TITLE:   GCN CIRCULAR
NUMBER:  28400
SUBJECT: GRB 200907B: Swift/UVOT Upper Limits
DATE:    20/09/09 03:50:55 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <mhs18@psu.edu>

M. H. Siegel (PSU) and A. P. Beardmore (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 200907B
84 s after the BAT trigger (Beardmore et al., GCN Circ. 28384).
No optical afterglow consistent with the XRT position
(Evans GCN Circ. 28385) 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            84          233          147         >20.4
u_FC               296          546          246         >19.7
white               84         4892          383         >21.0
v                  625          819           39         >17.7
b                  551         4687          236         >19.4
u                  296         4482          462         >20.4
w1                 675         4277          216         >19.2
m2                 650          670           19         >18.3
w2                 601         5048          186         >19.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.61 in the direction of the burst
(Schlegel et al. 1998).