GCN Circular 21155

S. R. Oates (Uni. of Warwick) and B. Sbarufatti (INAF-OAB/PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170526A
128 s after the BAT trigger (Sbarufatti et al., GCN Circ. 21149
Not found
 
 
).
No optical afterglow consistent with the XRT position
(Goad et al. GCN Circ. 21151
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         >19.9
white              128         4127          344         >20.4
v                4338         4537          197         >18.5
b                 3722         5197          235         >19.7
u                  286         5152          404         >19.4
w1                4748         4947          196         >19.1
m2                4542         4742          197         >19.3
w2                4133         4333          197         >19.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).