2010CBET.2476....1V

J. Vinko, University of Szeged; J. C. Wheeler and E. Chatzopoulos, University of Texas; and G. H. Marion, Harvard-Smithsonian Center for Astrophysics and University of Texas, report that a spectrogram, obtained on Sept. 30.15 UT with the 9.2-m Hobby-Eberly Telescope (+ Marcario Low- Resolution Spectrograph) by J. Caldwell, confirms the previous finding by Cenko et al. (CBET 2461) that 2010hy is a type-Ic supernova. SNID (Blondin and Tonry 2007, Ap.J. 666, 1024) indicates that the spectrum of 2010hy is most similar to those of SN 2004aw within a few days of maximum light. The features of Mg II at 448.1 nm, the Fe II "W" feature around 500 nm, and Si II 635.5-nm can be unambigously identified. O I at 777.4 nm and the Ca II near- infrared triplet may be present but heavily contaminated by telluric lines and buried by noise. The average redshift from these supernova features is z = 0.19. Because SN 2010hy presumably brightened since its discovery before maximum (Sept. 4 at unfiltered CCD mag 19.1), this redshift value indicates a peak absolute magnitude brighter than -20.4. SN 2010hy is very probably an overluminous event, similar to SN 2007bi, which was suggested as a possible pair-instability supernova explosion (Gal-Yam et al. 2009, Nature 462, 624).