Optical and ultraviolet observations of the narrow-lined type Ia SN 2012fr in NGC 1365

Abstract

Extensive optical and ultraviolet (UV) observations of the type Ia supernova (SN Ia) 2012fr are presented in this paper. It has a relatively high luminosity, with an absolute B-band peak magnitude of about -19.5 mag and a smaller post-maximum decline rate than normal SNe Ia (e.g., Δm 15(B) =0.85 ± 0.05 mag). Based on the UV and optical light curves, we derived that a 56Ni mass of about 0.88 M⊙ was synthesized in the explosion. The earlier spectra are characterized by noticeable high-velocity features of Si II λ6355 and Ca II with velocities in the range of ∼22, 000-25, 000 km s-1. At around the maximum light, these spectral features are dominated by the photospheric components which are noticeably narrower than normal SNe Ia. The post-maximum velocity of the photosphere remains almost constant at ∼12,000 km s -1 for about one month, reminiscent of the behavior of some luminous SNe Ia like SN 1991T. We propose that SN 2012fr may represent a subset of the SN 1991T-like SNe Ia viewed in a direction with a clumpy or shell-like structure of ejecta, in terms of a significant level of polarization reported in Maund et al. in 2013. © 2014. The American Astronomical Society. All rights reserved.