GCN Circular 22674

S.W.K. Emery (UCL-MSSL) and F. E. Marshall (NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180425A
88 s after the BAT trigger (Marshall et al., GCN Circ. 22672
Not found
 
 
).
No optical afterglow consistent with the XRT position
(Osborne et al., GCN Circ. 22673
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 early exposures are:

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

white               88         1201          353         >21.0
u                  302         1152          285         >20.5
v                  631         1250           78         >18.5
b                  557         1176           58         >19.4
uvw1               680         1299           78         >19.0
uvm2               827         1275           58         >18.5
uvw2               606         1226           58         >19.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).