The detonation of a sub-Chandrasekhar-mass white dwarf at the origin of the low-luminosity Type Ia supernova 1999by

Understand

While Chandrasekhar-mass ($M_{\rm Ch}$) models with a low $^{56}\rm{Ni}$ yield can match the peak luminosities of fast-declining, 91bg-like Type Ia supernovae (SNe Ia), they systematically fail to reproduce their faster light-curve evolution.

• Here we illustrate the impact of a low ejecta mass on the radiative display of low-luminosity SNe Ia, by comparing a sub-$M_{\rm Ch}$ model resulting from the pure central detonation of a C-O White Dwarf (WD) to a $M_{\rm Ch}$ delayed-detonation model with the same $^{56}\rm{Ni}$ yield of 0.12 M$_{\odot}$.
• Our sub-$M_{\rm Ch}$ model from a 0.90 M$_{\odot}$ WD progenitor has a $\sim$5 day shorter rise time in the integrated UV-optical-IR (uvoir) luminosity, as well as in the $B$-band, and a $\sim$20 per cent higher peak uvoir luminosity ($\sim$1 mag brighter peak $M_B$).
• This sub-$M_{\rm Ch}$ model also displays bluer maximum-light colours due to the larger specific heating rate, and larger post-maximum uvoir and $B$-band decline rates.