Evidence for sub-Chandrasekhar-mass progenitors of Type Ia supernovae at the faint end of the width-luminosity relation

Stéphane Blondin; Luc Dessart; D. John Hillier; Alexei M. Khokhlov

doi:10.1093/mnras/stw2492

paper

Evidence for sub-Chandrasekhar-mass progenitors of Type Ia supernovae at the faint end of the width-luminosity relation

arXiv:1706.01901 · doi:10.1093/mnras/stw2492

Abstract

The faster light-curve evolution of low-luminosity Type Ia supernovae (SNe Ia) suggests that they could result from the explosion of white dwarf (WD) progenitors below the Chandrasekhar mass ( $M_{Ch}$ ). Here we present 1D non-LTE time-dependent radiative transfer simulations of pure central detonations of carbon-oxygen WDs with a mass ($M_\rm{tot}$) between 0.88 M $_{⊙}$ and 1.15 M $_{⊙}$ , and a $^{56} Ni$ yield between 0.08 M $_{⊙}$ and 0.84 M $_{⊙}$ . Their lower ejecta density compared to $M_{Ch}$ models results in a more rapid increase of the luminosity at early times and an enhanced $γ$ -ray escape fraction past maximum light. Consequently, their bolometric light curves display shorter rise times and larger post-maximum decline rates. Moreover, the higher $M(^{56}\rm{Ni})/M_\rm{tot}$ ratio at a given $^{56} Ni$ mass enhances the temperature and ionization level in the spectrum-formation region for the less luminous models, giving rise to bluer colours at maximum light and a faster post-maximum evolution of the $B - V$ colour. For sub- $M_{Ch}$ models fainter than $M_{B} \approx - 18.5$ mag at peak, the greater bolometric decline and faster colour evolution lead to a larger $B$ -band post-maximum decline rate, $Δ M_{15} (B)$ . In particular, all of our previously-published $M_{Ch}$ models (standard and pulsational delayed detonations) are confined to $Δ M_{15} (B) < 1.4$ mag, while the sub- $M_{Ch}$ models with $M_\rm{tot}\lesssim 1$ M $_{⊙}$ extend beyond this limit to $Δ M_{15} (B) \approx 1.65$ mag for a peak $M_{B} \approx - 17$ mag, in better agreement with the observed width-luminosity relation (WLR). Regardless of the precise ignition mechanism, these simulations suggest that fast-declining SNe Ia at the faint end of the WLR could result from the explosion of WDs whose mass is significantly below the Chandrasekhar limit.

10 pages, 6 figures. Accepted for publication in MNRAS

Evidence for sub-Chandrasekhar-mass progenitors of Type Ia supernovae at the faint end of the width-luminosity relation

Abstract

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