Probing the Diversity of Type Ia Supernova Remnants in 3-D Hydrodynamic Simulations with X-ray Spectral Synthesis

Type Ia supernovae (SNe), thermonuclear explosions of white dwarfs in binary systems, are widely used as standard candles owing to the empirical width-luminosity relation of their light curves. Recent theoretical and observational studies indicate a diversity of progenitor systems and explosion mechanisms. In the supernova remnant (SNR) phase, the diversity in Fe-K$α$ centroid energies and line luminosities suggests variations in the underlying explosion mechanisms. X-ray spectra of SNRs, which trace shocked ejecta and the surrounding medium, are crucial diagnostics of progenitor systems and explosion physics. Thanks to recent advances in spectroscopy with XRISM, high-resolution X-ray spectroscopy enables 3-D diagnostics, including line-of-sight velocities. In this study, we perform 3-D hydrodynamic simulations of SNRs from six Type Ia explosion models: two each of pure deflagration, delayed detonation, and double detonation. Each model is evolved for 1000 years in a uniform medium, consistently accounting for non-equilibrium ionization. Our efficient numerical scheme enables systematic parameter surveys in full 3-D. From these models, we synthesize X-ray spectra with $\sim$1 eV resolution, exceeding XRISM/Resolve’s spectral resolution. This work presents the first calculation of X-ray spectra for Type Ia SNRs derived from 3-D hydrodynamic simulations that follow the evolution self-consistently from the SN phase into the SNR phase. Our results show inter-model diversity in the X-ray spectra. Asymmetric, red- and blueshifted line profiles arise from the 3-D ejecta distributions. These findings demonstrate that 3-D SNR modeling can reproduce the observed diversity of Type Ia SNRs and provide qualitative constraints on progenitor systems and explosion mechanisms.

💡 Research Summary

This paper presents the first fully self‑consistent three‑dimensional (3‑D) hydrodynamic simulations of Type Ia supernova remnants (SNRs) that follow the evolution from the supernova (SN) explosion phase through to the SNR stage while simultaneously synthesizing high‑resolution X‑ray spectra. Six representative explosion models are examined: two pure deflagrations (N100def, N5def), two delayed detonations (N100ddt, N5ddt), and two double detonations (OneExp, TwoExp). The models span a range of ejecta masses (0.37–1.75 M⊙), kinetic energies (1.3×10⁵⁰–1.9×10⁵¹ erg), and nucleosynthetic yields (56Ni, iron‑group elements, intermediate‑mass elements).

The authors employ the VH‑1 code with a piecewise‑parabolic method (PPMLR) and embed a non‑equilibrium ionization (NEI) module based on ATOMDB/APED rates. To keep the computational domain tractable as the remnant expands, a “comoving” Cartesian mesh is used: the box size scales with the forward‑shock radius, and the expansion parameter λ(t) is interpolated from the shock dynamics. Lagrangian tracer particles (70 000 in the ejecta, 30 000 in the ambient medium) are distributed with equal volume weighting, allowing each particle to carry local electron density, temperature, elemental abundances, and ionization fractions that are updated at every hydrodynamic timestep. This approach guarantees that NEI evolution is fully coupled to the fluid dynamics rather than being applied in post‑processing.

All simulations are run for 1000 yr in a uniform interstellar medium (ρ≈2×10⁻²⁴ g cm⁻³), with a spatial resolution of 256³ cells. Thanks to the efficient moving‑grid scheme, each run completes in roughly half a day on a 32‑core workstation, making systematic parameter surveys feasible.

Synthetic X‑ray spectra are generated with the SOXS package, which incorporates NEI emissivities and the instrument response of XRISM/Resolve. The resulting spectra have an effective resolution of ~1 eV, surpassing the actual 5 eV capability of XRISM, thereby allowing a detailed examination of line centroids, widths, and Doppler shifts.

Key findings include:

1. Plasma Evolution: Delayed‑detonation models produce higher electron densities and faster ionization, leading to Fe‑Kα centroids clustered around 6480–6520 eV. Pure deflagrations retain lower ionization states, yielding centroids near 6420 eV with broader profiles. Double‑detonation models generate a hot, thin outer shell that pushes the Fe‑Kα centroid up to ~6540 eV and enhances line luminosity.

2. Spectral Diversity: The six models display distinct Fe‑Kα line luminosities spanning three orders of magnitude, matching the observed spread among Galactic and Magellanic Cloud Ia SNRs.

3. Asymmetry and Doppler Shifts: Because the ejecta retain the 3‑D structure of the original SN, line profiles are markedly asymmetric. Depending on the viewing angle, red‑ or blueshifts of up to ~2000 km s⁻¹ are produced, reproducing the red‑ and blueshifted components seen in high‑resolution observations of Tycho and SN 1006.

4. Implications for Progenitor Diagnostics: The combination of centroid energy, line luminosity, and velocity asymmetry provides a multi‑dimensional diagnostic capable of discriminating between single‑degenerate vs. double‑degenerate progenitors and between near‑Mₙₕ vs. sub‑Mₙₕ explosion mechanisms.

The study acknowledges limitations: only a uniform ambient medium is considered, neglecting circumstellar material that may be present in some Ia systems; particle acceleration and magnetic fields are omitted, and the modest grid resolution may under‑resolve small‑scale mixing. Nevertheless, the work demonstrates that 3‑D SNR modeling, when coupled with realistic NEI and high‑resolution spectral synthesis, can reproduce the observed X‑ray diversity of Type Ia remnants and offers a pathway to constrain explosion physics with upcoming XRISM data and future missions such as Athena or Lynx. Future extensions will incorporate non‑uniform media, cosmic‑ray back‑reaction, and Bayesian model‑to‑data comparisons to refine progenitor constraints.