arXiv subjects

Kuo-Chuan Pan

Publications and source records attributed to Kuo-Chuan Pan.

At least 19 recordsLinked to original sources

arXiv2026

From Jets to Failed Supernovae: Morphologies and Gravitational-Wave Signatures in Two-Dimensional Magnetorotational Core-Collapse Supernovae

Magnetized and rotating core-collapse supernovae (CCSNe) are promising candidates for producing long gamma-ray bursts and hypernovae. In this project, we present 34 two-dimensional magnetized core-collapse supernova simulations with self-consistent neutrino transport, systematically exploring the parameter space of initial magnetic field strengths ($B_0 = 0$--$3.5 \times 10^{12}$~G) and rotation rates ($\Omega_0 = 0$--$0.5$~rad~s$^{-1}$) for a 40~$M_\odot$ progenitor. Our simulations reveal four distinct explosion morphologies: failed explosions leading to black hole formation, monopolar jet explosions, bipolar jet explosions, and neutrino-driven explosions. We find that the 40 $M_\odot$ progenitor model failed to explode without magnetic fields in two dimensions, even with rapid rotation. The non-rotating models require strong seed magnetic fields ($B_0 \gtrsim 1.5 \times 10^{12}$~G) to launch magnetically driven explosions, while the introduction of rotation substantially lowers this threshold. The explosion timescale decreases systematically with both increasing magnetic field strength and rotation rate, ranging from $>500$~ms in marginally successful models to $<150$~ms in strongly magnetized, rapidly rotating systems. Diagnostic explosion energies in the most extreme models approach $\sim 10^{51}$~erg within 250~ms and continue growing in time, making them potential hypernovae and long gamma-ray burst progenitors. Finally, we analyze the gravitational wave signatures associated with each morphology and find that the gravitational wave frequencies mainly depend on the rotation rates but are less sensitive to the magnetic field strengths and explosion morphologies. However, the gravitational wave amplitudes strongly depend on the explosion morphologies and magnetic fields, making searches for gravitational waves from magnetorotational core-collapse supernovae more challenging.

astro-ph.HE↗

arXiv2026

Three-dimensional Global Relativistic Radiation Magnetohydrodynamics of Magnetically Arrested Disk Accretion Flows in AGNs

We perform three-dimensional radiation-relativistic magnetohydrodynamic (3D Rad-RMHD) simulations of accretion flows around spinning active galactic nuclei (AGNs). Our study focuses on the magnetically arrested disk (MAD) state, adopting a single-temperature model that includes bremsstrahlung opacity as the sole radiation process while varying the black hole spin from non-spinning to rapidly spinning cases. We find that the MAD state persists across all spin values, as demonstrated by the normalized magnetic flux at the horizon and the physically motivated spatially averaged plasma beta. The overall flow dynamics remain qualitatively similar for all spin models in 3D flow, suggesting that black hole spin has minimal influence on the accretion dynamics. In addition, we conduct post-processing using a two-temperature model to calculate the luminosities from synchrotron and bremsstrahlung radiation. We find that the total radiation luminosity is significantly higher than the luminosities from synchrotron and bremsstrahlung. This finding highlights the influence of radiation on the dynamics of the accretion flow. Our analysis shows that the electron temperature is significantly high in the jet region, regardless of spin. We further find that the temporal evolution of both radiative and synchrotron luminosities exhibits qualitatively similar behavior across all spin values. Finally, our results indicate that black hole spin has minimal impact on the spectral energy distribution (SED) in MAD state accretion flows.

astro-ph.HE↗

arXiv2025

$r$-process Heating Feedback on Disk Outflows from Neutron Star Mergers

Neutron star mergers produce $r$-process elements, with yields that are sensitive to the kinematic and thermodynamic properties of the ejecta. These ejecta properties are potentially affected by dynamically-important feedback from $r$-process heating, which is usually not coupled to the hydrodynamics in post-merger simulations modeling the ejecta launching and expansion. The multi-messenger detection of GW170817 showed the importance of producing reliable ejecta predictions, to maximize the diagnostic potential of future events. In this paper, we develop a prescription for including $r$-process heating as a source term in the hydrodynamic equations. This prescription depends on local fluid properties and on the $Y_{e}$ history as recorded by dedicated tracer particles, which exchange information with the grid using the Cloud-in-Cell method. The method is implemented in long-term viscous hydrodynamic simulations of accretion disk outflows to investigate its feedback on ejecta properties. We find that $r$-process heating can increase the unbound disk ejecta mass by $\sim 10\%$ relative to a baseline case that only considers alpha particle recombination. Nuclear heating also enhances the radial velocity of the ejecta with $Y_e < 0.25$ by up to a factor of two, while concurrently suppressing marginally-bound convective ejecta.

