NOTE: uvot_fluxes_wget.pl vrs. 2018-01-16 fem at 180721d15h30m24s707583usUT
NOTE: Source region spec. is: 347.71088 4.85592 4"
NOTE: Used archived XRT position of 347.71088   4.85592  4.00
NOTE: position reference is GRB_Auto_Processing

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

GRB 180721A: Swift/UVOT Upper Limits

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

The Swift/UVOT began settled observations of the field of GRB 180721A
120 s after the BAT trigger (Sbarufatti et al., GCN Circ. 22994).
No optical afterglow consistent with the XRT position
*** POSITION REFERENCE is GRB_Auto_Processing ***
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               120          370          246         >20.1
v                  425         1693          156         >19.1
b                  375         1642          175         >19.9
u                  120         1617          529         >20.1
w1                 474         1742          156         >19.6
m2                1697         1717           19         >18.3
w2                 401         1668          156         >20.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.07 in the direction of the burst
(Schlegel et al. 1998).