NOTE: uvot_fluxes_wget.pl vrs. 2024-08-27 fem at 250818d11h09m59s834941usUT
NOTE: Source region spec. is: 213.80021 -58.01339 4"
NOTE: Used archived XRT position of 213.80021 -58.01339  4.00
NOTE: position reference is GCN_Circulars-41403

=========== Draft Upper Limit Circular ========

GRB 250818A: Swift/UVOT Upper Limits

***UBS*** (***INSTITUTION***) and S. B. Cenko (GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 250818A
162 s after the BAT trigger (Cenko et al., GCN Circ. 41403).
No optical afterglow consistent with the XRT position
*** POSITION REFERENCE is GCN_Circulars-41403 ***
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

u_FC               162          412          246         >20.3
b                  418          438           19         >18.6
u                  162          412          246         >20.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 1.602 in the direction of the burst
(Schlegel et al. 1998).