Search

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., Comment: Comments welcome. Accepted for publication of MNRAS Letter

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 $\xi_m(m) \propto m^{-\alpha}$ (single power law), we find that $\alpha \gtrsim 2.8$ 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., Comment: 6 pages, 9 figures, 1 table. Accepted for publication in MNRAS Letters

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., 12 pages, 4 figures, 1 table, PASJ accepted

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., Accepted to ApJ. comments welcome

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., 12 pages, 8 figures, matches published version

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., 26 pages, 13 figures, 2 tables, ApJ accepted. BSEEMP, a binary population synthesis code used in this paper, is published on github: https://github.com/atrtnkw/bseemp

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 $f(M) \propto M^{-\alpha}$, population synthesis numerical simulations with $0\leq \alpha \leq 1.5$ 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., Comment: published in MNRAS Letter

HiZ-GUNDAM is a future satellite mission which will lead the time-domain astronomy and the multi-messenger astronomy through observations of high-energy transient phenomena. A mission concept of HiZ-GUNDAM was approved by ISAS/JAXA, and it is one of the future satellite candidates of JAXA’s medium-class mission. We are in pre-phase A (before pre-project) and elaborating the mission concept, mission/system requirements for the launch in the late 2020s. The main themes of HiZ-GUNDAM mission are (1) exploration of the early universe with high-redshift gamma-ray bursts, and (2) contribution to the multi-messenger astronomy. HiZ-GUNDAM has two kinds of mission payload. The wide field X-ray monitors consist of Lobster Eye optics array and focal imaging sensor, and monitor ~1 steradian field of view in 0.5 – 4 keV energy range. The near infrared telescope has an aperture size 30 cm in diameter, and simultaneously observes four wavelength bands between 0.5 – 2.5 μm. In this paper, we introduce the mission overview of HiZ-GUNDAM.

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 $\sigma_{\rm k}=0$--$500$ 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., Comment: comments welcome. accepted by PTEP

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., Comment: 38 pages, 33 figures, accepted for publication in ApJ

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$~(\rho_{\rm SFR}/(6\times10^5~M_{\odot}/{\rm Mpc}^3))~Err_{\rm sys}~{\rm yr^{-1}~Gpc^{-3}}$, where $\rho_{\rm SFR}$ 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 $\rho_{\rm SFR}=6\times10^5~M_{\odot}/{\rm Mpc}^3$ 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$~{\rm yr^{-1}~Gpc^{-3}}$., Comment: accepted by MNRAS Letter. comments welcome

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., Comment: 8 pages, 6 figures, 1 table, MNRAS accepted

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 $\left\langle \chi_{\rm eff} \right\rangle$ 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., Comment: comments welcome. Accepted by MNRAS

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 $\sim 0.01 (\rho_{\rm oc} / 10^4 M_\odot \mbox{pc}^{-3})$, where $\rho_{\rm oc}$ 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 $\sim 0.03 (\rho_{\rm oc} / 10^4 M_\odot \mbox{pc}^{-3})$. 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., Comment: 9 pages, 1 figure, accepted for publication in PASJ

In this study, a novel rectangular slot restriction-type externally pressurized gas journal bearing was developed for use in high-speed rotating machinery, such as medical devices and industrial machines. The proposed bearing has several rectangular slot restrictors arranged in the inner surface of the bearing. To measure the bearing characteristics, a model was developed for the numerical calculation of the pressure distribution in the bearing clearance and the static characteristics of the bearing. The proposed bearing, which consists of two parts, was designed and can be manufactured using appropriate techniques. In this study, a prototype bearing with eight slots in its surface was manufactured as a test piece for fundamental tests. The diameter and length of the test bearing are 30 and 40 mm, respectively. The roundness of the bearing was measured using a three-dimensional coordinate measuring machine, and the results were used in the analysis. The pressure distribution and static characteristics obtained experimentally were found to be in good agreement with the calculated values. In the rotational tests, the rotor speed exceeded 380 Hz (22,800 rpm), and whirl vibration did not occur. During testing, the maximum rotor vibration amplitude was 0.002 mm, corresponding to an eccentricity ratio of 0.3.

