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-Time evolution of the total radioactive heating rate per unit mass, Q, mass number A, and temperature T (all mass-averaged over the ejecta) for the 1.35-1.35M (solid lines) and 1.2-1.5M (dotted lines) NS mergers.
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Although the rapid neutron-capture process, or r-process, is fundamentally important for explaining the origin of approximately half of the stable nuclei with A > 60, the astrophysical site of this process has not been identified yet. Here we study r-process nucleosynthesis in material that is dynamically ejected by tidal and pressure forces during...
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Citations
... If BNS mergers are the dominant site for r -process nucleosynthesis (see e.g. Lattimer & Schramm 1974;Goriely et al. 2011;Just et al. 2015;Côté et al. 2017), another more indirect evidence is provided by the observed large scatter of [Eu/Fe] abundances in extremely metal-poor stars (see the compilation by Suda et al. 2008), which requires fast mergers allowing the production of r -process elements when the environment is still extremely metal-poor (see e.g. Vangioni et al. 2016;Côté et al. 2019;Dvorkin et al. 2021). ...
We present a complete numerical model of the afterglow of a laterally-structured relativistic ejecta from radio to very high energy (VHE). This includes a self-consistent calculation of the synchrotron radiation, with its maximum frequency, and of Synchrotron Self-Compton (SSC) scatterings taking into account the Klein-Nishina regime. The attenuation due to pair production is also included. This model is computationally-efficient, allowing for multi-wavelength data fitting. As a validation test, the radiative model is used to fit the broad-band spectrum of GRB 190114C at 90 s up to the TeV range. The full model is then used to fit the afterglow of GW 170817 and predict its VHE emission. We find that the SSC flux at the peak was much dimmer than the upper limit from H.E.S.S. observations. However, we show that either a smaller viewing angle or a larger external density would make similar off-axis events detectable in the future at VHE, even above 100 Mpc with the sensitivity of the CTA. Large external densities are expected in the case of fast mergers, but the existence of a formation channel for such binary neutron stars is still uncertain. We highlight that VHE afterglow detections would help probing efficiently such systems.
... On the other hand, relativistic outflows play a pivotal role in a multitude of astronomical phenomena. For example, it has been speculated that the BNS merger remnants and relativistic ejecta are the central engines of gamma-ray bursts [20][21][22][23] and kilo-nova [24][25][26][27][28][29]. Relativistic outflows or jets are instrumental in shaping the emission profiles and contributing significantly to the high-energy radiation observed. ...
Relativistic jets accompany the collapse of massive stars, the merger of compact objects, or the accretion of gas in active galactic nuclei. They carry information about the central engine and generate electromagnetic radiation. No self-consistent simulations have been able to follow these jets from their birth at the black hole scale to the Newtonian dissipation phase, making the inference of central engine property through astronomical observations undetermined. We present the general relativistic moving-mesh framework to achieve the continuity of jet simulations throughout space and time. We implement the general relativistic extension for the moving-mesh relativistic hydrodynamic code, , and develop a tetrad formulation to utilize the Harten-Lax-van Leer Contact Riemann solver in the general relativistic moving-mesh code. The new framework is able to trace the radial movement of relativistic jets from central regions where strong gravity holds all the way to distances of jet dissipation.
Published by the American Physical Society 2024
... To do so, these authors provided a shortlist of forbidden trans-itions that were coincident with the two emission features appearing at ∼2.1 µm and ∼4.4 µm. Among those transitions, chosen to fit into the fairly broad profiles of these observed features, namely between 1.94 and 2.35 µm for the first one and between 4.18 and 4.55 µm for the second one, the [Nd III] line at 41 884 Å was presented as one of the candidate forbidden transitions contributing to the 4.4 µm emission feature based on the argument that neodymium is expected to be one of the most abundant lanthanide elements synthesised (Goriely et al 2011, Gillanders et al 2022 and on the fact that this particular transition has an upper level of low excitation energy making it possible to have a high relative population. However, given the extremely low transition probability obtained in the present work for this line using both theoretical approaches, i.e. gA HFR = 6.53 × 10 −8 s −1 and gA MCDHF = 3.87 × 10 −8 s −1 , it seems very unlikely that the latter contributes to the observed spectral feature. ...
