Delayed wind onset in Pa 30, the remnant of type Iax SN 1181

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 (${\sim }10^9~\mathrm{cm}~\mathrm{s}^{-1}$) 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 AD 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 $T_{\rm c} \simeq 6\times 10^8~\mathrm{K}$. 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.