GCN Circular 23865

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
Not found
 
 
).
A source consistent with the XRT position
(Goad et al. GCN Circ. 23848
Not found
 
 
)
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
Not found
 
 
).

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).