NOTE: uvot_fluxes_wget.pl vrs. 2020-11-03a fem at 210318d19h43m15s233330usUT
NOTE: Source region spec. is: 264.2328 -35.822 4"
NOTE: Used archived XRT position of 264.23280 -35.82200  4.00
NOTE: position reference is GCN_Circ-29663

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

GRB 210318B: Swift/UVOT Upper Limits

M. H. Siegel (PSU) and E. Troja (NASA/GSFC, UMCP)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210318B
70 s after the BAT trigger (Troja et al., GCN Circ. 29663).
No optical afterglow consistent with the XRT position
*** POSITION REFERENCE is GCN_Circ-29663 ***
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            70          219          147         >20.0
u_FC               282          532          246         >20.1
white               70         1357          373         >20.9
v                  612         1406           97         >18.2
b                  538         1500           92         >19.1
u                  282         1479          324         >20.1
w1                 661         1455           97         >18.8
m2                1066         1430           58         >19.3
w2                 588         1382           97         >19.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 1.718 in the direction of the burst
(Schlegel et al. 1998).