astro-ph.HE↗

arXiv2025

Type Ia Supernova Progenitors and Surviving Companions within the Symbiotic Channel

The symbiotic channel of Type Ia supernovae progenitors is crucial for explaining the observed circumstellar material in some Type Ia supernovae. While extensive numerical and observational efforts have been dedicated to exploring the progenitor system, limited emphasis has been placed on studying the surviving companions arising from the symbiotic channel. In this paper, we present a numerical study of the symbiotic systems using {\tt MESA} as potential Type Ia supernova progenitors. We conduct 1260 binary stellar evolution simulations, over a wide range of parameters, incorporating the optically thick wind model developed by Hachisu et al., and predict the post-impact evolution of these surviving companions. We classify four types of progenitor systems based on the evolutionary stage of the companion at the onset of the explosion: red giant companions, with or without prior helium flash events, and asymptotic giant branch companions, with or without the thermal pulsing phase. After the SN impact, a blue dwarf star with either a helium or carbon-oxygen core is left behind. However, if a small portion of the envelope ($\gtrsim$ 0.3\%) remains on the core of the surviving companion, the overall post-supernova evolution may remain similar to its pre-explosion state, albeit slightly fainter, making observation a challenging endeavor.

astro-ph.HE↗

arXiv2025

Supernova Ia Remnants with M dwarf surviving companions

We study the possibility that Type Ia supernovae might be produced by binary systems where the companion of the exploding white dwarf is an M-dwarf star. Such companion would appear as a runaway star, retaining its pre-explosion orbital velocity along with a kick imparted by the supernova ejecta. It might be rapidly rotating, from being tidally locked with the white dwarf prior to explosion in a very close binary. For this study, we perform a series of multidimensional hydrodynamic simulations to investigate the interaction between M-dwarf companions and SN ejecta, followed by post-impact stellar evolution modeling using the MESA code. Our initial models in the 3D simulations had high spin angular momenta and the effects of magnetic braking have been included. They very significantly reduce the final rotation. A surviving companion candidate, MV-G272, has recently been discovered in the supernova remnant G272.2-3.2, which is an 8.9$\sigma$ proper motion outlier, although being slowly rotating. Our results show that the properties of this companion (luminosity, effective temperature, surface gravity) can be reproduced by our post-impact M-dwarf models. The slow rotation, which is a common characteristic with several proposed hypervelocity SN companions, can be explained by magnetic braking during the post-impact evolution, thus supporting the possibility that the MV-G272 star is the surviving companion of the Type Ia supernova now found as G272.2-3.2 SNR.

astro-ph.HE↗

arXiv2025

Effectiveness of Stacks in the Stacked Hilbert-Huang Transform

The Hilbert-Huang transform (HHT) consists of empirical mode decomposition (EMD), which is a template-free method that represents the combination of different intrinsic modes on a time-frequency map (i.e., the Hilbert spectrum). The application of HHT involves introducing trials by imposing white noise on the signal and then calculating the ensemble mean process of the corresponding EMD to demonstrate its significance on the Hilbert spectrum. In this study, we develop a stacked Hilbert-Huang Transform (sHHT) method that generates the Hilbert spectrum for each trial and compiles all results to enhance the strength of the real instantaneous frequency of the main signal on the time-frequency map. This new approach is more sensitive to detecting/tracing the nonlinear and transient features of a signal embedded in astronomical databases than the conventional HHT, particularly when the signal experiences dramatic frequency changes in a short time. We analytically investigate the consistency of HHT and sHHT and perform numerical simulations to examine the dispersion of the instantaneous frequency obtained through sHHT and compare its advantages and effectiveness with those of conventional HHT. To confirm the feasibility of the sHHT, we demonstrate its application in verifying the signal of superorbital modulation in X-ray and binary black hole mergers in gravitational waves.

