TITLE:   GCN CIRCULAR
NUMBER:  23865
SUBJECT: GRB190203A: UVOT analysis
DATE:    19/02/04 17:01:34 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 190203A
121 s after the BAT trigger (Lien et al., GCN Circ. 23845).
A source consistent with the XRT position
(Goad et al. GCN Circ. 23848)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  01:30:23.21 =  22.59672 (deg.)
    Dec (J2000) = +55:43:20.6  =  55.72240 (deg.)
with an estimated uncertainty of 0.46 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              121          271          147         18.66 +/- 0.06
v                  609         5462          225        >19.2
b                  535         4846          236        >20.5
u                  279         5967          551        >21.0
w1                 658         5872          413        >20.2
m2                 634         5666          413        >21.0
w2                 585         5257          236        >20.2


The short v image during settling, i.e., prior to the settled
images reported here, shows a 16.3 +/- 0.3 mag source as well.
Usually we have a detection in the other bands besides in the
early white filter. Either the GRB decayed so fast as to be
below u > 19.8 mag between To+278 and 529s or this burst is
of a high redshift. A rapid decay is consistent with Watson
et al. (GCN Circ. 23864).

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.64 in the direction of the burst
(Schlegel et al. 1998).