Properties of Kilonovae from Dynamical and Post-merger Ejecta of Neutron Star Mergers

Tanaka, Masaomi; Kato, Daiji; Gaigalas, Gediminas; Rynkun, Pavel; Radžiūtė, Laima; Wanajo, Shinya; Sekiguchi, Y.; Nakamura, Nobuyuki; Tanuma, H.; Murakami, Izumi; Sakaue, Hiroyuki

doi:10.3847/1538-4357/aaa0cb

Cited by 148 publications

(169 citation statements)

References 88 publications

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“…Conversely, the late EM emission, which dominates at longer timescales ∼a week and shows a lower luminosity ∼10 40 -10 41 erg s −1 fits well with the so called Red KN model [64]: in [67][68][69][70] it was first presented the study of the effect of higher opacity of the ejecta on the resulting KN emission. This high opacity (k up to 10 cm 2 s −1 ) is attributed to the presence of Lanthanide elements, heavy nuclei with A > 140, so the Red KN represents an indication of nucleosyntesis reactions filling the third peak of r-processes.…”

Section: Analysis Of the Optical Transientsupporting

confidence: 57%

“…First of all, the wind ejecta for angles >30 • are less affected by the neutrino flux maintaining an electron fraction Y e ∼ 0.25-0.3 and fitting the required opacity [70,75,77]. At the same time, a contribution can also come from the secular ejecta which affects all the solid angles, but which is equatorial dominated: this viscous-driven ejection can result in the expulsion of up to 30% of the mass of the disk and the Y e of the material depends on the lifetime of the HMNS with respect to that of the disk (∼ten of ms).…”

Section: Role Of Different Ejection Mechanismsmentioning

confidence: 99%

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The Merger of Two Compact Stars: A Tool for Dense Matter Nuclear Physics

et al. 2018

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Abstract:We discuss the different signals, in gravitational and electromagnetic waves, emitted during the merger of two compact stars. We will focus in particular on the possible contraints that those signals can provide on the equation of state of dense matter. Indeed, the stiffness of the equation of state and the particle composition of the merging compact stars strongly affect, e.g., the life time of the post-merger remnant and its gravitational wave signal, the emission of the short gamma-ray-burst, the amount of ejected mass and the related kilonova. The first detection of gravitational waves from the merger of two compact stars in August 2017, GW170817, and the subsequent detections of its electromagnetic counterparts, GRB170817A and AT2017gfo, is the first example of the era of "multi-messenger astronomy": we discuss what we have learned from this detection on the equation of state of compact stars and we provide a tentative interpretation of this event, within the two families scenario, as being due to the merger of a hadronic star with a quark star.

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Section: Analysis Of the Optical Transientsupporting

confidence: 57%

Section: Role Of Different Ejection Mechanismsmentioning

confidence: 99%

The Merger of Two Compact Stars: A Tool for Dense Matter Nuclear Physics

et al. 2018

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“…The major caveat in identifying line features is the possibility that missing lines could significantly influence the broad spectral shape compared to what is predicted from known lines. Of particular concern are the large numbers of unknown lines from the lanthanide elements that are likely to dominate the line-expansion opacity 22,44 . While we argue here that our line lists are reasonably complete in strong lines at these temperatures and densities (and since they are used for modelling stars with similar temperatures and densities, this makes sense), it is possible that a very large number of weaker lines could contribute.…”

