2008CBET.1462....2C

R. Chornock, A. A. Miller, D. A. Perley, and J. S. Bloom, University of California, Berkeley, report on further spectroscopic observations of the 2008es, observing the object for 840 s using the Low-Resolution Imaging Spectrometer (Oke et al. 1995, PASP 107, 375) on the Keck I 10-m telescope on Aug. 3.25 UT. The initial observations of this object (reported at the following website URL: http://www.astronomerstelegram.org/?read=1576) showed a blue and largely featureless spectrum, but at later epochs several unidentified weak spectral features appeared (ibid.,/?read=1576, 1593). The object now has developed a prominent broad (FWHM about 10000 km/s) emission feature centered near 790 nm, which is identified as H-alpha near redshift 0.2. The spectrum shows several other P-Cyg absorption features consistent with higher-order Balmer lines and Fe II at a similar redshift, leading to the conclusion that the object is a type-II supernova. Application of the "SuperNova IDentification" code (Blondin and Tonry 2007, Ap.J. 666, 1024) to this spectrum confirms the identification as a type-II supernova and gives a best-fit redshift of z = 0.206 ± 0.005. At this redshift, the peak apparent optical magnitude of around 17.8 (see text by Yuan et al., above) corresponds to an absolute magnitude of M_V less-than- or-equal-to -22.2, making this object one of the most luminous supernovae ever observed, comparable to, if not brighter than, the extreme supernova 2006gy (Smith et al. 2007, Ap.J. 666, 1116; Ofek et al. 2007, Ap.J. 659, L13). Chornock et al. thank M. Malkan (UCLA) for the exchange of observing time.