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IAUC 7857: 2000 CF_105; 2001ke

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                                                  Circular No. 7857
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
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2000 CF_105
     K. Noll and D. Stephens, Space Telescope Science Institute; W.
Grundy, J. Spencer, R. Millis, and M. Buie, Lowell Observatory; D.
Cruikshank, Ames Research Center, NASA; S. Tegler, Northern Arizona
University; and W. Romanishin, University of Oklahoma, report the
identification of a binary companion to the transneptunian object
2000 CF_105 (MPEC 2000-F02, MPO 25770) on two exposures each with
the F555W and F814W filters taken on Jan. 12.050-12.076 UT with the
Hubble Space Telescope (+ WFPC2).  The companion is cleanly
separated in all four images at a distance of 0".78 +/- 0".03 at
p.a. 107 +/- 2 deg; then at Delta = 41.32 AU, the two components
were separated by at least 23 000 km.  The spacecraft was tracking
2000 CF_105 during the observations.  Stars and galaxies moved by
1".1 between the first and last exposure of the sequence.  The
magnitudes of the primary were V = 24.25 +/- 0.11 and I = 22.99 +/-
0.08; those of the secondary were V = 25.12 +/- 0.24 and I = 23.55
+/- 0.13.

     K. Z. Stanek, Center for Astrophysics (CfA); P. M. Garnavich
and S. T. Holland, University of Notre Dame; and S. Jha, R. P.
Kirshner, and D. Bersier, CfA, report that R-band images of GRB
011121 (cf. GCN 1147) were obtained with the Walter Baade 6.5-m
Magellan telescope on 2001 Dec. 4.3 (12.5 days after the gamma-ray
burst).  Using point-spread-function fitting, a magnitude of R =
23.0 +/- 0.1 is derived (two magnitudes brighter than expected from
the power-law decline observed in the first three days after the
burst; e.g., GCN 1154).  Recently released Hubble Space Telescope
(HST) images taken 13, 23, and 28 days after the burst (GCN 1273,
1274, 1276) confirm that the Magellan magnitude is not contaminated
by host light and indicate a slow decline consistent with a
supernova's reaching peak brightness < 2 rest-frame weeks after the
GRB.  HST images yield a position R.A. = 11h34m29s.64, Decl. =
-76o01'41".51 (equinox J2000; uncertainty +/- 0".2), which is 0".87
west and 0".11 north of the host-galaxy's center.  For a redshift
of z = 0.36 (GCN 1152), and correcting for a large Galactic dust
extinction of E(B-V) = 0.5, an absolute magnitude of M_v = -19.3
+/- 0.2 is found for Dec. 4.  This is consistent with the peak
luminosity of a bright supernova, such as SN 1998bw.  The
reddening-corrected spectral-energy distribution from the HST
photometry peaks at a rest wavelength of approximately 500 nm
(indicating a thermal source) and is inconsistent with a typical
GRB power-law distribution.  It is concluded that late-time
observations were dominated by a supernova that was likely the
origin of GRB 011121.

                      (C) Copyright 2002 CBAT
2002 March 22                  (7857)            Daniel W. E. Green

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