Section: Could Large Numbers Of Weak Lines Dominate the Optical/nir Omentioning

confidence: 99%

Identification of strontium in the merger of two neutron stars

Watson

Hansen

Selsing

et al. 2019

Nature

405

317

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Half of all the elements in the universe heavier than iron were created by rapid neutron capture. The theory for this astrophysical 'r-process' was worked out six decades ago and requires an enormous neutron flux to make the bulk of these elements. 1 Where this happens is still debated. 2 A key piece of missing evidence is the identification of freshly-synthesised r-process elements in an astrophysical site. Current models 3-5 and circumstantial evidence 6 point to neutron star mergers as a probable r-process site, with the optical/infrared 'kilonova' emerging in the days after the merger a likely place to detect the spectral signatures of newly-created neutron-capture elements. 7-9 The kilonova, AT2017gfo, emerging from the gravitational-wave-discovered neutron star merger, GW170817, 10 was the first kilonova where detailed spectra were recorded. When these spectra were first reported 11, 12 it was argued that they were broadly consonant with an outflow of radioactive heavy elements, however, there was no robust identification of any element. Here we report the identification of the neutron-capture element strontium in a re-analysis of these spectra. The detection of a neutron-capture element associated with the collision of two extreme-density stars establishes the origin of r-process elements in neutron star mergers, and demonstrates that neutron stars comprise neutron-rich matter 13 .The most detailed information available for a kilonova comes from a series of spectra of AT2017gfo taken over several weeks with the medium resolution, ultraviolet (320 nm) to near-infrared (2,480 nm) spectrograph, X-shooter, mounted at the Very Large Telescope at the European Southern Observatory. These spectra 11, 12 , allow us to track the evolution of the kilonova's primary electromagnetic output from 1.5 days until 10 days after the event. Detailed modelling of these spectra has yet to be done owing to the limited understanding of the phenomenon and the expectation that a very large number of moderate to weak lanthanide lines with unknown oscillator strengths would dominate the spectra 14,15 . Despite the expected complexity, we sought to identify individual elements in the early spectra because these spectra are well-reproduced by relatively simple models 11 .The first epoch spectrum can be reproduced over the entire observed spectral range with a single-temperature blackbody with an observed temperature 4, 800 K. The two major deviations short of 1 µm from a pure blackbody are due to two very broad (∼ 0.2c) absorption components. These components are observed centred at about 350 nm and 810 nm (Fig. 1). The shape of the ultraviolet absorption component is not well constrained because it lies close to the edge of our sensitivity limit and may simply be cut off below about 350 nm. The presence of the absorption feature at 810 nm at this epoch has been noted in earlier publications 11,12 .The fact that the spectrum is very well reproduced by a single temperature blackbody in the first epoch suggests a population of states 0.3...

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“…Notably, the bound-bound absorption opacity of open f -shell elements (lanthanides and actinides) differs significantly from the opacity of others, because open f -shell elements have such a high number of excited levels with relatively low excitation energy that the number of transition lines in the optical and IR bands is greatly enhanced (125,17,18). Radiation transfer simulations of merger ejecta show that the mean opacity, κ, is ∼ > 10 cm 2 /g for lanthanide-rich ejecta while it is ∼ 0.1 cm 2 /g for lanthanide-free ejecta (125,17,18,116,126,127). This finding implies that the Ye distribution of ejecta, which primarily determines the abundance pattern of r-process elements, is the key for determining the features of kilonovae.…”

Section: 22mentioning

confidence: 99%

Merger and Mass Ejection of Neutron Star Binaries

Shibata

Hotokezaka

2019

Annu. Rev. Nucl. Part. Sci.

265

191

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Mergers of binary neutron stars and black hole-neutron star binaries are one of the most promising sources for the ground-based gravitationalwave (GW) detectors and also a high-energy astrophysical phenomenon as illustrated by the observations of gravitational waves and electromagnetic (EM) waves in the event of GW170817. Mergers of these neutron-star binaries are also the most promising site for r-process nucleosynthesis. Numerical simulation in full general relativity (numerical relativity) is a unique approach to the theoretical prediction of the merger process, GWs emitted, mass ejection process, and resulting EM emission. We summarize our current understanding for the processes of neutron star mergers and subsequent mass ejection based on the results of the latest numerical-relativity simulations. We emphasize that the predictions of the numerical-relativity simulations agrees broadly with the optical and infrared observations of GW170817.

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Properties of Kilonovae from Dynamical and Post-merger Ejecta of Neutron Star Mergers

Cited by 148 publications

References 88 publications

The Merger of Two Compact Stars: A Tool for Dense Matter Nuclear Physics

The Merger of Two Compact Stars: A Tool for Dense Matter Nuclear Physics

Identification of strontium in the merger of two neutron stars

Merger and Mass Ejection of Neutron Star Binaries

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