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

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 SNe have slowly declining light curves (∆m 15 (B) <1.3 mag), and peak absolute B-band magnitudes between −19 < M B < −21 mag. Many 2003fg-like SNe are located in the same part of the luminosity width relation as normal SNe Ia. In the optical B and V bands, 2003fg-like SNe look like normal SNe Ia, but at redder wavelengths they diverge from normal objects. Unlike other luminous SNe Ia, 2003fg-like SNe generally have only one i-band maximum which peaks after the epoch of B-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 M H < −19 mag, and generally have negative Hubble residuals. Spectroscopically, 2003fg-like SNe exhibit peculiarities such as unburnt carbon well past maximum light, a large spread (8000-12000 km s −1 ) in Si ii λ6355 velocities at maximum light with no rapid early velocity decline, no clear H-band break at +10 d, and low ionization lines in the nebular phase. We find that SNe with a larger pseudo equivalent width of C ii at maximum light have lower Si ii λ6355 velocities and slower declining light curves. There are also multiple factors that contribute to the peak luminosity of 2003fg-like SNe. 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.

A Carbon/Oxygen-dominated Atmosphere Days After Explosion for the "Super-Chandrasekhar" Type Ia SN 2020esm

“…Finally, we used the luminosity distance to the SN to convert the integrated flux to luminosity. For the NIR wavelengths regime (10,000-24,000 Angstroms), we used bolometric corrections derived from SN 2009dc, which shows similar color evolution in the UV and optical bands (however, see Ashall et al (2021) for the variations at early NIR light curves of SC SNe Ia). Adding this NIR luminosity to our UV and optical one, we derive a total pseudo-bolometric UVOIR light curve, as a function of phase from B-band maximum, shown in Figure 11, with grey circles.…”

“…Many (but not all) SC SNe Ia do not conform to the WLR, generally having peak luminosities higher than expected for their decline rate. SC SNe Ia have slowly declining light curves, high early-time UV flux, an i-band primary maximum several days before the Bband maximum, a lack of a secondary maximum in the i and NIR bands, relatively hot photospheres, abnormally low ejecta velocities, a weak (or delayed) NIR H-band break, and relatively strong carbon features in peak-light spectra (Ashall et al 2021). Modeling their light curves in the same way as typical SNe Ia (Arnett 1982;Jeffery 1999), one finds that their total ejecta mass, and occasionally the 56 Ni mass alone, is in excess of the Chandrasekhar mass, M Ch ≈ 1.4 M (Scalzo et al 2010).…”

“…A merger of two WDs (Iben & Tutukov 1984;Webbink 1984) that exceed M Ch can naturally explain the high ejecta mass (Moll et al 2014), while increased luminosity at early times can be achieved with hydrogen-free circumstellar medium (CSM) of material ejected during the merger in the close vicinity of the system (Raskin & Kasen 2013;Raskin et al 2014;Noebauer et al 2016), however, an open question remains whether this binary configuration can lead to a type Ia explosion or an accretion induced collapse (see Marsh et al 2004;Saio & Nomoto 2004;Dan et al 2011;Shen et al 2012, for relevant discussions). On the other hand, Hsiao et al (2020), Ashall et al (2021) and Lu et al (2021) favor an explosion of a C-O degenerate core inside a carbon-rich envelope (Hoeflich & Khokhlov 1996), possibly under the "core-degenerate" scenario (Kashi & Soker 2011).…”

“…Throughout this paper, we will use the moniker SC SNe Ia to describe the members of the "super-Chandrasekhar" SNe Ia class. We note that, in the literature, different monikers have been proposed, such as 09dclike in Taubenberger et al (2019) and 03fg-like in Ashall et al (2021), however we choose to use the historical designation. Moreover, we adopt the AB magnitude system, unless where noted, and a Hubble constant of H 0 = 73 km s −1 Mpc −1 .…”

An imaging polarimetry survey of Type Ia supernovae: are peculiar extinction and polarization properties produced by circumstellar or interstellar matter?

“…The curves in PPNe are shown to be produced by CSM scattering (Oppenheimer et al 2005). Therefore, the common continuum polarization properties between PPNe and SNe Ia might be an indication that some SNe Ia explode within a PPN after the WD (formed from the initially more-massive star) merges with the core of the companion AGB star during the common-envelope phase (core-degenerate scenario, Kashi & Soker 2011; see also Jones & Boffin 2017;Soker 2019a,b;Chiotellis et al 2021;Hsiao et al 2020;Wu et al 2021;Ashall et al 2021).…”