GCN Circular 5068

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
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 ) 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
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 ). 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.

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