In this paper, we present new radiative rate calculations for forbidden transitions, namely magnetic dipole (M1) and electric quadrupole (E2) transitions, involving all the experimentally known energy levels within the 4f⁴ ground configuration of doubly ionized neodymium (Nd III). To do this, and in order to estimate the accuracy of the results obtained, two independent computational approaches based on the pseudo-relativistic Hartree–Fock and the fully relativistic Dirac-Hartree–Fock methods were used. The transition probabilities calculated with these two approaches showed good overall agreement, in particular for the most intense forbidden lines for which the relative differences did not exceed 25%. From these new atomic data, some astrophysical implications were deduced such as the possibility (or not) of observing some [Nd III] lines on the infrared spectra recorded by the James Webb Space Telescope, more precisely for the analysis of nebular phase kilonova spectra following compact object mergers.
... A comprehensive understanding of the magnetic dipole (M1) nuclear response is essential to various aspects of nuclear structure phenomena, such as isospin-mixing, isospinsplitting, and ground-state correlations [1][2][3]. It also aids in the study of radiative neutron capture, which has a key role in the production of neutron-rich elements in hot stellar environments [4][5][6][7]. Several experimental and theoretical studies have revealed intriguing behavior in γ -ray strength functions (γ SFs), and a notable enhancement is observed in the strength function toward lower transition energies [8][9][10][11][12][13][14][15]. ...
Finite-temperature effects in electromagnetic transitions in nuclei contribute to many aspects of nuclear structure and astrophysically relevant nuclear reactions. While electric dipole transitions have already been extensively studied, the temperature sensitivity of magnetic transitions remains largely unknown. This work comprises the study of isovector magnetic dipole excitations (M1) occurring between spin-orbit (SO) partner states using the recently developed self-consistent finite-temperature relativistic quasiparticle random-phase approximation (FT-RQRPA) in the temperature range from T = 0 to 2 MeV. The M1 strength distributions of 40−60 Ca and 100−140 Sn isotopic chains exhibit a considerable temperature dependence. The M1 strength peaks shift significantly towards the lower energies due to the decrease in SO splitting energies and weakening of the residual interaction, especially above the critical temperatures where the pairing correlations vanish. By exploring the relevant two-quasiparticle configurations contributing to the M1 strength of closed-and open-shell nuclei, new proton and neutron excitation channels between SO partners are observed in low-and high-energy regions due to the thermal unblocking effects around the Fermi level. At higher temperatures, we have noticed an interesting result in 40,60 Ca nuclei, the appearance of M1 excitations, which are forbidden at zero temperature due to fully occupied (or fully vacant) spin-orbit partner states.
... Approximately half of the elements in the Universe heavier than iron are synthesized by rapid neutron capture nucleosynthesis: the r-process (see Cowan et al. 2021 for a review). Extreme astrophysical environments-namely, mergers of neutron stars (NS-NS) or an NS and a black hole (NS-BH), and other proposed sources like collapsars or magnetorotational supernovae-offer leading candidate sites for this r-process nucleosynthesis owing to their exceptionally high densities of free neutrons (Lattimer & Schramm 1974;Symbalisty & Schramm 1982;Eichler et al. 1989;Freiburghaus et al. 1999;Goriely et al. 2011;Korobkin et al. 2012;Bauswein et al. 2013). However, it is still unclear which of these channels dominates. ...
In kilonovae, freshly synthesized r -process elements imprint features on optical spectra, as observed in AT2017gfo, the counterpart to the GW170817 binary neutron star merger. However, measuring the r -process compositions of the merger ejecta is computationally challenging. Vieira et al. introduced Spectroscopic r -process Abundance Retrieval for Kilonovae ( SPARK ), a software tool to infer elemental abundance patterns of the ejecta and associate spectral features with particular species. Previously, we applied SPARK to the 1.4-day spectrum of AT2017gfo and inferred its abundance pattern for the first time, characterized by electron fraction Y e = 0.31, a substantial abundance of strontium, and a dearth of lanthanides and heavier elements. This ejecta is consistent with wind from a remnant hypermassive neutron star and/or accretion disk. We now extend our inference to spectra at 2.4 and 3.4 days and test the need for multicomponent ejecta, where we stratify the ejecta in composition. The ejecta at 1.4 and 2.4 days is described by the same single blue component. At 3.4 days, a new redder component with lower Y e = 0.16 and a significant abundance of lanthanides emerges. This new redder component is consistent with dynamical ejecta and/or neutron-rich ejecta from a magnetized accretion disk. As expected from photometric modeling, this component emerges as the ejecta expands, the photosphere recedes, and the earlier bluer component dims. At 3.4 days, we find an ensemble of lanthanides, with the presence of cerium most concrete. This presence of lanthanides has important implications for the contribution of kilonovae to the r -process abundances observed in the Universe.
