arXiv subjects

Takami Kuroda

Publications and source records attributed to Takami Kuroda.

At least 19 recordsLinked to original sources

arXiv2026

ANRe-M1: a GPU-accelerated numerical relativity code with multi-energy M1 neutrino transport

We present ANRe-M1 (Accelerated Numerical Relativity code with multi-energy M1 neutrino transport), a performance-portable, GPU-accelerated code for multidimensional core-collapse supernova simulations in full general relativity. ANRe-M1 builds on our original CPU-based Fortran framework and is implemented in C++ using Kokkos. It retains the underlying general-relativistic neutrino-radiation-hydrodynamics algorithms while redesigning the data layout, parallel decomposition, and memory-access patterns for accelerator-resident execution. The spacetime sector employs the BSSN--Z4c formulation and is coupled to relativistic hydrodynamics and energy-dependent M1 neutrino transport. We validate the implementation through a suite of hydrodynamic, radiation-transport, and dynamical-spacetime tests, together with comparisons to results from an earlier code-comparison study. We further demonstrate its applicability with a representative three-dimensional stellar-collapse computation including multi-energy neutrino transport. For the benchmark and computing systems considered here, ANRe-M1 runs approximately an order of magnitude faster on a cluster of AMD MI300A accelerated processing units than the Fortran version on a CPU cluster. When the allocation is increased from 2 to 128 MI300A APUs, the aggregate throughput rises by a factor of 39.7, corresponding to a weak-scaling efficiency of 62 per cent relative to the two-APU case. These results establish ANRe-M1 as an efficient and portable framework for long-term, multidimensional supernova simulations on current and forthcoming accelerator-based supercomputers.

astro-ph.HE↗

arXiv2026

Nucleosynthesis in the Accretion-induced Collapse of magnetised, Rotating White Dwarfs

Accretion-induced collapse (AIC) of a rotating oxygen-neon-magnesium white dwarf (WD) is an alternative channel of neutron-star formation, in which a mass-accreting star near the Chandrasekhar mass collapses instead of being disrupted thermonuclearly. If the progenitor WD is sufficiently magnetised, it can drive magnetorotational outflows analogous to those of magnetorotational supernovae and may serve as a site for rapid neutron-capture ($r$-process) nucleosynthesis. We post-process tracer particles from five three-dimensional general-relativistic neutrino-(magneto)hydrodynamic AIC simulations, spanning four initial rotation rates, with the WinNet nuclear reaction network. Ejecta mass, the fraction of matter reaching nuclear statistical equilibrium, and the mass ejected beyond the iron group all increase monotonically with rotation rate, with magnetic fields amplifying these trends. The slowest-rotating model synthesises essentially only iron-group material, while the most rapidly rotating and magnetised model reaches the second $r$-process abundance peak at mass number $A \approx 130$, with a trace, non-robust signal up to $A \approx 244$. The corresponding $^{56}$Ni mass rises from $0.007$ to $0.014 M_\odot$, lower than representative yields for core-collapse supernovae and hypernovae by factors of five to more than forty, implying a correspondingly faint radioactively powered component. Contrary to the picture established for magnetorotationally driven supernovae, the heaviest ejecta do not track the polar outflow: they instead reside in equatorial-to-mid-latitude, moderate-entropy lobes, while the polar column is itself a local minimum in some heavy elements. We conclude that rapidly rotating, magnetised AIC events could contribute to the Galactic yields of trans-iron and weak $r$-process nuclei, although none of our models produces a robust third $r$-process peak.

astro-ph.HE↗

arXiv2026

Exploring Physics beyond the Standard Model from kHz-Gravitational-Wave Signals of Core-Collapse Supernovae

