TITLE: GCN CIRCULAR NUMBER: 7808 SUBJECT: GRB 080603B: Swift/UVOT detection of the afterglow DATE: 08/06/04 13:57:29 GMT FROM: Paul Kuin at MSSL N. P. M. Kuin (MSSL/UCL), and V. Mangano (INAF-IASFPA), report on behalf of the Swift UVOT team The Swift UltraViolet/Optical Telescope (UVOT) began observations of GRB 080603A, on June 3, 2008, at 19:39:07 UT, 63 seconds after the initial Swift BAT trigger (Mangano et al., GCN Circ. 7794).. The refined uvot position is RA = 11:46:07.66 = 176.5316 DEC =+68:03:39.99 = 68.061105 with an error or 0.3". The first finding chart in the wh filter has problems due to the brightness of the image, and needs detailed analysis. We start our report with the second finding chart. The magnitudes with 1-sigma errors for GRB080603B are given below for the initial observation sequence. Filter Tstart(s) Tstop(s) Exp(s) Magnitude v 187.8 393.1 202 16.48 +/- 0.06 uvm2 5778.0 5977.8 197 > 19.51 (3-sigma UL) uvw1 5983.9 6183.7 197 20.02 +/- 0.56 u 6188.8 6388.6 197 18.80 +/- 0.23 b 6395.3 12274.3 643 19.34 +/- 0.14 The absence of a detection in the uvm2 filter is consitent with the reported redshift of 2.69 (Fynbo et al., GCN Circ. 7797). Magnitude variation in the b observations shor evidence of flaring or rebrightening.. The values quoted above are on the UVOT Photometric System (Poole et al, 2008, MNRAS 383,627). They are not corrected for the expected galactic reddening of E(B-V) = 0.013 in the direction of the burst (Schlegel et al. 1998).