TITLE:   GCN CIRCULAR
NUMBER:  18369
SUBJECT: GRB 150925A: Swift/UVOT Upper Limits
DATE:    15/09/26 03:01:53 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <siegel@swift.psu.edu>

M. H. Siegel (PSU) and J. L. Racusin (NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150925A
149 s after the BAT trigger (Racusin et al., GCN Circ. 18365).
No optical afterglow consistent with the XRT position
(Osborne et al. GCN Circ. 18366)
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           149          298          147         >20.2
u_FC               307          557          246         >19.7
white              149        13178         1385         >21.2
v                  637         7068          510         >19.7
b                  563        18924         1676         >20.7
u                  307        18430         2310         >20.2
w1                 688        17516         1333         >20.8
m2                1589        22808          586         >21.1
w2                1019         6864          452         >19.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.10 in the direction of the burst
(Schlegel et al. 1998).