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

• 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 lambda 6355 line that can be cleanly decoupled from the lower velocity photospheric component. This Si 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 similar to 12,000 km s(-1) until at least five weeks after maximum brightness. The Ca II infrared triplet exhibits similar evidence for both a photospheric component at v approximate to 12,000 km s(-1) with narrow line width and long velocity plateau, as well as an HVF beginning at v approximate to 31,000 km s(-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.

Ämnesord

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

Nyckelord

galaxies: individual (NGC 1365)

supernovae: general

supernovae: individual (SN 2012fr)

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ref (ämneskategori)

art (ämneskategori)