scholarly journals A line-binned treatment of opacities for the spectra and light curves from neutron star mergers

2020 ◽  
Vol 493 (3) ◽  
pp. 4143-4171 ◽  
Author(s):  
C J Fontes ◽  
C L Fryer ◽  
A L Hungerford ◽  
R T Wollaeger ◽  
O Korobkin
Keyword(s):  
Neutron Star ◽  
Gamma Ray ◽  
Radiation Transport ◽  
Electromagnetic Transients ◽  
Actinide Element ◽  
Structure Line ◽  
Spectral Simulations ◽  
R Process ◽  
Process Elements ◽  
Area Preserving

ABSTRACT The electromagnetic observations of GW170817 were able to dramatically increase our understanding of neutron star mergers beyond what we learned from gravitational waves alone. These observations provided insight on all aspects of the merger from the nature of the gamma-ray burst to the characteristics of the ejected material. The ejecta of neutron star mergers are expected to produce such electromagnetic transients, called kilonovae or macronovae. Characteristics of the ejecta include large velocity gradients, relative to supernovae, and the presence of heavy r-process elements, which pose significant challenges to the accurate calculation of radiative opacities and radiation transport. For example, these opacities include a dense forest of bound–bound features arising from near-neutral lanthanide and actinide elements. Here we investigate the use of fine-structure, line-binned opacities that preserve the integral of the opacity over frequency. Advantages of this area-preserving approach over the traditional expansion–opacity formalism include the ability to pre-calculate opacity tables that are independent of the type of hydrodynamic expansion and thus eliminate the computational expense of calculating opacities within radiation-transport simulations. Tabular opacities are generated for all 14 lanthanides as well as a representative actinide element, uranium. We demonstrate that spectral simulations produced with the line-binned opacities agree well with results produced with the more accurate continuous Monte Carlo Sobolev approach, as well as with the commonly used expansion–opacity formalism. The agreement between the line-binned and expansion–opacity results is explained as arising from the similarity in their opacities in the limit of low optical depth, where radiation transport is important in the ejecta. Additional investigations illustrate the convergence of opacity with respect to the number of included lines, and elucidate sensitivities to different atomic physics approximations, such as fully and semirelativistic approaches.

scholarly journals Neutron star mergers as sites of r-process nucleosynthesis and short gamma-ray bursts

2018 ◽  
Vol 27 (13) ◽  
pp. 1842005 ◽  
Author(s):  
Kenta Hotokezaka ◽  
Paz Beniamini ◽  
Tsvi Piran
Keyword(s):  
Neutron Star ◽  
Chemical Evolution ◽  
Near Infrared ◽  
Gamma Ray ◽  
Ultra Violet ◽  
Gamma Ray Bursts ◽  
Galactic Model ◽  
Multi Wavelength ◽  
R Process ◽  
Process Elements

Neutron star mergers have been long considered as promising sites of heavy [Formula: see text]-process nucleosynthesis. We overview the observational evidence supporting this scenario including: the total amount of [Formula: see text]-process elements in the galaxy, extreme metal-poor stars, geological radioactive elemental abundances, dwarf galaxies and short gamma-ray bursts (sGRBs). Recently, the advanced LIGO and Virgo observatories discovered a gravitational-wave signal of a neutron star merger, GW170817, as well as accompanying multi-wavelength electromagnetic (EM) counterparts. The ultra-violet, optical and near infrared (n/R) observations point to [Formula: see text]-process elements that have been synthesized in the merger ejecta. The rate and ejected mass inferred from GW170817 and the EM counterparts are consistent with other observations. We however, find that, within the simple one zone chemical evolution models (based on merger rates with reasonable delay time distributions as expected from evolutionary models, or from observations of sGRBs), it is difficult to reconcile the current observations of the Eu abundance history of galactic stars for [Fe/H] [Formula: see text]. This implies that to account for the role of mergers in the galactic chemical evolution, we need a galactic model with multiple populations that have different spatial distributions and/or varying formation rates.

scholarly journals Gamma-Ray Emission Produced by r-process Elements from Neutron Star Mergers

2021 ◽  
Vol 919 (1) ◽  
pp. 59
Author(s):  
Meng-Hua Chen ◽  
Li-Xin Li ◽  
Da-Bin Lin ◽  
En-Wei Liang
Keyword(s):  
Neutron Star ◽  
Gamma Ray ◽  
Gamma Ray Emission ◽  
R Process ◽  
Process Elements

Gravitational-wave astrophysics from neutron star inspiral and coalescence

2018 ◽  
Vol 27 (11) ◽  
pp. 1843018 ◽  
Author(s):  
John L. Friedman
Keyword(s):  
Neutron Star ◽  
Gravitational Wave ◽  
Gamma Ray ◽  
Hubble Constant ◽  
Gamma Ray Bursts ◽  
Nuclear Density ◽  
Independent Measurement ◽  
Process Elements ◽  
Heaviest Elements ◽  
Cold Matter

