NLTE Spectra of Kilonovae

Abstract

The electromagnetic transient following a binary neutron star merger is known as a kilonova (KN). Owing to rapid expansion velocities and small ejecta masses, KNe rapidly transition into the Non-Local Thermodynamic Equilibrium (NLTE) regime. In this study, we present synthetic NLTE spectra of KNe from 5 to 20 days after merger using the \texttt{SUMO} spectral synthesis code. We study three homogeneous composition, 1D multi-zone models with characteristic electron fractions of $Y_e\sim 0.35,0.25$ and $0.15$. We find that emission features in the spectra tend to emerge in windows of reduced line blocking, as the ejecta are still only partially transparent even at 20 days. For the $Y_e\sim 0.35$ (lanthanide-free) ejecta, we find that the neutral and singly ionised species of Rb, Sr, Y and Zr dominate the spectra, all with good potential for identification. We directly test and confirm an impact of Sr on the 10000 angstrom spectral region in lanthanide-free ejecta, but also see that its signatures may be complex. We suggest the Rb I $5{\mathrm{p}}^1$- $5{\mathrm{s}}^1$ 7900 angstrom transition as a candidate for the ${\lambda }_0\sim$ 7500--7900 angstrom P-Cygni feature in AT2017gfo. For the $Y_e\sim 0.25$ and $0.15$ compositions, lanthanides are dominant in the spectral formation, in particular Nd, Sm, and Dy. We identify key processes in KN spectral formation, notably that scattering and fluorescence play important roles even up to 20 days after merger, implying that the KN ejecta are not yet optically thin at this time.

arXiv comment20 pages (30 with appendices), 17 figures, accepted to MNRAS

References in corpus (66)

• Multi-messenger Observations of a Binary Neutron Star Merger
• Transient Events from Neutron Star Mergers
• Origin of the heavy elements in binary neutron-star mergers from a gravitational wave event
• Electromagnetic Counterparts of Compact Object Mergers Powered by the Radioactive Decay of R-process Nuclei
• Spectroscopic identification of r-process nucleosynthesis in a double neutron star merger
• A kilonova as the electromagnetic counterpart to a gravitational-wave source
• The X-ray counterpart to the gravitational wave event GW 170817
• The Emergence of a Lanthanide-Rich Kilonova Following the Merger of Two Neutron Stars
• Production of all the r-process nuclides in the dynamical ejecta of neutron star mergers
• The Combined Ultraviolet, Optical, and Near-Infrared Light Curves of the Kilonova Associated with the Binary Neutron Star Merger GW170817: Unified Data Set, Analytic Models, and Physical Implications
• Opacities and Spectra of the r-process Ejecta from Neutron Star Mergers
• Identification of strontium in the merger of two neutron stars
• Radiative Transfer Simulations for Neutron Star Merger Ejecta
• Kilonovae
• Time Dependent Monte Carlo Radiative Transfer Calculations For 3-Dimensional Supernova Spectra, Lightcurves, and Polarization
• Radioactivity and thermalization in the ejecta of compact object mergers and their impact on kilonova light curves
• Kilonova from post-merger ejecta as an optical and near-infrared counterpart of GW170817
• AT2017gfo: an anisotropic and three-component kilonova counterpart of GW170817
• Merger and Mass Ejection of Neutron-Star Binaries
• Systematic Opacity Calculations for Kilonovae
• Neutron Star Mergers Might not be the Only Source of r-Process Elements in the Milky Way
• Impact of ejecta morphology and composition on the electromagnetic signatures of neutron star mergers
• The progenitor mass of the Type IIP supernova SN 2004et from late-time spectral modeling
• POSSIS: predicting spectra, light curves and polarization for multi-dimensional models of supernovae and kilonovae
• Constraints on the ejecta of the GW170817 neutron-star merger from its electromagnetic emission
• The first direct double neutron star merger detection: implications for cosmic nucleosynthesis
• Properties of Kilonovae from Dynamical and Post-Merger Ejecta of Neutron Star Mergers
• The 44Ti-powered spectrum of SN 1987A
• Mass ejection in neutron star mergers
• Numerical Relativity Simulations of the Neutron Star Merger GW170817: Long-Term Remnant Evolutions, Winds, Remnant Disks, and Nucleosynthesis
• Chemical evolution with rotating massive star yields II. A new assessment of the solar s- and r- process components
• A line-binned treatment of opacities for the spectra and light curves from neutron star mergers
• Kilonovae across the nuclear physics landscape: The impact of nuclear physics uncertainties on r-process-powered emission
• Radioactive heating rate of r-process elements and macronova light curve
• Modelling the spectra of the kilonova AT2017gfo -- I: The photospheric epochs
• Spectra of supernovae in the nebular phase
• Signatures of r-process elements in kilonova spectra
• Production of very light elements and strontium in the early ejecta of neutron star mergers
• Simulations of early kilonova emission from neutron star mergers
• Non-Local Thermodynamic Equilibrium Radiative Transfer Simulations of Sub-Chandrasekhar-Mass White Dwarf Detonations
• Radioactive Heating and Late Time Kilonova Light Curves
• Measuring the viewing angle of GW170817 with electromagnetic and gravitational waves
• The critical role of nuclear heating rates, thermalization efficiencies and opacities for kilonova modelling and parameter inference
• Nebular spectra of pair-instability supernovae
• Physical conditions for the r-process I. radioactive energy sources of kilonovae
• Extended calculations of energy levels and transition rates of Nd II-IV ions for application to neutron star mergers
• A low-mass binary neutron star: long-term ejecta evolution and kilonovae with weak blue emission
• NLTE Effects on Kilonova Expansion Opacities
• Constraints on the presence of platinum and gold in the spectra of the kilonova AT2017gfo
• Nebular Emission from Lanthanide-rich Ejecta of Neutron Star Merger
• On the Validity of Steady-State for Nebular Phase Kilonovae
• Monte Carlo radiative transfer for the nebular phase of Type Ia supernovae
• Self-consistent 3D radiative transfer for kilonovae: directional spectra from merger simulations
• Discovery of a 760 nm P Cygni line in AT2017gfo: Identification of yttrium in the kilonova photosphere
• Extended calculations of energy levels and transition rates for singly ionized lanthanide elements I: Pr - Gd
• 3D radiative transfer kilonova modelling for binary neutron star merger simulations
• Actinide opacities for modeling the spectra and light curves of kilonovae
• How do Type Ia Supernova Nebular Spectra Depend on Explosion Properties? Insights from Systematic non-LTE Modeling
• Late time kilonova light curves and implications to GW 170817
• Energy level structure and transition data of Er${}^{2+}$
• Opacities of Singly and Doubly Ionised Neodymium and Uranium for Kilonova Emission Modeling
• Tungsten vs Selenium as a potential source of kilonova nebular emission observed by Spitzer
• Spectroscopic r-Process Abundance Retrieval for Kilonovae I: The Inferred Abundance Pattern of Early Emission from GW170817
• Neutron-Capture elements in planetary nebulae: first detections of near-Infrared [Te III] and [Br V] emission lines
• Long-Term Simulations of Dynamical Ejecta: Homologous Expansion and Kilonova Properties
• Radiative rates and opacity calculations in Ce II-IV Multiconfiguration Dirac-Hartree-Fock radiative parameters for emission lines in Ce II-IV ions and cerium opacity calculations for kilonovae

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• Modeling the emission lines from r-process elements in Supernova nebulae
• Exploring the connection between compact object mergers and fast X-ray transients: The cases of LXT 240402A and EP250207b
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