Recent advances in multidimensional modeling of core-collapse supernovae (CCSNe) have enabled detailed predictions of high-frequency gravitational-wave (GW) signals, offering a new probe of extreme matter and gravity. A proto-neutron star (PNS) emits quasi-continuous GWs through the excitation of its characteristic oscillation modes. State-of-the-art CCSN simulations show that these oscillations, in particular $g$- and $f$-modes, dominate the GW spectrum, with frequencies rising from a few hundred hertz to the kilohertz (kHz) range as the PNS compactness increases in the post-bounce phase. Therefore, the temporal evolution of these GW frequencies, if detected, would provide a direct and quantitative tracer of the PNS internal structure and the surrounding explosive dynamics. In addition to such standard GW emission mechanism, fully general relativistic (GR) simulations have revealed additional GW sources linked to more exotic physical processes. In highly massive progenitors, continuous mass accretion drives rapid PNS contraction and early black-hole (BH) formation, producing strong kHz GW emission that abruptly ceases when the PNS core is swallowed by the BH horizon. Similarly, a strong first-order quantum chromodynamics (QCD) phase transition can induce a secondary collapse and rebound of the nascent quark core, generating powerful, millisecond-duration GW bursts with frequencies exceeding $\sim$2 kHz. Alternative theories of gravity, such as scalar-tensor frameworks, predict spontaneous scalarization that can trigger multiple collapses of the PNS, yielding analogous high-frequency and broadband GW signals. The combined analysis of these GW signals, together with their detection by next-generation GW detectors, offers a promising multi-messenger pathway to identify smoking-gun signatures of new physics beyond the standard model of the CCSN GW mechanism and general relativity.

astro-ph.HE↗

arXiv2026

Circular polarization of gravitational waves from magnetorotational supernovae

Context. Gravitational waves (GWs) provide a unique probe of the explosion mechanism of massive stars and the evolution of nascent proto-neutron stars (PNSs). Magnetorotational explosions are one of the promising noncanonical core-collapse supernova scenarios, possibly linked to magnetar formation and energetic supernova explosions. However, the GW signatures of such events remain incompletely understood. Aims. We investigate the origin and nature of GW polarization arising from a magnetorotational core-collapse model and examine its potential detectability by current GW observatories. Methods. We performed a 3D GRMHD simulation of a rapidly rotating, strongly magnetized 20 $M_{\odot}$ progenitor, including multi-energy neutrino transport. The GW signals were extracted using the standard quadrupole formalism, and their polarization states were analyzed with Stokes parameters. Results. Strong circular polarization emerges along the rotation axis during the early post-bounce phase ($\lesssim$ 230 ms). The characteristic GW spectrum peaks at ~90 Hz, consistent with the emission at twice the local angular velocity (~45 Hz) around the PNS surface at cylindrical radii of ~50 km. These features are attributed to the low-$T/\vert{}W\vert{}$ instabilities and nonaxisymmetric motions near the PNS and not to the MHD jets themselves. The polarization signals lie within the sensitivity bands of current detectors such as Advanced LIGO, Advanced Virgo, and KAGRA. Conclusions. Models launching magnetorotationally driven jets can produce circularly polarized GW signals originating from the inner PNS region. This provides an observational signature that complements previous findings from nonmagnetized rotating models. Thus, GW polarization is a promising diagnostic of noncanonical core-collapse supernovae. Future third-generation detectors will be crucial to fully exploit this potential.

astro-ph.HE↗

arXiv2025

Collapse of Rotating White Dwarfs and Multimessenger Signals

We present results of numerical relativity simulations for the collapse of rotating magnetized white dwarfs (WDs) in three dimension, aiming at discussing the explosion dynamics and associate multi-messenger signals: gravitational waves (GWs), neutrinos, and electromagnetic counterparts. All WDs initiate gravitational collapse due to electron captures and then experience prompt type explosions after the proto neutron star formation. We observe the explosions dominated by a bipolar structure and the emergence of strong spiral waves in rapidly rotating models. The spiral waves facilitate to increase both the explosion energy and ejecta mass, though the final values still fall in the category of low explosion energy supernovae with small ejecta mass. The spiral waves also produce strong GWs, which may expand the horizon distance of such events against GWs up to ~10 Mpc for third-generation ground-based detectors. Additionally as an intriguing implication, we demonstrate that such accretion or merger induced collapse of WDs might be able to explain some of the rapidly evolving optical transients, such as fast blue optical transients (FBOTs), as previously suggested. Based on the simulation results together with several assumptions, we confirm that the magnetar may account for the brighter side of some of observed FBOTs, while a combination of ejecta-envelope interaction which can be also followed by radioactive decay of heavy elements synthesized along with the explosion might still explain the fainter branch even in the absence of magnetar formation.

