GCN Circular 18393

M. De Pasquale (UCL-MSSL) and S. B. Cenko (GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of
the trigger 657564 (possible GRB 151004A) 3613 s after the
BAT trigger (Cenko et al., GCN Circ. 18389
Not found
 
 
).
No optical afterglow consistent with the BAT position
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          3613         3763          147         >20
white             3613         4994          344         >20.3
v                 3770         5404          393         >18.7
b                 4590         4789          197         >19.2
u                 4384         4584          197         >18.9
w1                4179         4379          197         >19.0
m2                3974         5565          350         >19.3
w2                5000         5200          197         >19.1

The magnitudes in the table are not corrected for the heavy Galactic
extinction due to the reddening of E(B-V) = 1.03 in the direction of
the burst (Schlegel et al. 1998).

-- 

Dr. Massimiliano De Pasquale
Research associate - Swift UVOT scientist
Mullard Space Science Laboratory, University College London