OPTICAL AND ULTRAVIOLET OBSERVATIONS OF THE NARROW-LINED TYPE Ia SN 2012fr IN NGC 1365

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., Δ m 15 ( B ) =0.85 ± 0.05 mag). Based on the UV and optical light curves, we derived that a 56 Ni 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.