NOTE: uvot_fluxes_wget.pl vrs. 2023-03-23 fem at 240421d19h17m24s269001usUT
NOTE: Source region spec. is: 299.70083 -14.85961 4"
NOTE: Used archived XRT position of 299.70083 -14.85961  4.00
NOTE: position reference is GCN_Circulars-36213

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

GRB 240421B: Swift/UVOT Upper Limits

N. P. M. Kuin (UCL-MSSL) and M. Williams (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 240421B
130 s after the BAT trigger (Williams et al., GCN Circ. 36208).
No optical afterglow consistent with the XRT position
*** POSITION REFERENCE is GCN_Circulars-36213 ***
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           130          279          147         >20.7
u_FC               343          592          246         >20.1
white              130         1715          411         >21.2
v                  672         1764          136         >18.6
b                  598         1861          134         >20.3
u                  343         1839          363         >20.3
w1                 721         1813          117         >20.0
m2                1423         1616           39         >19.4
w2                 648         1740          136         >19.4

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.183 in the direction of the burst
(Schlegel et al. 1998).