arXiv subjects

Tomoya Kinugawa

Publications and source records attributed to Tomoya Kinugawa.

At least 19 recordsLinked to original sources

arXiv2026

No Surviving Companion to the Galactic SN 1181: Evidence for a Double-Degenerate Channel for Type Iax Supernovae

Type Iax supernovae (SNe Iax) are the recently-established, yet peculiar subclass of thermonuclear supernovae, whose progenitor systems and explosion mechanisms remain debated. A leading scenario is a single-degenerate channel, in which a white dwarf accreting from a He-star companion undergoes a pure deflagration, leaving both a bound remnant and surviving companion. The Galactic SN 1181, whose distinctive properties are consistent with an SN Iax involving a weak explosion and bound white dwarf remnant, offers a unique opportunity to test this scenario. Here, we perform a deep search for a surviving He-star companion, a hallmark of the single-degenerate He-donor channel, within $30^{\prime\prime}$ ($\sim 0.3$ pc) of the remnant using archival Gaia and Pan-STARRS1 data. The parallaxes and proper motions exclude all Gaia sources, while the spectral energy distributions of the remaining Pan-STARRS1 sources are inconsistent with both the He-star spectral templates and known hot-subdwarf population. Binary evolution calculations predict a minimum mass of a companion with an absolute $g$-band magnitude of $M_{g} \lesssim 6.5$ mag, much brighter than the Pan-STARRS1 detection limit of $M_{g} > 8$ mag. Our non-detection rules out He-star and luminous hydrogen-rich companions for SN 1181, favoring a double-degenerate channel (i.e., a white dwarf merger). Adding to the luminous He-star companion identified in the pre-explosion imaging of SN 2012Z, our results provide direct evidence for multiple progenitor channels leading to SNe Iax.

astro-ph.HE↗

arXiv2026

Impact of Spin Priors on the Population Inference of Merging Binary Black Holes

The spins of merging binary black holes (BBHs) inferred from gravitational-wave (GW) observations provide key insights into their formation channels. However, spin parameters are typically weakly constrained from data, and their inferred values are often strongly influenced by the assumed prior in Bayesian analyses. A commonly used prior, uniform in spin magnitudes and isotropic in spin directions, assigns vanishing probability density to spin-orbit-aligned configurations, potentially biasing inferences for BBH parameters. The prior choice can also affect population-level analyses by degrading the convergence of Monte Carlo integrations used to evaluate the likelihood in hierarchical Bayesian inference. In this work, we propose a novel spin prior that is uniform in the effective spin parameters Xeff and Xp, two spin combinations that can be relatively well measured from GW data, conditioned on the mass ratio. Using simulated BBH populations, we show that the inferred spin population can depend on the choice of prior, and that the proposed prior more accurately recovers the underlying spin population, particularly when the true distribution favors aligned-spin configurations. Because mass and spin measurements are correlated, our prior also enables a more accurate recovery of the underlying mass distribution.

gr-qc↗

arXiv2025

The diffuse supernova neutrino background: an update with modern population synthesis and core-collapse simulations

We present a new, state-of-the-art computation of the Diffuse Supernova Neutrino Background (DSNB), where we use neutrino spectra from multi-dimensional, multi-second core collapse supernova simulations - including both neutron-star and black-hole forming collapses - and binary evolution effects from modern population synthesis codes. Large sets of numerical results are processed and connected in a consistent manner, using two key quantities: the mass of the star's Carbon-Oxygen (CO) core at an advanced pre-collapse stage - which depends on binary evolution effects - and the compactness parameter, which is the main descriptor of the post-collapse neutrino emission. The method enables us to model the neutrino emission of a very diverse, binary-affected population of stars, which cannot unambiguously be mapped in detail by existing core collapse simulations. We find that including black hole-forming collapses enhances the DSNB by up to 50% at energies greater than 30-40 MeV. Binary evolution effects can change the total rate of collapses and generate a sub-population of high core mass stars that are stronger neutrino emitters. However, the net effect on the DSNB is moderate - up to a 15% increase in flux - due to the rarity of these super-massive cores and to the relatively modest dependence of the neutrino emission on the CO core mass. The methodology presented here is suitable for extensions and generalizations, and therefore it lays the foundation for modern treatments of the DSNB.

