Electronic Telegram No. 1041 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions) CBAT@CFA.HARVARD.EDU (science) URL http://www.cfa.harvard.edu/iau/cbat.html 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. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2007 CBAT 2007 August 23 (CBET 1041) Daniel W. E. Green