2D simulations of the double-detonation model for thermonuclear transients from low-mass carbon-oxygen white dwarfs

Abstract

Thermonuclear explosions may arise in binary star systems in which a carbon-oxygen (CO) white dwarf (WD) accretes helium-rich material from a companion star. If the accretion rate allows a sufficiently large mass of helium to accumulate prior to ignition of nuclear burning, the helium surface layer may detonate, giving rise to an astrophysical transient. Detonation of the accreted helium layer generates shock waves that propagate into the underlying CO WD. This might directly ignite a detonation of the CO WD at its surface (an edge-lit secondary detonation) or compress the core of the WD sufficiently to trigger a CO detonation near the centre. If either of these ignition mechanisms works, the two detonations (helium and CO) can then release sufficient energy to completely unbind the WD. These 'double-detonation' scenarios for thermonuclear explosion of WDs have previously been investigated as a potential channel for the production of Type Ia supernovae from WDs of ∼1 M . Here we extend our 2D studies of the double-detonation model to significantly less massive CO WDs, the explosion of which could produce fainter, more rapidly evolving transients. We investigate the feasibility of triggering a secondary core detonation by shock convergence in low-mass CO WDs and the observable consequences of such a detonation. Our results suggest that core detonation is probable, even for the lowest CO core masses that are likely to be realized in nature. To quantify the observable signatures of core detonation, we compute spectra and light curves for models in which either an edge-lit or compression-triggered CO detonation is assumed to occur. We compare these to synthetic observables for models in which no CO detonation was allowed to occur. If significant shock compression of the CO WD occurs prior to detonation, explosion of the CO WD can produce a sufficiently large mass of radioactive iron-group nuclei to significantly affect the light curves. In particular, this can lead to relatively slow post-maximum decline. If the secondary detonation is edge-lit, however, the CO WD explosion primarily yields intermediate-mass elements that affect the observables more subtly. In this case, near-infrared observations and detailed spectroscopic analysis would be needed to determine whether a core detonation occurred. We comment on the implications of our results for understanding peculiar astrophysical transients including SN 2002bj, SN 2010X and SN 2005E.

Optical and near-IR observations of the faint and fast 2008ha-like supernova 2010ae

“…Past efforts to model sub luminous SNe Ia consist of edge-lit explosions where a helium layer is accreted onto either a subChandrasekhar or a Chandrasekhar mass carbon-oxygen white dwarf, and subsequently initiates a detonation (Livne 1990;Woosley & Weaver 1994;Livne & Arnett 1995) or a double detonation explosion (Fink et al 2010;Sim et al 2012;Townsley et al 2012). Within this realm, even less robust explosions could occur if the edge-lit explosion does not successfully unbind the white dwarf (Bildsten et al 2007;Shen et al 2010;Wang et al 2013a,b).…”

A progenitor binary and an ejected mass donor remnant of faint type Ia supernovae

“…According to hydrodynamic simulations the minimum mass of the WD should be ∼0.8 M , because carbon burning is not triggered for objects of much lower mass (Sim et al 2012). On the other hand, the WD must consist of carbon and oxygen to be able to explode as a SN Ia.…”

Producing Type Iax supernovae from a specific class of helium-ignited WD explosions

“…, Livne 1990;Woosley & Weaver 1994). Helium double-detonation subChandrasekhar mass explosions have previously been considered as promising explanations for standard SNe Ia (e.g., Branch et al 1995;Höflich & Khokhlov 1996), but modern models disagree over which known SNe, if any, these systems might produce (e.g., Fink et al 2007Fink et al , 2010Kromer et al 2010;Woosley & Kasen 2011;Sim et al 2012). In principle, there is no reason why some double-detonation events could not produce normal SNe Ia whilst other similar progenitor systems lead to SNe Iax.…”