astro-ph.HE↗

arXiv2025

Population Synthesis Study on the Binary Origin of Type Ibn Supernovae

Type Ibn supernovae (SNe) are a class of SN explosions whose progenitors are surrounded by dense helium-rich circumstellar matter (CSM). Some models have been proposed for how to form the dense CSM, with promising scenarios involving either binaries with a low-mass ($\lesssim 3~M_\odot$) helium (He) star, or mergers following common envelope phases between a He star and a compact object. Using rapid binary population synthesis calculations, we estimate the event rate of these channels and compare it with the observed SN Ibn rate. We find that exploding low-mass He stars in close binaries (of separations $\lesssim$ a few 100 $R_\odot$) can be sufficiently produced to account for the observed event rate of SN Ibn, while the merger scenario can likely account for only a fraction of these SNe. We discuss the types of companions expected in the low-mass He star scenario, finding massive main sequence stars ($10$--$20\ M_\odot$) to be typical, with a potentially non-negligible fraction ($<10\%$) of binaries with white dwarf (WD) companions that have long delay times of up to $100$ Myrs.

astro-ph.SR↗

arXiv2024

An analytical joint prior for effective spins for inference on the spin distribution of binary black holes

We derive an analytical form of the joint prior of effective spin parameters, $\chi_\mathrm{eff}$ and $\chi_\mathrm{p}$, assuming an isotropic and uniform-in-magnitude spin distribution. This is a vital factor in performing hierarchical Bayesian inference for studying the population properties of merging compact binaries observed with gravitational waves. In previous analyses, this was evaluated numerically using kernel density estimation (KDE). However, we find that this numerical approach is inaccurate in certain parameter regions, where both $|\chi_\mathrm{eff}|$ and $\chi_\mathrm{p}$ are small. Our analytical approach provides accurate computations of the joint prior across the entire parameter space and enables more reliable population inference. Employing our analytic prior, we reanalyze binary black holes in the Gravitational-Wave Transient Catalog 3 (GWTC-3) by the LIGO-Virgo-KAGRA collaboration. While the results are largely unchanged, log-likelihood errors due to the use of the inaccurate prior evaluations are $\mathcal{O}(1)$. Since these errors accumulate with the increasing number of events, our analytical prior will be crucial in the future analyses.

gr-qc↗

arXiv2024

Hidden in Pixels. I. Discovery of dual "little red dots" indicates excess clustering on kilo-parsec scales

``Little Red Dots'' (LRDs) are an abundant high-redshift population newly discovered by the James Webb Space Telescope (JWST) and considered to be an early growth phase of supermassive black holes (SMBHs). Using a method of pixel-by-pixel color selection and relaxing the compactness criteria, we identify four dual LRD candidates in the COSMOS-Web survey with projected separations of $0.\!\!^{\prime\prime}2$-$1.\!\!^{\prime\prime}2$. A comparison between existing LRD samples and mock data reveals that the projected separations of these dual LRD candidates are unlikely to result from chance projections of objects at different redshifts. Furthermore, two of the four systems are covered by COSMOS-3D slitless spectroscopy, and a single-line detection at the same observed wavelength for each LRD in a pair strongly supports that they are at identical redshifts. Assuming that the detected lines are H$\alpha$ based on their high equivalent width and broad profile, the spectroscopic redshifts of $z=5.822$ and $5.464$ for the two pairs are consistent with their photometric redshifts, yielding projected separations of $1.64$ and $7.36\,{\rm kpc}$. These discoveries suggest that the angular auto-correlation function (ACF) of LRDs exhibits an excess ($\sim20$-$30$ times) on sub-arcsec (kilo-parsec) separations compared to an extrapolation of a power-law ACF of JWST-found AGNs measured over $10^{\prime\prime}$-$100^{\prime\prime}$. Our sample is likely to represent precursors of mergers between LRDs, and such mergers may be one of the mechanisms that can drive the rapid growth of SMBHs in their early evolutionary stages.

