arXiv subjects

Tomoya Kinugawa

Publications and source records attributed to Tomoya Kinugawa.

At least 37 records · Page 2Linked to original sources

arXiv2021

On the population III binary black hole mergers beyond the pair-instability mass gap

We perform a binary population synthesis calculation incorporating very massive population (Pop.) III stars up to 1500 $M_\odot$, and investigate the nature of binary black hole (BBH) mergers. Above the pair-instability mass gap, we find that the typical primary black hole (BH) mass is 135-340 $M_\odot$. The maximum primary BH mass is as massive as 686 $M_\odot$. The BBHs with both of their components above the mass gap have low effective inspiral spin $\sim$ 0. So far, no conclusive BBH merger beyond the mass gap has been detected, and the upper limit on the merger rate density is obtained. If the initial mass function (IMF) of Pop. III stars is simply expressed as $ξ_m(m) \propto m^{-α}$ (single power law), we find that $α\gtrsim 2.8$ is needed in order for the merger rate density not to exceed the upper limit. In the future, the gravitational wave detectors such as Einstein telescope and Pre-DECIGO will observe BBH mergers at high redshift. We suggest that we may be able to impose a stringent limit on the Pop. III IMF by comparing the merger rate density obtained from future observations with that derived theoretically.

astro-ph.HE↗

arXiv2021

Merger rate density of Population III binary black holes below, above, and in the pair-instability mass gap

We present the merger rate density of Population (Pop.) III binary black holes (BHs) by means of a widely-used binary population synthesis code BSE with extensions to very massive and extreme metal-poor stars. We consider not only low-mass BHs (lBHs: $5-50 M_\odot$) but also high-mass BHs (hBHs: $130-200 M_\odot$), where lBHs and hBHs are below and above the pair-instability mass gap ($50-130 M_\odot$), respectively. Pop. III BH-BHs can be categorized into three subpopulations: BH-BHs without hBHs (hBH0s: $m_{\rm tot} \lesssim 100 M_\odot$), with one hBH (hBH1s: $m_{\rm tot} \sim 130-260 M_\odot$), and with two hBHs (hBH2s: $m_{\rm tot} \sim 270-400 M_\odot$), where $m_{\rm tot}$ is the total mass of a BH-BH. Their merger rate densities at the current universe are $\sim 0.1$ yr$^{-1}$ Gpc$^{-3}$ for hBH0s, and $\sim 0.01$ yr$^{-1}$ Gpc$^{-3}$ for the sum of hBH1s and hBH2s, provided that the mass density of Pop. III stars is $\sim 10^{13} M_\odot$ Gpc$^{-3}$. These rates are modestly insensitive to initial conditions and single star models. The hBH1 and hBH2 mergers can dominate BH-BHs with hBHs discovered in near future. They have low effective spins $\lesssim 0.2$ in the current universe. The number ratio of the hBH2s to the hBH1s is high, $\gtrsim 0.1$. We also find BHs in the mass gap (up to $\sim 85 M_\odot$) merge. These merger rates can be reduced to nearly zero if Pop. III binaries are always wide ($\gtrsim 100 R_\odot$), and if Pop. III stars always enter into chemically homogeneous evolution. The presence of close Pop. III binaries ($\sim 10 R_\odot$) are crucial for avoiding the worst scenario.

astro-ph.HE↗

arXiv2021

Impact of binary interactions on the diffuse supernova neutrino background

Binary interactions, especially mass transfer and mergers, can strongly influence the evolution of massive stars and change their final properties and the occurrence of supernovae. Here, we investigate how binary interactions affect predictions of the diffuse flux of neutrinos. By performing stellar population syntheses including prescriptions for binary interactions, we show that the resulting detection rates of the diffuse supernova neutrino background is enhanced by 15%-20% compared to estimates without binary considerations. A source of significant uncertainty arises due to the presently sparse knowledge of the evolution of rapidly rotating carbon-oxygen cores, especially those created as a result of mergers near the white dwarf to core collapse boundary. The enhancement effect may be as small as a few percent if the effects of rotation in postmerger systems are neglected, or as large as 75% if trends are extrapolated. Our estimates serve to highlight that binary effects can be important.

astro-ph.HE↗

arXiv2020

Formation of mass gap compact object and black hole binary from Population III stars

We performed population synthesis simulations of Population III binary stars with Maxwellian kick velocity distribution when MGCOs (Mass Gap Compact Objects with mass 2--5$\,M_{\odot}$) are formed. We found that for eight kick velocity dispersion models of $σ_{\rm k}=0$--$500$ km/s, the mean mass of black hole (BH)-MGCO binary is $\sim (30 \,M_\odot,\,2.6 \,M_\odot)$. In numerical data of our simulations, we found the existence of BH-MGCO binary with mass $(22.9 \,M_\odot,\,2.5 \,M_\odot)$ which looks like GW190814.

