TITLE:   GCN CIRCULAR
NUMBER:  17603
SUBJECT: GRB 150318A: Swift/UVOT Upper Limits
DATE:    15/03/18 13:52:59 GMT
FROM:    Alice Breeveld at MSSL-UCL  <a.breeveld@ucl.ac.uk>

A. A. Breeveld (UCL-MSSL) and C. Pagani (U Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150318A
151 s after the BAT trigger (Pagani et al., GCN Circ. 17599).
No optical afterglow consistent with the XRT position (Evans et al. GCN 
Circ. 17600) 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           151          300          147         >20.8
u_FC               308          558          246         >19.8
white              151         5695          530         >21.4
v                  638         6106          432         >20.0
b                  736         6762          252         >20.4
u                  308         6721          659         >20.4
w1                 687         6516          413         >20.2
m2                4676         6311          393         >20.1
w2                4266         5901          393         >20.8

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.04 in the direction of the 
burst (Schlegel et al. 1998).