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Spectral synthesis of multidimensional supernova explosion models

Periodic Reporting for period 1 - SNSM (Spectral synthesis of multidimensional supernova explosion models)

Reporting period: 2016-10-01 to 2018-09-30

This project aimed to develop improved spectral synthesis models for core-collapse supernovae. Supernovae play an important role in modern astrophysics, as the end-points of massive star evolution, the production sites of most elements between oxygen and nickel in the periodic table, and the birth places for neutron stars and black holes. A better understanding of these events, in and in particular their explosion physics and element production, requires advanced spectral modelling tools and analysis. Development of techniques can also find use in other science areas such as atmospheric climate modelling, with broad benefits for society. The project contained three main objectives: 1) To develop the first spectral predictions for 1D neutrino-powered supernovae, 3) To develop 3D code capability, and 3) To use this 3D code to analyze current 3D hydrodynamic models. The first project highlights that not only dimensionality is important in modelling, but also realistic stellar evolution and explosion physics. We produced in this work package the first spectral predictions of neutrino-powered models, and by comparison with observations could draw a strong conclusion that the class of low-velocity Type II supernovae likely originate from low-mass progenitors, 8-10 solar masses. A 3D code version has been successfully developed, although with some more limited microphysical treatments compared to the 1D version. This 3D code is nevertheless a major breakthrough, and the code is currently being used to analyze spectral predictions from 3D explosion models. We expect this to give a series of papers with significant new results with regard to how element production can be inferred from observed lines, and how the supernova explosion occurs.
"For WP1 (1D modelling) we choose to focus on a case study of a particular model : a 9 solar mass iron-core progenitor that is representative of the 8-10 solar mass range that is believed to give rise to about a third of all core-collapse supernovae. Our results have been presented in the Monthly Notices of the Royal Astronomical Society (https://academic.oup.com/mnras/article/475/1/277/4622958) and disseminated at several conferences and workshops, e.g. in Rome 2017/03 and at EWASS 2017/04. The 3D code version will be developed in two variants; a ""3D-Lite"" version and a ""3D-Full"" version. The ""3D-Full"" version will be able to treat the full set of microphysics in detail, but requires a fundamental algorithm restructuring. This work will be be pursued under the awarded ERC Starting Grant which will build upon the foundation laid by the MSC project. The ""3D-Lite"" version retains the original algorithm of the code, upgrading to a 3D grid. It can handle 3D grids at moderate resolution, and with some simplifications in the radiative transfer. A first working version of this code has been completed. WP3 is focused on the application of the new 3D code to analyze Type II models relevant for SN 1987A. This work is in progress. Specific analysis of the gamma-ray field in 3D vs 1D is completed, as is the analysis of emergent line profiles. This will define the content in a first publication, together with analysis of radiative transfer effects with a simplified scheme. In a planned third publication, full spectral modelling will be presented. Dissemination of WP2 and WP3 is planned for a conference in May 2019, and also at a workshop organized by the fellow for summer 2019."
The new 3D code version defines a new state of the art, as such simulations have not yet been published. By going to
3D modelling, we are able to remove significant parametrization occurring in current 1D models, and present
predictions with significantly improved accuracy. At the same time it allows the first tests of 3D explosion simulations.

The new spherical coordinate system transport algorithm has generic value beyond astronomy; it can find potential
application in any kind of 3D transport simulations, including climate and particle physics.

Application-wise, the analysis of neutrino-exploded stars is also a new state-of-the-art, as previous simulations have relied
on artificially triggered explosions by pistons or thermal bombs. The new improved models make more realistic
representation of the inner dynamic structure and nucleosynthesis.
SN 2008bk compared to the new 9 Msun neutrino-driven model.