astro-ph.IM↗

arXiv2025

Global resistive MHD accretion flows around spinning AGNs: impact of resistivity on MAD state

In this study, we investigate the effect of resistivity on the dynamics of global magnetohydrodynamic accretion flows (Res-MHD) around a spinning supermassive black hole. We perform a comparative study of 2D and 3D resistive models around black holes. We examine accretion flow dynamics considering globally uniform resistivity values, ranging from $\sim 0$ to 0.1. During the simulation time of $t \lesssim 1000~t_g$, we find that the mass accretion rate is comparable for both the 2D and 3D models. However, as the flow becomes increasingly turbulent, non-axisymmetric effects begin to dominate, resulting in significant differences in the mass accretion rates between the 3D and 2D. All the resistive models in a highly magnetized flow belong to the Magnetically Arrested Disk (MAD) state. We propose an efficient and physically motivated approach to examine the magnetic state by estimating the spatial average plasma beta parameter across the computational domain. We find that when the average plasma beta is close to or below unity $( \beta_{\text{ave}} \lesssim 1 )$, the accretion flow enters the MAD state. Additionally, we find that high-resistivity flow reduces magnetorotational instability (MRI) turbulence in the accretion flow, while the turbulence structures remain qualitatively similar in low-resistivity flows. Moreover, we observe indications of plasmoid formations in low-resistivity flow compared to high-resistivity flow. Furthermore, we do not find a clear relationship between the variability of the accretion rate, magnetic flux, and resistivity. Lastly, our findings suggest that low-resistivity models produce higher power jets than those with higher resistivity.

astro-ph.HE↗

arXiv2024

Radiation RMHD accretion flows around spinning AGNs: a comparative study of MAD and SANE state

In our study, we examine a 2D radiation, relativistic, magnetohydrodynamics (Rad-RMHD) accretion flows around a spinning supermassive black hole. We begin by setting an initial equilibrium torus around the black hole, with an embedded initial magnetic field inside the torus. The strength of the initial magnetic field is determined by the plasma beta parameter, which is the ratio of the gas pressure to the magnetic pressure. In this paper, we perform a comparative study of the `magnetically arrested disc (MAD)' and `standard and normal evolution (SANE)' states. We observe that MAD state is possible for comparatively high initial magnetic field strength flow. Additionally, we also adopt a self-consistent two-temperature model to evaluate the luminosity and energy spectrum for our model. We observe that the total luminosity is mostly dominated by bremsstrahlung luminosity compared to the synchrotron luminosity due to the presence of highly dense torus. We also identify similar quasi-periodic oscillations (QPOs) for both MAD and SANE states based on power density spectrum analysis. Furthermore, our comparative study of the energy spectrum does not reveal any characteristic differences between MAD and SANE states. Lastly, we note that the MAD state is possible for both prograde and retrograde accretion flow.

astro-ph.HE↗

arXiv2024

The Influence of Stellar Rotation in Binary Systems on Core-Collapse Supernova Progenitors and Multi-messenger Signals

The detailed structure of core-collapse supernova progenitors is crucial for studying supernova explosion engines and the corresponding multimessenger signals. In this paper, we investigate the influence of stellar rotation on binary systems consisting of a 30 solar mass donor star and a 20 solar mass accretor using the MESA stellar evolution code. We find that through mass transfer in binary systems, fast-rotating red- and blue-supergiant progenitors can be formed within a certain range of initial orbital periods, albeit the correlation is not linear. We also find that even with the same initial mass ratio of the binary system, the resulting final masses of the collapsars, the iron core masses, the compactness parameters, and the final rotational rates can vary widely and are sensitive to the initial orbital periods. For instance, the progenitors with strong convection form a thinner Si-shell and a wider O-shell compared to those in single-star systems. In addition, we conduct two-dimensional self-consistent core-collapse supernova simulations with neutrino transport for these rotating progenitors derived from binary stellar evolution. We find that the neutrino and gravitational-wave signatures of these binary progenitors could exhibit significant variations. Progenitors with larger compactness parameters produce more massive proto-neutron stars, have higher mass-accretion rates, and emit brighter neutrino luminosity and louder gravitational emissions. Finally, we observe stellar-mass black hole formation in some of our failed exploding models.

