arXiv subjects

Patrick Chi-Kit Cheong

Publications and source records attributed to Patrick Chi-Kit Cheong.

At least 19 recordsLinked to original sources

arXiv2026

Hyperaccreting Magnetised Neutron Stars inside Rotating Massive Envelopes: Low-Power Jets and Precursor Flares

The engulfment of a neutron star (NS) by a massive companion initiates a highly dynamic common-envelope (CE) evolution phase. As the NS spirals into the dense stellar core, it is subjected to hypercritical accretion rates that threaten to rapidly collapse the NS into a black hole (BH). However, if the infalling envelope possesses sufficient angular momentum and magnetic fields, the NS might survive longer and launch feedback-driving jets. To investigate this, we perform fully coupled, axisymmetric General Relativistic Magnetohydrodynamic (GRMHD) simulations of hyperaccreting NSs, featuring energy-integrated two-moment neutrino transport and a 13-isotope nuclear reaction network. We systematically vary the envelope rotation profile and the magnetic field strength of the NS surface ($B_{\rm surf} \sim 5 \times 10^{10} - 5 \times 10^{13}$~G). In non-magnetised models, we find that envelope rotation naturally forms a centrifugal barrier and a geometrically thick accretion disk, which suppresses the mass accretion rate and lowers the neutrino luminosity; conversely, the intrinsic spin of the NS has a negligible global impact. In magnetised models, the differential rotation of the accretion flow vigorously amplifies the toroidal magnetic field via the $\Omega$-effect, driving the expansion of magnetic towers. Crucially, for strong initial surface magnetic fields ($B_{\rm surf} \gtrsim 2.3 \times 10^{13}$~G), the intense magnetic pressure could completely halt the accretion flow at the NS surface and evacuates a low-density polar funnel. We conclude that while this highly magnetised NS engine successfully delays prompt BH formation and may launche low-power precursor jets (with powers up to ${\sim} 10^{46}~{\rm erg/s}$) capable of generating observable X-ray flares, it lacks the energy budget to unbind the massive envelope, setting the stage for a subsequent BH-driven explosion.

astro-ph.HE↗

arXiv2026

Magnetar Formation from Accretion Induced Collapse of White Dwarfs

We aim to characterize the post-collapse evolution of accretion-induced collapse (AIC) remnants of rapidly rotating, magnetized white dwarfs, focusing on their rotational, magnetic, and thermal structure, as well as the development of instabilities and their energy content. We perform nine axis-symmetric general-relativistic neutrino magnetohydrodynamic (MHD) simulations of collapsing, rapidly rotating, magnetized white dwarfs. The simulations follow the system from collapse through bounce and up to $\sim$1 s post-bounce. The simulations are performed by the conformally flat general relativistic neutrino MHD code \texttt{Gmunu}. The collapse produces a rapidly rotating proto-magnetar surrounded by a persistent accretion disk lasting at least $\sim 1$ s after bounce. The remnant mass and spin span 1.15--1.45 $M_{\odot}$ and 2.9--4.9 kHz, respectively, with stronger initial magnetic fields generally leading to lower rotation rates. During the first $\sim 10$ ms, the proto-magnetar exhibits global oscillations that drive both gravitational-wave emission and coherent modulation of the poloidal magnetic field energy. The magnetic energy evolution, normalized to its bounce value, follows an approximately universal behavior across all models. The remnant interior remains strongly magnetized ($\gtrsim 10^{13}$ G) and hot ($\gtrsim 20$ MeV) up to 1 s after bounce, with maxima of both quantities co-located in the inner $\sim 10$ km. The magnetic field topology shows surface poloidal fields of ${\sim}10^{12}$ G and toroidal fields of ${\sim}10^{14}$ G, with strong toroidal components extending into the equatorial region. When the magnetic energy exceeds the rotational energy ($\sim 10^{52}$ erg), the remnant core becomes unstable, leading to episodic magnetic flux expulsion, mass ejection, and flare-like activity in which magnetic energy is released and thermalized in the surrounding material.

astro-ph.HE↗

arXiv2026

Impact of neutrino-electron scattering and an improved treatment of pair processes on binary neutron star mergers