astro-ph.HE↗

arXiv2020

Formation of Binary Black Holes Similar to GW190521 with a Total Mass of $\sim 150\,M_{\odot}$ from Population III Binary Star Evolution

In the case of zero-metal (population III or Pop III) stars, we show that the total mass of binary black holes from binary Pop III star evolution can be $\sim 150 \,M_{\odot}$, which agrees with the mass of the binary black hole GW190521 recently discovered by LIGO/Virgo. The event rate of such binary black hole mergers is estimated as 0.13--0.66$~(ρ_{\rm SFR}/(6\times10^5~M_{\odot}/{\rm Mpc}^3))~Err_{\rm sys}~{\rm yr^{-1}~Gpc^{-3}}$, where $ρ_{\rm SFR}$ and $Err_{\rm sys}$ are the cumulative comoving mass density of Pop III stars depending on star formation rate and the systematic errors depending on uncertainties in the Pop III binary parameters, respectively. The event rate in our fiducial model with $ρ_{\rm SFR}=6\times10^5~M_{\odot}/{\rm Mpc}^3$ and $ Err_{\rm sys}=1$ is 0.13--0.66$~{\rm yr^{-1}~Gpc^{-3}}$, which is consistent with the observed value of 0.02--0.43$~{\rm yr^{-1}~Gpc^{-3}}$.

astro-ph.HE↗

arXiv2020

Chirp Mass and Spin of Binary Black Holes from First Star Remnants

We performed Population III (Pop III) binary evolution by using population synthesis simulations for seven different models. We found that Pop III binaries tend to be binary black holes (BBHs) with chirp mass $M_{\rm chirp} \sim 30~M_{\odot}$ and they can merge at present day due to long merger time. The merger rate densities of Pop III BBHs at $z=0$ ranges 3.34--21.2 $\rm /yr/Gpc^3$ which is consistent with the aLIGO/aVIRGO result of 9.7--101 $\rm /yr/Gpc^3$. These Pop III binaries might contribute to some part of the massive BBH gravitational wave (GW) sources detected by aLIGO/aVIRGO. We also calculated the redshift dependence of Pop III BBH mergers. We found that Pop III low spin BBHs tend to merge at low redshift, while Pop III high spin BBHs do at high redshift, which can be confirmed by future GW detectors such as ET, CE, and DECIGO. These detectors can also check the redshift dependence of BBH merger rate and spin distribution. Our results show that except for one model, the mean effective spin $\left\langle χ_{\rm eff} \right\rangle$ at $z=0$ ranges $0.02$--$0.3$ while at $z=10$ it does $0.16$--$0.64$. Therefore, massive stellar-mass BBH detection by GWs will be a key for the stellar evolution study in the early universe.

astro-ph.HE↗

arXiv2020

Metallicity dependence of black hole main sequence binaries detectable with Gaia

LIGO has detected gravitational waves from massive binary black hole mergers. In order to explain the origin of such massive stellar-mass black holes, extreme metal poor stars including first stars have been invoked. However, black holes do not carry information of the metallicity. In order to check the metallicity dependence of the black hole formation, we focus on galactic black hole-main sequence binaries (BH-MSs). Using a binary population synthesis method, we find that $\gaia$ can detect $\sim200-400$ BH-MSs whose metallicity is $\zsun$ and $\sim70-400$ BH-MSs whose metallicity is $0.1\zsun$. With the spectroscopic observation on 4-m class telescopes, we can check the metallicity of BH-MSs. The metallicity dependence of the black hole formation might be checked by the astrometry and spectroscopic observations.

astro-ph.HE↗

arXiv2020

Fitting formulae for evolution tracks of massive stars under extreme metal poor environments for population synthesis calculations and star cluster simulations

We have devised fitting formulae for evolution tracks of massive stars with $8 \lesssim M/M_\odot \lesssim 160$ under extreme metal poor (EMP) environments for $\log (Z/Z_\odot) = -2, -4, -5, -6$, and $-8$, where $M_\odot$ and $Z_\odot$ are the solar mass and metallicity, respectively. Our fitting formulae are based on reference stellar models which we have newly obtained by simulating the time evolutions of EMP stars. Our fitting formulae take into account stars ending with blue supergiant (BSG) stars, and stars skipping Hertzsprung gap (HG) phases and blue loops, which are characteristics of massive EMP stars. In our fitting formulae, stars may remain BSG stars when they finish their core Helium burning (CHeB) phases. Our fitting formulae are in good agreement with our stellar evolution models. We can use these fitting formulae on the SSE, BSE, NBODY4, and NBODY6 codes, which are widely used for population synthesis calculations and star cluster simulations. These fitting formulae should be useful to make theoretical templates of binary black holes formed under EMP environments.

