[vsnet-grb-info 11171] GRB 111121A: Magellan/Megacam observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12583
SUBJECT: GRB 111121A: Magellan/Megacam observations
DATE:    11/11/22 12:58:18 GMT
FROM:    Edo Berger at Harvard  <eberger at cfa.harvard.edu>

W. Fong (Harvard), A. Seth (U. Utah), R. Chornock and E. Berger (Harvard)
report:

"We imaged the field of the short GRB 111121A (GCN 12578) with Megacam on
the Magellan/Clay 6.5-m telescope at a mid-time of 2011 November 22.27 UT
(13.9 hours post-burst).  We obtained 25x30-sec exposures in r-band at an
airmass of 1.7 in ~0.7" seeing.

The location of the latest enhanced XRT error circle (improved from GCN
12579 at http://www.swift.ac.uk/xrt_positions/ with RA(J2000) =
10:19:02.71, Dec(J2000) = -46:40:14.5, 1.4" uncertainty) is contaminated by
emission from a nearby bright (R~12.5) star.  However, we find a faint
source on the southern edge of the XRT circle at (J2000):

RA = 10:19:02.7
Dec = -46:40:15.6,

with an uncertainty of ~0.5" in each coordinate that includes contributions
from the centroiding error of the source and a 0.27" rms uncertainty from
the astrometric tie to USNO-B.

Due to the location of the source near a diffraction spike from the bright
star, it is unclear at present whether it is extended or point-like.
Additional analysis to extract a magnitude for the source is on-going, and
additional observations to check for variability are planned."