GCN Circular 23283

N. P. M. Kuin (UCL-MSSL) and A. Tohuvavohu (PSU)

report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180930A
212 s after the BAT trigger (Tohuvavohu et al., GCN Circ. 23279
Not found
 
 
).
No optical afterglow consistent with the XRT position
(Evans GCN Circ. 23280
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 first
finding chart (FC) exposure and subsequent exposures are:

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

white_FC           212          362          147         >21.2
white              212         2818          602         >21.1
v                  517         2620          226         >20.1
b                  443         2718          240         >20.7
u                  418         2693          245         >19.7
w1                 394         2669          253         >20.8
m2                 369         2644          233         >19.3
w2                 659         2595          194         >19.9

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).