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., comments welcome. Accepted to ApJ

著者人数: KAGRA collaboration 198名 (所属. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS): 和泉, 究), Number of authors: KAGRA collaboration 198 (Affiliation. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS): Izumi, Kiwamu), Accepted: 2018-11-19, 資料番号: SA1180423000

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., Comment: 12 pages, 5 figures, published in ApJ

著者人数: KAGRA Collaboration 203名 (所属. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS): 和泉, 究), Number of authors: KAGRA collaboration 203 (Affiliation. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS): Izumi, Kiwamu), Accepted: 2019-06-11, 資料番号: SA1190107000

In this study, new rectangular slot restriction-type externally pressurized gas journal bearing has been developed for use in high-speed rotating machinery. The proposed bearing has several rectangular slot restrictors arranged in the inner sur-face of the bearing. This restrictors has high stiffness for couple of force. The material of the prototype bearing was PPS (Poly Phenylene Sulfide) resin, the machining accuracy (roundness) of the bearing was improved. Experimental verification using large unbalanced rotor was carried out. Unbalance to the rotor was set to generate vibration in cylindrical mode and conical mode. The rotational speed is 11,000rpm. The bearing diameter and length are 30mm and 40mm, respectively. As a result, it was clarified that the proposed bearings have smaller rotor vibration and improved rigidity than the conventional type.

Using our population synthesis code, we found that the typical chirp mass of Pop III BH-BHs is $\sim30~\msun$ with the total mass of $\sim60~\msun$ so that the inspiral chirp signal as well as quasi normal mode (QNM) of the merging BH are interesting targets of KAGRA. The detection rate of the coalescing Pop III BH-BHs is $\sim$180 $\rm events~yr^{-1}$$(\rm SFR_p/(10^{-2.5}~\msun \rm~yr^{-1}~Mpc^{-3}))\cdot([f_b/(1+f_b)]/0.33)\cdot Err_{sys}$ in our standard model where $\rm SFR_{p},~f_b$ and $\rm Err_{sys}$ are the peak value of the Pop III star formation rate, the binary fraction and the systematic error with $\rm Err_{sys}=1$ for our standard model, respectively. To evaluate the robustness of chirp mass distribution and the range of $\rm Err_{sys}$, we examine the dependence of the results on the unknown parameters and the distribution functions. We found that the chirp mass has a peak at $\sim 30 ~\msun$ in most of parameters and distribution functions as well as $\rm Err_{sys}$ ranges from 0.046 to 4. The minimum rate corresponds to the worst model which we think unlikely so that unless $ {\rm ~(SFR_p/(10^{-2.5}~\msun~yr^{-1}~Mpc^{-3}))\cdot([f_b/(1+f_b)]/0.33) \ll 0.1}$, we expect the Pop III BH-BHs merger rate of at least one event per year by KAGRA. Nakano, Tanaka \& Nakamura (2015) show that if S/N of QNM is larger than 35, we can confirm or refute the General Relativity (GR) more than 5 sigma level. In our standard model, the detection rate of Pop III BH-BHs whose S/N is larger than 35 is $3.2~\rm events~yr^{-1}$$(\rm SFR_p/(10^{-2.5}~\msun \rm~yr^{-1}~Mpc^{-3}))\cdot([f_b/(1+f_b)]/0.33)\cdot Err_{sys}$. Thus, there is a good chance to check whether GR is correct or not in the strong gravity region., 29 pages, 24 figures, accepted to MNRAS

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., accepted to ApJ Letters, comments welcome

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., Comment: 14 pages, 10 figures, accepted for publication in MNRAS