... Neutron-rich material ejected during the merger can synthesize heavy elements via rapid neutron capture (the r-process; Burbidge et al. 1957;Cameron 1957). Numerical simulations have shown that these mergers can produce vastly different quantities and varieties of r-process elements, depending on the exact properties of the merging binary and the resulting physical conditions of the post-merger ejecta (e.g., Lattimer & Schramm 1974;Eichler et al. 1989;Freiburghaus et al. 1999;Rosswog et al. 1999;Goriely et al. 2011;Korobkin et al. 2012;Perego et al. 2014;Wanajo et al. 2014;Just et al. 2015;Kasen et al. 2017;Kawaguchi et al. 2020;Tanaka et al. 2020). To determine the contribution of the merger channel to producing the cosmic abundances of various r-process elements, we need observational measurements for which (and how many) elements are produced in mergers. ...
Kilonovae are likely a key site of heavy r -process element production in the Universe, and their optical/infrared spectra contain insights into both the properties of the ejecta and the conditions of the r -process. However, the event GW170817/AT2017gfo is the only kilonova so far with well-observed spectra. To understand the diversity of absorption features that might be observed in future kilonovae spectra, we use the TARDIS Monte Carlo radiative transfer code to simulate a suite of optical spectra spanning a wide range of kilonova ejecta properties and r -process abundance patterns. To identify the most common and prominent absorption lines, we perform dimensionality reduction using an autoencoder, and we find spectra clusters in the latent space representation using a Bayesian Gaussian Mixture model. Our synthetic kilonovae spectra commonly display strong absorption by strontium 38 Sr ii , yttrium 38 Y ii , and zirconium 40 Zr i–ii , with strong lanthanide contributions at low electron fractions ( Y e ≲ 0.25). When a new kilonova is observed, our machine-learning framework will provide context on the dominant absorption lines and key ejecta properties, helping to determine where this event falls within the larger “zoo” of kilonovae spectra.
... In Gillanders et al. (2022), hereafter referred to as Paper I, we presented analysis of the early, photospheric spectra of the kilonova (KN) AT2017gfo, the electromagnetic (EM) counterpart to a binary neutron star merger (Abbott et al. 2017;Andreoni et al. 2017;Arcavi et al. 2017;Chornock et al. 2017;Coulter et al. 2017;Cowperthwaite et al. 2017;Drout et al. 2017;Evans et al. 2017;Kasliwal et al. 2017;Lipunov et al. 2017;Nicholl et al. 2017;Pian et al. 2017;Shappee et al. 2017;Soares-Santos et al. 2017;Smartt et al. 2017;Tanvir et al. 2017;Troja et al. 2017;Utsumi et al. 2017;Valenti et al. 2017). KNe are thought to be ideal locations for the synthesis of material by the -process, and many theoretical simulations have corroborated this (Lattimer & Schramm 1974;Eichler et al. 1989;Freiburghaus et al. 1999;Rosswog et al. 1999;Goriely et al. 2011Goriely et al. , 2013Goriely et al. , 2015Korobkin et al. 2012;Perego et al. 2014;Wanajo et al. 2014;Just et al. 2015). In Paper I, we focussed on identifying features that we can attribute to a single transition (or a set of transitions) belonging to a specific species. ...
... The horizontal grey dashed line marks a wavelength ratio of unity -the ratios for all features should tend towards this value (by design). that a composition extracted from a realistic hydrodynamical simulation of a binary neutron star (BNS) merger (Goriely et al. 2011Bauswein et al. 2013) contained sufficient strontium for this feature to be produced by Sr ii. As the ejecta material evolves from its photospheric phase, through to a quasi-nebular regime, the peak of the feature emission should broadly line up with that of the rest wavelength of the transition (or set of transitions) that produce it. ...