astro-ph.GA↗

arXiv2023

Constraint on the progenitor of binary black hole merger using Population III star formation channel

The observations of gravitational waves have revealed the existence of black holes above $30 M_\odot$. A variety of channels have been proposed as their origin, including the Population III (Pop. III) star channel. In this channel, Binary Black Holes (BBHs) containing such massive BHs are naturally produced. In this paper, we examine the relative fractions of five formation channels that may contribute to the origins of BBHs: isolated binaries of either Population I or Population II stars, PopIII isolated binaries, chemically homogeneous evolution, and the dynamical evolution in globular clusters and nuclear star clusters, using the LIGO-Virgo-KAGRA gravitational-wave transient catalog (GWTC-3) events through hierarchical Bayesian inference. We find that the branching fraction of the Pop. III BBH channel is $0.11^{+0.08}_{-0.06}$ within our framework, consistent with the local merger rate density of the model of the Pop. III BBH channel we adopt. We also evaluate the contributions to the catalogue using the selection effect of each formation channel and find that Pop. III BBH could contribute at a non-negligible rate, though the adequacy of these ratios should be subject to ongoing discussion.

astro-ph.HE↗

arXiv2023

Fate of supernova progenitors in massive binary systems

How massive stars end their lives depends on the core mass, core angular momentum, and hydrogen envelopes at death. However, these key physical facets of stellar evolution can be severely affected by binary interactions. In turn, the effectiveness of binary interactions itself varies greatly depending on the initial conditions of the binaries, making the situation much more complex. We investigate systematically how binary interactions influence core-collapse progenitors and their fates. Binary evolution simulations are performed to survey the parameter space of supernova progenitors in solar metallicity binary systems and to delineate major evolutionary paths. We first study fixed binary mass ratios ($q=M_2/M_1$ = 0.5, 0.7, and 0.9) to elucidate the impacts of initial mass and initial separation on the outcomes, treating separately Type Ibc supernova, Type II supernova, accretion induced collapse (AIC), rapidly rotating supernova (RSN), black hole formation, and gamma ray burst (GRB). We then conduct Binary Population Synthesis calculations for 12 models, varying the initial parameter distributions and binary evolution parameters, to estimate various supernova fractions. We obtain a Milky Way supernova rate $R_{\rm SN} = (1.14$--$1.57) \times10^{-2} \, {\rm yr}^{-1}$ which is consistent with observations. We find the rates of AIC, RSN, and GRB to be $\sim 1/100$ the rate of regular supernovae. Our estimated GRB rates are higher than the observed long GRB rate, but very close to the low luminosity GRB rate. Furthering binary modeling and improving the inputs one by one will enable more detailed studies of these and other transients associated with massive stars.

astro-ph.HE↗

arXiv2023

Mass Ratio of Binary Black Holes Determined from LIGO/Virgo Data Restricted to Small False Alarm Rate

We focus on gravitational-wave events of binary black-hole mergers up to the third observing run with the minimum false alarm rate smaller than $10^{-5}\,{\rm yr}^{-1}$. These events tell us that the mass ratio of two black holes follows $m_2/m_1=0.723$ with the chance probability of 0.00301% for the chirp mass $M_{\rm chirp} > 18\,M_{\odot}$. We show that the relation of $m_2/m_1=0.723$ is consistent with the binaries originated from population III stars which are the first stars in the universe. On the other hand, it is found for ${\rm chirp} < 18 M_{\odot}$ that the mass ratio follows $m_2/m_1=0.601$ with the chance probability of 0.117% if we ignore GW190412 with $m_2/m_1\sim 0.32$. This suggests a different origin from that for $M_{\rm chirp} > 18 M_{\odot}$.