astro-ph.HE↗

arXiv2023

A New Kilohertz Gravitational-Wave Feature from Rapidly Rotating Core-Collapse Supernovae

We present self-consistent three-dimensional core-collapse supernova simulations of a rotating $20M_\odot$ progenitor model with various initial angular velocities from $0.0$ to $4.0$ rad s$^{-1}$ using a smoothed particle hydrodynamics code, SPHYNX, and a grid-based hydrodynamics code, FLASH. We identify two strong gravitational-wave features, with peak frequencies of $\sim300$ Hz and $\sim1.3$ kHz in the first $100$ ms postbounce. We demonstrate that these two features are associated with the $m=1$ deformation from the proto-neutron star (PNS) modulation induced by the low-$T/|W|$ instability, regardless of the simulation code. The $300$ Hz feature is present in models with an initial angular velocity between $1.0$ and $4.0$ rad s$^{-1}$, while the $1.3$ kHz feature is present only in a narrower range, from $1.5$ to $3.5$ rad s$^{-1}$. We show that the $1.3$ kHz signal originates from the high-density inner core of the PNS, and the $m=1$ deformation triggers a strong asymmetric distribution of electron anti-neutrinos. In addition to the $300$ Hz and $1.3$ kHz features, we also observe one weaker but noticeable gravitational-wave feature from higher-order modes in the range between $1.5$ and $3.5$ rad s$^{-1}$. Its peak frequency is around $800$ Hz initially and gradually increases to $900-1000$ Hz. Therefore, in addition to the gravitational bounce signal, the detection of the $300$ Hz, $1.3$ kHz, the higher-order mode, and even the related asymmetric emission of neutrinos, could provide additional diagnostics to estimate the initial angular velocity of a collapsing core.

astro-ph.HE↗

arXiv2023

Characterizing the Directionality of Gravitational Wave Emission from Matter Motions within Core-collapse Supernovae

We analyze the directional dependence of the gravitational wave (GW) emission from 15 3D neutrino radiation hydrodynamic simulations of core-collapse supernovae. Using spin weighted spherical harmonics, we develop a new analytic technique to quantify the evolution of the distribution of GW emission over all angles. We construct a physics-informed toy model that can be used to approximate GW distributions for general ellipsoid-like systems, and use it to provide closed form expressions for the distribution of GWs for different CCSN phases. Using these toy models, we approximate the PNS dynamics during multiple CCSN stages and obtain similar GW distributions to simulation outputs. When considering all viewing angles, we apply this new technique to quantify the evolution of preferred directions of GW emission. For nonrotating cases, this dominant viewing angle drifts isotropically throughout the supernova, set by the dynamical timescale of the protoneutron star. For rotating cases, during core bounce and the following tens of ms, the strongest GW signal is observed along the equator. During the accretion phase, comparable -- if not stronger -- GW amplitudes are generated along the axis of rotation, which can be enhanced by the low T/|W| instability. We show two dominant factors influencing the directionality of GW emission are the degree of initial rotation and explosion morphology. Lastly, looking forward, we note the sensitive interplay between GW detector site and supernova orientation, along with its effect on detecting individual polarization modes.

astro-ph.HE↗

arXiv2023

Evolution of MHD Torus and Mass Outflow Around Spinning AGN

We perform axisymmetric, two-dimensional magnetohydrodynamic (MHD) simulations to investigate accretion flows around spinning AGN. To mimic the space-time geometry of spinning black holes, we consider effective Kerr potential, and the mass of the black holes is $10^8 M_{\odot}$. We initialize the accretion disc with a magnetized torus by adopting the toroidal component of the magnetic vector potential. The initial magnetic field strength is set by using the plasma beta parameter ($β_0$). We observe self-consistent turbulence generated by magneto rotational instability (MRI) in the disc. The MRI turbulence transports angular momentum in the disc, resulting in an angular momentum distribution that approaches a Keplerian distribution. We investigate the effect of the magnetic field on the dynamics of the torus and associated mass outflow from the disc around a maximally spinning black hole $(a_k = 0.99)$. For the purpose of our analysis, we investigate the magnetic state of our simulation model. The model $β_0 = 10$ indicates the behaviour similar to the "magnetically arrested disk (MAD)'' state, and all the other low magnetic model remains in the SANE state. We observe that mass outflow rates are significantly enhanced with the increased magnetic field in the disc. We find a positive correlation between the magnetic field and mass outflow rates. We also investigate the effect of black hole spin on the magnetized torus evolution. However, we have not found any significant effect of black hole spin on mass outflows in our model. Finally, we discuss the possible astrophysical applications of our simulation results.

