TITLE:   GCN CIRCULAR
NUMBER:  23190
SUBJECT: GRB 180828A: Swift/UVOT Upper Limits
DATE:    18/08/29 17:21:47 GMT
FROM:    Sam Emery at MSSL-UCL  <samuel.emery.15@ucl.ac.uk>

S.W.K. Emery (UCL-MSSL) and A. P. Beardmore (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180828A
124 s after the BAT trigger (Beardmore et al., GCN Circ. 23182).
No optical afterglow consistent with the XRT position
(LaPorte et al., GCN Circ. 23185) or the position of the source 
detected outside the enhanced XRT error region by RATIR 
(Butler et al., GCN Circ. 23189)
is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white              124        23102         1057         >21.8
v                16882        39624         1367         >20.3
b                 5752        28839         1439         >21.7
u                 5547        34577         1709         >21.1
uvw1              5342        33925         1082         >20.7
uvm2              5137        40314         1756         >21.0
uvw2             11215        38709         2087         >21.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 23.65 in the direction of the burst
(Schlegel et al. 1998).