NOTE: uvot_fluxes_wget.pl vrs. 2018-01-16 fem at 180331d19h03m54s156362usUT
NOTE: Source region spec. is: 196.78296 61.72636 4"
NOTE: Used archived XRT position of 196.78296  61.72636  4.00
NOTE: position reference is GRB_Auto_Processing

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

GRB 180331B: Swift/UVOT Upper Limits

N. P. M. Kuin (UCL-MSSL) and A. Y. Lien (GSFC/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180331B
668 s after the BAT trigger (Lien et al., GCN Circ. 22573).
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

white_FC           668          818          147         >21.2
white              668         2066          412         >21.8
v                 1056         2115          136         >19.2
b                 1156         2041          117         >20.3
u                 1130         2016          117         >20.3
w1                 849         1992           78         >20.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.01 in the direction of the burst
(Schlegel et al. 1998).