Heavy Elements and Electromagnetic Transients from Neutron Star Mergers

Abstract

Compact binary mergers involving neutron stars can eject a fraction of their mass to space. Being extremely neutron rich, this material undergoes rapid neutron capture nucleosynthesis, and the resulting radioactivity powers fast, short‐lived electromagnetic transients known as kilonova or macronova. Such transients are exciting probes of the most extreme physical conditions and their observation signals the enrichment of the Universe with heavy elements. Here the current understanding of the mass ejection mechanisms, the properties of the ejecta, and the resulting radioactive transients are reviewed. The first well‐observed event in the aftermath of GW170817 delivered a wealth of insights, but much of today's picture of such events is still based on a patchwork of theoretical studies. Apart from summarizing the current understanding, questions where no consensus has been reached yet are also pointed out, and possible directions for the future research are sketched. In an appendix, a publicly available heating rate library based on the WinNet nuclear reaction network is described, and a simple fit formula to alleviate the implementation in hydrodynamic simulations is provided.

KilonovAE: Exploring Kilonova Spectral Features with Autoencoders

“…Additionally, TARDIS is time-independent and only simulates one epoch of kilonovae spectra at a time-we cannot evolve physical parameters between epochs. In reality, the luminosity should evolve over time based on the heating rate (Rosswog & Korobkin 2022) and thermalization efficiency (e.g., Barnes et al 2016). This self-consistent luminosity evolution is necessary to produce realistic kilonova light curves, but in this work our focus is on identifying spectral absorption features.…”

ULTRASAT: A Wide-field Time-domain UV Space Telescope

“…Direct calculations of the structure and composition of the ejecta produced in NS-NS/BH mergers are highly complicated and computationally demanding since they involve a density range of over 30 decades, the entire periodic table, subrelativistic to relativistic flows, and require consideration of neutrino transport, general relativity, and magnetic field effects (Shibata & Hotokezaka 2019;Radice et al 2020;Rosswog & Korobkin 2022). Modeling the EM output is thus a challenging but vibrant field (Fernández & Metzger 2016;Nakar 2020;Margutti & Chornock 2021).…”