astro-ph.HE↗

arXiv2020

Formation rate of LB-1-like systems through dynamical interactions

We estimate formation rates of LB-1-like systems through dynamical interactions in the framework of the theory of stellar evolution before the discovery of the LB-1 system. The LB-1 system contains $\sim 70M_\odot$ black hole (BH), so-called pair instability (PI)-gap BH, and B-type star with solar metallicity, and has nearly zero eccentricity. The most efficient formation mechanism is as follows. In an open cluster, a naked helium (He) star (with $\sim 20M_\odot$) collides with a heavy main-sequence (MS) star (with $\sim 50M_\odot$) which has a B-type companion. The collision results in a binary consisting of the collision product and B-type star with a high eccentricity. The binary can be circularized through the dynamical tide with radiative damping of the collision-product envelope. Finally, the collision product collapses to a PI-gap BH, avoiding pulsational pair instability and pair instability supernovae because its He core is as massive as the pre-colliding naked He star. We find that the number of LB-1-like systems in the Milky Way galaxy is $\sim 0.01 (ρ_{\rm oc} / 10^4 M_\odot \mbox{pc}^{-3})$, where $ρ_{\rm oc}$ is the initial mass densities of open clusters. If we take into account LB-1-like systems with O-type companion stars, the number increases to $\sim 0.03 (ρ_{\rm oc} / 10^4 M_\odot \mbox{pc}^{-3})$. This mechanism can form LB-1-like systems at least 10 times more efficiently than the other mechanisms: captures of B-type stars by PI-gap BHs, stellar collisions between other type stars, and stellar mergers in hierarchical triple systems. We conclude that no dynamical mechanism can explain the presence of the LB-1 system.

astro-ph.HE↗

arXiv2019

The rate of iPTF 14gqr like ultra-stripped supernovae and binary evolution leading to double neutron star formation

Double neutron star (DNS) systems are produced from massive binaries. A supernova (SN) explosion of an extremely stripped star is expected to occur at the final stage of DNS formation. This type of SN is called ultra-stripped SN (USSN). A recent research reveals that a type Ic SN, iPTF 14gqr (SN 2014ft) has low ejecta mass ($\approx0.2~\mathrm{M}_\odot$) and its progenitor has a helium envelope with its mass $\sim0.01~\mathrm{M}_\odot$. Then this SN is interpreted as an USSN, and this is the first discovery of the USSN. Furthermore, the observation of iPTF 14gqr provides us with some information about its formation history. Here, we perform population synthesis calculations so as to estimate the detection rate of iPTF 14gqr like USSNe by optical transient surveys, intermediate Palomar Transient Factory (iPTF), Zwicky Transient Facility (ZTF), and Large Synoptic Survey Telescope (LSST). We find that iPTF, ZTF, and LSST can observe iPTF 14gqr like USSNe at the rates of 1, 40, and 5 $\mathrm{yr}^{-1}$, respectively. The iPTF may detect 4 iPTF 14gqr like USSNe during four years observation. Additionally, we investigate effects of some binary physics on the orbital parameters of DNS systems and formation channels.

astro-ph.HE↗

arXiv2019

Prospects for improving the sensitivity of KAGRA gravitational wave detector

KAGRA is a new gravitational wave detector which aims to begin joint observation with Advanced LIGO and Advanced Virgo from late 2019. Here, we present KAGRA's possible upgrade plans to improve the sensitivity in the decade ahead. Unlike other state-of-the-art detectors, KAGRA requires different investigations for the upgrade since it is the only detector which employs cryogenic cooling of the test mass mirrors. In this paper, investigations on the upgrade plans which can be realized by changing the input laser power, increasing the mirror mass, and injecting frequency dependent squeezed vacuum are presented. We show how each upgrade affects to the detector frequency bands and also discuss impacts on gravitational-wave science. We then propose an effective progression of upgrades based on technical feasibility and scientific scenarios.

