Type Ia supernovae from exploding oxygen-neon white dwarfs

Abstract

Context. The progenitor problem of Type Ia supernovae (SNe Ia) is still unsolved. Most of these events are thought to be explosions of carbon-oxygen (CO) white dwarfs (WDs), but for many of the explosion scenarios, particularly those involving the externally triggered detonation of a sub-Chandrasekhar mass WD (sub-M Ch WD), there is also a possibility of having an oxygen-neon (ONe) WD as progenitor. Aims. We simulate detonations of ONe WDs and calculate synthetic observables from these models. The results are compared with detonations in CO WDs of similar mass and observational data of SNe Ia. Methods. We perform hydrodynamic explosion simulations of detonations in initially hydrostatic ONe WDs for a range of masses below the Chandrasekhar mass (M Ch ), followed by detailed nucleosynthetic postprocessing with a 384-isotope nuclear reaction network. The results are used to calculate synthetic spectra and light curves, which are then compared with observations of SNe Ia. We also perform binary evolution calculations to determine the number of SNe Ia involving ONe WDs relative to the number of other promising progenitor channels. Results. The ejecta structures of our simulated detonations in sub-M Ch ONe WDs are similar to those from CO WDs. There are, however, small systematic deviations in the mass fractions and the ejecta velocities. These lead to spectral features that are systematically less blueshifted. Nevertheless, the synthetic observables of our ONe WD explosions are similar to those obtained from CO models. Conclusions. Our binary evolution calculations show that a significant fraction (3-10%) of potential progenitor systems should contain an ONe WD. The comparison of our ONe models with our CO models of comparable mass (∼1.2 M ) shows that the less blueshifted spectral features fit the observations better, although they are too bright for normal SNe Ia.

LATE-TIME PHOTOMETRY OF TYPE IA SUPERNOVA SN 2012cg REVEALS THE RADIOACTIVE DECAY OF 57Co

“…Model yields where the primary WD is significantly less massive than M Ch predict even lower 57 Ni/ 56 Ni ratios: the merger model of a 1.1M e CO WD with a 0.9M e CO WD of Pakmor et al (2012) predicts ∼1.1 times Solar and the pure detonation models of CO and ONe WDs of Marquardt et al (2015) predict around 0.3-0.5 times Solar. Parikh et al (2013) have found that the 57 Ni/ 56 Ni production ratio is very robust (at the 10% level) to individual changes of nuclear reaction rates by a factor of 10; rate uncertainties are therefore unlikely to solely account for the difference.…”

Thermonuclear detonations ensuing white dwarf mergers

“…Recently, Marquardt et al (2015) have studied the detonations of massive, ONe WDs under the assumptions that they ignite at the center of the star. Compared to our models, they start with larger masses, between 1.18 and 1.23 M , and they are not the remnants of a merger process, but "naked", hydrostatic WDs.…”

Type Ia supernovae from non-accreting progenitors

“…This hypothesis is strongly supported by 3D hydrodynamic simula- tions of ECSN deflagrations by Jones et al (2016Jones et al ( , 2019: their least compact progenitor ingites at log 10 (ρ c /g cm −3 ) = 9.90 but still manages to eject ∼ 1 M of material. Similarly, Marquardt et al (2015) simulate ONe WD detonations at lower densities and demonstrate that the explosion is practically identical to a typical SN Ia. Interestingly in our 1D simulations, both models experience significant expansion.…”

“…These delay times could help account for the high SN Ia rates in star-forming galaxies, compared to ellipticals (Maoz & Badenes 2010;Claeys et al 2014b), but some variant of the DD channel, or more generally a model in which the delay time much larger than the MS lifetime of intermediate-mass stars, would still be required to explain events with much longer delay times. However, if the (C)NeO core of a WD were to evolve in a similar way due to mass accretion from a companion as in the SD scenarios, or in a merger similar to the DD and CD scenarios, then the corresponding explosion could contribute a SN Ia several Gyrs after star formation (see also Kashi & Soker 2011;Chen et al 2014;Meng & Podsiadlowski 2014;Marquardt et al 2015;Schwab et al 2015;Jones et al 2016;Schwab et al 2017;Schwab & Rocha 2019;Kashyap et al 2018;Augustine et al 2019;Soker 2019, and references therein). Finally, if (C)NeO explosions produce less nickel than typical SNe Ia, then the short delay times would match those of under-luminous SNe Iax which predominately occur in star-forming regions (Lyman et al 2013;Jha 2017).…”