gr-qc↗

arXiv2023

Merger Conditions of Population III Protostar Binaries

Massive close binary stars with extremely small separations have been observed, and they are possible progenitors of gravitational-wave sources. The evolution of massive binaries in the protostellar accretion stage is key to understanding their formation process. We, therefore, investigate how close the protostars, consisting of a high-density core and a vast low-density envelope, can approach each other but not coalesce. To investigate the coalescence conditions, we conduct smoothed particle hydrodynamics simulations following the evolution of equal-mass binaries with different initial separations. Since Population (Pop) I and III protostars have similar interior structures, we adopt a specific Pop~III model with the mass and radius of $7.75\;M_{\odot}$ and $61.1\;R_{\odot}$ obtained by the stellar evolution calculations. Our results show that the binary separation decreases due to the transport of the orbital angular momentum to spin angular momentum. If the initial separation is less than about 80 per~cent of the sum of the protostellar radius, the binary coalesces in a time shorter than the tidal lock timescale. The mass loss up to the merging is $\lesssim 3$ per~cent. After coalescence, the star rotates rapidly, and its interior structure is independent of the initial separation. We conclude that there must be some orbital shrinking mechanism after the protostars contract to enter the zero-age main-sequence stage.

astro-ph.SR↗

arXiv2023

Search for a Black Hole Binary in Gaia DR3 Astrometric Binary Stars with Spectroscopic Data

We report the discovery of a candidate binary system consisting of a black hole (BH) and a red giant branch star from the Gaia DR3. This binary system is discovered from 64108 binary solutions for which both astrometric and spectroscopic data are available. For this system, the astrometric and spectroscopic solutions are consistent with each other, making this system a confident candidate of a BH binary. The primary (visible) star in this system, Gaia DR3 5870569352746779008, is a red giant branch whose mass is quite uncertain. Fortunately, albeit the uncertainty of the primary's mass, we can estimate the mass of the secondary (dark) object in this system to be $>5.68$ $M_\odot$ with a probability of $99$ \%, based on the orbital parameters. The mass of the secondary object is much larger than the maximum neutron star mass ($\sim 2.0$ $M_\odot$), which indicates that the secondary object is likely a BH. We argue that, if this dark object is not a BH, this system must be a more exotic system, in which the primary red giant branch star orbits around a quadruple star system (or a higher-order multiple star system) whose total mass is more than $5.68$ $M_\odot$. If this is a genuine BH binary, this has the longest period ($1352.22 \pm 45.81$ days) among discovered so far. As our conclusion entirely relies on the Gaia DR3 data, independent confirmation with follow-up observations (e.g. long-term spectra) is desired.

astro-ph.SR↗

arXiv2022

On the population III binary black hole mergers with intermediate mass black holes: dependence on common envelope parameter

The current gravitational wave (GW) detectors have successfully observed many binary compact objects, and the third generation ground-based GW detectors such as Einstein telescope and space-borne detectors such as LISA will start their GW observation in a decade. Ahead of the arrival of this new era, we perform a binary population synthesis calculation for very massive ($\sim$ 100--1000 $M_\odot$) population (Pop.) III stars, derive the various property of binary black hole (BBH) mergers with intermediate mass black holes (IMBHs) and investigate the dependence on common envelope parameter $αλ$ which is still not a well understood parameter. We find that the maximum mass of primary BH mass is larger for smaller value of common envelope parameter. In this study, we adopt double power law initial mass function (IMF) for Pop. III stars, and put some constraints on Pop. III IMF by comparing our obtained merger rate density at the local Universe with that derived from gravitational wave (GW) observation. We compute the detection rate and show that the third generation ground-based GW detector, Einstein telescope, have a potential to detect $\sim$ 10--1000 BBHs with IMBHs per year. We also find that we may be able to obtain the insight into $αλ$ if a BBH with total mass $\gtrsim500M_\odot$ are detected by advanced LIGO (O4) or LISA.

