TITLE:   GCN CIRCULAR
NUMBER:  35440
SUBJECT: GRB 231230A: Swift/UVOT Upper Limits
DATE:    23/12/30 11:25:57 GMT
FROM:    Paul Kuin at MSSL <npkuin@gmail.com>

N. P. M. Kuin (UCL-MSSL) and M. J. Moss (GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 231230A
1511 s after the BAT trigger (Moss et al., GCN Circ. 35436).
No optical afterglow consistent with the XRT position
is 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 initial exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white             1511         1705           39         >18.9
b                 1661         1681           19         >18.5
w1                1612         1632           19         >18.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.014 in the direction of the burst
(Schlegel et al. 1998).