TITLE:   GCN CIRCULAR
NUMBER:  22181
SUBJECT: GRB 171205A: Swift/UVOT Detection
DATE:    17/12/05 13:45:32 GMT
FROM:    Sam Emery at MSSL-UCL  <samuel.emery.15@ucl.ac.uk>

S.W.K. Emery (UCL-MSSL) and V. D'Elia (ASDC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 171205A
154 s after the BAT trigger (D'Elia et al., GCN Circ. 22177).
A source consistent with the XRT position
(J.P. Osborne et al. GCN Circ. 22179)
is detected in the initial UVOT exposures.
There is marginal evidence for brightening in the white filter.
The revised source position is
RA(J2000)=11:09:39.547 Dec.(J2000)=-12:35:17.93. This position
 is within the XRT error circle  and is consistent with the VLT/X-shooter
 optical position  (L. Izzo et al. GCN Circ. 22180).

Preliminary detections using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white_FC           154          303          147         18.10 +/- 0.08
white             3812         3849           36         17.70 +/- 0.09
u                  312          390           78         17.78 +/- 0.18
v                 4499         4698          197         18.22 +/- 0.15
b                 3607         3807          197         18.45 +/- 0.09
uvw1              4908         5108          197         17.13 +/- 0.09
uvm2              4703         4903          197         17.11 +/- 0.11
uvw2              4294         4494          197         16.96 +/- 0.10

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.05 in the direction of the burst
(Schlegel et al. 1998), nor from any contribution of the host galaxy.