astro-ph.HE↗

arXiv2023

Cosmic ray calorimetry in star-forming galaxy populations and implications for their contribution to the extra-galactic $γ$-ray background

Star-forming galaxies (SFGs) have been established as an important source population in the extra-galactic $γ$-ray background (EGB). Their intensive star-formation creates an abundance of environments able to accelerate particles, and these build-up a rich sea of cosmic rays (CRs). Above GeV energies, CR protons can undergo hadronic interactions with their environment to produce $γ$-rays. SFGs can operate as CR proton "calorimeters", where a large fraction of the CR energy is converted to $γ$-rays. However, CRs also deposit energy and momentum to modify the thermal and hydrodynamic conditions of the gas in SFGs, and can become a powerful driver of outflows. Such outflows are ubiquitous among some types of SFGs, and have the potential to severely degrade their CR proton calorimetry. This diminishes their contribution to the EGB. In this work, we adopt a self-consistent treatment of particle transport in outflows from SFGs to assess their calorimetry. We use 1D numerical treatments of galactic outflows driven by CRs and thermal gas pressure, accounting for the dynamical effects and interactions of CRs. We show the impact CR-driven flows have on the relative contribution of SFG populations to the EGB, and investigate the properties of SFGs that contribute most strongly.

astro-ph.HE↗

arXiv2023

Exploring the Observability of Surviving Companions of Stripped-Envelope Supernovae: A Case Study of Type Ic SN 2020oi

Stripped-envelope supernovae (SE SNe) were considered as the explosions of single massive stars with strong stellar winds, while later observations favor binary origins. One direct evidence to support the binary origins is to find the surviving companions of SE SNe since previous numerical studies suggested that the binary companion should survive the supernova impact and could be detectable. Recently, Gagliano et al. (2022) reported that the nearby Type Ic SN 2020oi in M100 (~17.1 Mpc) resulted from a binary system based on the HST photometric and spectroscopic observation. Based on the suggested binary properties of SN 2020oi, we conduct two-dimensional hydrodynamics simulations of supernova-companion interactions and the subsequent post-impact evolution of the companion. Our results suggest that a surviving companion becomes brighter in two orders of magnitude and temporarily redder after the SN impact. The companion might be detectable with the JWST NIRCam short wavelength channel in a few years. Furthermore, the predicted magnitudes of surviving companions show a significant magnitude gradient around the peak. This could be another indicator to identify the surviving companion from a SE SN.

astro-ph.HE↗

arXiv2022

Determine the Core Structure and Nuclear Equation of State of Rotating Core-Collapse Supernovae with Gravitational Waves by Convolutional Neural Networks

Detecting gravitational waves from a nearby core-collapse supernova would place meaningful constraints on the supernova engine and nuclear equation of state. Here we use Convolutional Neural Network models to identify the core rotational rates, rotation length scales, and the nuclear equation of state (EoS), using the 1824 waveforms from Richers et al. (2017) for a 12 solar mass progenitor. High prediction accuracy for the classifications of the rotation length scales ($93\%$) and the rotational rates ($95\%$) can be achieved using the gravitational wave signals from -10 ms to 6 ms core bounce. By including additional 48 ms signals during the prompt convection phase, we could achieve $96\%$ accuracy on the classification of four major EoS groups. Combining three models above, we could correctly predict the core rotational rates, rotation length scales, and the EoS at the same time with more than $85\%$ accuracy. Finally, applying a transfer learning method for additional 74 waveforms from FLASH simulations (Pan et al. 2018), we show that our model using Richers' waveforms could successfully predict the rotational rates from Pan's waveforms even for a continuous value with a mean absolute errors of 0.32 rad s$^{-1}$ only. These results demonstrate a much broader parameter regimes our model can be applied for the identification of core-collapse supernova events through GW signals.

