TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4107
SUBJECT: GRB 051016B: Swift/UVOT detection
DATE:    05/10/17 13:45:59 GMT
FROM:    Alexander Blustin at MSSL-UCL  <ajb@mssl.ucl.ac.uk>

A. J. Blustin (UCL-MSSL), A. Parsons (GSFC), S. T. Holland (GSFC),
P. Meszaros, M. Chester (PSU), N. Gehrels (GSFC) on behalf of
the Swift/UVOT team report:

The Swift/UVOT began taking a settled exposure of the field of
GRB 051016B 78 s after the trigger (Parsons et al. GCN 4103).
A faint optical/UV source (not visible in the DSS) is detected
in summed images at the position reported by Chen et al. (GCN 4105)
at greater than 3 sigma in four of the UVOT filters; the
magnitudes and upper limits are as follows:

Filter  T_range(sec)  Exp(sec)  Mag/3-sig upper limit

V       78-29720      2418      20.5 (upper limit)
B       445-28020     2748      22.0 +/- 0.5
U       391-35505     2507      20.9 +/- 0.3
UVW1    337-34740     2796      21.7 +/- 0.4
UVM2    283-33833     2798      21.0 (upper limit)
UVW2    554-28928     2748      22.8 +/- 0.6

The detection in UVW2 would imply that the redshift of the source
is less than ~1.3.

There was a further uncatalogued nearby UV-only source at
(J2000 08:48:27.7 +13:39:12.0), outside the XRT error circle,
with the following magnitudes:

Filter   Mag

UVW1     21.9 +/- 0.4
UVM2     22.3 +/- 0.4
UVW2     22.0 +/- 0.3

Further data will be required to tell whether either source is
variable.











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