TITLE: GCN CIRCULAR NUMBER: 8095 SUBJECT: GRB 080810: Swift/UVOT Refined Analysis DATE: 08/08/11 17:31:57 GMT FROM: Stephen Holland at USRA/NASA/GSFC/SSC S. T. Holland (CRESST/USRA/GSFC) & K. L. Page (U Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT observed the field of GRB 080810 starting 65 s after the BAT trigger (Page et al., GCNC. 8080). Settled observations started at T + 85 s. We detect the optical afterglow (Page et al., GCNC 8080) in the v, b, and white filters at the UVOT-enhanced location of the XRT afterglow (Evans et al., 2008, GCNC 8086). The refined UVOT source position is RA (J2000.0) = 23:47:10.48 Dec (J2000.0) = +00:19:11.3 with an estimated uncertainty of +/-0.6 arcsec (radius, 90% confidence). This is consistent with the positions of the optical afterglow reported by Rykoff (GCNC 8084) and de Ugarte Postigo (GCNC 8089) Magnitudes and upper limits are reported below. Filter T_start (s) T_stop Exposure Mag Err Comment white 85 185 98 14.63 0.07 v 191 459 264 14.06 0.06 b 4432 4632 197 17.85 0.08 u 4227 68,686 727 >21.4 3-sigma UL uvw1 4022 68,283 3099 >22.3 3-sigma UL uvm2 3817 62,540 3229 >22.2 3-sigma UL uvw2 4843 50,866 1510 >22.0 3-sigma UL 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). The non-detections in the u, uvw1, uvm2, and uvw2 filters are consistent with a redshift of z = 3.35 (Prochaska, GCNC 8083). The power-law decay index in the b band between 4532 and 27,387 s is -1.29 +/- 0.22. [GCN OPS NOTE(10sep08): Per author's request, the RA value was changed from 23:47:10.26" to "23:47:10.48".]