Multimessenger observations of neutron star mergers are unique opportunities to constrain the properties of dense matter and the production site of heavy nuclei. To leverage these observations, we require reliable models of the electromagnetic signals powered by mergers. An important limitation to our ability to develop such models is the use of approximate neutrino physics in simulations. Here, we present simulations using an improved version of our Monte Carlo transport algorithm specifically designed to allow for more advanced on-the-fly calculations of reaction rates that use the simulated energy distribution of neutrinos, including in blocking factors, while still relying on approximations for the angular distribution of neutrinos. We use these new methods to include in simulations inelastic scattering of neutrinos on electrons, and to improve our treatment of neutrino-antineutrino pair annihilation. We find that, without increasing the cost of simulations, we can marginally get to the point when the addition of a single packet represents a change $\Delta f_\nu<1$ in the angle-integrated distribution function, at the cost of increased shot noise in the coupling to the fluid. With inelastic scattering and a better treatment of pair processes, we find a reduction in the average energy and total luminosity of heavy-lepton neutrinos, and an increase in the amount of mass ejected -- here by $50\%$, although on a relatively low amount of total ejected mass $<0.005M_\odot$. In a separate set of simulations varying the total mass of the binary away from its prompt collapse threshold, we find rapid variations in the amount of ejected matter and in the geometry and composition of the outflows with the total mass of the system. Finally, we use the simulations with our more advanced transport scheme to study in more detail the energy spectrum of neutrinos across the merger remnant.

astro-ph.HE↗

arXiv2026

Distinct neutrino signatures and onset condition of quark deconfinement in accretion-induced collapse of white dwarfs

We present the first general relativistic, neutrino-radiation hydrodynamics simulations of accretion-induced collapse (AIC) extending to seconds after core bounce, using realistic hadron-quark hybrid equations of state (EOSs). A first-order QCD phase transition (PT) triggers a second dynamical collapse and the formation of a quasistable protohybrid star (PHS) with a deconfined quark core and a distinctive second neutrino burst. We find that the thermally suppressed onset of the mixed phase allows low-mass protoneutron stars to enter the hadron-quark mixed phase during long-term evolution, even for hybrid EOSs with high onset densities. In contrast to core-collapse supernovae (CCSNe), AIC models exhibit a tightly constrained onset mass with minimal EOS dependence, owing to the absence of a massive envelope and thus the reduced postbounce accretion. This enhances the sensitivity of neutrino observables in AIC to hybrid EOS properties. We establish empirical relations between PT onset density and neutrino signatures, revealing a distinct behavior in AIC not seen in CCSNe. Our results suggest that a single Galactic AIC neutrino detection could place strong constraints on QCD PT thresholds, hybrid EOS characteristics, and the existence of PHSs. PT in AIC may also produce gravitational waves, gamma-ray bursts, and $r$-process elements, motivating multidimensional simulations with rotation, magnetic fields, and improved microphysics for realistic multimessenger predictions.

hep-th↗

arXiv2026

Hyperaccreting Neutron Stars inside Massive Envelopes: The Implausibility of Thorne-\.Zytkow Objects

The evolution of neutron stars (NSs) embedded within massive stellar envelopes is a critical phase in binary stellar evolution, potentially leading to the formation of Thorne-\.Zytkow Objects (T\.ZOs) or catastrophic collapse. We present the first fully coupled general relativistic hydrodynamics (GRHD) simulations of hypercritical accretion onto NSs that simultaneously incorporate grey two-moment (M1) neutrino transport and an $\alpha$-chain nuclear reaction network. By investigating four distinct progenitor evolutionary stages, we resolve the complex interplay between intense neutrino cooling, multidimensional fluid dynamics, and nuclear feedback. Our results show that while vigorous convection is triggered in the post-shock region, the global energy budget is primarily governed by neutrino cooling, which effectively balances the accretion power. Crucially, even though our M1 transport scheme captures neutrino absorption and localized heating, the efficient cooling sink and high ram pressure of the infalling envelope prevent the formation of any core-collapse supernova-like explosion. We find that all nucleosynthetically processed material ($T > 5$~GK) remains strictly gravitationally bound, challenging the assumption that these systems contribute significantly to galactic nucleosynthetic yields via convective dredge-up. The lack of sustained outflows and the persistent hypercritical accretion rates suggest that embedded NSs will rapidly exceed the Tolman-Oppenheimer-Volkoff mass limit on timescales of minutes to hours. We conclude that these systems are not stable T\.ZOs, but are rather transient precursors to catastrophic black hole formation and potential central engines for high-energy transients.

