Electronic Telegram No. 793 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://cfa-www.harvard.edu/iau/cbat.html SUPERNOVA 2006tf Further to IAUC 8622, R. Quimby, F. Castro, and P. Mondol, University of Texas, report the discovery of a supernova on unfiltered CCD images taken on Dec. 12.48 and 16.48 UT (both at mag about 16.7) using the 0.45-m ROTSE-IIIb telescope at the McDonald Observatory. SN 2006tf is located at R.A. = 12h46m15s.82, Decl. = +11o25'56".3 (equinox 2000.0), which is 0".2 east and 0".7 north of the center of an anonymous galaxy (which itself has magnitude r = 20.68 from the SDSS DR5). The new object was found by subtracting a co-addition of ROTSE-IIIb images taken between 2004 December and 2005 June (limiting mag about 19.1). A spectrum (range 420-890 nm) of 2006tf, obtained on Dec. 22.50 with the 9.2-m Hobby-Eberly Telescope (+ Marcario Low-Resolution Spectrograph) by J. Caldwell and E. Terrazas, shows it to be a type-IIn supernova. The spectrum is characterized by a blue continuum with prominent emission lines from H-alpha, H-beta, and H-gamma at a redshift of z = 0.074. The corresponding absolute magnitude for the presumed host is M_r = -16.9. Additional ROTSE-IIIb data taken between Dec. 10 and 28 indicate that 2006tf remained at mag about 16.7. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2007 CBAT 2007 January 3 (CBET 793) Daniel W. E. Green