Electronic Telegram No. 2224 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION CBAT Director: Daniel W. E. Green; Room 209; Dept. of Earth and Planetary Sciences; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbat@iau.org; cbatiau@eps.harvard.edu URL http://www.cfa.harvard.edu/iau/cbat.html SUPERNOVA 2010ay Further to CBET 2208, A. J. Drake, S. G. Djorgovski, A. Mahabal, M. J. Graham, and R. Williams, California Institute of Technology; J. L. Prieto, Carnegie Observatories; M. Catelan, Pontificia Universidad Catolica de Chile; E. C. Beshore and S. M. Larson, Lunar and Planetary Laboratory, University of Arizona; and E. Christensen, Gemini Observatory, report the CRTS discovery of an apparent supernova in unfiltered Catalina Sky Survey (CSS) images: SN 2010 UT R.A. (2000.0) Decl. Mag. 2010ay Mar. 17.38 12 35 27.19 +27 04 02.8 17.5 Further CSS magnitudes for 2010ay: Feb. 17.45 UT, [18.3; Mar. 5.45, 18.2. The supernova is not resolved from the galaxy in CSS images (it is located within an arcsecond of the host galaxy's center, perhaps slightly toward the northwest); however, the object matches the star forming galaxy SDSS J123527.19+270402.7 (the SDSS gunn magnitudes are u = 19.6, g = 19.0, r = 19.0, i = 18.7, z = 18.9, and the spectroscopic redshift is z = 0.067). A. V. Filippenko, J. M. Silverman, I. K. W. Kleiser, and A. J. L. Morton, University of California, Berkeley, report that inspection of CCD spectra (range 340-1000 nm), obtained on Mar. 22 UT with the 3-m Shane reflector (+ Kast) at Lick Observatory, shows that 2010ay is a broad-lined type-Ic supernova similar to SN 1998bw (e.g., Patat et al. 2001, Ap.J. 555, 900), probably within a few days of maximum brightness. The redshift of the host galaxy, determined from strong, narrow emission lines produced by H II regions in the host galaxy, is 0.067, in agreement with the SDSS redshift cited above. By far the most prominent feature is a very broad peak centered roughly at rest wavelength 515 nm. Given that such supernovae are sometimes associated with long-duration gamma-ray bursts (e.g., Woosley and Bloom 2006, ARAA 44, 507), a search for a possibly corresponding GRB in the weeks prior to discovery (Mar. 17) should be conducted. Further observations of the supernova are encouraged. J. Prieto, Carnegie Observatories, reports on a low-resolution spectrum (range 350-950 nm; resolution 0.3 nm) and images of 2010ay obtained with the du Pont 2.5-m telescope (+ WFCCD) at Las Campanas Observatory on Mar. 22.2 UT. The spectrum shows very broad spectral features characteristic of broad-line type-Ic supernovae around maximum light, confirming the classification by Filippenko et al., above. The Si II 635.5-nm absorption feature is detected in the supernova spectrum with a blueshifted velocity of 22600 km/s after correcting for the host-galaxy redshift. The spectrum is contaminated by strong, nebular emission lines ([O II], [O III], [N II] and the Balmer series) from the blue, star-forming dwarf host galaxy at z = 0.067, catalogued in the Sloan Digital Sky Survey as SDSS J123527.19+270402.7. Prieto obtained almost- simultaneous BVR photometry of the field with WFCCD. The magnitudes of the source, which include both supernova and host-galaxy flux and were calibrated using an SDSS star in the field, are B = 18.39, V = 17.61, R = 17.44 (uncertainty +/- 0.05 mag). After correcting for the distance modulus (mu = 37.4 mag for standard cosmology) and the estimated contamination from the host flux estimated from SDSS photometry (V = 19.0), an absolute magnitude of the supernova of Mv = -19.4 was obtained for 2010ay. This potentially makes it one of the most luminous broad-line type-Ic supernovae (see, e.g., Young et al. 2010, http://arxiv.org/abs/0910.2248; A.Ap., in press). The luminous nature of the event and star-forming dwarf host makes 2010ay an interesting target to search for radio emission, as was seen at late times in the broad- lined type-Ic supernova 2007bg (Prieto et al. 2009, posted at website URL http://www.astronomerstelegram.org/?read=2065). NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2010 CBAT 2010 March 23 (CBET 2224) Daniel W. E. Green