Electronic Telegram No. 927 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 2007bg Further to IAUC 8622, R. Quimby, University of Texas; and E. Rykoff and F. Yuan, University of Michigan, report the discovery of an apparent supernova in unfiltered CCD images taken around Apr. 16.15 (at mag about 17.7), and 18.15 UT (mag about 17.8) using the 0.45-m ROTSE-IIIb telescope at the McDonald Observatory. The new object was also detected at mag about 17.7 on Apr. 16.81 in unfiltered CCD images from the ROTSE-IIId telescope in Bakirlitepe, Turkey. SN 2007bg is located at R.A. = 11h49m26s.18, Decl. = +51o49'21".8 (equinox 2000.0), which is coincident with a faint, uncatalogued source in the Sloan Digital Sky Survey. Nothing was present at this location in ROTSE-IIIb images taken around Apr. 6.15 (limiting magnitude about 18.2), nor in a co-addition of ROTSE-IIIb images taken between 2004 Dec. 11 and 2006 Dec. 27 (limiting mag about 20.5). A spectrum (range 420-890 nm) of 2007bg, obtained on Apr. 18.30 UT with the 9.2-m Hobby-Eberly Telescope (+ Marcario Low-Resolution Spectrograph) by H. Edelmann and E. Terrazas, shows it to be a type-Ic supernova. Narrow emission lines seen in the spectrum correspond to H-alpha and O III 500.7-nm, redshifted by z about 0.034. The spectrum is similar to that of SN 2002ap at around 11 days after maximum, although for 2007bg the absorption around 610 nm is significantly stronger, and the O I 777-nm absorption is much weaker. Despite the comparatively strong 610-nm absorption, the lack of any discernable S II 545- or 562-nm features supports the clasification as a type-Ic supernova. At this redshift, the ROTSE-III photometry corresponds to an absolute magnitude of about -18.0. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2007 CBAT 2007 April 19 (CBET 927) Daniel W. E. Green