TITLE:   GCN CIRCULAR
NUMBER:  21155
SUBJECT: GRB 170526A: Swift/UVOT Upper Limits 
DATE:    17/05/27 13:28:48 GMT
FROM:    Samantha Oates at MSSL  <sro@mssl.ucl.ac.uk>

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).
No optical afterglow consistent with the XRT position
(Goad et al. GCN Circ. 21151) 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).