Wait for It: Post-Supernova Winds Driven by Delayed Radioactive Decays

Abstract

In most astrophysical situations, the radioactive decay of 56 Ni to 56 Co occurs via electron capture with a fixed half-life of 6.1 days. However, this decay rate is significantly slowed when the nuclei are fully ionized because K-shell electrons are unavailable for capture. In this paper, we explore the effect of these delayed decays on white dwarfs (WDs) that may survive Type Ia and Type Iax supernovae (SNe Ia and SNe Iax). The energy released by the delayed radioactive decays of 56 Ni and 56 Co drives a persistent wind from the surviving WD's surface that contributes to the late-time appearance of these SNe after emission from the bulk of the SN ejecta has faded. We use the stellar evolution code MESA to calculate the hydrodynamical evolution and resulting light curves of these winds. Our post-SN Ia models conflict with late-time observations of SN 2011fe, but uncertainties in our initial conditions prevent us from ruling out the existence of surviving WD donors. Much better agreement with observations is achieved with our post-SN Iax bound remnant models, providing evidence that these explosions are due to deflagrations in accreting WDs that fail to completely unbind the WDs. Future radiative transfer calculations and wind models utilizing explosion simulations for more accurate initial conditions will extend our study of radioactively-powered winds from post-SN surviving WDs and enable their use as powerful discriminants among the various SN Ia and SN Iax progenitor scenarios.

Three-dimensional Simulation of Double Detonations in the Double-degenerate Model for Type Ia Supernovae and Interaction of Ejecta with a Surviving White Dwarf Companion

“…In general, when CO detonation passes a high-density region, it mostly synthesizes 56 Ni owing to the rapid nuclear reactions, and leaves a small amount of He as residuals of He produced by photo-dissociation. Shen & Schwab (2017) have estimated that a 0.6M WD captures 0.03M 56 Ni, which is consistent with our results.…”

Double-degenerate Carbon–Oxygen and Oxygen–Neon White Dwarf Mergers: A New Mechanism for Faint and Rapid Type Ia Supernovae

“…The ejecta is powered by a small amount of 56 Ni, and would be visible as a rapidly-fading optical transient, rich in intermediate-mass elements including Ca, with low velocities compared to normal Iaall properties of observed low-velocity SNe Ia. Moreover, recent work suggests that the hot, ionized fall-back 56 Ni will slowly decay, and power a longer-lived transient tail of the light curve (Shen & Schwab 2017), consistent with observations which indicate that SNe Iax fail to enter the nebular phase as in normal SNe Ia (Jha 2017).…”

“…We use parameters relevant to our model, with ejecta mass M c = 0.079 M and a 56 Ni mass 8.6 × 10 −3 M . The fallback 56 Ni will remain ionized and decay over much longer timescales (Shen & Schwab 2017), and is therefore not included in the computation of the light curve. The bolometric luminosity peaks around day 6 post-explosion, which is comparatively earlier than the typical SNe Ia peak time, approximately 20 days post-explosion (Riess et al 1999).…”

Double-detonation Models for Type Ia Supernovae: Trigger of Detonation in Companion White Dwarfs and Signatures of Companions’ Stripped-off Materials

“…The captured masses are 0.02M for He45, 0.03M for CO60He00 and CO60He06, and 0.06 -0.07M for CO90He00 and CO90He09. Shen & Schwab (2017) have analytically estimated that the captured masses are 0.006, 0.03, and 0.08M for companion WDs with 0.3, 0.6, and 0.9M , respectively. Our results are in good agreement with the Shen's estimate.…”