Nebular-phase spectra of Type Ia supernovae from the Las Cumbres Observatory Global Supernova Project

Abstract

The observed diversity in Type Ia supernovae (SNe Ia) – the thermonuclear explosions of carbon-oxygen white dwarf stars used as cosmological standard candles – is currently met with a variety of explosion models and progenitor scenarios. To help improve our understanding of whether and how often different models contribute to the occurrence of SNe Ia and their assorted properties, we present a comprehensive analysis of seven nearby SNe Ia. We obtained one to two epochs of optical spectra with Gemini Observatory during the nebular phase (>200 days past peak) for each of these events, all of which had time-series of photometry and spectroscopy at early times (the first ∼8 weeks after explosion). We use the combination of early- and late-time observations to assess the predictions of various models for the explosion (e.g., double-detonation, off-center detonation, stellar collisions), progenitor star (e.g., ejecta mass, metallicity), and binary companion (e.g., another white dwarf or a non-degenerate star). Overall, we find general consistency in our observations with spherically-symmetric models for SN Ia explosions, and with scenarios in which the binary companion is another degenerate star. We also present an in-depth analysis of SN 2017fzw, a member of the sub-group of SNe Ia which appear to be transitional between the subluminous “91bg-like” events and normal SNe Ia, and for which nebular-phase spectra are rare.

A JWST Near- and Mid-infrared Nebular Spectrum of the Type Ia Supernova 2021aefx

“…We identify nebular emission lines in the optical, NIR, and MIR spectra presented in this work using line identifications from the Atomic Line List 50 ; the Atomic-Infrared Space Observatory line list 51 ; previous optical line identifications by Graham et al (2022), Tucker et al (2022), and Wilk et al (2020; previous NIR line identifications by Diamond et al (2018), Dhawan et al (2018), Hoeflich et al (2021), and Mazzali et al (2015; previous MIR line identifications by Gerardy et al (2007) and Telesco et al (2015); and optical + NIR + MIR lines from models by Flörs et al (2020).…”

Serendipitous Nebular-phase JWST Imaging of SN Ia SN 2021aefx: Testing the Confinement of 56Co Decay Energy

“…38 http://svo2.cab.inta-csic.es/theory/fps3/ spectroscopic evolution of SNe Ia during this time span (e.g., Mazzali et al 2020;Tucker et al 2022a;Graham et al 2022). Our F2100W detection is unique because it was not covered by the spectrum obtained by Kwok et al (2022).…”

Near-infrared and Optical Nebular-phase Spectra of Type Ia Supernovae SN 2013aa and SN 2017cbv in NGC 5643

“…These optical spectra were obtained with the Gemini Multi-Object Spectrograph (GMOS; Hook et al 2004) on the 8.1 m Gemini South telescope and were reduced using the method presented in Graham et al (2017). Two GMOS spectra of SN 2013aa are presented in Graham et al (2017), and one GMOS spectrum of SN 2017cbv is presented in Graham et al (2022). Finally, we include two XShooter spectra of SN 2013aa published by Maguire et al (2018) and one LDSS-3 spectrum of SN 2017cbv published by Tucker et al (2020).…”

“…Thus, Maeda et al (2010a) adopted the simple two-Gaussian fit to determine the velocity shift, attributing the blue-side emission to [Fe II] λ7155 and the redside emission to [Ni II] λ7378. More recently, a six-Gaussian fit method emerged in an attempt to account for the line blending (e.g., Maguire et al 2018;Graham et al 2022). The six components included are four [Fe II] lines (λλ7155, 7172, 7388, and 7453) and two [Ni II] lines (λλ7378 and 7412).…”

“…However, the NIR [Fe II] velocity shifts measured using the ∼1.2 μm feature are consistently larger than those from the 1.644 μm feature, despite being measured from the same observed spectrum. This may be due to line blending and multi-Gaussian fit degeneracies that can affect measurement results (Graham et al 2022).…”