TITLE:   GCN CIRCULAR
NUMBER:  3031
SUBJECT: GRB 050215B: candidate afterglow
DATE:    05/02/17 14:48:33 GMT
FROM:    Nial Tanvir at IofA U.Cambridge  <nrt@ast.cam.ac.uk>

N. Tanvir, S. Pak, R. Priddey, M. Hughes (U. Hertfordshire),
E. Rol, A. Levan, P. O'Brien (U. Leicester), C. Simpson (U. Durham),
E. Vardoulaki (U. Oxford), T. Carroll (JACH) report on behalf of a
larger collaboration:

We have obtained a second epoch of UKIRT/UFTI K-band imaging of
the Swift/BAT position reported for GRB 050215B.  Seeing was
again good (approx 0.5 arcsec compared to 0.4 arcsec on the
previous night).  The observation began at Feb 16.49 UT, roughly
34 hrs post burst.

We find no variable sources within the XRT error circle for the object
reported by Page et al (GCN circular 3027). However we find a faint,
apparently variable, point source about 30 arcsec from the centre of the
BAT error circle.  It has magnitude K=20.23+-0.11 on night 1 and
K=20.75+-0.22 on night 2 (both measured in a 0.9 arcsec aperture),
which we believe is therefore a good candidate for the afterglow of
this burst.

Although near the detection limit, the source on the second night
may be slightly extended (possibly also on the first), which would
indicate a host contribution, and hence that particularly the second
magnitude should be treated as an upper limit on the afterglow
magnitude.

The location of this object, is 15.7 arcsec E and 12.7 arcsec S
of the 2MASS/USNO-B1 catalogued object (whose magnitude we refine to
K=15.46 based on our standard star calibration).  ie. in the USNO-B1
system the candidate afterglow is located at:

 11:37:47.90 40:47:45.6

Postage stamp images are available on:

  http://star-www.herts.ac.uk/~nrt/050215b.html

Further followup is ongoing.