astro-ph.HE↗

arXiv2024

Numerical relativity simulations of black hole and relativistic jet formation

We investigate impacts of stellar rotation and magnetic fields on black hole (BH) formation and its subsequent explosive activities, by conducting axisymmetric radiation-magnetohydrodynamics simulations of gravitational collapse of a 70 $M_\odot$ star with two-moment multi energy neutrino transport in numerical relativity. Due to its dense stellar structure, all models cannot avoid the eventual BH formation even though a strongly magnetized model experiences the so-called magnetorotational explosion prior to the BH formation. One intriguing phenomenon observed in the strongly magnetized model is the formation of a relativistic jet in the post-BH formation. The relativistic jet is the outcome of a combination of strong magnetic fields and low-density materials above the BH. The jet further enhances the explosion energy beyond $\sim10^{52}$ erg, which is well exceeding the gravitational overburden ahead of the shock. Our self-consistent supernova models demonstrate that rotating magnetized massive stars at the high-mass end of supernova progenitors could be a potential candidate of hypernova and long gamma-ray burst progenitors.

astro-ph.HE↗

arXiv2023

Three-dimensional GRMHD Simulations of Rapidly Rotating Stellar Core-Collapse

We present results from fully general relativistic (GR), three-dimensional (3D), neutrino-radiation magneto-hydrodynamic (MHD) simulations of stellar core collapse of a 20 M$_\odot$ star with spectral neutrino transport. Our focus is to study the gravitational-wave (GW) signatures from the magnetorotationally (MR)-driven models. By parametrically changing the initial angular velocity and the strength of the magnetic fields in the core, we compute four models. Our results show that the MHD outflows are produced only for models (two out of four), to which magnetic field strengths of 10$^{12}$ G and rotation rates of 1 or 2 rad s$^{-1}$ are initially imposed in the core. Seen from the direction perpendicular to the rotational axis, a characteristic waveform is obtained exhibiting a monotonic time increase in the wave amplitude. As previously identified, this stems from the propagating MHD outflows along the axis. We show that the GW amplitude from anisotropic neutrino emission becomes more than one order-of-magnitude bigger than that from the matter contribution, whereas seen from the rotational axis, both of the two components are in the same order-of-magnitudes. Due to the memory effect, the frequency of the neutrino GW from our full-fledged 3D-MHD models is in the range less than $\sim$10 Hz. Toward the future GW detection for a Galactic core-collapse supernova, if driven by the MR mechanism, the planned next-generation detector as DECIGO is urgently needed to catch the low-frequency signals.

astro-ph.HE↗

arXiv2023

Failed supernova simulations beyond black hole formation

We present an axisymmetric failed supernova simulation beyond black hole formation, for the first time with numerical relativity and two-moment multi energy neutrino transport. To ensure stable numerical evolution, we use an excision method for neutrino radiation-hydrodynamics within the inner part of black hole domain. We demonstrate that our excision method is capable to stably evolve the radiation-hydrodynamics in dynamical black hole spacetime. As a remarkable signature of the final moment of PNS, we find the emergence of high energy neutrinos. Those high energy neutrinos are associated with the proto-neutron star shock surface being swallowed by the central black hole and could be a possible observable of failed supernovae.

astro-ph.HE↗

arXiv2023

Spontaneous Scalarization as a New Core-Collapse Supernova Mechanism and its Multi-Messenger Signals

We perform multi-dimensional core-collapse supernova (CCSN) simulations in a massive scalar-tensor theory for the first time with a realistic equation of state and multi-energy neutrino radiation. Among the set of our models varying the scalar mass and the coupling strength between the scalar and gravitational fields, a particular model allows for recurrent spontaneous scalarizations (SSs) in the proto-neutron star (PNS). Each SS induces the PNS collapse and subsequent bounce, from which devastating shock waves emanate and eject the PNS envelope. The explosion energy can easily exceed $\mathcal O(10^{51})$ erg. This study reveals new aspects of SS as the explosion mechanism of CCSNe. We also discuss its characteristic multi-messenger signals: neutrinos and gravitational waves.

