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Discovery of a supernova ROTSE3 J231226+135449

ATel #1255; F. Yuan (U. Mich.), R. Quimby (Caltech), J. Aretakis, C. Akerlof (U. Mich.) and J. C. Wheeler (U. Texas) on behalf of the ROTSE collaboration
on 2 Nov 2007; 04:06 UT
Credential Certification: Fang Yuan (yuanfang@umich.edu)

Subjects: Optical, Nova, Supernovae

We report the discovery of a supernova, located at RA: 23:12:25.99, Dec: +13:54:49.3 (J2000, uncertainty <1"), in unfiltered CCD images taken by the 0.45m ROTSE-IIIb telescope at McDonald Observatory, Texas. The supernova is 0.1" east and 0.7" south from the center of galaxy 2MASX J23122598+1354503. It was discovered at ~17 mag (with poor seeing) on Oct 28.13 UT by subtracting a co-addition of images taken between Jul 15 and Aug 16(limiting mag about 19.6). On Oct 30.23 UT, it was observed at ~17.5 mag. A finding chart can be found at: http://www.rotse.net/transients/j2312+1355/index.html

A spectrum (420-890 nm) was obtained on November 1.22 UT with the 9.2m Hobby-Eberly Telescope (+ Marcario Low-Resolution Spectrograph) by J. Caldwell, V. Riley, and E. Terrazas. The data are heavily contaminated by galaxy light; however, we detect several broad features indicative of a Type Ia supernova. Specifically, an absorption trough is observed around 630-nm, which we identify as Si II 635.5. Correcting for the recession velocity using the host redshift from the SDSS, the expansion velocity derived from the minimum of this Si II feature is about 12,000 km/s.