TITLE:   GCN CIRCULAR
NUMBER:  23863
SUBJECT: GRB 190204A: Swift/UVOT Detection
DATE:    19/02/04 13:47:25 GMT
FROM:    Paul Kuin at MSSL  <npkuin@gmail.com>

Paul 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 190204A
84 s after the BAT trigger (Lien et al., GCN Circ. 23852).
The updated UVOT position is:

The preliminary UVOT position is:
    RA  (J2000) =  23:25:54.58 = 351.47744 (deg.)
    Dec (J2000) = +54:52:35.1  =  54.87642 (deg.)
with an estimated uncertainty of 0.4 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits using the UVOT photometric
system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures
are:

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white               84          233          147         16.84 +/- 0.07
white              576          596           20         18.66 +/- 0.20
v                  626         1247           78         18.30 +/- 0.23
b                  551         1507           85         19.29 +/- 0.21
u                  296          546          246         17.85 +/- 0.10
w1                 676         1470           97        >18.3
m2                 651         1444           97        >19.5
w2                 602         1395           97        >18.7

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.38 in the direction of the burst
(Schlegel et al. 1998).