2014/01/31 by Subo Dong, Boaz Katz, Doron Kushnir +1 · 1 citation
Physics and Astronomy · #astro-ph.HE #astro-ph.SR
paper · pdf · doi:10.1093/mnrasl/slv129
published as MNRAS (November 21, 2015) 454 (1): L61-L65 · To be published by MNRAS Letters. Minor changes of the main text, an Appendix added
arxiv created 2015/09/01 · arxiv updated 2015/10/05
We discover clear doubly-peaked line profiles in 3 out of ~20 type Ia supernovae (SNe Ia) with high-quality nebular-phase spectra. The profiles are consistently present in three well-separated Co/Fe emission features. The two peaks are respectively blue-shifted and red-shifted relative to the host galaxies and are separated by ~5000 km/s. The doubly-peaked profiles directly reflect a bi-modal velocity distribution of the radioactive Ni56 in the ejecta that powers the emission of these SNe. Due to their random orientations, only a fraction of SNe with intrinsically bi-modal velocity distributions will appear as doubly-peaked spectra. Therefore SNe with intrinsic bi-modality are likely common, especially among the SNe in the low-luminosity part on the Philips relation (Δm15(B) >~ 1.3; ~40% of all SNe Ia). Such bi-modality is naturally expected from direct collisions of white dwarfs (WDs) due to the detonation of both WDs and is demonstrated in a 3D 0.64 MSun-0.64 MSun WD collision simulation. In the future, with a large sample of nebular spectra and a comprehensive set of numerical simulations, the collision model can be unambiguously tested as the primary channel for type Ia SNe, and the distribution of nebular line profiles will either be a smoking gun or rule it out.