Electronic Telegram No. 488 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 2006bk S. Blondin, M. Modjaz, R. Kirshner, and P. Challis, Harvard-Smithsonian Center for Astrophysics, report that a spectrum (range 350-740 nm) of SN 2006bk (cf. CBET 462, CBET 475), obtained on Apr. 21.31 UT by W. Peters with the F. L. Whipple Observatory 1.5-m telescope (+ FAST), shows it to be a type-Ia supernova, roughly three weeks past maximum light. SN 2006bk was classified as a type-Ic supernova around maximum light in CBET 475, on the basis of a "W-shaped" feature around 500 nm. This feature is due to unresolved blends of Fe II lines, and is common to both type-Ia and type-Ic post-maximum spectra -- hence the possible confusion. However, cross-correlation with a library of supernova spectra shows that SN 2006bk is similar to the type-Ia supernova 1997br at 21 days past maximum. The best-match type-Ic spectrum is that of SN 1990B at 28 days past maximum; however, it does not concur well with all the spectral features of SN 2006bk. A comparison plot can be seen at the following URL: http://cfa-www.harvard.edu/oir/Research/supernova/ spectra/sn2006bk_comp.gif Blondin et al. add that another spectrum of SN 2006bk, obtained on Apr. 23.33 by J. Hernandez (University of Michigan), shows the spectrum to be similar to the type-Ia supernova 2000fa several weeks past maximum, which confirms that SN 2006bk is a type-Ia supernova. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2006 CBAT 2006 April 27 (CBET 488) Daniel W. E. Green