[IAUC] CBET 1041: 20070823 : SUPERNOVA 2007gr IN NGC 1058

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                                                  Electronic Telegram No. 1041
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 2007gr IN NGC 1058
     W. Li, University of California at Berkeley (UCB); J.-C. Cuillandre,
Canada-France-Hawaii Telescope (CFHT) Corporation; S. D. Van Dyk, Spitzer
Science Center, California Institute of Technology; and A. V. Filippenko,
UCB, report that they obtained optical (r'-band) CFHT images of 2007gr (cf.
CBET 1034, 1036) on Aug. 19.6 UT and that they attempted to isolate a
possible progenitor for this young type-Ib/c supernova in archival Hubble
Space Telescope (HST) images of the host galaxy taken with the Wide Field
Planetary Camera 2 (WFPC2) on 2001 July 3 ("GO/SNAP program 9042").
Geometrical transformation between the CFHT and HST/WFPC2 images yields a
precision of 0.2 WFPC2 pixel, or 0".02, for the supernova's location in the
WFPC2 images.  Assuming no reddening from the host galaxy to 2007gr, a
Galactic reddening of E(B-V) = 0.062 mag in the direction of NGC 1058
(Schlegel et al. 1998, Ap.J. 500, 525), and the Cepheid distance of 9.3 Mpc
to NGC 925 (Silbermann et al. 1996, Ap.J. 470, 1), which is in the same
"NGC 1023" group of galaxies as NGC 1058, it is noted that the supernova
occurred in a prominent cluster of several highly luminous [absolute
magnitude M(B) = -7 to -8.5] stars with a range of colors and less-luminous
[M(B) = -5 to -6] blue stars, all of which are consistent with massive
supergiants.  In particular, a star with M(I) = -9.0 and M(B-I) = +0.45
(corrected for extinction and reddening, respectively) is located 0".12
east and 0".01 south of the nominal progenitor position.  This star is
consistent with a high-mass supergiant.  However, as this star has a
position difference from the nominal progenitor position that is six
times the uncertainty in the geometrical transformation, it is considered
less likely to be the supernova progenitor at this point.  Rather, the
progenitor is probably significantly fainter and not detectable in the
archival data, due to the presence of the brighter, neighboring star.
However, higher-precision observations with HST/WFPC2 of the supernova will
be used in the near future to verify this.  Further analysis is ongoing.


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                         (C) Copyright 2007 CBAT
2007 August 23                   (CBET 1041)              Daniel W. E. Green