paper

SN 2012fr: Ultraviolet, Optical, and Near-Infrared Light Curves of a Type Ia Supernova Observed Within a Day of Explosion

arXiv:1803.10095 · doi:10.3847/1538-4357/aabaf8

Abstract

We present detailed ultraviolet, optical and near-infrared light curves of the Type Ia supernova (SN) 2012fr, which exploded in the Fornax cluster member NGC 1365. These precise high-cadence light curves provide a dense coverage of the flux evolution from 12 to 140 days with respect to the epoch of -band maximum (\tmax). Supplementary imaging at the earliest epochs reveals an initial slow, nearly linear rise in luminosity with a duration of 2.5 days, followed by a faster rising phase that is well reproduced by an explosion model with a moderate amount of Ni mixing in the ejecta. From an analysis of the light curves, we conclude: explosion occurred hours before the first detection of the supernova, the rise time to peak bolometric (Å) luminosity was days, the supernova suffered little or no host-galaxy dust reddening, the peak luminosity in both the optical and near-infrared was consistent with the bright end of normal Type Ia diversity, and of Ni was synthesized in the explosion. Despite its normal luminosity, SN 2012fr displayed unusually prevalent high-velocity \ion{Ca}{2} and \ion{Si}{2} absorption features, and a nearly constant photospheric velocity of the \ion{Si}{2} 6355 line at 12,000 \kms\ beginning 5 days before \tmax. Other peculiarities in the early phase photometry and the spectral evolution are highlighted. SN 2012fr also adds to a growing number of Type Ia supernovae hosted by galaxies with direct Cepheid distance measurements.

arXiv comment88 pages, 29 figures, 12 tables

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