Electronic Telegram No. 1178 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 2007su 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 in unfiltered CCD images taken with the 0.45-m ROTSE-IIIb telescope at McDonald Observatory on Dec. 19.10 (at mag about 17.1) and 21.09 UT (mag about 16.9). The new object is located at R.A. = 22h19m08s.88, Decl. = +13o10'40".3 (equinox 2000.0; uncertainty < 1"), which is 0".4 east and 0".2 south of the center of the apparent host galaxy. A spectrogram (range 420-890 nm) of 2007su, obtained on Dec. 23.05 with the 9.2-m Hobby-Eberly Telescope (+ Marcario Low-Resolution Spectrograph) by M. Shetrone and F. Deglman, shows it to be a type-Ia supernova around maximum light. Adopting the recession velocity of the host galaxy (z = 0.028, apparently taken from the Sloan Digital Sky Survey), the minimum of the Si II 635.5-nm feature is blushifted by 11700 km/s. A finding chart of 2007su can be found at this website URL: http://www.rotse.net/rsvp/j221908+131040/j221908.9+131040.jpg. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2007 CBAT 2007 December 24 (CBET 1178) Daniel W. E. Green