astro-ph.HE↗

arXiv2022

Probe for Type Ia supernova progenitor in decihertz gravitational wave astronomy

It is generally believed that Type Ia supernovae are thermonuclear explosions of carbon-oxygen white dwarfs (WDs). However, there is currently no consensus regarding the events leading to the explosion. A binary WD (WD-WD) merger is a possible progenitor of Type Ia supernovae. Space-based gravitational wave (GW) detectors with considerable sensitivity in the deci-Hz range such as the DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) can observe WD-WD mergers directly. Therefore, access to the deci-Hz band of GWs would enable multi-messenger observations of Type Ia supernovae to determine their progenitor and explosion mechanism. In this paper, we consider the event rate of WD-WD mergers and minimum detection range to observe one WD-WD merger per year, using a nearby galaxy catalog and the relation between the Ia supernova and host galaxy. Furthermore, we calculate DECIGO's ability to localize WD-WD mergers and to determine the masses of binary mergers. We estimate that the deci-Hz GW observatory can detect GWs with amplitudes $h\sim10^{-20}[\rm Hz^{-1/2}]$ at 0.01-0.1 Hz, which is 1000 times higher than the detection limit of DECIGO. Assuming progenitors of Ia supernovae are merging WD-WD ($1M_{\odot}-0.8M_{\odot}$), DECIGO is expected to detect 6600 WD-WD mergers within $z=0.08$, and identify the host galaxy of such WD-WD mergers within $z\sim0.065$ using GW detection alone.

astro-ph.HE↗

arXiv2022

Constraints on Population I/II neutron star-black hole binary formation by gravitational wave and radio observations

Two neutron star (NS)-black hole (BH) binaries, GW200105 and GW200115 found in the LIGO/Virgo O3b run have smaller BH mass of 6--9\,$M_{\odot}$ which is consistent with Population I and II origin. Our population synthesis simulations using $10^6$ Population I and II binaries with appropriate initial parameters show consistent binary mass, event rate, and no detection of radio pulsar (PSR) and BH binaries in our galaxy so far. Especially, we found possible progenitors of GW200105 and GW200115 which were formed at redshift $z=0.15$ and $z=1.6$ with binary mass of $(34M_{\odot},\, 9.2M_{\odot})$ and $(23.7M_{\odot},\, 10.6M_{\odot})$, respectively. The final masses of these binaries are $(6.85M_{\odot},\,2.14M_{\odot})$ and $(6.04M_{\odot},\,1.31M_{\odot})$ which look like $(9.0_{-1.7}^{+1.7}M_{\odot},\, 1.91_{-0.24}^{+0.33}M_{\odot})$ of GW200105 and $(5.9_{-2.5}^{+2.0}M_{\odot},\,1.44_{-0.29}^{+0.85}M_{\odot})$ of GW200115, respectively. We also estimate that 2.68-19.7 PSR-BH binaries in our galaxy will be observed by SKA. The existence of NS-BHs in our galaxy can be confirmed in future SKA era. Using the GW observation of NS-BH mergers and the radio observation of PSR-BHs in future, we can get more severe constraints on the NS-BH formation process.

astro-ph.HE↗

arXiv2022

Merger rate density of binary black holes through isolated Population I, II, III and extremely metal-poor binary star evolution

We investigate the formation of merging binary black holes (BHs) through isolated binary evolution, performing binary population synthesis calculations covering an unprecedentedly wide metallicity range of Population (Pop) I, II, III, and extremely metal-poor (EMP) binary stars. We find that the predicted merger rate density and primary BH mass ($m_1$) distribution are consistent with the gravitational wave (GW) observations. Notably, Pop III and EMP ($< 10^{-2}$ $Z_\odot$) binary stars yield most of the pair instability (PI) mass gap events with $m_1 = 65$--$130$ $M_\odot$. Pop III binary stars contribute more to the PI mass gap events with increasing redshift, and all the PI mass gap events have the Pop III origin at redshifts $\gtrsim 8$. Our result can be assessed by future GW observations in the following two points. First, there are no binary BHs with $m_1=100$--$130$ $M_\odot$ in our result, and thus the $m_1$ distribution should suddenly drop in the range of $m_1=100$--$130$ $M_\odot$. Second, the PI mass gap event rate should increase toward higher redshift up to $\sim 11$, since those events mainly originate from the Pop III binary stars. We find that the following three assumptions are needed to reproduce the current GW observations: a top-heavy stellar initial mass function and the presence of close binary stars for Pop III and EMP binary stars, and inefficient convective overshoot in the main-sequence phase of stellar evolution. Without any of the above, the number of PI mass gap events becomes too low to reproduce current GW observations.

astro-ph.HE↗

arXiv2022

Can Population III stars be major origins of both merging binary black holes and extremely metal poor stars?

