Spectroscopic r-Process Abundance Retrieval for Kilonovae I: The Inferred Abundance Pattern of Early Emission from GW170817

Abstract

Freshly-synthesized r-process elements in kilonovae ejecta imprint absorption features on optical spectra, as observed in the GW170817 binary neutron star merger. These spectral features encode insights into the physical conditions of the r-process and the origins of the ejected material, but associating features with particular elements and inferring the resultant abundance pattern is computationally challenging. We introduce Spectroscopic r-Process Abundance Retrieval for Kilonovae (SPARK), a modular framework to perform Bayesian inference on kilonova spectra with the goals of inferring elemental abundance patterns and identifying absorption features at early times. SPARK inputs an atomic line list and abundance patterns from reaction network calculations into the TARDIS radiative transfer code. It then performs fast Bayesian inference on observed kilonova spectra by training a Gaussian process surrogate for the approximate posteriors of kilonova ejecta parameters, via active learning. We use the spectrum of GW170817 at 1.4 days to perform the first inference on a kilonova spectrum, and recover a complete abundance pattern. Our inference shows that this ejecta was generated by an r-process with either (1) high electron fraction Y_e ~ 0.35 and high entropy s/k_B ~ 25, or, (2) a more moderate Y_e ~ 0.30 and s/k_B ~ 14. These parameters are consistent with a shocked, polar dynamical component, and a viscously-driven outflow from a remnant accretion disk, respectively. We also recover previous identifications of strontium absorption at ~8000 AA, and tentatively identify yttrium and/or zirconium at < 4500 AA. Our approach will enable computationally-tractable inference on the spectra of future kilonovae discovered through multi-messenger observations.

Accepted to ApJ; 34 pages, 13 figures

References in corpus (47)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• Multi-messenger Observations of a Binary Neutron Star Merger
• Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A
• Origin of the heavy elements in binary neutron-star mergers from a gravitational wave event
• Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source
• Spectroscopic identification of r-process nucleosynthesis in a double neutron star merger
• The X-ray counterpart to the gravitational wave event GW 170817
• A kilonova as the electromagnetic counterpart to a gravitational-wave source
• Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis
• Illuminating Gravitational Waves: A Concordant Picture of Photons from a Neutron Star Merger
• The Emergence of a Lanthanide-Rich Kilonova Following the Merger of Two Neutron Stars
• Optical emission from a kilonova following a gravitational-wave-detected neutron-star merger
• Comprehensive nucleosynthesis analysis for ejecta of compact binary mergers
• Swift and NuSTAR observations of GW170817: detection of a blue kilonova
• 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
• The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. IV. Detection of Near-infrared Signatures of r-process Nucleosynthesis with Gemini-South
• Identification of strontium in the merger of two neutron stars
• Neutrino-driven winds from neutron star merger remnants
• Kilonovae
• The discovery of the electromagnetic counterpart of GW170817: kilonova AT 2017gfo/DLT17ck
• Kilonova from post-merger ejecta as an optical and near-infrared counterpart of GW170817
• Kilonova Light Curves from the Disk Wind Outflows of Compact Object Mergers
• CMasher: Scientific colormaps for making accessible, informative and 'cmashing' plots
• Galactic Chemical Evolution and solar s-process abundances: dependence on the 13C-pocket structure
• MASTER optical detection of the first LIGO/Virgo neutron stars merging GW170817
• The Dynamics of Binary Neutron Star Mergers and of GW170817
• Follow up of GW170817 and its electromagnetic counterpart by Australian-led observing programs
• J-GEM observations of an electromagnetic counterpart to the neutron star merger GW170817
• Full Transport Model of GW170817-Like Disk Produces a Blue Kilonova
• Production of the entire range of r-process nuclides by black hole accretion disc outflows from neutron star mergers
• Observations of the first electromagnetic counterpart to a gravitational wave source by the TOROS collaboration
• Optical follow-up of the neutron star-black hole mergers S200105ae and S200115j
• Post-merger Mass Ejection of Low-mass Binary Neutron Stars
• Monte Carlo Radiative Transfer
• Modelling the spectra of the kilonova AT2017gfo -- I: The photospheric epochs
• r-process Production Sites as inferred from Eu Abundances in Dwarf Galaxies
• Hyperfine Splitting in the VALD Database of Spectral-line Parameters
• NLTE Effects on Kilonova Expansion Opacities
• On the Validity of Steady-State for Nebular Phase Kilonovae
• Probing the production of actinides under different r-process conditions
• The high redshift SFR-M* relation is sensitive to the employed star formation rate and stellar mass indicators: Towards addressing the tension between observations and simulations
• Spectral modeling of type II supernovae II. A machine learning approach to quantitative spectroscopic analysis
• Neutron star mergers as the astrophysical site of the r-process in the Milky Way and its satellite galaxies
• Query Efficient Posterior Estimation in Scientific Experiments via Bayesian Active Learning
• Engine-fed Kilonovae (Mergernovae) -- I. Dynamical Evolution and Energy Injection / Heating Efficiencies
• KilonovaNet: Surrogate Models of Kilonova Spectra with Conditional Variational Autoencoders
• A Broad Grid of 2D Kilonova Emission Models

Cited by in corpus (13)

• End-to-end kilonova models of neutron-star mergers with delayed black-hole formation
• Self-consistent picture of the mass ejection from a one second-long binary neutron star merger leaving a short-lived remnant in general-relativistic neutrino-radiation magnetohydrodynamic simulation
• Discovery of a 760 nm P Cygni line in AT2017gfo: Identification of yttrium in the kilonova photosphere
• NLTE Spectra of Kilonovae
• Superheavy Elements in Kilonovae
• Emergence hour-by-hour of $r$-process features in the kilonova AT2017gfo
• Kilonova evolution -- the rapid emergence of spectral features
• KilonovAE: Exploring Kilonova Spectral Features with Autoencoders
• Helium features are inconsistent with the spectral evolution of the kilonova AT2017gfo
• Improved lanthanide constraints for the kilonova AT 2017gfo
• Spectral synthesis techniques for supernovae and kilonovae
• Critically Evaluated Atomic Data for Au IV Spectrum
• Light Travel Time Effects in Kilonova Models