Electronic Telegram No. 582 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 2006dt IN NGC 5681 S. Blondin, M. Modjaz, R. Kirshner, and P. Challis, Harvard-Smithsonian Center for Astrophysics, report that a spectrum (range 350-740 nm) of SN 2006dt (cf. CBET 581), obtained on July 21.22 UT by M. Calkins with the F. L. Whipple Observatory 1.5-m telescope (+ FAST), shows it to be a type-Ia supernova around maximum light. Cross-correlation with a library of type-Ia supernova spectra indicates that SN 2006dt is most similar to SN 1998aq (Branch et al. 2003, A.J. 126, 1489) at maximum. Adopting a recession velocity of 7899 km/s for the host galaxy (from The Updated Zwicky Catalog, http://tdc-www.harvard.edu/uzc/), the maximum absorption in the Si II line (rest 635.5 nm) is blueshifted by roughly 11000 km/s. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2006 CBAT 2006 July 21 (CBET 582) Daniel W. E. Green