2009CBET.1901....1V

J. Vinko, University of Texas; F. Yuan, University of Michigan; H. Marion, University of Texas and Texas A&M University; R. Quimby, California Institute of Technology; D. Chamarro, M. D. Sisson, and C. Akerlof, University of Michigan; and J. C. Wheeler and E. Chatzopoulos, University of Texas, on behalf of the ROTSE collaboration, report the discovery of a type-Ia supernova (mag about 17.5) in unfiltered CCD images taken on July 22.25 UT with the 0.45-m ROTSE-IIIb telescope at McDonald Observatory. The transient, located at R.A. = 17:26:11.25, Decl. = +59:18:31.3 (equinox 2000.0; uncertainty < 1"), is 0".2 east and 0".2 north of the center of the galaxy SDSS J172611.22+591831.1 (z = 0.027, as measured by Sloan Digital Sky Survey). SN 2009ia was discovered by subtracting a reference image built from images taken in August 2007. A finding chart of 2009ia is posted at URL http://www.rotse.net/rsvp/j172611.3+591831/j172611.3+591831.jpg. An optical spectrum, obtained on Aug. 1.22 at McDonald Observatory with the 9.2-m Hobby-Eberly Telescope (+ Marcario Low-Resolution Spectrograph) by M. Shetrone, shows that 2009ia is a type-Ia supernova, but the spectrum looks peculiar. There is a strong, narrow H-alpha emission line superimposed on the supernova spectrum, which is consistent with the host galaxy, being a strong H-alpha emitter. The SiI I 635.5-nm and 580.0-nm features are both weak, suggesting a pre-maximum phase; their ratio is R(Si II) = 0.4, which is higher than the usual value of 0.1-0.3 for normal type-Ia events close to maximum light (Benetti et al. 2004, MNRAS 348, 261). The O I 777-nm feature is not detected. The Ca II infrared triplet is present but weak. According to the SuperNova IDentification (SNID) code, the spectrum most resembles those of SNe 2003du and 2002er at roughly 10 days before maximum, assuming a redshift of z = 0.03, which is consistent with that of the host galaxy. The ROTSE unfiltered light curve, however, does not show significant brightening after Aug. 1, thus, it does not support the spectroscopic age determination. The expansion velocity, calculated from the absorption minimum of the Si II 635.5-nm line, after correcting for host-galaxy redshift, is 11000 km/s.