TITLE:   GCN CIRCULAR
NUMBER:  21722
SUBJECT: GRB 170827A: Swift/UVOT Upper Limits
DATE:    17/08/27 15:15:10 GMT
FROM:    Frank Marshall at GSFC  <femarsha@khamseen.gsfc.nasa.gov>

F. E. Marshall (NASA/GSFC) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170827A
134 s after the BAT trigger (Marshall et al., GCN Circ. 21718).
No optical afterglow consistent with the XRT position
(Marshall et al. GCN Circ. 21718)
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 a subsequent short exposure are:

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

white_FC           134          284          147         >19.8
u                  292          298            6         >17.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.11 in the direction of the burst
(Schlegel et al. 1998).