TITLE:   GCN CIRCULAR
NUMBER:  34240
SUBJECT: GRB 230723B: Swift/UVOT Upper Limits
DATE:    23/07/23 21:12:26 GMT
FROM:    Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>

M. H. Siegel (PSU) and K. L. Page (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 230723B
3298 s after the BAT trigger (Page et al., GCN Circ. 34234).
No optical afterglow consistent with the XRT position (Page and Evans, 
GCN Circ. 34238)  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 first
finding chart (FC) exposure and subsequent exposures are:

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

white_FC          3298         3448          147         >20.6
white             3298         4680          344         >20.9
v                 3456         3655          197         >19.1
b                 4276         4475          197         >20.1
u                 4070         4270          197         >20.0
w1                3866         4065          197         >19.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.411 in the direction of the burst
(Schlegel et al. 1998).