TITLE:   GCN CIRCULAR
NUMBER:  40858
SUBJECT: GRB 250628A: Swift/UVOT Upper Limits
DATE:    25/06/28 12:44:42 GMT
FROM:    Paul Kuin at MSSL <npkuin@gmail.com>

Paul Kuin (MSSL/UCL) and M Ferro (INAF-OAB) report on behalf of
the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of
GRB 250628A  130 s after the BAT trigger (Ferro et al.,
GCN Circ. 40853).
No optical afterglow consistent with the enhanced XRT position
(Evans et al. GCN Circ. 40854) 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           130          280          147         >20.8
u_FC               342          591          246         >19.3
white              130          641          167         >20.8
v                  671          691           19         >17.8
b                  597          617           19         >18.5
u                  342          591          246         >19.3
w1                 720          740           19         >18.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.023 in the direction of the burst
(Schlegel et al. 1998).