TITLE:   GCN CIRCULAR
NUMBER:  19839
SUBJECT: GRB 160821B: Swift/UVOT Upper Limits
DATE:    16/08/22 12:46:33 GMT
FROM:    Alice Breeveld at MSSL-UCL  <a.breeveld@ucl.ac.uk>

A. A. Breeveld (UCL-MSSL) and M. H. Siegel (PSU) report on behalf of the 
Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 160821B 76 
s after the BAT trigger (Siegel et al., GCN Circ. 19833).
No optical afterglow consistent with the XRT position (Evans et al. GCN 
Circ. 19837) or the NOT position (Xu et al. GCN Circ. 19834) 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            76          226          147         >21.1
u_FC               288          501          209         >20.4
white               76         6306          344         >21.7
v                 5080         5280          197         >19.1
b                 5901         6101          197         >20.2
u                  288         5895          406         >20.6
w1                5491         5691          197         >19.6
m2                5285         5485          197         >19.5
w2                4875         6439          322         >20.1

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.05 in the direction of the 
burst (Schlegel et al. 1998).