Simulating spectra of supernovae and kilonovae

Dnr:

NAISS 2023/5-255

Type:

NAISS Medium Compute

Principal Investigator:

Anders Jerkstrand

Affiliation:

Stockholms universitet

Start Date:

2023-06-29

End Date:

2024-07-01

Primary Classification:

10305: Astronomy, Astrophysics and Cosmology

Webpage:

Supernovae and kilonovae are transients resulting from the collapse of massive stars, and the merger of two neutron stars, respectively. Together they produce most of the elements in the periodic table, and probe astrophysics in its most extreme regimes. This project carries out simulation work for the ERC Starting Grant Project "SUPERSPEC: Three-dimensional spectral modelling of astrophysical transients : unravelling the nucleosynthetic content of supernovae and kilonovae", as well as work for Swedish Research Council and Wallenberg Foundation projects. Our research group is developing and applying state-of-the-art spectral models for these astrophysical explosions, considering the key physical processes to a high degree of realism including sophisticated radiative transfer. These models can be used to analyse observed spectra of supernovae and kilonovae, and from those comparisons we can infer important properties such as which elements are produced in which explosions, what is the mass and velocity of the expanding debris, and what is the nature of the compact objects (neutron stars and black holes) left behind.
The physical modelling involves solving the energy equation, the statistical equilibrium populations (several hundred levels per ion), and the non-thermal cascade of Compton electrons produced by radioactive decays. The most computationally expensive part if the radiative transfer which we perform line-by-line in about 300,000 lines in supernovae and even larger numbers for kilonovae.
Over the previous 12-month period we have used our Dardel allocation to compute models that have led to several accepted publications (Liljegren & Jerkstrand 2023, Pognan, Jerkstrand & Grumer 2022a,b, van Baal, Jerkstrand, Wongwathanarat & Janka 2023, Omand & Jerkstrand 2022). Over the next 12 months, we aim to compute two large grids of 3D models, one for supernovae and one for kilonovae. For supernovae we have a set of 3D hydrodynamic models for He-core explosions (from our collaboration group in Garching, Germany), with mass and explosion energy varying. Following our proof-of-concept paper analysing a single model (https://ui.adsabs.harvard.edu/abs/2023arXiv230508933V/abstract), we are now poised to carry out an extensive grid analysis. The 3D modelling will be supported by parallell 1D modelling, in which more sophisticated microphysics is possible. For kilonovae, we have completed a first set of full spectral models (Pognan, Grumer & Jerkstrand 2023, in prep). The next step here is grid analysis both in 1D and 3D. We have several 3D hydrodynamic models available from our collaborator Stephan Rosswog.
We ask for a somewhat larger allocation than in the last round, as with completion the 3D version of our code, more runs will now be carried out in 3D compared to 1D, with correspondingly larger demands on CPU time.