astro-ph.HE↗

arXiv2022

3D template-based $Fermi$-LAT constraints on the diffuse supernova axion-like particle background

Axion-like particles (ALPs) may be abundantly produced in core-collapse (CC) supernovae (SNe), hence the cumulative signal from all past SN events can create a diffuse flux peaked at energies of about 25~MeV. We improve upon the modeling of the ALPs flux by including a set of CC SN models with different progenitor masses, as well as the effects of failed CC SNe -- which yield the formation of black holes instead of explosions. Relying on the coupling strength of ALPs to photons and the related Primakoff process, the diffuse SN ALP flux is converted into gamma rays while traversing the magnetic field of the Milky Way. The spatial morphology of this signal is expected to follow the shape of the Galactic magnetic field lines. We make use of this via a template-based analysis that utilizes 12 years of $Fermi$-LAT data in the energy range from 50 MeV to 500 GeV. In our benchmark case of the realization of astrophysical and cosmological parameters, we find an upper limit of $g_{aγ} \lesssim 3.76\times10^{-11}\;\mathrm{GeV}^{-1}$ at 95$\%$ confidence level for $m_a \ll 10^{-11}$ eV, while we find that systematic deviations from this benchmark scenario induce an uncertainty as large as about a factor of two. Our result slightly improves the CAST bound, while still being a factor of six (baseline scenario) weaker than the SN1987A gamma-ray burst limit.

astro-ph.HE↗

arXiv2021

Core-collapse supernova simulations and the formation of neutron stars, hybrid stars, and black holes

We investigate observable signatures of a first-order quantum chromodynamics (QCD) phase transition in the context of core collapse supernovae. To this end, we conduct axially symmetric numerical relativity simulations with multi-energy neutrino transport, using a hadron-quark hybrid equation of state (EOS). We consider four non-rotating progenitor models, whose masses range from $9.6$ to $70$ M$_\odot$. We find that the two less massive progenitor stars (9.6 and 11.2 M$_\odot$) show a successful explosion, which is driven by the neutrino heating. They do not undergo the QCD phase transition and leave behind a neutron star (NS). As for the more massive progenitor stars (50 and 70 M$_\odot$), the proto-neutron star (PNS) core enters the phase transition region and experiences the second collapse. Because of a sudden stiffening of the EOS entering to the pure quark matter regime, a strong shock wave is formed and blows off the PNS envelope in the 50 M$_\odot$ model. Consequently, the remnant becomes a quark core surrounded by hadronic matters, leading to the formation of the hybrid star. However for the 70 M$_\odot$ model, the shock wave cannot overcome the continuous mass accretion and it readily becomes a black hole. We find that the neutrino and gravitational wave (GW) signals from supernova explosions driven by the hadron-quark phase transition are detectable for the present generation of neutrino and GW detectors. Furthermore, the analysis of the GW detector response reveals unique kHz signatures, which will allow us to distinguish this class of supernova explosions from failed and neutrino-driven explosions.

astro-ph.HE↗

arXiv2021

Axion-like Particles from Hypernovae

It was recently pointed out that very energetic subclasses of supernovae (SNe), like hypernovae and superluminous SNe, might host ultra-strong magnetic fields in their core. Such fields may catalyze the production of feebly interacting particles, changing the predicted emission rates. Here we consider the case of axion-like particles (ALPs) and show that the predicted large scale magnetic fields in the core contribute significantly to the ALP production, via a coherent conversion of thermal photons. Using recent state-of-the-art SN simulations including magnetohydrodynamics, we find that if ALPs have masses $m_a \sim {\mathcal O}(10)\, \rm MeV$, their emissivity via magnetic conversions is over two orders of magnitude larger than previously estimated. Moreover, the radiative decay of these massive ALPs would lead to a peculiar delay in the arrival times of the daughter photons. Therefore, high-statistics gamma-ray satellites can potentially discover MeV ALPs in an unprobed region of the parameter space and shed light on the magnetohydrodinamical nature of the SN explosion.

hep-ph↗

arXiv2021

Characteristic Time Variability of Gravitational-Wave and Neutrino Signals from Three-dimensional Simulations of Non-Rotating and Rapidly Rotating Stellar Core-Collapse

