GCN Circular 13751

N. P. M. Kuin (MSSL-UCL) and J. K. Cannizzo (NASA/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120911A
3323 s after the BAT trigger (Cannizzo et al., GCN Circ. 13744
Not found
 
 
).
No optical afterglow consistent with the XRT position (Beardmore et al.
GCN Circ. 13748
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

white_FC          3323         3473          147         >20.5
white             3323        11009         1229         >21.6
v                 3479        15918         1278         >19.9
b                 4300        10097         1160         >21.5
u                 4095         5730          393         >20.4
w1                3890         5526          393         >20.0
m2                3684         5320          393         >21.1
w2                4710        11585          757         >20.9

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 1.12 in the direction of the burst
(Schlegel et al. 1998).