GCN Circular 13226

A. A. Breeveld (MSSL-UCL) and G. Stratta (ASDC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120404A
139 s after the BAT trigger (Stratta et al., GCN Circ. 13208
Not found
 
 
).
A source at the UVOT position given in Stratta et al., GCN Circ. 13208
Not found
 
 
, 
and consistent with the enhanced XRT position (Osborne et al., GCN Circ. 
13218
Not found
 
 
), is detected in the initial UVOT exposures. The source is only 
seen in the optical filters and rises initially and then fades. The fact 
that the source is not detected in the UV filters is consistent with the 
redshift of z=2.876 reported by Cucchiara et al., GCN Circ. 13217
Not found
 
 
.

Preliminary detections and 3-sigma upper limits using the UVOT 
photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for 
the early exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white              139          288          147         19.43 � 0.12
v                 4734         4934          197         17.69 � 0.10
b                  606         1178           58         19.22 � 0.28
u                  351         1327          304         19.90 � 0.19
w1                 729         6779          452        >20.3
m2                 704         6574          432        >21.5
w2                 656        11408         1179        >22.1

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.05 in the direction of the 
burst (Schlegel et al. 1998).