Monte Carlo radiative transfer for the nebular phase of Type Ia supernovae

Abstract

We extend the range of validity of the artis 3D radiative transfer code up to hundreds of days after explosion, when Type Ia supernovae are in their nebular phase. To achieve this, we add a non-local thermodynamic equilibrium (non-LTE) population and ionisation solver, a new multi-frequency radiation field model, and a new atomic dataset with forbidden transitions. We treat collisions with non-thermal leptons resulting from nuclear decays to account for their contribution to excitation, ionisation, and heating. We validate our method with a variety of tests including comparing our synthetic nebular spectra for the well-known onedimensional W7 model with the results of other studies. As an illustrative application of the code, we present synthetic nebular spectra for the detonation of a sub-Chandrasekhar white dwarf in which the possible effects of gravitational settling of 22 Ne prior to explosion have been explored. Specifically, we compare synthetic nebular spectra for a 1.06 M white dwarf model obtained when 5.5 Gyr of very-efficient settling is assumed to a similar model without settling. We find that this degree of 22 Ne settling has only a modest effect on the resulting nebular spectra due to increased 58 Ni abundance. Due to the high ionisation in sub-Chandrasekhar models, the nebular [Ni ii] emission remains negligible, while the [Ni iii] line strengths are increased and the overall ionisation balance is slightly lowered in the model with 22 Ne settling.In common with previous studies of sub-Chandrasekhar models at nebular epochs, these models overproduce [Fe iii] emission relative to [Fe ii] in comparison to observations of normal Type Ia supernovae.A natural candidate for triggering the ignition is for the WD to

Metallicity-dependent nucleosynthetic yields of Type Ia supernovae originating from double detonations of sub-MCh white dwarfs

“…Therefore, the abundance of this stable isotope can be directly probed in nebular spectra (Ruiz-Lapuente & Lucy 1992). Increasing metallicity provides a mechanism by which sub-M Ch models can produce increasing amounts of stable Ni, although it remains unclear whether conditions in sub-M Ch models can yield [Ni ii] emission to the degree required by data (Shingles et al 2020;Wilk et al 2020).…”

UV Spectroscopy of Massive Stars

“…Monte Carlo methods have the potential to model complex binary systems with colliding winds. MC methods are routinely used to model, for example, SNe (e.g., [124][125][126]). Non-LTE MC codes have also been used to study disk winds in cataclysmic variables (CVs) (e.g., [127][128][129]) and Be stars (e.g., [130]).…”

Mergers of Binary Neutron Star Systems: A Multimessenger Revolution

“…Furthermore, broadening causes the lines to blend, which makes it difficult to isolate and identify individual atomic species (Iwamoto et al, 1998;Mazzali et al, 2000;Nakamura et al, 2001). While these effects can be controlled and deconvolved with the aid of a radiation transport model as it has been done for supernovae of all types (Mazzali et al, 2016;Hoeflich et al, 2017;Ergon et al, 2018;Hillier and Dessart, 2019;Ashall and Mazzali, 2020;Shingles et al, 2020), a more fundamental hurdle in modeling kilonova spectra consists in the much larger number of electronic transitions occurring in r-process element atoms than in the lighter ones that populate supernova ejecta, and in our extremely limited knowledge of individual atomic opacities of these neutron-rich elements, owing to the lack of suitable atomic data. First systematic atomic structure calculations for lanthanides and for all r-process elements were presented by Fontes et al (2020) and Tanaka et al (2020), respectively.…”