TITLE:   GCN CIRCULAR
NUMBER:  15168
SUBJECT: GRB 130831A:  Swift/UVOT Observations
DATE:    13/09/02 14:17:51 GMT
FROM:    Margaret Chester at PSU  <chester@astro.psu.edu>

M. M. Chester (PSU) and L.M.Z. Hagen (PSU) report on behalf of the
Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 130831A
(Hagen et al., GCN Circ. 15139) 191 seconds after the BAT trigger.
A source consistent with the enhanced XRT position (Evans et al.,
GCN Circ. 15147) is detected in the initial UVOT exposures.

Preliminary detections and 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)           Mag
v                498          818           58      14.4 +/- 0.1
v              10802        11709          885      18.0 +/- 0.1
v              46801        47000          196      > 18.9

b               448           767           58      14.9 +/- 0.1
b             23522         23925          393      19.2 +/- 0.2
b             40193         41100          885      20.1 +/- 0.2

u_FC            191            441         246      14.6 +/- 0.1
u               572            742          39      13.9 +/- 0.1
u             16594          23517        1645      18.3 +/- 0.1

w1              548            849          40      13.9 +/- 0.1
w1            15688          16588         886      18.1 +/- 0.1

m2              673            843          39      13.6 +/- 0.1
m2            11714          12387         663      17.5 +/- 0.1

w2              474            494          19      14.8 +/- 0.1
w2             9896          10796         886      17.5 +/- 0.1
w2            41107          46795        1009      19.3 +/- 0.2

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).