gr-qc↗

arXiv2019

Long gamma-ray burst rate at very high redshift

Future missions for long gammma-ray burst (GRB) observations at high redshift such as HiZ-GUNDAM and THESEUS will provide clue to the star formation history in our universe. In this paper focusing on high redshift (z>8) GRBs, we calculate the detection rate of long GRBs by future observations, considering both Population (Pop) I&II stars and Pop III stars as GRB progenitors. For the Pop I&II star formation rate (SFR), we adopt an up-to-date model of high-redshift SFR based on the halo mass function and dark matter accretion rate obtained from cosmological simulations. We show that the Pop I&II GRB rate steeply decreases with redshift. This would rather enable us to detect the different type of GRBs, Pop III GRBs, at very high redshift. If 10% or more Pop III stars die as an ultra-long GRB, the future missions would detect such GRBs in one year in spite of their low fluence. More luminous GRBs are expected from massive compact Pop III stars produced via the binary merger. In our conventional case, the detection rate of such luminous GRBs is 3-20 /yr (z>8). Those future observations contribute to revealing of the Pop III star formation history.

astro-ph.HE↗

arXiv2017

Long gamma ray burst rate in the binary merger progenitor model

The long gamma ray bursts (GRBs) may arise from the core collapse of massive stars. However, the long GRB rate does not follow the star formation rate (SFR) at high redshifts. In this Letter, we focus on the binary merger model and consider the high spin helium stars after the merger as the progenitor of long GRBs. With this scenario, we estimate the GRB rate by the population synthesis method with the metallicity evolution. Low metallicity binaries are easier to become long GRB progenitors than those for solar metallicity due to the weak wind mass loss and the difference in the stellar evolution. In our results, the long GRB rate roughly agrees with the observed rate, and shows a similar behavior to the observed redshift evolution.

astro-ph.HE↗

arXiv2017

How to confirm the existence of population III stars by observations of gravitational waves

We propose a method for confirmation of the existence of Population III (Pop III) stars with massive black hole binaries as GW150914 in gravitational wave (GW) observation. When we get enough number of events, we want to determine which model is closer to reality, with and without Pop III stars. We need to prepare various "Pop I/II models" and various "Pop I/II/III models" and investigate which model is consistent with the events. To demonstrate our analysis, we simulate detections of GW events for some examples of population synthesis models with and without Pop III stars. We calculate the likelihood ratio with the realistic number of events and evaluate the probability of identifying the existence of Pop III stars. In typical cases, our analysis can distinguish between Pop I/II model and Pop I/II/III model with 90% probability by 22 GW signals from black hole-black hole binary mergers.

astro-ph.HE↗

arXiv2017

Formation pathway of Population III coalescing binary black holes through stable mass transfer

We study formation of stellar mass binary black holes (BBHs) originating from Population III (PopIII) stars, performing stellar evolution simulations for PopIII binaries with MESA. We find that a significant fraction of PopIII binaries form massive BBHs through stable mass transfer between two stars in a binary, without experiencing common envelope phases. We investigate necessary conditions required for PopIII binaries to form BBHs coalescing within the Hubble time with a semi-analytical model calibrated by the stellar evolution simulations. The formation efficiency of coalescing PopIII BBHs is estimated for two different initial conditions for PopIII binaries with large and small separations, respectively. Consequently, in both models, $\sim 10\%$ of the total PopIII binaries form BBHs only through stable mass transfer and $\sim 10\%$ of these BBHs merge due to gravitational wave emission within the Hubble time. Furthermore, the chirp mass of merging BBHs has a flat distribution over $15\lesssim M_{\rm chirp}/M_\odot \lesssim 35$. This formation pathway of PopIII BBHs is presumably robust because stable mass transfer is less uncertain than common envelope evolution, which is the main formation channel for Population II BBHs. We also test the hypothesis that the BBH mergers detected by LIGO originate from PopIII stars using our result and the total number of PopIII stars formed in the early universe as inferred from the optical depth measured by Planck. We conclude that the PopIII BBH formation scenario can explain the mass-weighted merger rate of the LIGO's O1 events with the maximal PopIII formation efficiency inferred from the Planck measurement, even without BBHs formed by unstable mass transfer or common envelope phases.

astro-ph.HE↗

arXiv2016

The possible existence of Pop III NS-BH binary and its detectability

In the population synthesis simulations of Pop III stars, many BH (Black Hole)-BH binaries with merger time less than the age of the Universe $(τ_{\rm H})$ are formed, while NS (Neutron Star)-BH binaries are not. The reason is that Pop III stars have no metal so that no mass loss is expected. Then, in the final supernova explosion to NS, much mass is lost so that the semi major axis becomes too large for Pop III NS-BH binaries to merge within $τ_{\rm H}$. However it is almost established that the kick velocity of the order of $200-500{\rm~ km~s^{-1}}$ exists for NS from the observation of the proper motion of the pulsar. Therefore, the semi major axis of the half of NS-BH binaries can be smaller than that of the previous argument for Pop III NS-BH binaries to decrease the merging time. We perform population synthesis Monte Carlo simulations of Pop III NS-BH binaries including the kick of NS and find that the event rate of Pop III NS-BH merger rate is $\sim 1 {\rm Gpc^{-3} yr^{-1}}$. This suggests that there is a good chance of the detection of Pop III NS-BH mergers in O2 of Advanced LIGO and Advanced Virgo from this autumn.

