Kilonova light curves from the disc wind outflows of compact object mergers

By D. Kasen, R. Fern'andez, B. Metzger. 2014

260 citations recorded by the source corpus.

We study the radioactively-powered transients produced by accretion disk winds following a compact object merger. Starting with the outflows generated in two-dimensional hydrodynamical disk models, we use wavelength-dependent radiative transfer calculations to generate synthetic light curves and spectra. We show that the brightness and color of the resulting kilonova transients carry information about the merger physics. In the regions of the wind where neutrino irradiation raises the electron fraction to Ye > 0.25, r-process nucleosynthesis halts before producing high-opacity, complex ions (the lanthanides). The kilonova light curves thus show two distinct components: a brief (~2 day) blue optical transient produced in the outer lanthanide-free ejecta, and a longer (~10 day) infrared transient produced in the inner, lanthanide line-blanketed region. Mergers producing a longer-lived neutron star, or a more rapidly spinning black hole, have stronger neutrino irradiation, generate more lanthanide-free ejecta, and are optically brighter and bluer. At least some optical emission is produced in all disk wind models, which should enhance the detectability of electromagnetic counterparts to gravitational wave sources. However, the presence of even a small amount (10^{-4} Msun) of overlying, neutron-rich dynamical ejecta will act as a "lanthanide-curtain", obscuring the optical wind emission from certain viewing angles. Because the disk outflows have moderate velocities (~10,000 km/s), numerous resolved line features are discernible in the spectra, distinguishing disk winds from fast-moving dynamical ejecta, and offering a potential diagnostic of the detailed composition of freshly produced r-process material.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/9eb93ef295950d10a4e7a9c607be025c8b106fd0

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In Astronomy and Astrophysics

1. B. Metzger
2. Bing Zhang
3. E. Berger
4. E. Quataert
5. D. Kasen
6. P. Hopkins
7. L. Hernquist
8. David Radice

Citations in the corpus

• RADIOACTIVITY AND THERMALIZATION IN THE EJECTA OF COMPACT OBJECT MERGERS AND THEIR IMPACT ON KILONOVA LIGHT CURVES (2016, background): “The opacities for such models would be much lower, and the associated light curves would be shorter, brighter, and bluer (e.g., Metzger et al. 2010; Barnes & Kasen 2013; Kasen et al. 2015).”
• 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 (2017, background): “This is relevant because models invoking strong accretion disk winds (e.g., Kasen et al. 2015; Siegel & Metzger 2017) predict a range of ejection velocities from 0.03 to 0.1c.”
• A kilonova as the electromagnetic counterpart to a gravitational-wave source (2017, methodology): “From Kasen et al.(32), we use the t300 disk wind outflow model corresponding to a simulation where the resultant neutron star survives 300 ms before collapsing to a black hole.”
• NEUTRINO-DRIVEN WINDS IN THE AFTERMATH OF A NEUTRON STAR MERGER: NUCLEOSYNTHESIS AND ELECTROMAGNETIC TRANSIENTS (2015, background): “As pointed out by Kasen et al. (2015), even a small amount of dynamic ejecta can completely obscure the optical emission from the winds.”
• The THESEUS space mission concept: science case, design and expected performances (2017, background): “1-2 days after the merger), with luminosity of the order of a few times 1040−41 erg s−1, depending also on the nature of the central remnant (Kasen et al., 2015).”
• Production of the entire range of r-process nuclides by black hole accretion disc outflows from neutron star mergers (2016, background): “This nonetheless depends on the viewing directions close to the rotation axis to be relatively free of Lanthanide-rich dynamical ejecta material, which is usually the case for BH-NS mergers (Fernández et al. 2015; Kasen et al. 2015).”
• J-GEM observations of an electromagnetic counterpart to the neutron star merger GW170817 (2017, background): “…by guest on 26 July 2018 elements in the Universe as emission properties reflect the ejected mass and abundances of r-process elements (e.g., Kasen et al. 2013; Barnes & Kasen 2013; Tanaka & Hotokezaka 2013; Tanaka et al. 2014; Metzger & Fernández 2014; Kasen et al. 2015).”
• DETAILED CHEMICAL ABUNDANCES IN THE r-PROCESS-RICH ULTRA-FAINT DWARF GALAXY RETICULUM 2 (2016, background): “…modeling the light curves associated with r-process events that might be found in transient surveys (Metzger et al. 2010; Goriely et al. 2011; Kasen et al. 2015), and searching for shortlived radioactive nuclides produced by the r process in deep-sea crust or sediments (Wallner et al. 2015;…”
• 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 (2017, background): “…outflow from a black hole accretion disk (Just et al. 2015) but would disfavor a particularly longlived (100 ms) hyper-massive or supra-massive neutron star remnant (Metzger & Fernández 2014; Murguia-Berthier et al. 2014; Kasen et al. 2015; Lippuner et al. 2017; see also Margalit & Metzger 2017).”
• Kilonova from post-merger ejecta as an optical and near-infrared counterpart of GW170817 (2017, background): “In addition, we speculate that a relatively long-lived massive NS is present after the merger (Metzger & Fernández 2014; Kasen et al. 2015; Lippuner et al. 2017) so that neutrino emission from the central NS can increase Ye of the surrounding disk as well as the ejecta from the disk.”
• Impact of ejecta morphology and composition on the electromagnetic signatures of neutron star mergers (2017, background): “…Kyutoku et al. 2013; Metzger & Fernández 2014) including detailed radiative transfer simulations (Tanaka & Hotokezaka 2013; Tanaka et al. 2014; Kasen et al. 2015) with updated opacities predicted dimmer light curves that would 1 However, see Côté et al. (2017) for a literature review and a…”
• The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. II. UV, Optical, and Near-infrared Light Curves and Comparison to Kilonova Models (2017, background): “This feature is suggested in several models that consider lanthanide-rich material ejected in the equatorial plane while the lanthanide-poor material is ejected from the polar regions (Kasen et al. 2015; Metzger 2017).”