TITLE: GCN CIRCULAR NUMBER: 7497 SUBJECT: GRB 080319C: UVOT Observations DATE: 08/03/21 11:37:34 GMT FROM: Stephen Holland at USRA/NASA/GSFC/SSC S. T. Holland (CRESST/USRA/GSFC) & C. Pagani (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT observed the field of GRB 080319C starting 210 s after the BAT trigger (Pagani et al., GCN Circ. 7442). We detect the optical afterglow in the v, b, u, and white filters at location of the KAIT optical afterglow (Li, et al., 2008, GCNC 7441). The UVOT source position is RA(J2000.0) = 17:15:55.49 Dec(J2000.0) = +55:23:30.6 with an estimated uncertainty of +/-0.53 arcsec (radius, 90% confidence). Magnitudes and upper limits are reported below. Filter T_start (s) T_stop Exposure Mag Err Comment v 334 353 19 18.09 0.30 b 433 443 10 19.02 0.53 u 408 581 39 19.08 0.36 uvw1 383 2410 214 >20.0 3-sigma UL uvm2 358 2385 175 >19.6 3-sigma UL uvw2 463 2336 175 >19.9 3-sigma UL white 227 327 98 18.81 0.08 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 flight system described in Poole et al. (2008, MNRAS, 383,627). The non-detections in the three ultraviolet filters may indicate that the redshift is z >~ 3.