We present results from full general relativistic three-dimensional hydrodynamics simulations of stellar core collapse of a 70 M$_\odot$ star with spectral neutrino transport. To investigate the impact of rotation on non-axisymmetric instabilities, we compute three models by parametrically changing the initial strength of rotation. The most rapidly rotating model exhibits a transient development of the low-$T/|W|$ instability with one-armed spiral flow at the early postbounce phase. Subsequently, the two-armed spiral flow appears, which persists during the simulation time. The moderately rotating model also shows the growth of the low-$T/|W|$ instability, but only with the two-armed spiral flow. In the nonrotating model, a vigorous activity of the standing accretion-shock instability (SASI) is only observed. The SASI is first dominated by the sloshing mode, which is followed by the spiral SASI until the black hole formation. We present a spectrogram analysis of the gravitational waves (GWs) and neutrinos, focusing on the time correlation. Our results show that characteristic time modulations in the GW and neutrino signals can be linked to the growth of the non-axisymmetric instabilities. We find that the degree of the protoneutron star (PNS) deformation, depending upon which modes of the non-axisymmetric instabilities develop, predominantly affects the characteristic frequencies of the correlated GW and neutrino signals. We point out that these signals would be simultaneously detectable by the current-generation detectors up to $\sim10$ kpc. Our findings suggest that the joint observation of GWs and neutrinos is indispensable for extracting information on the PNS evolution preceding the black hole formation.

astro-ph.HE↗

arXiv2020

Impact of magnetic field on neutrino-matter interactions in core-collapse supernova

We explore the impact of magnetic field on neutrino-matter interactions in core-collapse supernova. We first derive the modified source terms for neutrino-nucleon scattering and neutrino absorption and emission processes in the moment formalism. Then we perform full relativistic three-dimensional, magnetorotational core-collapse supernova simulations of a 20 $M_\odot$ star with spectral neutrino transport. Our simulations treat self-consistently the parity violation effects of weak interaction in the presence of external magnetic field. The result shows a significant global asymmetry, mostly confined in the proto-neutron star, with clearly reflecting the magnetic field structure. The asymmetric property arises from two factors: the angle between the neutrino flux and magnetic field, and the term, which is parallel to the magnetic field and is also proportional to the deviation of distribution function of neutrinos from thermal equilibrium. The typical correction value amounts to $\sim1$ % relative to the total neutrino-matter interaction rate for the magnetic field strength of $\sim 10^{15-16}$~G. Although these asymmetric properties do not immediately affect the explosion dynamics, our results imply that they would be significant once the neutrinos diffuse out the proto-neutron star core carrying those asymmetries away. We also show that, during our simulation time of $\sim370$ ms after bounce, our results indicate that the correction value due to the modified inelastic scattering process dominates over that of the modified neutrino absorption and emission process.

astro-ph.HE↗

arXiv2020

Magnetorotational Explosion of A Massive Star Supported by Neutrino Heating in General Relativistic Three Dimensional Simulations

We present results of three-dimensional (3D), radiation-magnetohydrodynamics (MHD) simulations of core-collapse supernovae in full general relativity (GR) with spectral neutrino transport. In order to study the effects of progenitor's rotation and magnetic fields, we compute three models, where the precollapse rotation rate and magnetic fields are included parametrically to a 20 M$_{\odot}$ star. While we find no shock revival in our two non-magnetized models during our simulation times ($\sim500$ ms after bounce), the magnetorotationally (MR) driven shock expansion immediately initiates after bounce in our rapidly rotating and strongly magnetized model. We show that the expansion of the MR-driven flows toward the polar directions is predominantly driven by the magnetic pressure, whereas the shock expansion toward the equatorial direction is supported by neutrino heating. Our detailed analysis indicates that the growth of the so-called kink instability may hinder the collimation of jets, resulting in the formation of broader outflows. Furthermore we find a dipole emission of lepton number, only in the MR explosion model, whose asymmetry is consistent with the explosion morphology. Although it is similar to the lepton-number emission self-sustained asymmetry (LESA), our analysis shows that the dipole emission occurs not from the protoneutron star convection zone but from above the neutrino sphere indicating that it is not associated with the LESA. We also report several unique neutrino signatures, which are significantly dependent on both the time and the viewing angle, if observed, possibly providing a rich information regarding the onset of the MR-driven explosion.

