GCN Circular 30975

N. P. M. Kuin (UCL-MSSL) and S. Dichiara (NASA/GSFC/UMCP) report
on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 211023B
98 s after the BAT trigger (Dichiara et al., GCN Circ. 30960
Not found
 
 
).
A source consistent with the XRT position (Beardmore et al. GCN Circ. 30966
Not found
 
 
)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  11:21:14.33 = 170.30971 (deg.)
    Dec (J2000) = +39:08:08.8  =  39.13579 (deg.)
with an estimated uncertainty of 0.53 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               98          247          147         19.44 +/- 0.11
v                  640         1753          136        >18.8
b                  566         1679          117        >19.9
u                  310          734          265         19.50 +/- 0.20
w1                 690         1803          117        >19.3
w2                 615         1039           39        >19.9

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.024 in the direction of the burst
(Schlegel et al. 1998).