Matter expelled from binary neutron star (BNS) mergers can harbor r-process nucleosynthesis and power a Kilonova (KN), which represents a major EM counterpart to gravitational wave (GW) signals.
Both the elemental yields and the subsequent KN transient are intimately related to the astrophysical conditions of the merger ejecta, which in turn indirectly depend on the EOS describing the nuclear...
We present three-dimensional radiative transfer calculations for the ejecta from a neutron star merger that include line-by-line opacities for tens of millions of bound-bound transitions, composition from an r-process nuclear network, and time-dependent thermalization of decay products from individual $\alpha$ and $\beta^-$ decay reactions. In contrast to expansion opacities and other...
The simultaneous observation of the gravitational-wave and electromagnetic-wave signals from the event provides a great opportunity to study physics in extreme conditions. The quantitative and accurate prediction of the signals is the key to maximizing the scientific returns from the observation, and dramatic progress has been achieved in the field since the first detection of a binary neutron...
The concurrent gravitational- and electromagnetic wave observations of GW170817 both proved the importance of neutron star mergers in the production of r-process elements and demonstrated the difficulties in accurately estimating the mass from EM emission. Although a growing number of potential “kilonovae” have been observed associated with short (and long) gamma-ray bursts, these events...
The detection of the gravitational wave (GW) signal GW170817 and the electromagnetic (EM) signal AT2017gfo confirmed the association between binary neutron star (BNS) mergers and kilonovae (KNe) and showed the potential of joint detection to unveil the nature of neutron stars and the nucleosynthesis of heavy elements in the Universe. The next-generation GW interferometers, such as the Einstein...
Since the extraordinary observations of AT2017gfo, we have seen many complementary advancements in our capability to observe kilonovae and model them. However, our sample of confident kilonovae candidates remains small, with many candidates since AT2017gfo contaminated by the afterglow from a gamma-ray burst. In this talk, I will highlight the issues we need to resolve to decouple kilonovae...
The detection of an electromagnetic counterpart to the gravitational-wave source GW 170817 marked year zero of the multi-messenger gravitational-wave era. This event was generated by the coalescence of two neutron stars and gave rise to an electromagnetic transient, dubbed a “kilonova”, powered by the radioactive decay of heavy (r-process) nuclei synthesised during the merger. In this talk, I...
Binary neutron star mergers are expected to produce a relativistic jet and a fast dynamical ejecta, with mildly relativistic velocities extending to $\beta=v/c>0.6$. We consider the radio to X-ray synchrotron emission produced by collisionless shocks driven by such spherical fast ejecta into the interstellar medium. We provide analytic expressions for this non-thermal emission, which are an...
Observed properties of kilonovae are largely controlled by atomic properties of synthesized heavy elements. This means that we can study the heavy element nucleosynthesis in neutron star mergers by decoding light curves and spectra of kilonovae. To have a better link between theory and observations, we have systematically constructed atomic data of heavy elements. In this talk, we will...
The detection of GW170817 and the accompanying electromagnetic counterpart, AT2017gfo, have provided an important set of observational constraints for the high density Equation of State and r-process nucleosynthesis. To interpret the observations of AT2017gfo, detailed theoretical models are required. The majority of binary neutron star ejecta models considered when simulating kilonovae have...
The observed luminosity of astronomical transients, such as Type Ia supernovae (Ia SNe) or Kilonovae (KNe) that follow neutron star mergers (NSMs), is powered by radioactive decay of unstable nuclei in rapidly expanding ejecta. Understanding the thermalization process of high energy particles produced by radioactive decay is essential for modeling the light curves, and thus for inferring from...
There are several computer packages such as HULLAC, FAC, AMBIT, GRASP, COWAN CODE for atomic structure calculations, each having their strengths and weaknesses [1-5]. Here we give an account for GRASP: theory, methodology, and issues of program handling [6,7]. Through a number examples, we discuss the applicability of GRASP for atomic systems of different complexity of relevance for...
With the recent detection of multiple neutron-star merger events, the need for a more comprehensive understanding of nuclear and atomic properties, as well as advanced astrophysical simulations, has become increasingly important to accurately predict r-process nucleosynthesis yields and electromagnetic signals when presented with observational data. The lack of atomic data has led to a number...
In 2017, the electromagnetic counterpart AT2017gfo to the binary neutron star merger GW170817 was observed by all major telescopes on Earth. While it was immediately clear that the transient following the merger event, is powered by the radioactive decay of r-process nuclei, only few tentative identifications of light r-process elements have been made so far. One of the major limitations for...
Modeling of the spectroscopic observations of kilonova rely on radiative data to have a good spectral coverage, being complete nad have a desired accuracy. Many of the r-process elements expected to be produced in kilonovas have very complex spectra, and thus a challenging task to provide accurate and large data sets for. Experimental data is sparce for these elements responsible for the...
Laser produced plasmas (LPPs) are key components for atomic and ionic spectroscopy. They act as sources of neutrals and ions, and of radiation to probe their structure.
