Failed-Detonation Supernovae: Sub-Luminous Low-Velocity Ia Supernovae and Their Kicked Remnant White Dwarfs with Iron-Rich Cores

Abstract: Type Ia supernovae (SNe Ia) originate from the thermonuclear explosions of carbon-oxygen (C-O) white dwarfs (WDs). The single-degenerate scenario is a well-explored model of SNe Ia where unstable thermonuclear burning initiates in an accreting, Chandrasekhar-mass WD and forms an advancing flame. By several proposed physical processes the rising, burning material triggers a detonation, which subsequently consumes and unbinds the WD. However, if a detonation is not triggered and the deflagration is too weak to unbind the star, a completely different scenario unfolds. We explore the failure of the Gravitationally-Confined Detonation (GCD) mechanism of SNe Ia, and demonstrate through 2D and 3D simulations the properties of failed-detonation SNe. We show that failed-detonation SNe expel a few 0.1 solar masses of burned and partially-burned material and that a fraction of the material falls back onto the WD, polluting the remnant WD with intermediate-mass and iron-group elements, that likely segregate to the core forming an WD whose core is iron rich. The remaining material is asymmetrically ejected at velocities comparable to the escape velocity from the WD, and in response, the WD is kicked to velocities of a few hundred km/s. These kicks may unbind the binary and eject a runaway/hyper-velocity WD. Although the energy and ejected mass of the failed-detonation SN are a fraction of typical thermonuclear SNe, they are likely to appear as sub-luminous low-velocity SNe Ia. Such failed detonations might therefore explain or are related to the observed branch of peculiar SNe Ia, such as the family of low-velocity sub-luminous SNe (SN 2002cx/SN 2008ha-like SNe).