paper

Carnegie Supernova Project: The First Homogeneous Sample of "Super-Chandrasekhar Mass"/2003fg-like Type Ia Supernova

arXiv:2106.12140 · doi:10.3847/1538-4357/ac19ac

Abstract

We present a multi-wavelength photometric and spectroscopic analysis of thirteen "Super-Chandrasekhar Mass"/2003fg-like type Ia Supernova (SNe~Ia). Nine of these objects were observed by the Carnegie Supernova Project. 2003fg-like have slowly declining light curves ((B) 1.3 mag), and peak absolute -band magnitudes between ~mag. Many 2003fg-like are located in the same part of the luminosity width relation as normal SNe~Ia. In the optical and bands, 2003fg-like look like normal SNe~Ia, but at redder wavelengths they diverge. Unlike other luminous SNe~Ia, 2003fg-like generally have only one -band maximum which peaks after the epoch of -band maximum, while their NIR light curve rise times can be 40 days longer than those of normal SNe~Ia. They are also at least one magnitude brighter in the NIR bands than normal SNe~Ia, peaking above ~mag, and generally have negative Hubble residuals, which may be the cause of some systematics in dark energy experiments. Spectroscopically, 2003fg-like exhibit peculiarities such as unburnt carbon well past maximum light, a large spread (8000--12000~km/s) in SiII 6355 velocities at maximum light with no rapid early velocity decline, and no clear -band break at +10~d, e. We find that SNe with a larger pseudo equivalent width of CII at maximum light have lower SiII 6355 velocities and slower declining light curves. There are also multiple factors that contribute to the peak luminosity of 2003fg-like. The explosion of a C-O degenerate core inside a carbon-rich envelope is consistent with these observations. Such a configuration may come from the core degenerate scenario.

Accepted for publication in ApJ

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