astro-ph.HE↗

arXiv2026

Toward First-Principles Multi-Messenger Predictions: Coupling Nuclear Networks with GR Radiation-MHD in {\tt Gmunu}

We present a new implementation of nuclear reaction networks in the \texttt{G}eneral-relativistic \texttt{mu}ltigrid \texttt{nu}merical (\texttt{Gmunu}) code, a framework for general relativistic radiation magnetohydrodynamics (GRRMHD). The extended code self-consistently evolves nuclear species coupled to hydrodynamics, magnetic fields, and neutrino radiation transport under the conformal flatness approximation to Einstein's equations. Four approximate nuclear networks are included, with stiff source terms integrated using implicit-explicit Runge-Kutta schemes. Validation is performed through benchmarks including conserved-to-primitive recovery with a tabulated stellar equation of state, one-zone silicon burning, and hydrodynamic tests of shock tubes, acoustic pulses, and detonation fronts of Type Ia supernovae. These tests confirm accurate coupling between nuclear reactions and fluid dynamics, conserving electron and nuclear mass fractions to machine precision. As an application, we conduct spherically symmetric core-collapse supernova simulations. The models reproduce the expected non-exploding behavior of standard progenitors, while enhanced neutrino heating revives the shock. Including nuclear burning modifies the post-shock composition and dynamics, converting silicon and oxygen layers into iron-group nuclei and strengthening the explosion. This demonstrates the impact of explosive burning on ejecta composition and shock evolution, and establishes the stability of the coupled GR radiation-MHD-nuclear framework. The implementation is fully compatible with multidimensional GRMHD simulations and represents the first GRRMHD code combining M1 neutrino transport with fully coupled nuclear burning.

astro-ph.IM↗

arXiv2026

Collapse of Magnetized White Dwarfs as site of Heavy Element Formation and Kilonova Signal

We present the first end-to-end calculation connecting the accretion-induced collapse (AIC) of a magnetized, rapidly rotating white dwarf to observable kilonova signatures, combining 2D general-relativistic neutrino-magnetohydrodynamic simulations, followed by radiation hydrodynamics with in-situ nuclear network and 2D Monte Carlo radiative transfer with spatially resolved heating rates. Unlike all previous unmagnetized AIC models - which predicted proton-rich, $^{56}$Ni-dominated ejecta - strong magnetic fields eject ${\sim 0.2 M_\odot}$ of neutron-rich material $(\langle Y_e \rangle \sim 0.24)$ on dynamical timescales, before neutrino irradiation can raise the electron fraction, enabling strong $r$-process nucleosynthesis up to and beyond the third peak. The resulting kilonova is lanthanide-rich $(X_{\rm lan} \approx 8\%)$ and dominated by near-infrared emission. We compute synthetic light curves in the LSST and JWST bands and find striking agreement, without parameter tuning, between the observations of AT 2023vfi/GRB 230307A and our broadband light curves for polar viewing angles. These results establish magnetized AIC as a viable channel for heavy $r$-process element production and a compelling progenitor candidate for long-duration gamma-ray bursts with kilonova signatures.

astro-ph.HE↗

arXiv2025

Axisymmetric hydrodynamics in numerical relativity: treating coordinate singularity, artificial heating and modeling MHD instabilities

Two-dimensional axisymmetric simulations of binary neutron star (BNS) merger remnant are a cheap alternative to 3D simulations. To maintain realism for secular timescales, simulations must avoid accumulated errors from drifts in conserved quantities and artificial heating, and they must model turbulent transport in a way that remains plausible throughout the evolution. It is also crucial to avoid numerical artifacts due to the polar coordinate axis singularity. Methods that behave well near the axis often break flux-conservative form of the hydrodynamic equations, resulting in significant drifts in conserved quantities. We present a flux-conservative scheme that maintains smoothness near the axis without sacrificing conservative formulation of the equations or incurring drifts in conserved global quantities. We compare the numerical performance of different treatments of the hydrodynamic equations when evolving a hypermassive neutron star resembling the remnant of a BNS merger. These simulations demonstrate that the new scheme combines the axis smoothness of non-conservative methods with the mass and angular momentum conservation of other conservative methods on $\sim$ $10^2$ ms timescales of viscous and neutrino-driven evolution. Because fluid profiles remain smooth in the remnant interior, it is possible to remove artificial heating by evolving the entropy density. We show how physical heating and cooling terms can be easily calculated from source terms of the conservative evolution variables and demonstrate our implementation. Finally, we discuss and implement improvements to the effective viscosity scheme to better model the effect of magnetohydrodynamic instabilities as the remnant evolves.

