TITLE:   GCN CIRCULAR
NUMBER:  19449
SUBJECT: GRB 160521B: Swift/UVOT Upper Limits
DATE:    16/05/22 17:23:14 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 GRB 160521B centered on
the LAT position (Axelsson et al., GCN Circ. 19444) 41882 seconds after
the trigger. The exposures for the optical filters (white, b, and u)
cover about 20% of the LAT statistical error circle, and
the uv filters (uvw1 and uvm2) cover about 44%.
Only the exposures with the uv filters cover
the possible XRT counterpart (Page et al., GCN Circ. 19448).
The preliminary upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are:

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

white           42794        43127          324          >20.8
b               41882        49001         1180          >20.7
u               47789        48695          885          >20.2
uvw1            46882        54226         1578          >20.1
uvw2            52616        53065          886          >20.4

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).