[vsnet-grb-info 10300] Swift XRT and UVOT Observations of OT 110215

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  11746
SUBJECT: Swift XRT and UVOT Observations of OT 110215
DATE:    11/02/17 23:07:06 GMT
FROM:    Margaret Chester at PSU  <chester at astro.psu.edu>

M. M. Chester (PSU), J. M. Gelbord (PSU), S. T. Holland
(CRESST/USRA/GSFC), J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA),
N. P. M. Kuin (MSSL-UCL), F. E. Marshall (NASA/GSFC), and
D. M. Palmer (LANL) report on behalf of the Swift team:

Swift began a target of opportunity observation of OT 110215
on February 16, 2011 at 20:00:13 UT, 26.2 hours after the first
detection of the optical transient (Sergey and Denisenko, GCN
Circ. 11739).  Swift data for these observations utilize Target
ID 31928.  We report a weak detection in XRT of a source
consistent with the position of the OT; we obtain UVOT upper
limits at the OT's position, but note a weak feature in the
v-band 3.5 arc sec away.  At the time the transient was first
detected, the source position was far outside the Swift/BAT
field of view (148 degrees from the boresight) and close to the
Earth's limb, making BAT insensitive to gamma-rays associated
with the event.  The transient was also out of the FoV during
the rebrightening reported by Sergey and Denisenko (GCN Circ.
11739).

We have analyzed 4.6 ks of XRT data spanning from T0+26.3 to
T0+28.5 hr.  The data are entirely in Photon Counting mode.
We detect a source with 3.8-sigma confidence consistent with
the coordinates of the OT, with a count rate of 1.8 (+/- 0.8) x
10^-3 counts per second.  No other source is detected within 3'
of the OT.  There is insufficient data to determine whether the
source is fading or to do a spectral analysis.  However, we note
that the six photons detected all have energies below 1.5 keV,
suggestive of a very soft source that would be more consistent
with a stellar flare than the afterglow of a GRB.

The UVOT instrument observed the field of the optical transient
starting 2011-02-16 at 20:02:57 UT, 26.3 hours after the start
of the OT, and ending at 22:18:33 UT.  Only upper limits are
obtained at the reported position of the transient.  We note a
weak feature in the reddest filter (v) at RA = 00:26:38,
DEC = +83:24:10.5 (J2000), 3.5 arc sec away.  The 3-sigma upper
limits are given below.  The magnitudes are based on the UVOT
photometric system (Poole et al. 2008, MNRAS, 383, 627); they
are not corrected for the Galactic extinction corresponding to
a reddening of E_{B-V} = 0.166 mag (Schlegel et al., 1998, ApJS,
500, 525).

  Filter   exposure(sec)  magnitude
  v         383          >20.1
  b         383          >20.3
  u         383          >19.8
  uvw1      766          >20.3
  uvm2     1092          >20.9
  uvw2     1534          >21.3