TITLE:   GCN CIRCULAR
NUMBER:  22379
SUBJECT: GRB 180204A: Swift/UVOT Upper Limits
DATE:    18/02/04 16:50:12 GMT
FROM:    Paul Kuin at MSSL  <npkuin@gmail.com>

N. P. M. Kuin (UCL-MSSL) and K. L. Page (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180204A
92 s after the BAT trigger (Page et al., GCN Circ. 22375). A star is
present in the GSC whos position is consistent with the enhanced XRT
position (Osborne et al. GCN Circ. 22377).   No optical afterglow above
the stellar flux has been 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            92          242          147         >20.3
u_FC               304          554          246         >19.9
white               92        17884         1210         >20.8
v                  633        10587         1107         >19.0
b                  560        23622         1840         >20.7
u                  304        23062         2409         >21.1
w1                3943        22148         1917         >21.0
m2                 658        11492         1095         >20.8
w2                 609         6398          413         >20.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.10 in the direction of the burst
(Schlegel et al. 1998).