Electronic Telegram No. 1124 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 2007op R. Quimby, California Institute of Technology; F. Yuan and C. Akerlof, University of Michigan; and J. C. Wheeler, University of Texas, report the discovery of a supernova in unfiltered CCD images taken on Oct. 20.22 (at mag about 18.7) and Nov. 4.20 UT (mag about 18.5) using the 0.45-m ROTSE-IIIb telescope at the McDonald Observatory. The new object is located at R.A. = 1h53m12s.36, Decl. = +33o44'34".0 (equinox 2000.0), which is 2".4 east and 2".6 south of the center of the apparent host galaxy. SN 2007op was found by subtracting a co-addition of images taken between Aug. 9 and Sept. 8 (limiting mag about 19.0). A spectrum (range 420-890 nm) of 2007op , obtained on Nov. 8.33 with the 9.2-m Hobby-Eberly Telescope (+ Marcario Low-Resolution Spectrograph) by S. Odewahn and A. Westfall, shows it to be a type-Ia supernova; the spectra are similar to those of SN 1994D at about 11 days after maximum light (Patat et al. 1996, MNRAS 278, 111). HET spectra of the host galaxy indicate a redshift of z = 0.085. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2007 CBAT 2007 November 9 (CBET 1124) Daniel W. E. Green