... The case for He i is also strengthened when considering nucleosynthesis arguments. He is among the most abundant elements in many of the composition profiles we present in Paper I. These composition profiles were extracted from nuclear network calculations based on a realistic hydrodynamical simulation of a BNS merger (Goriely et al. 2011Bauswein et al. 2013), with some modification. The data have a prescribed distribution of , from which we extract 'representative' composition profiles, effectively binned by . ...
Binary neutron star mergers are the first confirmed site of element nucleosynthesis by the rapid neutron-capture process (r-process). The kilonova AT2017gfo is the only electromagnetic counterpart of a neutron star merger spectroscopically observed. We analyse the entire spectral sequence of AT2017gfo (from merger to +10.4 days) and identify seven emission-like features. We confirm that the prominent 1.08 μm feature can be explained by the Sr ii near-infrared triplet evolving from a P-Cygni profile through to pure emission. We calculate the expected strength of the [Sr ii] doublet and show that its absence requires highly clumped ejecta. Near-infrared features at 1.58 and 2.07 μm emerge after three days and become more prominent as the spectra evolve. We model these as optically thick P-Cygni profiles and alternatively as pure emission features (with FWHM ≃ 35600 ± 6600 km s−1), and favour the latter interpretation. The profile of the strong 2.07 μm emission feature is best reproduced with two lines, centred at 2.059 and 2.135 μm. We search for candidate ions for all prominent features in the spectra. Strong, permitted transitions of La iii, Ce iii, Gd iii, Ra ii and Ac i are plausible candidates for the emission features. If any of these features are produced by intrinsically weak, forbidden transitions, we highlight candidate ions spanning the three r-process peaks. The second r-process peak elements Te and I have plausible matches to multiple features. We highlight the need for more detailed and quantitative atomic line transition data.
... The Odd-Z element Na showed a Solar value, while Al was slightly enhanced, with [Al/Fe] =+ 0.15, suggesting that these elemental abundances are in good agreement with the typical abundance behaviour found in other old BGCs such as NGC 6522 (Barbuy et al. 2009(Barbuy et al. , 2014Fern ández-Trincado et al. 2019b ) and HP 1 (Geisler et al. 2021 ). On the other hand, the authors also noted a spread in the abundances of Y and Ba, compatible with expectations from massive spinstars (Chiappini et al. 2011 ;Frischknecht et al. 2016 ), while the r -element Eu is highly enhanced, with [Eu/Fe] =+ 0.6, compatible with production by supernovae type II (SNII) or neutron star mergers (Goriely, Bauswein & Janka 2011 ;Wanajo, Hirai & Prantzos 2021 ). Such high values of Eu are usually found in field halo stars, while higher enhancements are typically found in some ultra-faint dwarf galaxies (see e.g. ...
This study presents the results concerning six red giant stars members of the globular cluster NGC 6558. Our analysis utilized high-resolution near-infrared spectra obtained through the CAPOS initiative (the APOgee Survey of Clusters in the Galactic Bulge), which focuses on surveying clusters within the Galactic Bulge, as a component of the Apache Point Observatory Galactic Evolution Experiment II survey (APOGEE-2). We employ the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS) code to provide line-by-line elemental-abundances for Fe-peak (Fe, Ni), α-(O, Mg, Si, Ca, Ti), light-(C, N), odd-Z (Al), and the s-process element (Ce) for the four stars with high-signal-to-noise ratios. This is the first reliable measure of the CNO abundances for NGC 6558. Our analysis yields a mean metallicity for NGC 6558 of 〈[Fe/H]〉 = −1.15 ± 0.08, with no evidence for a metallicity spread. We find a Solar Ni abundance, 〈[Ni/Fe]〉 ∼ +0.01, and a moderate enhancement of α-elements, ranging between +0.16 and <+0.42, and a slight enhancement of the s-process element 〈[Ce/Fe]〉 ∼ +0.19. We also found low levels of 〈[Al/Fe]〉 ∼ +0.09, but with a strong enrichment of nitrogen, [N/Fe] > +0.99, along with a low level of carbon, [C/Fe] < −0.12. This behaviour of Nitrogen-Carbon is a typical chemical signature for the presence of multiple stellar populations in virtually all GCs; this is the first time that it is reported in NGC 6558. We also observed a remarkable consistency in the behaviour of all the chemical species compared to the other CAPOS bulge GCs of the same metallicity.