Population (Pop) III stars, first stars, or metal-free stars are made of primordial gas. We have examined if they can be dominant origins of merging binary black holes (BHs) and extremely metal-poor stars. The abundance pattern of EMP stars is helpful to trace back the properties of Pop III stars. We have confirmed previous arguments that the observed BH merger rate needs Pop III star formation efficiency 10 times larger than theoretically predicted values, while the cosmic reionization history still permits such a high Pop III star formation efficiency. On the other hand, we have newly found that the elemental abundance pattern of EMP stars only allows the Pop III initial mass function with the minimum mass of $\sim 15 - 27$ $M_\odot$. In other words, the minimum mass must not deviate largely from the critical mass below and above which Pop III stars leave behind neutron stars and BHs, respectively. Pop III stars may be still a dominant origin of merging binary BHs but our study has reduced the allowed parameter space under a hypothesis that EMP stars are formed from primordial gas mixed with Pop III supernova ejecta.

astro-ph.HE↗

arXiv2021

Gravitational waves from Population III binary black holes are consistent with LIGO/Virgo O3a data for the chirp mass larger than $\sim 20M_{\odot}$

The probability number distribution function of binary black hole mergers observed by LIGO/Virgo O3a has double peaks as a function of chirp mass $M_c$, total mass $M_t$, primary black hole mass $M_1$ and secondary one $M_2$, respectively. The larger chirp mass peak is at $M_c \cong 30 M_{\odot}$. The distribution of $M_2$ vs. $M_1$ follows the relation of $M_2\cong 0.7M_1$. For initial mass functions of Population III stars in the form of $f(M) \propto M^{-α}$, population synthesis numerical simulations with $0\leq α\leq 1.5$ are consistent with O3a data for $M_c \gtrsim 20M_{\odot}$. The distribution of $M_2$ vs. $M_1$ for simulation data also agrees with $M_2\cong 0.7M_1$ relation of O3a data.

astro-ph.HE↗

arXiv2021

Population III Binary Black Holes: Effects of Convective Overshooting on Formation of GW190521

GW190521 is a merger of two black holes (BHs), wherein at least one BH lies within the pair-instability (PI) mass gap, and it is difficult to form because of the effects of PI supernovae (PISNe) and pulsational PI (PPI). In this study, we examined the formation of GW190521-like BH-BHs under Population (Pop) III environments by binary population synthesis calculations. We reveal that convective overshooting in stellar evolution strongly affects the formation of GW190521-like BH-BHs. A model with a small overshoot parameter (similar to GENEC) can form GW190521-like BH-BHs. The derived merger rate is $4 \times 10^{-2}$ ${\rm yr}^{-1}$ ${\rm Gpc}^{-3}$ at a redshift of $\sim 0.82$, which is comparable to the merger rate of GW190521-like BH-BHs inferred by gravitational wave (GW) observations. In this model, a $\sim 90~M_\odot$ star collapses to form a $\sim 90~M_\odot$ BH by avoiding PPI and PISN even if it is a member of a binary star. This is because it expands up to $10^2~R_\odot$, and lose only little mass through binary evolution. However, a model with a large overshoot parameter (similar to Stern) cannot form GW190521-like BH-BHs at all. Thus, we cannot conclude that a Pop~III binary system is the origin of GW190521 because determination of the overshoot parameter involves highly uncertain. If a Pop~III binary system is the origin of GW190521, the merger rate of BH-BHs including a $100-135~M_\odot$ BH is substantially smaller than that of GW190521-like BH-BHs. This will be assessed by GW observations in the near future.

astro-ph.HE↗