We perform population synthesis simulations for Population III (Pop III) coalescing binary neutron stars (NS-NSs), neutron star - black hole binaries (NS-BHs), and binary black holes (BH-BHs) which merge within the age of the universe. We found that the typical mass of Pop III BH-BHs is $\sim 30\ \rm{M}_{\odot}$ so that the inspiral chirp signal of gravitational waves can be detected up to z=0.28 by KAGRA, Adv. LIGO, Adv. Virgo and GEO network. Our simulations suggest that the detection rate of the coalescing Pop III BH-BHs is $140 (68) \cdot ({\rm SFR}_{\rm p}/10^{-2.5} \rm{M}_{\odot} {\rm yr}^{-1} {\rm Mpc}^{-3}) \cdot {\rm Err}_{\rm sys} ~{\rm events} ~{\rm yr}^{-1}$ for the flat (Salpeter) initial mass function (IMF), respectively, where $\rm SFR_p$ and $\rm Err_{sys}$ are the peak value of the Pop III star formation rate and the possible systematic errors due to the assumptions in Pop III population synthesis, respectively. $\rm Err_{sys}=1$ correspond to conventional parameters for Pop I stars. From the observation of the chirp signal of the coalescing Pop III BH-BHs, we can determine both the mass and the redshift of the binary for the cosmological parameters determined by Planck satellite. Our simulations suggest that the cumulative redshift distribution of the coalescing Pop III BH-BHs depends almost only on the cosmological parameters. We might be able to confirm the existence of Pop III massive stars of mass $\sim 30~\rm M_{\odot}$ by the detections of gravitational waves if the merger rate of the Pop III massive BH-BHs dominates that of Pop I BH-BHs., Comment: Accepted for publication in MNRAS

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], 17 pages, 10 figures, added some references, modifications to match the published version in PTEP

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., Submitted to PTEP. comments welcome

The existence of the ergoregion of the Kerr space-time has not been confirmed observationally yet. We show that the confirmation would be possible by observing the quasinormal mode in gravitational waves. As an example, using the recent population synthesis results of Pop III binary black holes, we find that the peak of the final merger mass ($M_f$) is about $50~\rm M_{\odot}$, while the fraction of the final spin $q_f = a_f/M_f > 0.7$ needed for the confirmation of a part of ergoregion is $\sim 77\%$. To confirm the frequency of the quasinormal mode, ${\rm SNR} > 35$ is needed. The standard model of Pop III population synthesis tells us that the event rate for the confirmation of more than $50\%$ of the ergoregion by the second generation gravitational wave detectors is $\sim 2.3$ ${\rm events\ yr^{-1}\ (SFR_p/(10^{-2.5}\ M_\odot yr^{-1}\ Mpc^{-3}))} \cdot (\rm [f_b/(1+f_b)]/0.33)$ where ${\rm SFR_p}$ and ${\rm f_b}$ are the peak value of the Pop III star formation rate and the fraction of binaries, respectively., Accepted for publication in PTEP. Comments welcome

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 $(\tau_{\rm H})$ 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 $\tau_{\rm H}$. 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., Comment: Submit ti PTEP letter. Comments welcome

Tetraarylbiladien-ab-ones bearing various substituents (R) in the para position of the phenyl groups were preprared by coupled oxidation of tetraarylporphyrin iron complexes. The yields of 5,10,15-triaryl-19-aroyl-15-hydroxybiladien-ab-ones were 74% (R = H), 85% (R = OMe), 44% (R = COOMe), and 28% (R = CN). Kinetic studies of the iron porphyrin oxidation revealed that the reaction is accelerated by an electron-withdrawing substituent with the Hammett reaction constant ρ = 0.295. 5,10,15-Triaryl-19-aroyl-15-hydroxybiladien-ab-ones undergo the acid-catalyzed elimination reaction either by acetic acid or by mesoporous silica to afford 5,10,15-triaryl-19-aroylbilatrien-abc-one. The elimination reaction in acetic acid is accelerated by an electron-donating substituent with the Hammett reaction constant ρ = −1.48.

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]

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., Comment: 7 pages, 3 figures, Proceedings for the Fifteenth Marcel Grossmann Meeting, Rome, July 1-7, 2018