TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5068 SUBJECT: GRB 060502A: Swift/UVOT source detection DATE: 06/05/03 10:35:52 GMT FROM: Tracey Poole at MSSL T. S. Poole (UCL-MSSL), and V. La Parola (INAF-IASFPA) on behalf of the Swift/UVOT team. The Swift/UVOT began observing the field of GRB060502 (BAT Trigger=208169, V. La Parola, et. al, GCN 5047) at 03:04:56 UT, 84s after the BAT trigger. We detect a fading source with a calculated position of RA = 16:03:42.48 and Dec = +66:36:02.5 (J2000) in the V, B and White filters, and the summed UVW1 filter. The error in the coordinates of the UVOT source is +/- 0.56 arcsec (90% confidence). The position is 4.4 arcseconds from the centre of the XRT error circle reported by V. La Parola, et. al, (GCN 5054). Checks against the Digitized Sky Survey images yield no known source at this position on the sky. The calculated magnitudes of the first afterglow observations in the UVOT filters are given below. The limiting magnitudes are given to a 3 sigma limit. These values are not corrected for Galactic extinction; E(B-V) = 0.033. Filter T_range(s) T_exp(s) Magnitude Comments V 190-536 346 18.70 +/- 0.14 - source detection V 5092-5292 200 20.19 - 3 sigma upper limit B 4478-4678 200 20.04 +/- 0.16 - source detection B 5910-6110 200 20.91 +/- 0.34 - source detection U 4273-4473 200 20.84 - 3 sigma upper limit U 5706-5905 200 20.78 - 3 sigma upper limit UVW1 4069-4269 200 20.63 - 3 sigma upper limit UVW1 5501-5701 200 20.61 - 3 sigma upper limit UVW1 4069-5701 400 20.89 +/- 0.40 - source detection UVM2 3864-4064 200 20.85 - 3 sigma upper limit UVM2 5296-5496 200 21.03 - 3 sigma upper limit UVW2 4888-5087 200 21.60 - 3 sigma upper limit WHITE 84-184 100 18.50 +/- 0.07 - source detection WHITE 4682-4882 200 20.53 +/- 0.20 - source detection WHITE 6115-6314 200 21.22 - 3 sigma upper limit Where T_range is time post-trigger, and T_exp is the exposure time of the observation. A 6 arcsec radius was used for all filters. When summing the two UVW1 200s exposures we see a source detection above 3 sigma. This give a z upper limit of 1.9. This message may be cited.