Prior to the observation of a double neutron star inspiral and merger, its possible implications were striking. Events whose light and gravitational waves are simultaneously detected could resolve the 50-year mystery of the origin of short gamma-ray bursts; they might provide strong evidence for (or against) mergers as the main source of half the heaviest elements (the [Formula: see text]-process elements); and they could give an independent measurement of the Hubble constant. The closest events can also address a primary goal of gravitational-wave astrophysics: From the imprint of tides on inspiral waveforms, one can find the radius and tidal distortion of the inspiraling stars and infer the behavior of cold matter above nuclear density. Remarkably, the first observation of the inspiral and coalescence of a double neutron star system was accompanied by a gamma-ray burst and then an array of electromagnetic counterparts, and the combined effort of the gravitational-wave and astronomy communities has led to dramatic advances along all of these anticipated avenues of multimessenger astrophysics.

scholarly journals Search for neutron star binaries in the Local Group galaxies using LISA

2019 ◽  
Vol 489 (4) ◽  
pp. 4513-4519 ◽  
Author(s):  
Naoki Seto
Keyword(s):  
Neutron Star ◽  
Local Group ◽  
Design Sensitivity ◽  
Signal To Noise ◽  
Frequency Distributions ◽  
Current Design ◽  
R Process ◽  
Merger Rate ◽  
Process Elements

ABSTRACT We discuss the prospects of LISA for detecting neutron star binaries (NSBs) in the Local Group galaxies such as LMC and M31. Using the recently estimated merger rate ${\rm 1540 \, Gpc^{-3}\, yr^{-1}}$ and inversely applying the conventional arguments based on the B-band galaxy luminosities, we estimate the frequency distributions of NSBs in the local galaxies. We find that, after 10 yr observation with its current design sensitivity, LISA might detect ∼5 NSBs both in LMC and M31 with signal-to-noise ratios larger than 10. Some of the NSBs might be three-dimensionally localized well within LMC. These binaries will be useful for studying various topics including the origin of r-process elements.

scholarly journals The Dynamics of Binary Neutron Star Mergers and GW170817

2020 ◽  
Vol 70 (1) ◽  
pp. 95-119 ◽  
Author(s):  
David Radice ◽  
Sebastiano Bernuzzi ◽  
Albino Perego
Keyword(s):  
Neutron Star ◽  
Nuclear Astrophysics ◽  
Theoretical Models ◽  
Physical Processes ◽  
Binary Neutron Star ◽  
Compact Binary ◽  
Open Questions ◽  
Binary Mergers ◽  
R Process ◽  
Process Elements

With the first observation of a binary neutron star merger through gravitational waves and light, GW170817, compact binary mergers have now taken the center stage in nuclear astrophysics. They are thought to be one of the main astrophysical sites of production of r-process elements, and merger observations have become a fundamental tool to constrain the properties of matter. Here, we review our current understanding of the dynamics of neutron star mergers in general and of GW170817 in particular. We discuss the physical processes governing the inspiral, merger, and postmerger evolution, and we highlight the connections between these processes, the dynamics, and the multimessenger observables. Finally, we discuss open questions and issues in the field and the need to address them through a combination of better theoretical models and new observations.

scholarly journals R-process enrichment in ultrafaint dwarf galaxies

2020 ◽  
Vol 494 (1) ◽  
pp. 120-128 ◽  
Author(s):  
Yuta Tarumi ◽  
Naoki Yoshida ◽  
Shigeki Inoue
Keyword(s):  
Star Formation ◽  
Neutron Star ◽  
Galaxy Formation ◽  
Dwarf Galaxies ◽  
Long Distance ◽  
Stellar Feedback ◽  
The Galaxy ◽  
Star Binary ◽  
R Process ◽  
Process Elements

ABSTRACT We study the enrichment and mixing of r-process elements in ultrafaint dwarf galaxies (UFDs). We assume that r-process elements are produced by neutron-star mergers (NSMs), and examine multiple models with different natal kick velocities and explosion energies. To this end, we perform cosmological simulations of galaxy formation to follow mixing of the dispersed r-process elements driven by star formation and the associated stellar feedback in progenitors of UFDs. We show that the observed europium abundance in Reticulum II is reproduced by our inner explosion model where an NSM is triggered at the centre of the galaxy, whereas the relatively low abundance in Tucana III is reproduced if an NSM occurs near the virial radius of the progenitor galaxy. The latter case is realized only if the neutron-star binary has a large natal kick velocity and travels over a long distance of a kiloparsec before merger. In both the inner and outer explosion cases, it is necessary for the progenitor galaxy to sustain prolonged star formation over a few hundred million years after the NSM, so that the dispersed r-process elements are well mixed within the interstellar medium. Short-duration star formation results in inefficient mixing, and then a large variation is imprinted in the stellar europium abundances, which is inconsistent with the observations of Reticulum II and Tucana III.

