arXiv subjects

Eleonora Loffredo

Publications and source records attributed to Eleonora Loffredo.

5 recordsLinked to original sources

arXiv2026

The MARTINI platform II. Tracing r-process nucleosynthesis in neutron star mergers with long-lived remnants

Binary neutron star (BNS) mergers are among the primary sites of the rapid neutron-capture (r-)process. In mergers with long-lived remnants, sustained neutrino irradiation raises the electron fraction of the disc wind ejecta, modifying the resulting nucleosynthesis pattern. Yields from numerical-relativity simulations with accurate neutrino transport are needed to quantify the contribution of BNS mergers to the Galactic production of heavy elements and to interpret kilonova spectra. We present and publicly release tracer trajectories and nucleosynthesis yields for eight BNS mergers forming long-lived neutron star remnants, obtained from general-relativistic simulations with M1 neutrino transport, spanning two equations of state (DD2 and SFHo), and a range of total masses and mass ratios. Passive tracer particles following the dynamical and wind ejecta were post-processed with the nuclear reaction network WinNet up to 1 Gyr. The yields and tracer trajectories are available on the MARTINI platform. At 1 day, the production of light and first-peak elements (He, Ni, Sr, and Y) is similar across models and is primarily enhanced by the neutrino-irradiated disc wind. The yields of heavy nuclei vary by more than one order of magnitude, with unequal-mass binaries producing the largest amounts owing to their more neutron-rich ejecta. Our He yields, particularly in the wind, exceed those of recent studies based on an M0 neutrino scheme, consistent with the stronger neutrino irradiation resulting from an M1 scheme. At 1 Gyr, all models reproduce the second and third solar r-process peaks, but differ in the first peak, the lanthanide region, the mass range between the first and second peaks, and the trans-lead region, reflecting the electron fraction distribution of the ejecta and the dynamical and wind contributions. Two equal-mass models provide a close match to the solar pattern.

astro-ph.HE↗

arXiv2025

$^{56}$Ni production in long-lived binary neutron star merger remnants

We investigate the nucleosynthesis and kilonova emission based on numerical-relativity binary neutron star merger simulations that incorporate a two-moment neutrino-transport scheme. Unlike in previous works with simpler neutrino treatments, a massive, fast (up to $v=0.3c$), proton-rich neutrino-driven wind develops in the post-merger phase of the simulations as long as the merger remnant does not collapse to a black hole. We evolve the ejecta for 100 days after the merger using 2D ray-by-ray radiation-hydrodynamics simulations coupled in-situ to a complete nuclear network. The most abundant nucleosynthesis products are He, $^{56}$Ni, and $^{56}$Co. We find a total yield of $\sim 10^{-3} M_\odot$ of $^{56}$Ni for all mergers that produce massive neutron star remnants, independently of the mass ratio and equation of state. After a few days, the decay of $^{56}$Ni and later $^{56}$Co becomes the primary source of heating in the matter expanding above the remnant. As a result, the kilonova light curve flattens on timescales of days for polar observation angles. The observation of this effect could serve as smoking gun for the presence of a long-lived neutron star remnant in future kilonova observations.

astro-ph.HE↗

arXiv2023

XKN: a Semi-analytic Framework for the Modelling of Kilonovae

After GW170817, kilonovae have become of great interest for the astronomical, astrophysics and nuclear physics communities, due to their potential in revealing key information on the compact binary merger from which they emerge, such as the fate of the central remnant or the composition of the expelled material. Therefore, the landscape of models employed for their analysis is rapidly evolving, with multiple approaches being used for different purposes. In this paper, we present xkn, a semi-analytic framework which predicts and interprets the bolometric luminosity and the broadband light curves of such transients. xkn models the merger ejecta structure accounting for different ejecta components and non-spherical geometries. In addition to light curve models from the literature based on time scale and random-walk arguments, it implements a new model, xkn-diff, which is grounded on a solution of the radiative transfer equation for homologously expanding material. In order to characterize the variety of the ejecta conditions, it employs time and composition dependent heating rates, thermalization efficiencies and opacities. We compare xkn light curves with reference radiative transfer calculations, and we find that xkn-diff significantly improves over previous semi-analytic prescriptions. We view xkn as an ideal tool for extensive parameter estimation data analysis applications.

astro-ph.HE↗

arXiv2023

Science with the Einstein Telescope: a comparison of different designs

The Einstein Telescope (ET), the European project for a third-generation gravitational-wave detector, has a reference configuration based on a triangular shape consisting of three nested detectors with 10 km arms, where in each arm there is a `xylophone' configuration made of an interferometer tuned toward high frequencies, and an interferometer tuned toward low frequencies and working at cryogenic temperature. Here, we examine the scientific perspectives under possible variations of this reference design. We perform a detailed evaluation of the science case for a single triangular geometry observatory, and we compare it with the results obtained for a network of two L-shaped detectors (either parallel or misaligned) located in Europe, considering different choices of arm-length for both the triangle and the 2L geometries. We also study how the science output changes in the absence of the low-frequency instrument, both for the triangle and the 2L configurations. We examine a broad class of simple `metrics' that quantify the science output, related to compact binary coalescences, multi-messenger astronomy and stochastic backgrounds, and we then examine the impact of different detector designs on a more specific set of scientific objectives.

gr-qc↗

arXiv2023

Muons in the aftermath of neutron star mergers and their impact on trapped neutrinos

In the upcoming years, present and next-generation gravitational wave observatories will detect a larger number of binary neutron star (BNS) mergers with increasing accuracy. In this context, improving BNS merger numerical simulations is crucial to correctly interpret the data and constrain the equation of state (EOS) of neutron stars (NSs). State-of-the-art simulations of BNS mergers do not include muons. However, muons are known to be relevant in the microphysics of cold NSs and are expected to have a significant role in mergers, where the typical thermodynamic conditions favour their production. Our work is aimed at investigating the impact of muons on the merger remnant. We post-process the outcome of four numerical relativity simulations of BNS mergers performed with three different baryonic EOSs and two mass ratios considering the first $15$ milliseconds after merger. We compute the abundance of muons in the remnant and analyse how muons affect the trapped neutrino component and the fluid pressure. We find that depending on the baryonic EOS, the net fraction of muons is between $30 \%$ and $70 \%$ the net fraction of electrons. Muons change the flavour hierarchy of trapped (anti-)neutrinos such that deep inside the remnant, muon anti-neutrinos are the most abundant, followed by electron anti-neutrinos. Finally, muons and trapped neutrinos modify the neutron-to-proton ratio, affecting the remnant pressure by up to $7\%$ when compared with calculations neglecting them. This work demonstrates that muons have a non-negligible effect on the outcome of BNS merger simulations, and they should be included to improve the accuracy of a simulation.

astro-ph.HE↗