TITLE:   GCN CIRCULAR
NUMBER:  13037
SUBJECT: GRB 120311A: Swift/UVOT Upper Limits
DATE:    12/03/11 15:16:25 GMT
FROM:    Patricia Schady at MPE/Swift  <msslba@googlemail.com>

S. R. Oates (MSSL-UCL) and C. B. Markwardt (NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120311A
3164 s after the BAT trigger (Markwardt et al., GCN Circ. 13032).
No optical afterglow, consistent with the refined XRT position
(Goad et al .,GCN Circ 13035) or optical position reported by the
Liverpool Telescope (Melandri et al., GCN Circ 13033), is detected within
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          3164         3314          147         >16.4
white             3164        16486         2114         >16.5
v                 3321        20754         1454         >15.8
b                 4141        15574         1224         >16.4
u                 3936         5571          393         >16.3
w1                3731         5366          393         >17.7
m2                3526         5161          393         >19.0
w2                4552        17272         1850         >19.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.13 in the direction of the burst
(Schlegel et al. 1998).