Both emission and absorption spectroscopy are facilitated using LPPs. As part of the HEAVYMETAL project, the team at UCD will develop new configurations of LPPs to enhance, and perhaps optimise, populations of desired species....
We will review atomic processes relevant to kilonovae and the current
state-of-play in servicing the needs of modellers.
The atomic processes relevant to kilonovae separate into their two plasma phases: the first few days, where LTE holds, and the subsequent non-LTE phase. In LTE, where fractional ionic abundances and level populations are given by the Saha--Boltzmann equations, the main...
In kilonovae, freshly-synthesized r-process elements imprint absorption features on optical spectra, as observed in AT2017gfo. These spectral features provide insights into the physical conditions of the r-process, but measuring the detailed composition of the ejecta is challenging. [Vieira et al. (2023)][1] introduced Spectroscopic r-Process Abundance Retrieval for Kilonovae (SPARK), a tool...
The atomic properties of r-process elements are predicted to play an important role in determining the electromagnetic emission from kilonovae, which result from the merger of two neutron stars. More specifically, the radiative opacity is an important quantity that determines the flow of radiation through the ejecta and wind material that result from the merger. In this talk, we discuss the...
Kilonovae light-curves depend on the efficiency with which beta decay e$^\pm$ deposit their energy in the expanding ejecta. We show that the time $t_{\rm e}$, at which the deposited energy fraction drops to $1/e$, depends mainly on ejecta density and velocity, and only weakly on the initial electron fraction $Y_e$ and entropy $s_0$: $t_{\rm e} = t_0 \times (\rho t^3/(\rho t^3)_0)^{s_{\rm e}}$...
Spectra of kilonovae, radioactively-powered electromagnetic radiation from neutron star mergers, provide us with information of r-process nucleosynthesis. In the photospheric phase, which photons diffuse out from optically thick matter, absorption features in the spectra can be used to identify individual elements. However, the decode of the spectra for the first detected kilonova...
Neutron star mergers are believed to be a major cosmological source of rapid neutron-capture elements, but only limited definite spectral identifiers of these heavy elements have been found. Identifying P$\,$Cygni lines are important because they provide significant information not just potentially on the elemental composition of the merger ejecta, but also on the velocity, geometry, and...
The production of elements heavier than iron in the Universe still remains an unsolved mystery. About half of them are thought to be notably produced by the astrophysical r-process (rapid neutron-capture process) [1], for which one of the most promising production sites are neutron star mergers (NSM) [2]. In August 2017, gravitational waves generated by a NSM event were detected by the LIGO...
I will present a summary of the observational properties of kilonovae. This sample includes AT2017gfo (associated with GW170817) and the more extensive but more sparsely sampled set of kilonovae identified in short and, more recently, in long-duration gamma-ray bursts. The broad photometric properties (peak magnitudes, timescales) are similar in many cases in which kilonovae are seen. However,...
A remarkable sequence of spectra were taken every 24hrs for 10 nights of the kilonova AT2017gfo. These covered 0.3-2.2microns at good signal to noise and spectral resolution (with the VLT X-shooter instrument). However AT2017gfo was at the relatively close distance of 40Mpc, and the volumetric rates of BNS mergers now imply this was a once in a decade (roughly) event. Application of radiative...
Kilonovae are expected to enter the nebular phase on a time scales of weeks. In the nebular phase, the kilonova spectra are considered to be composed of emission lines of r-process elements. Observing the nebular spectra may offer us unique opportunities to identify elements synthesized in neutron star merger ejecta. I will introduce some important concepts in the nebular modelings. Then the...
The electromagnetic transient following a binary neutron star merger is known as a kilonova (KN). KN ejecta evolve rapidly away from Local Thermodynamic Equilibrium (LTE) conditions to a regime where the thermodynamic conditions are defined by Non-Local Thermodynamic Equilibrium (NLTE) processes. In this talk, I will present results from the 1D NLTE modelling of KNe using the spectral...
Recent advancements in astrophysics, such as the James Webb space telescope (JWST) and the LIGO/Virgo gravitational wave detectors, have introduced new demands on atomic physics. With the JWST operating in the infrared spectral regime, and the LIGO/Virgo leading to the ground-breaking discovery of the first neutron-star-merger event accompanied by a kilonova transient (arguably a dominant...
The electromagnetic signals from the kilonova AT2017gfo present an opportunity to study an astrophysical site of the r-process which is considered to produce about half of the elements heavier than iron. The decline of the bolometric light curve is broadly consistent with being powered by the decays of unstable nuclei expected from r-process nucleosynthesis. The light curve is sensitive to the...
The spectroscopic data obtained for AT2017gfo remain the only spectral observations of a kilonova event. These data, despite being obtained ~6 years ago, are still not fully understood, and still contain a number of unexplored features. Composition studies investigating the abundance of the synthesised r-process material have proven challenging to undertake. Proposed identifications of...