astro-ph.HE↗

arXiv2022

A Comprehensive Analysis of the Gravitational Wave Events with the Hilbert-Huang Transform: From Compact Binary Coalescence to Supernova

We analyze the gravitational wave signals with a model-independent time-frequency analysis, which is improved from the Hilbert-Huang transform (HHT) and optimized for characterizing the frequency variability on the time-frequency map. Except for the regular HHT algorithm, i.e., obtaining intrinsic mode functions with ensemble empirical mode decomposition and yielding the instantaneous frequencies, we propose an alternative algorithm that operates the ensemble mean on the time-frequency map. We systematically analyze the known gravitational wave events of the compact binary coalescence observed in LIGO O1 and O2, and in the simulated gravitational wave signals from core-collapse supernovae (CCSNe) with our method. The time-frequency maps of the binary black hole coalescence cases show much better details compared to those wavelet spectra. Moreover, the oscillation in the instantaneous frequency caused by mode-mixing could be reduced with our algorithm. For the CCSNe data, the oscillation from the proto-neutron star and the radiation from the standing accretion shock instability can be precisely determined with the HHT in great detail. More importantly, the initial stage of different modes of oscillations can be clearly separated. These results provide new hints for further establishment of the detecting algorithm, and new probes to investigate the underlying physical mechanisms.

astro-ph.HE↗

arXiv2022

Evolution of Main-Sequence-like Surviving Companions in Type Ia Supernova Remnants

Recent theoretical and numerical studies of Type Ia supernova explosion within the single-degenerate scenario suggest that the non-degenerate companions could survive during the supernova impact and could be detectable in nearby supernova remnants. However, observational efforts show less promising evidence on the existence of surviving companions from the standard single-degenerate channels. The spin-up/spin-down models are possible mechanisms to explain the non-detection of surviving companions. In these models, the spin-up phase could increase the critical mass for explosion, leading to a super-Chandrasekhar mass explosion, and the spin-down phase could lead to extra mass loss and angular momentum redistribution. Since the spin-down timescale for the delayed explosion of a rotating white dwarf is unclear, in this paper, we explore a vast parameter space of main-sequence-like surviving companions via two-dimensional hydrodynamic simulations of supernova impact and the subsequent stellar evolution of surviving companions. Tight universal relations to describe the mass stripping effect, supernova kick, and depth of supernova heating are provided. Our results suggest that the not-yet detected surviving companions from observations of nearby Type Ia supernova remnants might favor low mass companions, short binary separation, or stronger supernova explosion energies than the standard singe-degenerate channels.

astro-ph.HE↗

arXiv2021

Search for Surviving Companions of Progenitors of Young LMC Type Ia Supernova Remnants

We have used two methods to search for surviving companions of Type Ia supernova progenitors in three Balmer-dominated supernova remnants (SNRs) in the Large Magellanic Cloud: 0519-69.0, 0505-67.9 (DEM L71), and 0548-70.4. In the first method, we use the Hubble Space Telescope photometric measurements of stars to construct color-magnitude diagrams (CMDs), and compare positions of stars in the CMDs with those expected from theoretical post-impact evolution of surviving main sequence or helium star companions. No obvious candidates of surviving companion are identified in this photometric search. Future models for surviving red giant companions or with different explosion mechanisms are needed for thorough comparisons with these observations in order to make more definitive conclusions. In the second method, we use Multi-Unit Spectroscopic Explorer (MUSE) observations of 0519-69.0 and DEM L71 to carry out spectroscopic analyses of stars in order to use large peculiar radial velocities as diagnostics of surviving companions. We find a star in 0519-69.0 and a star in DEM L71 moving at radial velocities of 182 $\pm$ 0 km s$^{-1}$ and 213 $\pm$ 0 km s$^{-1}$, more than 2.5$σ$ from the mean radial velocity of the underlying stellar population, 264 km s$^{-1}$ and 270 km s$^{-1}$, respectively. These stars need higher-quality spectra to investigate their abundances and rotation velocities to determine whether they are indeed surviving companions of the SN progenitors.

astro-ph.SR↗