TITLE:   GCN CIRCULAR
NUMBER:  18150
SUBJECT: GRB 150817A: Swift/UVOT Upper Limits
DATE:    15/08/17 16:34:51 GMT
FROM:    Frank Marshall at GSFC  <femarsha@khamseen.gsfc.nasa.gov>

F. E. Marshall (NASA/GSFC) and V. D'Elia (ASDC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150817A
3955 s after the BAT trigger (D'Elia et al., GCN Circ. 18143).
No optical afterglow consistent with the enhanced X-ray
position (Osborne et al. GCN Circ. 18146) or
the optical position (Butler et al. GCN Circ. 18145)
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          3955         4104          147         >20.5
white             3955        12079          930         >21.4
v                 4111        28678         1278         >20.9
b                 4932        17880         1723         >21.7
u                 4727        23627         2613         >21.7
w1                4522        22957         2144         >21.0
w2               26865        27765          886         >20.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.48 in the direction of the burst
(Schlegel et al. 1998).