... Binary neutron star (NS) mergers have been considered as promising sites of r-process nucleosynthesis (e.g., Eichler et al. 1989;Freiburghaus et al. 1999;Goriely et al. 2011;Korobkin et al. 2012;Wanajo et al. 2014). In 2017, associated with the detection of gravitational waves (GWs) from a NS merger (GW170817; Abbott et al. 2017a), the electromagnetic counterpart AT2017gfo was observed (Abbott et al. 2017b). ...
Kilonova spectra provide us with information of r -process nucleosynthesis in neutron star mergers. However, it is still challenging to identify individual elements in the spectra mainly due to the lack of experimentally accurate atomic data for heavy elements at near-infrared wavelengths. Recently, Domoto et al. proposed that the absorption features around 14500 Å in the observed spectra of GW170817/AT2017gfo are Ce iii lines. But they used theoretical transition probabilities ( gf -values) whose accuracy is uncertain. In this paper, we derive the astrophysical gf -values of three Ce iii lines, aiming at verifying this identification. We model high-resolution H -band spectra of four F-type supergiants showing clear Ce iii absorption features by assuming stellar parameters derived from optical spectra in the literature. We also test the validity of the derived astrophysical gf -values by estimating the Ce iii abundances of Ap stars. We find that the derived astrophysical gf -values of the Ce iii lines are systematically lower by about 0.25 dex than those used in previous work of kilonovae, while they are still compatible within the uncertainty ranges. By performing radiative transfer simulations of kilonovae with the derived gf -values, we find that the identification of Ce iii as a source of absorption features in the observed kilonova spectra still stands, even considering the uncertainties in the astrophysical gf -values. This supports the identification of Ce in the spectra of GW170817/AT2017gfo.
... As these nuclei decay, they release energy into the surrounding matter that would be emitted as ultraviolet, optical, and infrared thermal radiation once the ejecta becomes optically thin (Li & Paczyński 1998;Kulkarni 2005;Metzger et al. 2010). This thermal emission is now commonly referred to as a kilonova (Metzger 2019) and serves as the bridge between the r-process elements produced by neutron star mergers and their resultant electromagnetic emission (Goriely et al. 2011;Roberts et al. 2011;Korobkin et al. 2012;Metzger & Berger 2012;Cowan et al. 2021). Aside from the transient electromagnetic kilonova emission (including a gamma-ray burst; Abbott et al. 2017;Savchenko et al. 2017), r-process material ejecta from neutron star binary mergers like GW170817 could produce another observable signature: relic r-process abundances such as in ancient, metalpoor stars and in our solar system. ...
Kilonovae, one source of electromagnetic emission associated with neutron star mergers, are powered by the decay of radioactive isotopes in the neutron-rich merger ejecta. Models for kilonova emission consistent with the electromagnetic counterpart to GW170817 predict characteristic abundance patterns, determined by the relative balance of different types of material in the outflow. Assuming that the observed source is prototypical, this inferred abundance pattern in turn must match r -process abundances deduced by other means, such as what is observed in the solar system. We report on analysis comparing the input mass-weighted elemental compositions adopted in our radiative transfer simulations to the mass fractions of elements in the Sun, as a practical prototype for the potentially universal abundance signature from neutron star mergers. We characterize the extent to which our parameter inference results depend on our assumed composition for the dynamical and wind ejecta and examine how the new results compare to previous work. We find that a dynamical ejecta composition calculated using the FRDM2012 nuclear mass and FRLDM fission models with extremely neutron-rich ejecta ( Y e = 0.035) along with moderately neutron-rich ( Y e = 0.27) wind ejecta composition yields a wind-to-dynamical mass ratio of M w / M d = 0.47, which best matches the observed AT2017gfo kilonova light curves while also producing the best-matching abundance of neutron capture elements in the solar system, though, allowing for systematics, the ratio may be as high as of order unity.
