TITLE:   GCN CIRCULAR
NUMBER:  34288
SUBJECT: GRB 230728A: Swift/UVOT Upper Limits
DATE:    23/07/28 14:37:00 GMT
FROM:    Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>

S. R. Oates (U. Birmingham) and C. Salvaggio (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 230728A
100 s after the BAT trigger (Salvaggio et al., GCN Circ. 34282).
No optical afterglow consistent with the XRT position (Evans et al.,
GCN Circ. 34286) 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           100          250          147         >20.9
u_FC               312          562          246         >20.1
white              100         1361          372         >21.1
v                  641         5845          274         >19.4
b                  567         1338           78         >19.5
u                  312         1313          304         >20.0
w1                 691         1289           58         >18.5
m2                5851         6048          194         >19.5
w2                1023         1380           52         >18.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.080 in the direction of the burst
(Schlegel et al. 1998).