Mergers of binary neutron stars usually result in the formation a hypermassive star (HMNS). Whether and when this remnant collapses to black hole (BH) depends primarily on equation state angular momentum transport processes, both which are uncertain. Here, we show that lifetime merger may be directly imprinted radioactively powered kilonova emission following merger. We employ axisymmetric, time-dependent hydrodynamic simulations accretion discs orbiting an HMNS variable lifetime,...

Expulsion of neutron-rich matter following the merger neutron star binaries is crucial to radioactively powered electromagnetic counterparts these events and their relevance as sources r-process nucleosynthesis. Here we explore long-term (viscous) evolution remnant black hole accretion discs formed in such mergers by means two-dimensional, time-dependent hydrodynamical simulations. The electron fraction due charged-current weak interactions included, neutrino self-irradiation modelled a...

We study the radioactively-powered transients produced by accretion disk winds following a compact object merger. Starting with outflows generated in two-dimensional hydrodynamical models, we use wavelength-dependent radiative transfer calculations to generate synthetic light curves and spectra. show that brightness color of resulting kilonova carry information about merger physics. In regions wind where neutrino irradiation raises electron fraction Ye > 0.25, r-process nucleosynthesis halts...

Type Ia supernovae (SNe Ia), thermonuclear explosions of carbon–oxygen white dwarfs (CO-WDs), are currently the best cosmological "standard candles," but triggering mechanism explosion is unknown. It was recently shown that rate head-on collisions typical field CO-WDs in triple systems may be comparable to SNe rate. Here we provide evidence supporting a scenario which majority result such CO-WDs. In this case, nuclear detonation due well understood shock ignition, devoid commonly introduced...

We investigate the long-term evolution of black hole accretion disks formed in neutron star mergers. These expel matter that contributes to an $r$-process kilonova, and can produce relativistic jets powering short gamma-ray bursts. Here we report results a three-dimensional, general-relativistic magnetohydrodynamic (GRMHD) simulation such disk which is evolved for long enough ($\sim 9$s, or $\sim 6\times 10^5 r_{\rm g}/c$) achieve completion mass ejection far from disk. Our model starts with...

We investigate the nucleosynthesis of heavy elements in winds ejected by accretion disks formed neutron star mergers. compute element formation disk outflows from hypermassive (HMNS) remnants variable lifetime, including effect angular momentum transport evolution. employ long-term axisymmetric hydrodynamic simulations to model ejecta, and r-process with tracer particles using a nuclear reaction network containing $\sim 8000$ species. find that previously known strong correlation between...

We consider $r$-process nucleosynthesis in outflows from black hole accretion discs formed double neutron star and -- mergers. These outflows, powered by angular momentum transport processes nuclear recombination, represent an important some cases dominant contribution to the total mass ejected merger. Here we calculate yields disc using thermodynamic trajectories hydrodynamic simulations, coupled a reaction network. find that produce robust abundance pattern around second peak (mass number...

The mergers of binaries containing neutron stars and stellar-mass black holes are the most promising sources for direct detection in gravitational waves by interferometers Advanced LIGO Virgo over next few years. concurrent electromagnetic emission from these events would greatly enhance scientific return discoveries. Here we review state art modeling signal star binary across different phases merger multiple wavelengths. We focus on those observables which provide sensitive diagnostics...

The accretion disk that forms after a neutron star merger is source of neutron-rich ejecta. ejected material contributes to radioactively-powered electromagnetic transient, with properties depend sensitively on the composition outflow. Here we investigate how spin black hole remnant influences mass ejection thermal and viscous timescales. We carry out two-dimensional, time-dependent hydrodynamic simulations disks including angular momentum transport approximate neutrino self-irradiation....

Neutron star mergers are unique laboratories of accretion, ejection, and r-process nucleosynthesis. We used 3D general relativistic magnetohydrodynamic simulations to study the role post-merger magnetic geometry in evolution merger remnant discs around stationary Kerr black holes. Our fully capture mass jet production, owing their exceptionally long duration exceeding $4$ s. Poloidal field configurations produce jets with energies $E_\mathrm{jet} \sim (4{-}30)\times10^{50}$ erg, isotropic...

We develop analytic and numerical models of the properties super-Eddington stellar winds, motivated by phases in evolution when energy deposition (via, e.g. unstable fusion, wave heating, or a binary companion) heats region near surface. This appears to occur giant eruptions luminous blue variables (LBVs), Type IIn supernovae progenitors, classical novae, X-ray bursts. show that wind kinetic power exceeds Eddington, photons are trapped behave like fluid. Convection does not play significant...

We study the ejection of mass during stellar core-collapse when stalled shock does not revive and a black hole forms. Neutrino emission protoneutron star phase causes decrease in gravitational core, resulting an outward going sound pulse that steepens into as it travels out through star. explore properties this mechanism over range progenitors using spherically-symmetric, time-dependent hydrodynamic simulations treat neutrino loss parametrically follow propagation entire find all types...

