GCN Circular 30686

GRB 210820A: Swift/UVOT Detection

S. J. LaPorte (PSU) and A. P. Beardmore (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210820A
131 s after the BAT trigger (Beardmore et al., GCN Circ. 30664
Not found
 
 
).
A source consistent with the XRT position
(Beardmore et al., GCN Circ. 30664
Not found
 
 
)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  01:22:33.48 =  20.63952 (deg.)
    Dec (J2000) = +04:36:28.3  =   4.60786 (deg.)
with an estimated uncertainty of 0.45 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

v                  437         1684          156         18.86 +/- 0.24
b                  387          555           39         18.57 +/- 0.19
u                  131          381          246         17.60 +/- 0.06
w1                 784         1733           58        >19.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.030 in the direction of the burst
(Schlegel et al. 1998).