SPECTROSCOPIC OBSERVATIONS OF SN 2012fr: A LUMINOUS, NORMAL TYPE Ia SUPERNOVA WITH EARLY HIGH-VELOCITY FEATURES AND A LATE VELOCITY PLATEAU

• Published in: The Astrophysical journal Vol. 770; no. 1; pp. 1 - 20
• Main Authors: Childress, M J, Scalzo, R A, Sim, S A, Tucker, B E, Yuan, F, Schmidt, B P, Cenko, S B, Silverman, J M, Contreras, C, Hsiao, E Y
• Format: Journal Article
• Language: English
• Published: United States 10-06-2013
• Subjects: ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Asymptotic properties; Borders; BRIGHTNESS; Constants; GALAXIES; galaxies: individual (NGC 1365); Infrared; LINE WIDTHS; SILICON; SPECTRA; Spectroscopy; SUPERNOVAE; supernovae: general; supernovae: individual (SN 2012fr); Supernovas; TRIPLETS; VELOCITY
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.1088/0004-637X/770/1/29

We present 65 optical spectra of the Type Ia SN 2012fr, 33 of which were obtained before maximum light. At early times, SN 2012fr shows clear evidence of a high-velocity feature (HVF) in the Si II [lambda]6355 line that can be cleanly decoupled from the lower velocity "photospheric" component. This Si II [lambda]6355 HVF fades by phase -5; subsequently, the photospheric component exhibits a very narrow velocity width and remains at a nearly constant velocity of ~12,000 km s super(-1) until at least five weeks after maximum brightness. The Ca II infrared triplet exhibits similar evidence for both a photospheric component at [upsilon] [asymptotically =] 12,000 km s super(-1) with narrow line width and long velocity plateau, as well as an HVF beginning at [upsilon] [asymptotically =] 31,000 km s super(-1) two weeks before maximum. SN 2012fr resides on the border between the "shallow silicon" and "core-normal" subclasses in the Branch et al. classification scheme, and on the border between normal and high-velocity Type Ia supernovae (SNe Ia) in the Wang et al. system. Though it is a clear member of the "low velocity gradient" 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.