In recent years, there have been significant advances in multi-messenger astronomy due to the discovery of first, and so far only confirmed, gravitational wave event with a simultaneous electromagnetic (EM) counterpart, as well improvements numerical simulations, (GW) detectors, transient astronomy. This has led exciting possibility performing joint analyses GW EM data, providing additional constraints on fundamental properties binary progenitor merger remnant. Here, we present new Bayesian...

Neutron star mergers are of tremendous astrophysical interest for a variety reasons that include their role in initiating r-process nucleosynthesis ejecta. In this article, the authors tackle complex influence extremely rapid neutrino flavor conversion (fast instability - FFI) on ejecta from accretion disks around hypermassive neutron stars (HMNSs) formed mergers. By studying wide scenarios, detail FFI and show it depends strongly lifetime HMNS.

A stalled spherical accretion shock, such as that arising in core-collapse supernovae, is unstable to non-spherical perturbations. In three dimensions, this Standing Accretion Shock Instability can develop spiral modes spin-up the protoneutron star. Here, we study these non-axisymmetric by combining linear stability analysis and three-dimensional, time-dependent hydrodynamic simulations with Zeus-MP, focusing on characterizing their spatial structure angular momentum content. We do not...

We explore the evolution of different ejecta components generated during merger a neutron star (NS) and black hole (BH). Our focus is interplay between material ejected dynamically merger, wind launched on viscous timescale by remnant accretion disk. These are expected to contribute an electromagnetic transient produce r-process elements, each with signature when considered separately. Here we introduce two-step approach investigate their combined evolution, using two- three-dimensional...

We investigate the effect of dimensionality on transition to explosion in neutrino-driven core-collapse supernovae. Using parameterized hydrodynamic simulations stalled supernova shock one-, two- (2D), and three spatial dimensions (3D), we systematically probe extent which instabilities alone can tip balance favor explosion. In particular, focus systems that are well into regimes where Standing Accretion Shock Instability (SASI) or convection dominate dynamics, characterize difference...

We investigate mass ejection from accretion disks formed in mergers of black holes (BHs) and neutron stars (NSs). The third observing run the LIGO/Virgo interferometers provided BH-NS candidate events that yielded no electromagnetic (EM) counterparts. broad range disk configurations expected motivates a thorough exploration parameter space to improve EM signal predictions. Here we conduct 27 high-resolution, axisymmetric, long-term hydrodynamic simulations viscous evolution BH include...

Abstract Freshly synthesized r -process elements in kilonovae ejecta imprint absorption features on optical spectra, as observed the GW170817 binary neutron star merger. These spectral encode insights into physical conditions of and origins ejected material, but associating with particular inferring resultant abundance pattern is computationally challenging. We introduce Spectroscopic -Process Abundance Retrieval for Kilonovae ( SPARK ), a modular framework to perform Bayesian inference...

Abstract In kilonovae, freshly synthesized r -process elements imprint features on optical spectra, as observed in AT2017gfo, the counterpart to GW170817 binary neutron star merger. However, measuring compositions of merger ejecta is computationally challenging. Vieira et al. introduced Spectroscopic Abundance Retrieval for Kilonovae ( SPARK ), a software tool infer elemental abundance patterns and associate spectral with particular species. Previously, we applied 1.4-day spectrum AT2017gfo...

We investigate mass ejection from accretion disks formed during the collapse of rapidly rotating Wolf-Rayet stars. The neutrino-cooled, black hole (BH) disk system that forms at center star---and ensuing outflows---provides conditions for these systems to be candidate $r$-process element production sites and potential progenitors broad-line type Ic (Ic-BL) supernovae. present global, long-term axisymmetric hydrodynamic simulations collapsar include angular momentum transport through shear...

Although the surface of a magnetar is source bright thermal X-rays, its spectrum contains substantial non-thermal components. The X-ray emission pulsed, with pulsed fractions that can be as high ~ 70%. Several properties magnetars indicate presence persistent, static currents flowing across stellar and closing within magnetosphere. charges supporting these supply significant optical depth to resonant cyclotron scattering in 1-100 keV band. Here we describe Monte Carlo approach calculating...

We study the transition to runaway expansion of an initially stalled core-collapse supernova shock. The neutrino luminosity, mass accretion rate, and neutrinospheric radius are all treated as free parameters. In spherical symmetry, this is mediated by a global non-adiabatic instability that develops on advection time reaches non-linear amplitude. Here we perform high-resolution, time-dependent hydrodynamic simulations shocks with realistic microphysics analyze transition. find radial...

The success of the neutrino mechanism core-collapse supernovae relies on supporting action two hydrodynamic instabilities: neutrino-driven convection and Standing Accretion Shock Instability (SASI). Depending structure stellar progenitor, each these instabilities can dominate evolution gain region prior to onset explosion, with implications for ensuing asymmetries. Here we examine flow dynamics in neighborhood explosion by means parametric two-dimensional, time-dependent simulations which...