TITLE:   GCN CIRCULAR
NUMBER:  26282
SUBJECT: GRB 191123A: Swift/UVOT detection
DATE:    19/11/23 16:12:05 GMT
FROM:    Paul Kuin at MSSL  <npkuin@gmail.com>

N. P. M. Kuin (UCL-MSSL) and A. Tohuvavohu (U Toronto)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of
GRB 191123A  78 s after the BAT trigger (Tohuvavohu et al.,
GCN Circ. 26279). A candidate optical afterglow was
detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric
system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373)
for the first finding chart (FC) exposure and subsequent
exposures are:
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC         78          228          147     18.26+-0.07
u_FC            290          540          246    >19.89
white           869         1019          147     19.28+-0.13

The magnitudes in the table are not corrected for the Galactic
extinction due to the reddening of E(B-V) = 0.04 in the
direction of the burst (Schlegel et al. 1998).