TITLE: GCN CIRCULAR NUMBER: 8198 SUBJECT: GRB 080906: Refined Swift/UVOT Observations DATE: 08/09/07 22:00:22 GMT FROM: Stephen Holland at USRA/NASA/GSFC/SSC S. T. Holland (CRESST/USRA/GSFC) & L. Vetere (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT observed the field of GRB 080906 starting 62 s after the BAT trigger (Vetere et al., 2008, GCNC. 8186). Settled observations started at T + 82 s. We detect the optical afterglow (Vetere et al., GCNC 8186) in the v, b, u, and white filters. The refined UVOT source position is RA (J2000.0) = 15:12:10.65 Dec (J2000.0) = -80:31:03.2 with an estimated uncertainty of 0.64 arcsec (radius, 90% confidence). Magnitudes and upper limits are reported below. Filter TSTART TSTOP Exposure Mag Err Comment white 82 182 98 19.71 0.15 v 188 588 393 18.61 0.12 b 668 6204 216 21.02 0.44 u 643 5998 236 20.37 0.34 uvw1 619 5793 236 >20.9 2-sigma upper limit uvm2 594 5588 236 >20.5 2-sigma upper limit uvw2 698 6614 235 >21.1 2-sigma upper limit The above magnitudes are not corrected for the Galactic extinction corresponding to a reddening of E_{B-V} = 0.30 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 detection in the u filter, coupled with the non-detections in the uvw1, uvm2, and uvw2 filters, are consistent with a redshift of approximately z < 2.6. The power-law decay index in the v band between 338 and 6719 s is -0.50 +/- 0.04. Please update my e-mail address in your Address Book to . / \ /