GCN Circular 13057

S. R. Oates (MSSL-UCL) and M. Stamatikos (OSU/NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120312A
105 s after the BAT trigger (Stamatikos et al., GCN Circ. 13049
Not found
 
 
).
No optical afterglow consistent with the XRT position 
(Mangano et al., GCN Circ 13053) or the WHT optical candidate 
position (Tanvir et al., GCN Circ 13055) 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           105          255          147         >21.3
u_FC               318          567          246         >20.6
white              105         7764          861         >21.9
v                  647        18848         1378         >20.5
b                  573         7559          568         >20.9
u                  318        13854         1583         >21.3
w1                 696        13039         1434         >21.0
m2                 844        19630         1998         >21.4
w2                 795        17934         1434         >21.4

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.071 in the direction of the burst
(Schlegel et al. 1998).