astro-ph.HE↗

arXiv2025

Fundamental modes of rotating neutron stars with various degrees of differential rotation in dynamical spacetimes

Violent astrophysical events, including core-collapse supernovae and binary neutron star mergers, can result in rotating neutron stars with diverse degrees of differential rotation. Oscillation modes of these neutron stars could be excited and emit strong gravitational waves. Detecting these modes may provide information about neutron stars, including their structures and dynamics. Hence, dynamical simulations were employed to construct relations for quantifying the oscillation mode frequency in previous studies. Specifically, linear relations for the frequencies of fundamental $l=0$ quasi-radial mode $f_{F}$ and fundamental $l=2$ quadrupolar mode $f_{^2f}$ were constructed by simulations with the Cowling approximation. Nevertheless, these relations can overestimate $f_{F}$ and underestimate $f_{^2f}$ up to $\sim 30\%$. Furthermore, it has yet to be fully studied how the degree of differential rotation affects $f_{F}$ and $f_{^2f}$. Here, for the first time, we consider both various degrees of differential rotation $\Tilde{A}$ and dynamical spacetime to construct linear relations for quantifying $f_{F}$ and $f_{^2f}$. Through 2D axisymmetric simulations, we first show that both $f_{F}$ and $f_{^2f}$ scale almost linearly with the stellar compactness $M/R$ for different values of $\Tilde{A}$. We also observe the quasi-linear relations for both $f_{F}$ and $f_{^2f}$ with the kinetic-to-binding energy ratio $T/|W|$ for different $\Tilde{A}$ values. Finally, we constructed linear fits that can quantify $f_{F}$ and $f_{^2f}$ by $T/|W|$. Consequently, this work updated the relations for the fundamental modes of rotating neutron stars with differential rotations in dynamical spacetime.

astro-ph.HE↗

arXiv2025

Gravitational wave signatures from the phase-transition-induced collapse of a magnetized neutron star

Strong magnetic fields make neutron stars potential sources of detectable electromagnetic and gravitational-wave signals. Hence, inferring these magnetic fields is critical to understand the emissions of neutron stars. However, due to the lack of direct observational evidence, the interior magnetic field configuration remains ambiguous. Here, for the first time, we show that the internal magnetic field strength along with the composition of a neutron star can be directly constrained by detecting the gravitational waves from the \emph{phase-transition-induced collapse} of a magnetized neutron star. By dynamically simulating this collapsing event, we first find that the dominant peaks in the gravitational waveform are the fundamental $l=0$ quasi-radial $F$ mode and the fundamental $l=2$ quadrupolar $^2f$ mode. We next show that the maximum gravitational wave amplitude $|h|_\mathrm{max}$ increases with the maximum magnetic field strength of the interior toroidal field $\mathcal{B}_\mathrm{max}$ until the maximum rest-mass density at bounce $ρ_\mathrm{max,b}$ decreases due to the increasing $\mathcal{B}_\mathrm{max}$. We then demonstrated that the magnetic suppression of fundamental modes found in our previous work remains valid for the hybrid stars formed after the phase-transition-induced collapses. We finally show that measuring the frequency ratio between the two fundamental modes $f_{^2f}/f_{F}$ allows one to infer $\mathcal{B}_\mathrm{max}$ and the baryonic mass fraction of matter in the mixed phase $M_\mathrm{mp} / M_{0}$ of the resulting hybrid star. Consequently, taking $\mathcal{B}_\mathrm{max}$ and $M_\mathrm{mp} / M_{0}$ as examples, this work has demonstrated that much information inside neutron stars could be extracted similarly through measuring the oscillation modes of the stars.

astro-ph.HE↗

arXiv2025

Impact of rotation on magnetic field stability and orientation in isolated neutron stars

