Electronic Telegram No. 554 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 2006dd IN NGC 1316 S. Immler, Goddard Space Flight Center, NASA, and Universities Space Research Association; P. Milne, Steward Observatory, University of Arizona; and P. J. Brown, Pennsylvania State University -- on behalf of the Swift-satellite team -- report on Swift Ultraviolet/Optical Telescope (UVOT) and X-Ray Telescope (XRT) observations of SN 2006dd (cf. CBET 553) obtained on June 20.71 UT. They confirm, via comparison to Digitized Sky Survey images, the detection of a new object at R.A. = 03h22m41s.64, Decl. = -37o12'13".2 (equinox 2000.0), consistent with the position reported by Monard on CBET 553; the following UVOT magnitudes were measured for 2006dd (statistical and systematic errors are 0.1 mag each): V = 14.0 (167-s exposure), B = 14.5 (259 s), U = 13.7 (258 s), UVW1 [181-321 nm] = 15.5 (520 s), UVM2 [166-268 nm] = 17.9 (881 s), and UVW2 [112-264 nm] = 18.1 (881 s). Comparison to the photometry obtained on June 20.158 (B = 14.66, V = 14.41, from CBET 553) shows that the supernova is still pre-maximum. The B-V and U-B colors are similar to those of SN 2006bp (type II-P) before maximum (Immler and Brown, http://www.astronomerstelegram.org/?read=793). Furthermore, comparison of the colors with other supernovae from Poznanski et al. (2002, PASP 114, 833) indicates that 2006dd is a young type-II supernova before or around maximum. No x-ray source is detected at the position of 2006dd in a simultaneous 4100-s XRT observation. The 3-sigma upper limit to the XRT net count rate is 8.0 x 10^(-3) counts/s, corresponding to a (0.2- to 10-keV) x-ray flux and luminosity of < 4.0 x 10^(-13) ergs/cm/cm/s and < 2.9 x 10^(40) ergs/s, respectively, for an adopted thermal plasma spectrum with a temperature of kT = 10 keV, a Galactic foreground column density of N_H = 1.89 x 10^(20) (Dickey and Lockman, 1990, ARAA 28, 215), and a distance of 24.5 Mpc (z = 0.00587; Longhetti et al. 1998, A.Ap. Suppl. 130, 267, via NED). No further Swift observations are scheduled due to sun-angle constraints. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2006 CBAT 2006 June 21 (CBET 554) Daniel W. E. Green