Collapse of Magnetized White Dwarfs as site of Heavy Element Formation and Kilonova Signal

TL;DR

This study models the collapse of magnetized white dwarfs, showing they can produce neutron-rich ejecta and kilonova signals consistent with observations, thus serving as sites for heavy element formation and gamma-ray burst progenitors.

Contribution

It provides the first comprehensive simulation linking magnetized white dwarf collapse to observable kilonovae, highlighting the role of magnetic fields in heavy element synthesis.

Findings

Magnetized white dwarf collapse ejects neutron-rich material enabling r-process nucleosynthesis.

Resulting kilonovae are lanthanide-rich and match observed light curves of AT 2023vfi/GRB 230307A.

Magnetized AIC is a viable source of heavy elements and long-duration gamma-ray burst progenitors.

Abstract

We present the first end-to-end calculation connecting the accretion-induced collapse (AIC) of a magnetized, rapidly rotating white dwarf to observable kilonova signatures, combining 2D general-relativistic neutrino-magnetohydrodynamic simulations, followed by radiation hydrodynamics with in-situ nuclear network and 2D Monte Carlo radiative transfer with spatially resolved heating rates. Unlike all previous unmagnetized AIC models - which predicted proton-rich, $^{56}$Ni-dominated ejecta - strong magnetic fields eject ${\sim 0.2 M_\odot}$ of neutron-rich material $(\langle Y_e \rangle \sim 0.24)$ on dynamical timescales, before neutrino irradiation can raise the electron fraction, enabling strong $r$-process nucleosynthesis up to and beyond the third peak. The resulting kilonova is lanthanide-rich $(X_{\rm lan} \approx 6\%)$ and dominated by near-infrared emission. We compute synthetic light curves in the LSST and JWST bands and find striking agreement, without parameter tuning, between the observations of AT 2023vfi/GRB 230307A and our broadband light curves for polar viewing angles. These results establish magnetized AIC as a viable channel for heavy $r$-process element production and a compelling progenitor candidate for long-duration gamma-ray bursts with kilonova signatures.