TITLE:   GCN CIRCULAR
NUMBER:  25853
SUBJECT: GRB 190926A: Swift/UVOT Upper Limits
DATE:    19/09/26 20:47:53 GMT
FROM:    Samantha Oates at MSSL  <sro@mssl.ucl.ac.uk>

S. R. Oates (U.Warwick) and A. Melandri (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 190926A
144 s after the BAT trigger (Melandri et al., GCN Circ. 25848).
No optical afterglow consistent with the enhanced XRT position
(Goad et al. GCN Circ. 25850)
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           144          294          147         >20.2
u_FC               303          553          246         >19.3
white              144         6525          580         >20.9
v                  634        11670         1116         >20.0
b                  559         6321          432         >20.2
u                  303         6115          659         >20.0
w1                 685         5910          413         >19.8
m2                 659        12294         1022         >20.3
w2                 610        10756         1148         >20.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.06 in the direction of the burst
(Schlegel et al. 1998).