astro-ph.HE↗

arXiv2016

Pre-DECIGO can get the smoking gun to decide the astrophysical or cosmological origin of GW150914-like binary black holes

Pre-DECIGO consists of three spacecraft arranged in an equilateral triangle with 100km arm lengths orbiting 2000km above the surface of the earth. It is hoped that the launch date will be in the late 2020s. Pre-DECIGO has one clear target: binary black holes (BBHs) like GW150914 and GW151226. Pre-DECIGO can detect $\sim 30M_\odot-30M_\odot$ BBH mergers up to redshift $z\sim 30$. The cumulative event rate is $\sim 1.8\times 10^{5}\,{\rm events~yr^{-1}}$ in the Pop III origin model of BBHs like GW150914, and it saturates at $z\sim 10$, while in the primordial BBH (PBBH) model, the cumulative event rate is $ \sim 3\times 10^{4}\,{\rm events~ yr^{-1}}$ at $z=30$ even if only $0.1\%$ of the dark matter consists of PBHs, and it is still increasing at $z=30$. In the Pop I/II model of BBHs, the cumulative event rate is $(3-10)\times10^{5}\,{\rm events~ yr^{-1}}$ and it saturates at $z \sim 6$. We present the requirements on orbit accuracy, drag free techniques, laser power, frequency stability, and interferometer test mass. For BBHs like GW150914 at 1Gpc, SNR$\sim 90$ is achieved with the definition of Pre-DECIGO in the $0.01-100$Hz band. Pre-DECIGO can measure the mass spectrum and the $z$-dependence of the merger rate to distinguish various models of BBHs like GW150914. Pre-DECIGO can also predict the direction of BBHs at $z=0.1$ with an accuracy of $\sim 0.3\,{\rm deg}^2$ and a merging time accuracy of $\sim 1$s at about a day before the merger so that ground-based GW detectors further developed at that time as well as electromagnetic follow-up observations can prepare for the detection of merger in advance. For intermediate mass BBHs at a large redshift $z > 10$, the QNM frequency after the merger can be within the Pre-DECIGO band so that the ringing tail can also be detectable to confirm the Einstein theory of general relativity with SNR$\sim 35$. [abridged]

astro-ph.HE↗

arXiv2016

Gravitational wave quasinormal mode from Population III massive black hole binaries in various models of population synthesis

Focusing on the remnant black holes after merging binary black holes, we show that ringdown gravitational waves of Population III binary black holes mergers can be detected with the rate of $5.9-500~{\rm events~yr^{-1}}~({\rm SFR_p}/ (10^{-2.5}~M_\odot~{\rm yr^{-1}~Mpc^{-3}})) \cdot ({\rm [f_b/(1+f_b)]/0.33})$ for various parameters and functions. This rate is estimated for the events with SNR$>8$ for the second generation gravitational wave detectors such as KAGRA. Here, ${\rm SFR_p}$ and ${\rm f_b}$ are the peak value of the Population III star formation rate and the fraction of binaries, respectively. When we consider only the events with SNR$>35$, the event rate becomes $0.046-4.21~{\rm events~yr^{-1}}~({\rm SFR_p}/ (10^{-2.5}~M_\odot~{\rm yr^{-1}~Mpc^{-3}})) \cdot ({\rm [f_b/(1+f_b)]/0.33})$. This suggest that for remnant black hole's spin $q_f>0.95$ we have the event rate with SNR$>35$ less than $0.037~{\rm events~yr^{-1}}~({\rm SFR_p}/ (10^{-2.5}~M_\odot~{\rm yr^{-1}~Mpc^{-3}})) \cdot ({\rm [f_b/(1+f_b)]/0.33})$, while it is $3-30~{\rm events~yr^{-1}}~({\rm SFR_p}/ (10^{-2.5}~M_\odot~{\rm yr^{-1}~Mpc^{-3}})) \cdot ({\rm [f_b/(1+f_b)]/0.33})$ for the third generation detectors such as Einstein Telescope. If we detect many Population III binary black holes merger, it may be possible to constrain the Population III binary evolution paths not only by the mass distribution but also by the spin distribution.

astro-ph.HE↗