GCN Circular 13533

S. R. Oates (MSSL-UCL) and J. R. Cummings (NASA/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120728A
148 s after the BAT trigger (Cummings et al., GCN Circ. 13525
Not found
 
 
).
No optical afterglow consistent with the XRT position
(Osborne et al., GCN Circ.13528
Not found
 
 
) 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

u_FC               148          398          246         >19.5
v                  456        17454         1356         >20.6
b                  404        24174         2261         >22.3
u                  148        23261         2438         >21.0
w1                 505        19107         1200         >20.8
m2                 480        18359         1357         >21.0
w2                 430        24878         1735         >21.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.53 in the direction of the burst
(Schlegel et al. 1998).