GCN Circular 35308

M. H. Siegel (PSU) and P. A. Evans (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 231205B
216 s after the BAT trigger (Evans et al., GCN Circ. 35269
Not found
 
 
).
No optical afterglow consistent with the XRT position
(Osborne et al. 35275) 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           237          387          147         >21.3
white              237          536          167         >21.3
v                  216          414           33         >18.6
b                  492          512           19         >19.6
u                  468          487           19         >18.2
w1                 443          463           19         >19.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.204 in the direction of the burst
(Schlegel et al. 1998).