astro-ph.HE↗

arXiv2020

A New Gravitational Wave Signature of Low-$T/|W|$ Instability in Rapidly Rotating Stellar Core Collapse

We present results from a full general relativistic three-dimensional hydrodynamics simulation of rapidly rotating core-collapse of a 70 M$_{\odot}$ star with three-flavor spectral neutrino transport. We find a strong gravitational wave (GW) emission that originates from the growth of the one- and two-armed spiral waves extending from the nascent proto-neutron star (PNS). The GW spectrogram shows several unique features that are produced by the non-axisymmetric instabilities. After bounce, the spectrogram first shows a transient quasi-periodic time modulation at $\sim$ 450 Hz. In the second active phase, it again shows the quasi-periodic modulation but with the peak frequency increasing with time, which continues until the final simulation time. From our detailed analysis, such features can be well explained by a combination of the so-called low-$T/|W|$ instability and the PNS core contraction.

astro-ph.HE↗

arXiv2019

Dependence of outer boundary condition on protoneutron star asteroseismology with gravitational-wave signatures

To obtain the eigenfrequencies of a protoneutron star (PNS) in the postbounce phase of core-collapse supernovae (CCSNe), we perform a linear perturbation analysis of the angle-averaged PNS profiles using results from a general relativistic CCSN simulation of a $15 M_{\odot}$ star. In this work, we investigate how the choice of the outer boundary condition could affect the PNS oscillation modes in the linear analysis. By changing the density at the outer boundary of the PNS surface in a parametric manner, we show that the eigenfrequencies strongly depend on the surface density. By comparing with the gravitational wave (GW) signatures obtained in the hydrodynamics simulation, the so-called surface $g$-mode of the PNS can be well ascribed to the fundamental oscillations of the PNS. The frequency of the fundamental oscillations can be fitted by a function of the mass and radius of the PNS similar to the case of cold neutron stars. In the case that the position of the outer boundary is chosen to cover not only the PNS but also the surrounding postshock region, we obtain the eigenfrequencies close to the modulation frequencies of the standing accretion-shock instability (SASI). However, we point out that these oscillation modes are unlikely to have the same physical origin of the SASI modes seen in the hydrodynamics simulation. We discuss possible limitations of applying the angle-averaged, linear perturbation analysis to extract the full ingredients of the CCSN GW signatures.

astro-ph.HE↗

arXiv2018

Core-collapse supernovae in the hall of mirrors. A three-dimensional code-comparison project

Modeling core-collapse supernovae (CCSNe) with neutrino transport in three dimensions (3D) requires tremendous computing resources and some level of approximation. We present a first comparison study of CCSNe in 3D with different physics approximations and hydrodynamics codes. We aim to assess the impact of the hydrodynamics code, approximations for the neutrino and gravity treatments, and rotation on the simulation of CCSNe in 3D. We use four different hydrodynamics codes in this work (ELEPHANT, FLASH, fGR1, and SPHYNX) in combination with two different neutrino treatments, the isotropic diffusion source approximation (IDSA) and two-moment M1, and three different gravity treatments: Newtonian, 1D General Relativity (GR) correction, and full GR). Additional parameters discussed in this study are the inclusion of neutrino-electron scattering via a parametrized deleptonization (PD) and the influence of rotation. The four codes compared in this work include Eulerian and fully Lagrangian (smoothed particle hydrodynamics) codes for the first time. They show agreement in the overall evolution of the collapse phase and early post-bounce within the range of 10% (20% in some cases). The comparison of the different neutrino treatments highlights the need to further investigate the antineutrino luminosities in IDSA, which tend to be relatively high. We also demonstrate the requirement for a more detailed heavy-lepton neutrino leakage. When comparing with a full GR code, including an M1 transport method, we confirm the influence of neutrino-electron scattering during the collapse phase, which is adequately captured by the PD scheme. Also, the effective GR potential reproduces the overall dynamic evolution correctly in all Newtonian codes. Additionally, we verify that rotation aids the shock expansion and estimate the overall angular momentum losses for each code in rotating scenarios.

astro-ph.HE↗