Neutron stars are the most compact horizonless objects in the Universe, exhibiting the strongest known magnetic fields. They are potential sources of coincident gravitational waves and electromagnetic radiation across the entire spectrum. However, the internal configuration of their magnetic fields and the mechanisms that stabilize them remain open questions. As a step forward in understanding the timescale for the emergence of magnetic instabilities that disrupt stellar field configurations, we study the impact of stellar rotation using three-dimensional general relativistic numerical simulations of uniformly rotating, isolated neutron stars threaded by strong, poloidal, pulsar-like magnetic fields. The initial stellar configurations assume perfect conductivity and are stationary and axisymmetric. We explore a range of angular velocities, from non-rotating stars to those near the mass-shedding limit. We find that the stars spontaneously develop differential rotation, which triggers the appearance of a strong toroidal magnetic field component. Non-rotating neutron stars are unstable to the Tayler and Parker instabilities, which significantly change the magnetic field geometry. These instabilities lead to a rapid reduction of the initial magnetic energy by $\sim 99\%$ within $\sim 4$ Alfvén times of their onset. In contrast, rotation significantly delays the development of these instabilities and, in some cases, mitigates their effects. Highly rotating models retain up to $\sim 30\%$ of their magnetic energy for at least $\sim 10$ Alfvén times. Our results suggest that rotation plays a crucial role in stabilizing the magnetic field of neutron stars, regardless of its initial configuration.

astro-ph.HE↗

arXiv2025

Non-conservation of Lepton Numbers in the Neutrino Sector Could Change the Prospects for Core Collapse Supernova Explosions

We show that interactions violating the conservation of lepton numbers in the neutrino sector could significantly alter the standard low entropy picture for the pre-supernova collapsing core of a massive star. A rapid neutrino-antineutrino equilibration leads to entropy generation and enhanced electron capture and, hence, a lower electron fraction than in the standard model. This would affect the downstream core evolution, the prospects for a supernova explosion, and the emergent neutrino signal. If realized by lepton-number-violating neutrino self-interactions (LNV $ν$SI), the relevant mediator mass and coupling ranges can be probed by future accelerator-based experiments.

hep-ph↗

arXiv2025

General-relativistic resistive-magnetohydrodynamics simulations of self-consistent magnetized rotating neutron stars

We present the first general-relativistic resistive magnetohydrodynamics simulations of self-consistent, rotating neutron stars with mixed poloidal and toroidal magnetic fields. Specifically, we investigate the role of resistivity in the dynamical evolution of neutron stars over a period of up to 100 ms and its effects on their quasi-equilibrium configurations. Our results demonstrate that resistivity can significantly influence the development of magnetohydrodynamic instabilities, resulting in markedly different magnetic field geometries. Additionally, resistivity suppresses the growth of these instabilities, leading to a reduction in the amplitude of emitted gravitational waves. Despite the variations in magnetic field geometries, the ratio of poloidal to toroidal field energies remains consistently 9:1 throughout the simulations, for the models we investigated.

astro-ph.HE↗

arXiv2025

Gamma-ray bursts and kilonovae from the accretion-induced collapse of white dwarfs

We present the first seconds-long 2D general relativistic neutrino magnetohydrodynamic simulations of accretion-induced collapse (AIC) in rapidly rotating, strongly magnetized white dwarfs (WDs), which might originate as remnants of double-WD mergers. This study examines extreme combinations of magnetic fields and rotation rates, motivated both by the need to address the limitations of 2D axisymmetric simulations and to explore the physics of AIC under rare conditions that, while yet to be observationally confirmed, may be consistent with current theoretical models and account for unusual events. Under these assumptions, our results demonstrate that, if realizable, such systems can generate relativistic jets and neutron-rich outflows with properties consistent with long gamma-ray bursts (LGRBs) accompanied by kilonovae, such as GRB 211211A and GRB 230307A. These findings highlight the potential role of AIC in heavy $r$-process element production and offer a framework for understanding rare LGRBs associated with kilonova emission. Longer-duration 3D simulations are needed to fully capture magnetic field amplification, resolve instabilities, and determine the fate of the energy retained by the magnetar at the end of the simulations.

astro-ph.HE↗

arXiv2025

Influence of neutrino-electron scattering and neutrino-pair annihilation on hypermassive neutron star

We investigate the influence of inelastic neutrino microphysics in general-relativistic magnetohydrodynamics simulations of a hypermassive neutron star. In particular, we include species/energy groups coupled neutrino-matter interactions, such as inelastic neutrino-electron scattering and electron-positron annihilation kernels, into simulations up to 50 ms. Neutrino-electron inelastic scattering is known to have effective neutrino-matter energy exchange. We show that, with neutrino-electron inelastic scattering, simulations predict 75% higher disc mass with slightly different mass-averaged compositions, and 18% more ejected mass with similar distributions. The enhancement of the mass of the disc and the ejecta results in stronger baryon pollution, leading to less favourable jet launching environments. Furthermore, neutrino luminosities are about 50, 40, and 30% higher for electron neutrino, electron anti-neutrino, and heavy-lepton neutrinos. In contrast, we do not see any significant impacts due to electron-positron annihilation.

