TITLE:   GCN CIRCULAR
NUMBER:  13751
SUBJECT: GRB 120911A: Swift/UVOT Upper Limits
DATE:    12/09/11 18:48:50 GMT
FROM:    Paul Kuin at MSSL  <npkuin@gmail.com>

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).
No optical afterglow consistent with the XRT position (Beardmore et al.
GCN Circ. 13748) 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).