* Astronomy

Title: Spectroscopic Observations of SN 2012fr: A Luminous Normal Type Ia Supernova with Early High Velocity Features and Late Velocity Plateau
Authors: M. J. Childress, R. A. Scalzo, S. A. Sim, B. E. Tucker, F. Yuan, B. P. Schmidt, S. B. Cenko, J. M. Silverman, C. Contreras, E. Y. Hsiao, M. Phillips, N. Morrell, S. W. Jha, C. McCully, A. V. Filippenko, J. P. Anderson, S. Benetti, F. Bufano, T. de Jager, F. Forster, A. Gal-Yam, L. Le Guillou, K. Maguire, J. Maund, P. A. Mazzali, G. Pignata, S. Smartt, J. Spyromilio, M. Sullivan, F. Taddia, S. Valenti, D. D. R. Bayliss, M. Bessell, D. J. Carson, K. I. Clubb, C. de Burgh-Day, T. D. Desjardins, J. J. Fang, O. D. Fox, E. L. Gates, I-T. Ho, S. Keller, P. L. Kelly, C. Lidman, N. S. Loaring, J. R. Mould, M. Owers, S. Ozbilgen, L. Pei, M. B. Pracy, B. E. Schaefer, N. Scott, M. Stritzinger, F. P. A. Vogt, G. Zhou

We present spectroscopic observations of the Type Ia supernova SN 2012fr, comprising 50 optical spectra, of which 29 were obtained before maximum light, and five near infrared spectra. At early times SN 2012fr shows clear evidence of a high velocity feature (HVF) in the Si II 6355 line which can be cleanly decoupled from the lower velocity photospheric component. This Si II 6355 HVF fades by phase -5, then the photospheric component exhibits a very narrow velocity width and remains at a nearly constant velocity of v~12,000 km/s until at least 5 weeks post-maximum. The Ca II NIR triplet exhibits similar evidence for both a photospheric component at v~12,000 km/s with narrow line width and long velocity plateau, as well as a high velocity component beginning at v~32,000 km/s two weeks before maximum. SN 2012fr resides on the border between the "shallow silicon" and "core-normal" subclasses in the Branch et al. (2009) classification scheme, and on the border between normal and "high-velocity" SNe Ia in the Wang et al. (2009a) system. Though it is a clear member of the "low velocity gradient" (LVG - Benetii et al., 2005) group of SNe Ia and exhibits a very slow light curve decline, it shows key dissimilarities with the overluminous SN 1991T or SN 1999aa subclasses of SNe Ia. SN 2012fr represents a well observed SN Ia at the luminous end of the normal SN Ia distribution, and a key transitional event between nominal spectroscopic subclasses of SNe Ia.

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