Delayed Wind Onset in Pa 30, the Remnant of Type Iax SN 1181

TL;DR

The paper addresses why Pa 30, the remnant of the historical SN 1181, shows a wind onset centuries after explosion. It investigates delayed surface carbon ignition on an ONe WD caused by fallback CO-rich material forming an envelope, using MESA to evolve ONe WDs with attached CO envelopes across a grid of $M_{\rm ONe}$, $T_c$, $M_{\rm env,tot}$, and $R_{\rm env}$, tracking ignition via $L_{\rm nuc}>10^7 L_\odot$. The authors find that delays of ~800 years are possible in a broad parameter space, especially with $T_c\approx6\times10^8$ K, $M_{\rm env}\approx0.05 M_\odot$, and $M_{\rm WD}\approx1.1 M_\odot$, supporting a pure-deflagration SN Iax origin for SN 1181 and implying a surviving He-star companion. They discuss observational prospects to detect such a companion (inside or outside the wind photosphere) and note caveats about the wind-driving mechanism and the need for self-consistent fallback modeling. Overall, the work links the delayed wind in Pa 30 to the internal thermal state of the remnant WD and provides testable predictions for the progenitor system.

Abstract

Pa 30 is the recently identified remnant of the historical supernova SN 1181, likely a Type Iax event, and a nebula surrounding the central white dwarf launching a fast wind ($\sim10^9~\cm~\s^{-1}$) is observed in optical and infrared bands. X-ray observations show that this wind collides with the surrounding material and produces a termination shock, and the observed extent of the shock indicates that the wind started blowing centuries after 1181 A.D. rather than immediately after the SN explosion. We propose that the wind is triggered by delayed ignition of fallback carbon-rich material on the WD surface and investigate the conditions that reproduce such delayed ignition. We show that producing delays of several centuries requires a relatively hot post-explosion WD core with a temperature $T_c \simeq 6\times10^8~\mathrm{K}$. This supports the pure-deflagration progenitor scenario for Type Iax SN 1181, which implies the presence of a He star companion inside Pa~30; we also discuss why such a potential He star has not been detected and its prospects for discovery by future observations.

Figures (9)

• Figure 1: Decline rate $\Delta m_{15}$ versus peak absolute magnitude $M$ for normal SNe Ia and for the “bright” and “faint” subclasses of SNe Iax (reproduced from Fig. 11 of 2022MNRAS.511.2708S; filled/open symbols denote $r$/$R$). The red region marks SN 1181; its values are not measured in $r/R$ but inferred from historical visual (naked-eye) estimates: a peak $M\simeq-12.5$ to $-16$ mag 2021ApJ...918L..33R2023MNRAS.523.3885S. The SN 1181 region is placed on the $r/R$ plane for comparison only.
• Figure 2: Systematic diagram of the delayed-wind scenario examined in this work. In 1181 A.D. a Type Iax SN occurred. A fraction of the ejecta remained gravitationally bound and later fell back onto the central ONe WD. The fallback material formed an extended CO envelope on the WD surface, which eventually thermally contracts to reach higher temperatures and triggers carbon ignition, generating the energy necessary to launch the powerful wind. We model the evolution after the CO envelope has formed, up to the onset of surface carbon ignition.
• Figure 3: Initial radial profiles of density, temperature, and enclosed mass for representative models ($M_{\rm WD}=1.1\,M_\odot$, $M_{\rm env,tot} = 0.05~M_\odot$, $T_c=4\times10^8$ or $6\times10^8~\mathrm{K}$, $R_{\rm env}=1.0\times10^9$ or $2.0\times10^9\,\mathrm{cm}$). Dashed curves indicate the ONe composition of the central WD, and solid curves indicate the CO envelope.
• Figure 4: Time evolution of the temperature profile for an ONe WD with a CO envelope. Model 1 with $R_{\rm env}=2.0\times10^9~\mathrm{cm}$ (upper panels, ignition case) and $R_{\rm env}=1.0\times10^9~\mathrm{cm}$ (lower panels, non-ignition case). The ONe WD and CO envelope are distinguished in blue and red, respectively (dashed blue portions: regions with $X(^{12}\mathrm{C})\le 0.01$; solid red portions: $X(^{12}\mathrm{C})>0.01$).
• Figure 5: Time to carbon ignition at the surface of ONe WDs ($t_{\rm burn}$) as a function of the initial envelope expansion radius. Each panel compares different models by varying one of the key parameters: the ONe WD mass ($M_\mathrm{ONe}$), central temperature ($T_c$), and the carbon envelope mass ($M_\mathrm{env}$). The red shaded regions show the range for the delayed wind in Pa 30: although 2024ApJ...969..116K estimates the delayed time to be $\sim810-830$ yr, we conservatively highlight 600-800 year to allow for systematic uncertainties. These bands are for visual guides only.