GCN Circular 23190

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
Not found
 
 
).
No optical afterglow consistent with the XRT position
(LaPorte et al., GCN Circ. 23185
Not found
 
 
) or the position of the source 
detected outside the enhanced XRT error region by RATIR 
(Butler et al., GCN Circ. 23189
Not found
 
 
)
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).