[vsnet-grb-info 16874] GRB 150818A: Swift/UVOT candidate afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18155
SUBJECT: GRB 150818A: Swift/UVOT candidate afterglow
DATE:    15/08/18 14:59:35 GMT
FROM:    Frank Marshall at GSFC  <femarsha at khamseen.gsfc.nasa.gov>

F. E. Marshall (NASA/GSFC) and V. D'Elia (ASDC)
report on behalf of the Swift/UVOT team:

UVOT took a finding chart exposure of 28 seconds with the White filter
starting 94 seconds after the BAT trigger on GRB 150818A. 
There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =  15:21:25.48 = 230.35616
  DEC(J2000) =  68:20:34.0  = 68.34278
with a 90%-confidence error radius of about 1.0 arc sec. This position is 10
arcseconds from the center of the XRT error circle (D'Elia et al. GCN Circ. 18152). 
The estimated magnitude is 19.5 with a 1-sigma error of about 0.2. 
No correction has been made for extinction.