2008CBET.1350....1Y

F. Yuan, University of Michigan; R. Quimby, California Institute of Technology; D. Chamarro, M. D. Sisson, and C. Akerlof, University of Michigan; and J. C. Wheeler, University of Texas, on behalf of the ROTSE collaboration, report the discovery of a supernova (mag about 17.2) in unfiltered CCD images taken on Apr. 19.21 UT with the 0.45-m ROTSE-IIIb telescope at McDonald Observatory. The new object is located at R.A. = 12h05m20s.98, Decl. = +40o56'45".6 (equinox 2000.0; uncertainty < 1"), which is 1".9 east and 1".2 north from the apparent host galaxy (which itself has magnitude r = 18.9 in the Sloan Digital Sky Survey catalogue). A finding chart of 2008by can be found at http://www.rotse.net/rsvp/j120521.0+405646/j120521.0+405646.jpg. Spectroscopy (420-890 nm) of 2008by, obtained on Apr. 22.10 with the 9.2-m Hobby-Eberly Telescope (+ Marcario Low-Resolution Spectrograph) by S. Rostopchin and V. Riley, shows it to be a type-Ia supernova. The spectra are similar to those of SN 2005cg at about five days after explosion (Quimby et al. 2006, Ap.J. 636, 400). Narrow emission lines of H-alpha and O III (likely from the host galaxy) indicate a redshift of z = 0.045.