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Discovery of a peculiar supernova ROTSE3 J163238.3+412733

ATel #1556; F. Yuan (U. Mich.), R. Quimby (Caltech), D. Chamarro, M. D. Sisson, C. Akerlof, (U. Mich.) and J. C. Wheeler (U. Texas) on behalf of the ROTSE collaboration
on 3 Jun 2008; 23:44 UT
Credential Certification: Fang Yuan (yuanfang@umich.edu)

Subjects: Optical, Supernovae, Transient

We report the discovery of a supernova, located at RA: 16:32:38.27 Dec: +41:27:33.2 (J2000, uncertainty <1 "), in unfiltered CCD images taken by the 0.45m ROTSE-IIIb telescope at McDonald Observatory, Texas. The supernova was discovered at ~18.5 mag on Jun. 1.33 UT. It is 1.3 " east and 2.4 " north from the center of a galaxy at z=0.032 measured by SDSS. A ROTSE-III finding chart can be found at: http://www.rotse.net/rsvp/j163238.3+412733/j163238.3+412733.jpg

A spectrum (420-890 nm) of the SN obtained on June 3.15 UT with the 9.2m Hobby-Eberly Telescope (+ Marcario Low-Resolution Spectrograph) by M. Shetrone and E. Terrazas shows it to be a supernova. The spectra are roughly similar to the peculiar Type Ib supernova SN 2005bf at 32 days before maximum light (Folatelli et al. 2006, ApJ 641,1039) except that the 560-nm to 600-nm region is more similar to the Type Ic SN 1994I around 5 days before maximum light (Filippenko et al. 1995, ApJ 450,L11). Specifically, an absorption trough is seen at about (z=0.03 restframe) 573-nm, which if identified with HeI/NaI would correspond to a blueshift of about 8000 km/s. A weak P-Cygni profile corresponding to the CaII IR triplet at this same velocity is also detected. The OI 777-nm feature is not detected, which is similar to SN 2005bf, but contamination from the host galaxy may help mask this feature and dilute the CaII IR triplet as well.