Electronic Telegram No. 1157 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 2007rx F. Yuan, University of Michigan; R. Quimby, California Institute of Technology; C. Akerlof, University of Michigan; and J. C. Wheeler, University of Texas -- on behalf of the ROTSE collaboration -- report the discovery of a supernova (mag about 17.2) in unfiltered CCD images taken with the 0.45-m ROTSE-IIIb telescope at McDonald Observatory on Nov. 28.11 UT. The new object was also detected at mag about 18.2 on Nov. 24.06 and was observed to rise to mag about 16.3 by Dec. 5.11. SN 2007rx is located at R.A. = 23h40m11s.74, Decl. = +27o25'16".5 (equinox 2000.0; uncertainty < 1"), which is 2".2 east and 5".9 north of a possibly extended object (USNO-B1.0 catalogued magnitude R = 19.59) seen in the Digitized Sky Survey. A finding chart of the supernova can be found at the following WWW URL: http://www.rotse.net/transients/j2340+2725/j234011.7+272516.jpg A spectrum (range 420-890 nm) of 2007rx, obtained on Dec. 6.16 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 just prior to maximum light (Patat et al. 1996, MNRAS 278, 111). Using the 1994D spectra as a template, Yuan et al. find an approximate redshift of z = 0.03 for 2007rx, which is compatible with the nearby Abell 2634 galaxy cluster (z = 0.031; Oegerle and Hill 2001, A.J. 122, 2858). NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2007 CBAT 2007 December 8 (CBET 1157) Daniel W. E. Green