The Electromagnetic Counterpart of the Gravitational Wave Source GW170817

2017 ◽  
Vol 14 (S339) ◽  
pp. 56-60
Author(s):  
T.-W. Chen
Keyword(s):  
Neutron Star ◽  
Gravitational Wave ◽  
Near Infrared ◽  
Direct Evidence ◽  
Gamma Ray ◽  
Infrared Imaging ◽  
Wave Source ◽  
Strong Source ◽  
Process Elements

AbstractOn 17th August 2017 a strong source of gravitational waves was detected by the LIGO-Virgo collaboration. The signal lasted for 60 seconds, and the event was followed just 2 seconds later by a short burst of gamma-rays that was detected by Fermi and INTEGRAL. The gravitational-wave and gamma-ray source had consistent sky positions to within about 30 square degrees. Within 10 hours of the gravitational-wave source event, a fast fading optical and near-infrared counterpart was discovered, which was subsequently followed-up and studied intensively for several weeks and months by numerous facilities. This talk presented the results from our optical and near-infrared imaging and spectroscopic follow-up campaign of this unprecedented discovery, which was the first electromagnetic counterpart of a gravitational-wave source, the first identification of a neutron star–neutron star merger, and the first direct evidence of the source of r-process elements. It focussed on the results of the GROND and ePESSTO teams, showing that this remarkable transient truly opened up the era of multi-messenger astronomy.

scholarly journals Chemical Evolution of R-process Elements in the Hierarchical Galaxy Formation

2015 ◽  
Vol 11 (S317) ◽  
pp. 318-319
Author(s):  
Yutaka Komiya ◽  
Toshikazu Shigeyama
Keyword(s):  
Neutron Star ◽  
Chemical Evolution ◽  
Galaxy Formation ◽  
Milky Way ◽  
Galactic Chemical Evolution ◽  
Halo Stars ◽  
R Process ◽  
Process Elements ◽  
Milky Way Halo

AbstractThe main astronomical source of r-process elements has not yet been identified. One plausible site is neutron star mergers (NSMs). From the perspective of Galactic chemical evolution, however, it has been pointed out that the NSM scenario is incompatible with observations. Recently, Tsujimoto & Shigeyama (2014) pointed out that NSM ejecta can spread into much larger volume than ejecta from a supernova. We re-examine the chemical evolution of r-process elements under the NSM scenario considering this difference in propagation of the ejecta. We find that the NSM scenario can be compatible with the observed abundances of the Milky Way halo stars.

scholarly journals Imprints of r-process heating on fall-back accretion: distinguishing black hole–neutron star from double neutron star mergers

2019 ◽  
Vol 485 (3) ◽  
pp. 4404-4412 ◽  
Author(s):  
D Desai ◽  
B D Metzger ◽  
F Foucart
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Neutron Star ◽  
Gamma Ray ◽  
Late Time ◽  
X Ray ◽  
Power Law Decay ◽  
Process Heating ◽  
R Process ◽  
The Impact

ABSTRACT Mergers of compact binaries containing two neutron stars (NS–NS), or a neutron star and a stellar mass black hole (NS–BH), are likely progenitors of short-duration gamma-ray bursts (SGRBs). A fraction ${\gtrsim } 20{{\ \rm per\ cent}}$ of SGRBs is followed by temporally extended (≳minute-long), variable X-ray emission, attributed to ongoing activity of the central engine. One source of late-time engine activity is fall-back accretion of bound tidal ejecta; however, observed extended emission light curves do not track the naively anticipated, uninterrupted t−5/3 power-law decay, instead showing a lull or gap in emission typically lasting tens of seconds after the burst. Here, we re-examine the impact of heating due to rapid neutron capture (r-process) nucleosynthesis on the rate of the fall-back accretion, using ejecta properties extracted from numerical relativity simulations of NS–BH mergers. Heating by the r-process has its greatest impact on marginally bound matter, hence its relevance to late-time fall-back. Depending on the electron fraction of the ejecta and the mass of the remnant black hole, r-process heating can imprint a range of fall-back behaviour, ranging from temporal gaps of up to tens of seconds to complete late-time cut-off in the accretion rate. This behaviour is robust to realistic variations in the nuclear heating experienced by different parts of the ejecta. Central black holes with masses ${\lesssim } 3\, \mathrm{M}_{\odot }$ typically experience absolute cut-offs in the fall-back rate, while more massive ${\gtrsim } 6\!-\!8\, \mathrm{M}_{\odot }$ black holes instead show temporal gaps. We thus propose that SGRBs showing extended X-ray emission arise from NS–BH, rather than NS–NS, mergers. Our model implies an NS–BH merger detection rate by LIGO that, in steady state, is comparable to or greater than that of NS–NS mergers.

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