TITLE:   GCN CIRCULAR
NUMBER:  17787
SUBJECT: GRB 150428B: Swift/UVOT Upper Limits
DATE:    15/04/29 13:20:58 GMT
FROM:    Margaret Chester at PSU  <chester@swift.psu.edu>

M. M. Chester (PSU) and K. L. Page (U Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150428B 117
s after the BAT trigger (Page et al., GCN Circ. 17766). No optical
afterglow consistent with the enhanced XRT position (Beardmore et al., GCN
Circ. 17773) 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) exposures and subsequent exposures are:

Filter      T_start(s)   T_stop(s)   Exp(s)    UL (3-sigma)

white_FC       117          267        146       >20.9
u_FC           329          579        246       >20.1
white          117         5414        588       >21.6
v              659         5825        313       >19.6
b              584         6598        445       >20.8
u              329         6440        717       >20.8
w1             708         6235        293       >20.0
m2             683         6030        294       >19.9
w2             634         5620        313       >20.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.40 in the direction of the burst
(Schlegel et al. 1998).