TITLE:   GCN CIRCULAR
NUMBER:  21172
SUBJECT: GRB 170531A: Swift/UVOT Observations
DATE:    17/05/31 23:04:56 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <siegel@swift.psu.edu>

M. H. Siegel (PSU) and P. A. Evans (U Leicester) report on behalf of the Swift/UVOT team:

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 3522 seconds after the BAT trigger. No credible afterglow candidate
has been found in the initial data products. The 2.7'x2.7' sub-image covers
100% of the XRT error circle. The typical 3-sigma upper limit has been about
19.6 mag. The coverage of the XRT error circle by the 8'x8' region for the list
of sources generated on-board is uncertain because the large number of sources
filled the available telemetry. The list of sources is typically complete to
about 18 mag. No correction has been made for the expected extinction
corresponding to E(B-V) of 0.09.