected for the Galactic extinction corresponding to a reddening of E_{B-V} = 0.03 mag (Schlegel et al., 1998, ApJS, 500, 525). The photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383,627).