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Three-dimensional spectral modelling of astrophysical transients : unravelling the nucleosynthetic content of supernovae and kilonovae

Periodic Reporting for period 3 - SUPERSPEC (Three-dimensional spectral modelling of astrophysical transients : unravelling the nucleosynthetic content of supernovae and kilonovae)

Période du rapport: 2022-10-01 au 2024-03-31

The SUPERSPEC project aims to develop and apply the next generation of models for spectral formation in the element factories of the Universe: supernovae and kilonovae. Arising when massive stars collapse, and when neutron stars merge, respectively, these transients enrich cosmos with elements throughout the periodic table. The diagnosis of this production occurs through advanced spectral analysis with Non-Local-Thermodynamic-Equilibrium simulations. With improved models, applied to the analysis of new high-quality observations, we can take a leap forward in building up a systematic understanding for the origin of the elements and the structure of explosive transients. In addition will the inferred ejecta morphologies and composition tell us about fundamental physics such as the equation of state at the highest densities.

The objective of SUPERSPEC is to advance the state-of-the-art in transient spectral modelling both for the microphysics and macrophysics. This is achieved through parallel developments for the treatment of microphysical processes like time-dependent energy flows and new r-process atomic data, and macrophysical ones like 3D effects. These new models are then to be used to make inferences of both core-collapse supernova and kilonova nucleosynthesis.

For our society, the SUPERSPEC project will make an important contribution to better understanding the origin of the elements in the Universe - a pillar of modern astrophysics and for our sense of our origins in cosmos. It also plays a role in connecting areas in the emerging and revolutionary field of multi-messenger astronomy.
The work performed so far in the SUPERSPEC project includes:
* Development and application of a time-dependent treatment for the energy and ionization equations.
* Development of a 3D code to the point that Non-Local-Thermodynamic-Equilibrium ionization, excitation, and temperature can be calculated in the limit of weak diffuse radiation field.
* A scattering-by-scattering line transfer code has been developed to study the Sobolev approximation and its degree of validity.
* The modelling of hydrogen-stripped (Type Ib) supernovae in 3D is underway.
* The modelling of superluminous supernovae (SLSNe) is underway.
* Physical conditions of kilonova ejecta has been modelled in detail, and spectral modelling is underway.
* Build-up of nebular data samples is ongoing.
We have now in operation the only code doing kilonova (KN) Non-Local-Thermodynamic-Equilibrium (NLTE) modellering with radiative transfer, and a new code doing 3D supernova NLTE modelling.

In the remaining 2.5 years we aim to:

* Calculate (1D) KN model grids and draw inferences of AT2017gfo, as well as make useful predictions over parameter space for the upcoming LIGO O4 period.
* Perform crucial atomic data calculations for r-process processes including collision strengths and recombination rates.
* Produce a suite of 3D core-collapse supernova models, initially for Type Ibc supernovae and then for Type II SNe.
* Provide tests to the hypothesis of whether superluminous supernovae can be powered by pulsar wind nebulae.
* Provide a statistical analysis of the hydrostatic element production in Type II supernovae using 1D models.
* Implement self-consistent time-dependent thermalization physics - useful for both supernova and kilonova modelling.