TITLE:   GCN CIRCULAR
NUMBER:  18092
SUBJECT: GRB 150728A: Swift/UVOT Upper Limits
DATE:    15/07/28 21:08:25 GMT
FROM:    Alice Breeveld at MSSL-UCL  <a.breeveld@ucl.ac.uk>

A. A. Breeveld (UCL-MSSL) and H. A. Krimm (CRESST/GSFC/USRA) report on 
behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150728A 75 
s after the BAT trigger (Krimm et al., GCN Circ. 18087).
No optical afterglow consistent with the XRT position (Beardmore et al. 
GCN Circ. 18088) or the Faulkes position (Dichiara et al. GCN Circ. 
18090) 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            75          225          147         >21.3
u_FC               288          537          246         >20.4
white               75         6991          730         >22.0
v                  617         5982          275         >19.8
b                  543         6803          452         >21.1
u                  288         6597          678         >21.0
w1                 668         6392          452         >20.4
m2                 643         6187          452         >20.2
w2                 593         5777          255         >20.1

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.20 in the direction of the 
burst (Schlegel et al. 1998).