Electronic Telegram No. 1392 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 2008cs IN IRAS 17138-1017 Editor's Note: The text below replaces that on CBET 1391. E. Kankare and S. Mattila, Tuorla Observatory; S. Ryder, Anglo-Australian Observatory (AAO); A. Alonso-Herrero, T. Diaz Santos, and L. Colina Instituto de Estructura de la Materia (IEM), Consejo Superior de Investigaciones Cientificas (CSIC); J. Kotilainen, Tuorla Observatory; M.-A. Perez-Torres, Instituto de Astrofisica de Andalucia (IAA), CSIC; P. Vaisanen, South African Astronomical Observatory; A. Alberdi, IAA/CSIC; and A. Efstathiou, European University, Cyprus, report the discovery of an apparent supernova on near- infrared images of the luminous infrared galaxy IRAS 17138-1017 in the course of their infrared search program (cf. IAUCs 8473, 8474; CBET 858). The new object was detected in images obtained using the Altair/NIRI adaptive-optics system with "Laser Guide Star" on the Gemini-North Telescope on Apr. 21.6 and May 27.5 UT, via comparison with NICMOS images obtained with the Hubble Space Telescope (HST) on 2004 Sept. 23.0. SN 2008cs is located at R.A = 17h16m35s.85, Decl. = -10o20'43".0 (equinox 2000.0), which is 0".72 east and 4".19 south of the galaxy's K-band nucleus. Available magnitudes for 2008cs: 2004 Sept. 23.0, J = [22.0 (F110W HST filter; 0.8-1.4 microns), H = [21.0 (F160W HST filter; 1.4-1.8 microns), K = [18.5 (F187N HST filter; 1.87 microns); 2008 Apr. 21.6, K = 17.0 +/- 0.1; May 27.5, K = 16.0 +/- 0.1, H = 17.1 +/- 0.1. The light curve, absolute magnitude, and H-K color of 2008cs are consistent with a 'slowly declining' core-collapse supernova (Mattila and Meikle 2001, MNRAS 324, 325), similar to SNe 1998S and 1979C, having maximum light near the second-epoch observation and a high extinction of A(V) approximately 15. Infrared and radio follow-up observations of 2008cs are encouraged. M.-A. Perez-Torres, C. Romero and A. Alberdi, IAA/CSIC; L. Colina, A. Alonso-Herrero, and T. Diaz Santos, IEM/CSIC; S. Mattila and E. Kankare, Tuorla Observatory; and S. Ryder, AAO, report the detection of a compact component of radio emission in IRAS 17138-1017 at R.A. = 17h16m35s.853, Decl. = -10o20'43".05 (equinox 2000.0; estimated uncertainty 0".24 in each coordinate), using target-of-opportunity Very Large Array (VLA) observations at 1.3 cm obtained on May 19.4 UT. The flux density of this local radio maximum is 440 +/- 75 microJy. The position of the radio maximum is coincident (within 0".05 in each coordinate) with the transient near-infrared source reported by Kankare et al., above, which further suggests that this object is a supernova and, given its brightness, that it must be a core-collapse supernova in its early, rising phase, as also inferred from the near-infrared observations of Kankare et al. For an assumed distance of 75 Mpc to IRAS 17138-1017, the observed flux of 2008cs corresponds to a radio luminosity of (3.1 +/- 0.5) x 10^(27) erg/s/Hz. Since the radio supernova does not seem to have reached yet its maximum at wavelengths around and above 1.3 cm, further VLA observations of 2008cs at 1.3, 3.6, and 6 cm are planned to follow its time evolution and spectral evolution. Observations at other wavelengths are encouraged. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2008 CBAT 2008 June 3 (CBET 1392) Daniel W. E. Green