TITLE:   GCN CIRCULAR
NUMBER:  10442
SUBJECT: GRB 100216A: Swift/UVOT Observations
DATE:    10/02/20 05:01:15 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <siegel@astro.psu.edu>

M. H. Siegel (PSU) and A. Rowlinson (U. Leicester) report on behalf of
the SWIFT-UVOT team:

We have analysed 9787 ks of UVOT data for GRB 100216A (Cummings et al.,
GCN Circ. 10428), from 214.4 ks to 249.2 ks after the BAT trigger. The
data are entirely in the UVW2 filter.

We identify a source within the error circle of the XRT position given
by Rowlinson et al. (GCN Circ. 10435) with a UVW2 magnitude of 17.59
+- .03 and a position of 154.25872, +35.56806, which is equivalent to:

    RA(J2000)  = 10h 17m 02.09s
    Dec(J2000) = +35d 34m 05.0"

with a 90% confidence interval of 0.6 arc sec.  However, this source is
also seen in the Digital Sky Survey and exhibits no fading or measurable
variability over the 35 ks of observations.  It is likely the
ultraviolet counterpart to the known X-ray source 1RXS
J01702.9+353404 identified by Rowlinson et al.  We show no other
bright source near the XRT position to a 3-sigma upper limit of
UVW2=22.2.

    The quoted magnitudes have not been corrected for the expected
Galactic extinction along the line of sight corresponding to a
reddening of E_{B-V} = 0.10 mag (Schlegel, et al., 1998, ApJS, 500,
525).  All photometry is on the UVOT photometric system described in
Poole et al. (2008, MNRAS, 383, 627).