astro-ph.HE↗

arXiv2024

Formation of a magnetized hybrid star with a purely toroidal field from phase-transition-induced collapse

Strongly magnetized neutron stars are popular candidates for producing detectable electromagnetic and gravitational-wave signals. Gravitational collapses of neutron stars triggered by a phase transition from hadrons to deconfined quarks in the cores could also release a considerable amount of energy in the form of gravitational waves and neutrinos. Hence, the formation of a magnetized hybrid star from such a \emph{phase-transition-induced collapse} is an interesting scenario for detecting all these signals. These detections may provide essential probes for the magnetic field and composition of such stars. Thus far, a dynamical study of the formation of a magnetized hybrid star from a \emph{phase-transition-induced collapse} has yet to be realized. Here, we investigate the formation of a magnetized hybrid star with a purely toroidal field and its properties through dynamical simulations. We find that the maximum values of rest-mass density and magnetic field strength increase slightly and these two quantities are coupled in phase during the formation. We then demonstrate that all microscopic and macroscopic quantities of the resulting hybrid star vary drastically when the maximum magnetic field strength goes beyond a threshold of $\sim 5 \times 10^{17}$ G but they are insensitive to the magnetic field below this threshold. Specifically, the magnetic deformation makes the rest-mass density drop significantly, suppressing the matter fraction in the mixed phase. These behaviors agree with those in the equilibrium models of previous studies. Therefore, this work provides a solid support for the magnetic effects on a hybrid star.

astro-ph.HE↗

arXiv2024

Robustness of neutron star merger simulations to changes in neutrino transport and neutrino-matter interactions

Binary neutron star mergers play an important role in nuclear astrophysics: their gravitational wave and electromagnetic signals carry information about the equation of state of cold matter above nuclear saturation density, and they may be one of the main sources of r-process elements in the Universe. Neutrino-matter interactions during and after merger impact the properties of these electromagnetic signals, and the relative abundances of the produced r-process elements. Existing merger simulations are however limited in their ability to realistically model neutrino transport and neutrino-matter interactions. Here, we perform a comparison of the impact of the use of state-of-the art two-moment or Monte-Carlo transport schemes on the outcome of merger simulations, for a single binary neutron star system with a short-lived neutron star remnant ($(5-10)\,{\rm ms}$). We also investigate the use of different reaction rates in the simulations. While the best transport schemes generally agree well on the qualitative impact of neutrinos on the system, differences in the behavior of the high-density regions can significantly impact the collapse time and the properties of the hot tidal arms in this metastable merger remnant. The chosen interaction rates, transport algorithm, as well as recent improvements by Radice et al to the two-moment algorithms can all contribute to changes at the $(10-30)\%$ level in the global properties of the merger remnant and outflows. The limitations of previous moment schemes fixed by Radice et al also appear sufficient to explain the large difference that we observed in the production of heavy-lepton neutrinos in a previous comparison of Monte-Carlo and moment schemes in the context of a low mass binary neutron star system.

astro-ph.HE↗

arXiv2024

Energy-dependent and energy-integrated two-moment general-relativistic neutrino transport simulations of hypermassive neutron star

We compare two-moment based \emph{energy-dependent} and 3 variants of \emph{energy-integrated} neutrino transport general-relativistic magnetohydrodynamics simulations of hypermassive neutron star. To study the impacts due to the choice of the neutrino transport schemes, we perform simulations with the same setups and input neutrino microphysics. We show that the main differences between energy-dependent and energy-integrated neutrino transport are found in the disk and ejecta properties, as well as in the neutrino signals. The properties of the disk surrounding the neutron star and the ejecta in energy-dependent transport are very different from the ones obtained using energy-integrated schemes. Specifically, in the energy-dependent case, the disk is more neutron-rich at early times, and becomes geometrically thicker at later times. In addition, the ejecta is more massive, and on average more neutron-rich in the energy-dependent simulations. Moreover, the average neutrino energies and luminosities are about 30\% higher. Energy-dependent neutrino transport is necessary if one wants to better model the neutrino signals and matter outflows from neutron star merger remnants via numerical simulations.

astro-ph.HE↗