A JWST Medium Resolution MIRI Spectrum and Models of the Type Ia supernova 2021aefx at +415 d (2404.17043v2)

Abstract: We present a JWST MIRI/MRS spectrum (5-27 $\mathrm{\mu}$m) of the Type Ia supernova (SN Ia), SN 2021aefx at $+415$ days past $B$-band maximum. The spectrum, which was obtained during the iron-dominated nebular phase, has been analyzed in combination with previous JWST observations of SN 2021aefx, to provide the first JWST time series analysis of an SN Ia. We find the temporal evolution of the [Co III] 11.888 $\mathrm{\mu}$m feature directly traces the decay of $^{56}$Co. The spectra, line profiles, and their evolution are analyzed with off-center delayed-detonation models. Best fits were obtained with White Dwarf (WD) central densities of $\rho_c=0.9-1.1\times 10^9$g cm$^{-3}$, a WD mass of M${\mathrm{WD}}$=1.33-1.35M$\odot$, a WD magnetic field of $\approx10^6$G, and an off-center deflagration-to-detonation transition at $\approx$ 0.5 $M_\odot$ seen opposite to the line of sight of the observer (-30). The inner electron capture core is dominated by energy deposition from $\gamma$-rays whereas a broader region is dominated by positron deposition, placing SN 2021aefx at +415 d in the transitional phase of the evolution to the positron-dominated regime. The formerly `flat-tilted' profile at 9 $\mathrm{\mu}$m now has significant contribution from [Ni IV], [Fe II], and [Fe III] and less from [Ar III], which alters the shape of the feature as positrons excite mostly the low-velocity Ar. Overall, the strength of the stable Ni features in the spectrum is dominated by positron transport rather than the Ni mass. Based on multi-dimensional models, our analysis is consistent with a single-spot, close-to-central ignition with an indication for a pre-existing turbulent velocity field, and excludes a multiple-spot, off-center ignition.

• The paper presents the first JWST MIRI spectrum of a Type Ia supernova (SN 2021aefx) at +415 days, providing unprecedented insight into its late-time evolution.
• Analysis of the [Co III] emission line decay confirms persistent radioactive heating and helps constrain the mass of 56Ni produced in the explosion.
• Radiative transfer modeling supports an off-center delayed detonation scenario for SN 2021aefx, highlighting the significant role of positron transport on observed spectral features.

Analysis of "A JWST Medium Resolution MIRI Spectrum and Models of the Type Ia Supernova 2021aefx at +415~d"

The paper of Type Ia Supernovae (SNe Ia) serves as a critical area of research within astrophysics, advancing both our understanding of stellar evolution and our capacity to measure extragalactic distances. The paper "A JWST Medium Resolution MIRI Spectrum and Models of the Type Ia Supernova 2021aefx at +415~d" explores the analysis of SNe Ia, utilizing medium resolution spectra from the James Webb Space Telescope (JWST) to investigate the photometric and spectral properties of the supernova SN 2021aefx long after its peak brightness.

Key Findings

This paper provides an extensive analysis of SN 2021aefx, 415 days post B-band maximum brightness—a phase dominated by the slow decay of 56^Co to 56^Fe, leading to intricate spectral changes. Utilizing the Mid-Infrared Instrument (MIRI) on JWST—a first in the field—the authors observe and analyze mid-infrared spectra (5-27 microns) using the Medium Resolution Spectrometer (MRS), providing unprecedented insight into the supernova's physical conditions and nucleosynthesis processes at late times.

Spectral Analysis and Model Implications

1. Temporal Analysis and Spectral Evolution: The paper tracks the evolution of the forbidden [Co III] 11.888 µm emission line, finding its decay consistent with the half-life of 56^Co, thus confirming the persistence of radioactive heating in such late nebular stages. This resonance line offers a direct tracer of 56^Ni decay, providing constraints on the mass of 56^Ni and advancing our capability to measure supernova characteristics.
2. Model Validation and Physical Parameters: Through comprehensive radiative transfer models, this paper supports the hypothesis of an off-center delayed detonation scenario for SN 2021aefx with specific configurations: central densities around 0.9-1.1 × 10^9 g cm^-3 and a white dwarf mass close to the Chandrasekhar limit (1.33-1.35 M☉). Such modeling highlights the involvement of a high magnetic field (around 10^6 G), affecting positron transport and energy deposition, thereby shaping the spectral features observed.
3. Role of [Ni II], [Ni III], and [Fe II] Lines: The presence and strength of nickel and iron lines in the spectra indicate significant electron capture processes—a result typical of high-density environments in such supernovae. The paper confirmed that the nickel features were primarily influenced by positron transport, not the actual mass of nickel produced, a realization enabled by the high-resolution data from MRS.

Broader Implications

The paper underscores the observational power of JWST—a game-changing tool in the paper of the late stages of supernovae. By pushing observational boundaries into the mid-infrared, it provides critical data that enhance our theoretical astrophysical models. The findings illustrate the substantial role of nickel isotopes in late-stage emission spectra, refining our understanding of energy deposition processes and elemental synthesis in supernova remnants.

Future investigations, as proposed, aim to observe SN 2021aefx beyond 500 days to better probe the transition from a gamma-ray dominated regime to a positron-driven regime in such supernovae. This could open new avenues to paper the effects of initial magnetic fields on SNe Ia and further assess explosion asymmetries and progenitor scenarios.

In conclusion, this paper exemplifies a significant leap in our knowledge of Type Ia supernovae by showcasing advanced methodologies powered by JWST's MIRI/MRS, informing both theoretical models and observational strategies in supernova astrophysics. This paper presents a framework that can potentially resolve longstanding questions about the physical nature and diversity of Type Ia supernova explosions.