GCN Circular 18057

M. De Pasquale (UCL-MSSL) and J. L. Racusin (NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150724A
108 s after the BAT trigger (Racusin et al., GCN Circ. 18050
Not found
 
 
).
No optical afterglow consistent with the XRT position (Goad et al.
GCN Circ. 18054
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 summed exposures are:

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

u_FC               108          358          246         >19.7

v                  415         6930          510         >19.2
b                  364        12898         1165         >20.6
u                  108        12238         1769         >20.7
w1                 464        11324         1387         >20.5
m2                 439         7135          502         >19.9
w2                 390         6726          529         >20.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.27 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