Electronic Telegram No. 1940 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 2009iv Editor's note: this text replaces that on CBET 1939. E. Chatzopoulos, University of Texas; J. Vinko, University of Texas; F. Yuan, University of Michigan; R. Quimby, California Institute of Technology; D. Chamarro, M. D. Sisson, C. Akerlof, S. B. Pandey, University of Michigan; and J. C. Wheeler, University of Texas, on behalf of the ROTSE collaboration, report the discovery of a type-Ia supernova (mag about 17.6) in unfiltered images taken on Aug. 21.43 UT with the 0.45-m ROTSE-IIIb telescope at the McDonald Observatory. The new object was detected again ten days later at mag about 17.7 in confirmation images taken with the ROTSE-IIId telescope. SN 2009iv is located at R.A. = 2h58m14s.19, Decl. = +5o58'19".3 (equinox 2000.0; uncertainty about 1"), which is consistent with the core of the apparent host galaxy, 2MASX J02581424+0558189, at a redshift of z = 0.023 (according to the SIMBAD database). Two spectra (range 420-1020 nm), obtained on Aug. 29.43 and Sept. 9.72 with the Low Resolution Spectrograph on the 9.2-m Hobby-Eberly Telescope, show 2009iv to be a type-Ia supernova. The spectra contain the Si II 635.5-nm line, and also other S II/Mg II/Fe II features characteristic of type-Ia events, but they are heavily contaminated by the host galaxy; an E0-galaxy spectrum template was used to remove the contamination by the host galaxy. SNID (Blondin and Tonry 2007, Ap.J. 666, 1024) also identified the transient as a type-Ia supernova 28 days after maximum. A finding chart for 2009iv can be found at the following website URL: http://www.rotse.net/rsvp/j025814.2+055819/j025814.2+055819.jpg. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2009 CBAT 2009 September 11 (CBET 1940) Daniel W. E. Green