Aspherical Remnants of Triple and Quadruple Detonations in Binary White Dwarfs

TL;DR

This work addresses how to identify the detonation channel in binary white dwarf explosions by examining the remnant phase of triple and quadruple detonations and comparing them to double detonations with a surviving donor. It uses 3D hydrodynamic simulations with the Sprout code, evolving ejecta fields derived from BTS24 models in a uniform ISM across a range of donor configurations, and analyzes forward/reverse shocks and X-ray emission proxies over remnant ages from ~10 to ~3000 years. The results show that the donor wake and the donor-derived inner shell imprint distinctive asymmetries in the forward and reverse shocks, and that triple/quadruple detonations produce larger remnants with asymmetric iron-line and continuum emission patterns, especially in the southern hemisphere. The findings suggest that X-ray observations with XRISM Resolve can help distinguish detonation channels in galactic remnants, providing a new diagnostic of explosion physics, while acknowledging limitations from 2D ignition symmetry and neglected helium-shell ejecta and pointing to future work in fully 3D detonations and varied ISM conditions.

Abstract

White dwarfs which explode by the double-detonation mechanism may have a binary white dwarf donor which is subsequently ignited by its collision with the ejecta. This results in the destruction of the donor via either the triple- or quadruple-detonation mechanism, adding significant mass to the resulting ejecta as well as modifying its structure and composition. We simulate the evolution of supernova remnants resulting from such detonations in a variety of binary progenitors and compare them against a double detonation with a surviving donor. Because of the time delay between the detonations of the two white dwarfs, high-velocity ejecta from the first explosion governs the first few centuries of remnant evolution, whereas at later times the dense core resulting from the donor detonation drives both the forward and reverse shocks to larger radii. The collision between the highest-velocity ejecta of the primary explosion and the donor carves a conical wake into the ejecta, which persists into the remnant phase regardless of whether or not the donor detonates. Our suite of simulated remnants are found to exhibit multiple distinguishing features of the explosion properties: a distinct X-ray morphology in the thermal emission and iron lines for triple detonations and smaller remnants with centrally-concentrated emission for double detonations. The remnants are also varied in their elemental abundances and distributions, particularly for lighter elements, but these have limited observational utility and are sensitive to the properties of the progenitor binary.

Figures (11)

• Figure 1: Density (left), temperature (center), and ratio of radiation to gas pressure (right) for the $1+0.7$$M_{\odot}$ model at $t\approx 1$ minute after detonation. The bow shock and dense inner shell of ejecta are visible, as well as the shock-heated wake. We also show the definition of $\theta$, with $\theta=0$ along the center of the wake.
• Figure 2: Radial profiles of the mass fractions $X_{i}$ along $\theta=90^{\circ}$ in the $1+0.7$$M_{\odot}$ model at $t\approx 1$ min. Notably, significant $^{56}$Ni is found only at $v<15{,}000$ km/s. Ejecta from the donor detonation is primarily found at $v<10{,}000$ km/s.
• Figure 3: (Top) Ratio of gas pressure to radiation pressure along $\theta=90^{\circ}$ in the $1+0.7$$M_{\odot}$ model, showing only the optically-thick ejecta ($\tau>c/v$) assuming complete ionization. The $^{56}$Ni-rich ejecta quickly heats to become radiation-pressure dominated. (Bottom) A measure of the homology of fluid parcels at various velocities. All ejecta with $v>1{,}000$ km/s maintains a ram pressure which exceeds the gas and radiation pressure by an order of magnitude.
• Figure 4: Density slices for each SNR on the $x=0$ plane at $t=13$, 42, 230, 1276, and 3000 yrs. The red dashed circles in the bottom row represent the spherical fits discussed in section \ref{['sec:forwardshock']}, with their centers marked by red diamonds.
• Figure 5: Forward shock radius vs angle at $t=31$ yr (top) and $t=3000$ yr (center) for $\rho_{\rm ISM}=6.31\times 10^{-25}$ g/cm$^{3}$. At early times, $r_{\rm FS}$ scales with the primary mass (outside of the wake), while at late times there is a bifurcation between the double detonations and the rest. (Bottom) Fractional variation of the FS radius from the spherical fit, measured from the center of the spherical fit $c_{\rm FS,s}$. The variation is most pronounced for the triple detonations, particularly at the equatorial plane. The legend is the same for all panels.