GCN Circular 20965

N. P. M. Kuin (UCL-MSSL) and A. Melandri (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field
of GRB 170331A 128 s after the BAT trigger (Melandri et
al., GCN Circ. 20946
Not found
 
 
). No optical afterglow consistent
with the XRT position (Osborne et al. GCN Circ. 20960
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           128          278          147         >20.4
u_FC               286          536          246         >19.6
white              128         1532          392         >21.0
v                  616         1753          134         >18.5
b                  542         1680          117         >19.1
u                  286         1655          343         >19.7
w1                 665         1631          117         >19.1
m2                1069         1606           58         >19.4

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).