arXiv subjects

Masaki S. Yamaguchi

Publications and source records attributed to Masaki S. Yamaguchi.

8 recordsLinked to original sources

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↗

arXiv2019

The Hyper Suprime-Cam SSP Transient Survey in COSMOS: Overview

We present an overview of a deep transient survey of the COSMOS field with the Subaru Hyper Suprime-Cam (HSC). The survey was performed for the 1.77 deg$^2$ ultra-deep layer and 5.78 deg$^2$ deep layer in the Subaru Strategic Program over 6- and 4-month periods from 2016 to 2017, respectively. The ultra-deep layer shows a median depth per epoch of 26.4, 26.3, 26.0, 25.6, and 24.6 mag in $g$, $r$, $i$, $z$, and $y$ bands, respectively; the deep layer is $\sim0.6$ mag shallower. In total, 1,824 supernova candidates were identified. Based on light curve fitting and derived light curve shape parameter, we classified 433 objects as Type Ia supernovae (SNe); among these candidates, 129 objects have spectroscopic or COSMOS2015 photometric redshifts and 58 objects are located at $z > 1$. Our unique dataset doubles the number of Type Ia SNe at $z > 1$ and enables various time-domain analyses of Type II SNe, high redshift superluminous SNe, variable stars, and active galactic nuclei.

astro-ph.GA↗

arXiv2018

Detecting Black Hole Binaries by Gaia

We study the prospect of the Gaia satellite to identify black hole binary systems by detecting the orbital motion of the companion stars. Taking into account the initial mass function, mass transfer, common envelope phase, interstellar absorption and identifiability of black holes, we estimate the number of black hole binaries detected by Gaia and their distributions with respect to the black hole mass for several models with different parameters. We find that $\sim 200-1000$ black hole binaries will be detected by Gaia during its 5 years operation. The shape of distribution function of the black hole mass is affected most severely by the relation between the zero-age main sequence (ZAMS) stellar mass and the black hole mass in parameters adopted in this paper, which implies that black holes detected with Gaia enables us to constrain the mass relation.

astro-ph.SR↗

arXiv2018

Subaru Hyper Suprime-Cam Survey for An Optical Counterpart of GW170817

We perform a $z$-band survey for an optical counterpart of a binary neutron star coalescence GW170817 with Subaru/Hyper Suprime-Cam. Our untargeted transient search covers $23.6$ deg$^2$ corresponding to the $56.6\%$ credible region of GW170817 and reaches the $50\%$ completeness magnitude of $20.6$ mag on average. As a result, we find 60 candidates of extragalactic transients, including J-GEM17btc (a.k.a. SSS17a/DLT17ck). While J-GEM17btc is associated with NGC 4993 that is firmly located inside the 3D skymap of GW170817, the other 59 candidates do not have distance information in the GLADE v2 catalog or NASA/IPAC Extragalactic Database (NED). Among 59 candidates, 58 are located at the center of extended objects in the Pan-STARRS1 catalog, while one candidate has an offset. We present location, $z$-band apparent magnitude, and time variability of the candidates and evaluate the probabilities that they are located inside of the 3D skymap of GW170817. The probability for J-GEM17btc is $64\%$ being much higher than those for the other 59 candidates ($9.3\times10^{-3}-2.1\times10^{-1}\%$). Furthermore, the possibility, that at least one of the other 59 candidates is located within the 3D skymap, is only $3.2\%$. Therefore, we conclude that J-GEM17btc is the most-likely and distinguished candidate as the optical counterpart of GW170817.

astro-ph.HE↗

arXiv2017

Uncovering the identities of compact objects in high-mass X-ray binaries and gamma-ray binaries by astrometric measurements

We develop a method for identifying a compact object in binary systems with astrometric measurements and apply it to some binaries. Compact objects in some high-mass X-ray binaries and gamma-ray binaries are unknown, which is responsible for the fact that emission mechanisms in such systems have not yet confirmed. The accurate estimate of the mass of the compact object allows us to identify the compact object in such systems. Astrometric measurements are expected to enable us to estimate the masses of the compact objects in the binary systems via a determination of a binary orbit. We aim to evaluate the possibility of the identification of the compact objects for some binary systems. We then calculate probabilities that the compact object is correctly identified with astrometric observation (= confidence level) by taking into account a dependence of the orbital shape on orbital parameters and distributions of masses of white dwarfs, neutron stars, and black holes. We find that the astrometric measurements with the precision of 70 $μ$as for $γ$~Cas allows us to identify the compact object at 99% confidence level if the compact object is a white dwarf with 0.6 M$_{\odot}$. In addition, we can identify the compact object with the precision of 10 $μ$as at 97% or larger confidence level for LS~I~+61$^{\circ}$~303 and 99% or larger for HESS~J0632+057. These results imply that the astrometric measurements with the 10-$μ$as precision level can realize the identification of compact objects for $γ$~Cas, LS~I~+61$^{\circ}$~303, and HESS~J0632+057.

astro-ph.HE↗

arXiv2017

J-GEM observations of an electromagnetic counterpart to the neutron star merger GW170817

The first detected gravitational wave from a neutron star merger was GW170817. In this study, we present J-GEM follow-up observations of SSS17a, an electromagnetic counterpart of GW170817. SSS17a shows a 2.5-mag decline in the $z$-band from 1.7 days to 7.7 days after the merger. Such a rapid decline is not comparable with supernovae light curves at any epoch. The color of SSS17a also evolves rapidly and becomes redder for later epochs; the $z-H$ color changed by approximately 2.5 mag in the period of 0.7 days to 7.7 days. The rapid evolution of both the optical brightness and the color are consistent with the expected properties of a kilonova that is powered by the radioactive decay of newly synthesized $r$-process nuclei. Kilonova models with Lanthanide elements can reproduce the aforementioned observed properties well, which suggests that $r$-process nucleosynthesis beyond the second peak takes place in SSS17a. However, the absolute magnitude of SSS17a is brighter than the expected brightness of the kilonova models with the ejecta mass of 0.01 $\Msun$, which suggests a more intense mass ejection ($\sim 0.03 \Msun$) or possibly an additional energy source.

astro-ph.HE↗

arXiv2014

Effect of lift force on the aerodynamics of dust grains in the protoplanetary disk

We newly introduce lift force into the aerodynamics of dust grains in the protoplanetary disk. Although many authors have so far investigated the effects of the drag force, gravitational force and electric force on the dust grains, the lift force has never been considered as a force exerted on the dust grains in the gas disk. If the grains are spinning and moving in the fluid, then the lift force is exerted on them. We show in this paper that the dust grains can be continuously spinning due to the frequent collisions so that the lift force continues to be exerted on them, which is valid in a certain parameter space where the grain size is larger than ~ 1 m and where the distance from the central star is larger than 1 AU for the minimum mass solar nebula. In addition, we estimate the effects of the force on the grain motion and obtain the result that the mean relative velocity between the grains due to the lift force is comparable to the gas velocity in the Kepler rotational frame when the Stokes number and lift-drag ratio are both ~ 1. This estimation is performed under the assumptions of the steady state and the isotropic spin angular momentum. We also estimate the mean relative velocity when the grains keep spinning and conclude that the lift force marginally affects the mean relative velocity in the minimum mass solar nebula. If there is a grain-concentrated part in the disk, the relative velocity due to the lift force may dominate there because of high collision rate.

astro-ph.EP↗

arXiv2012

Inverse Compton Scattering Model for X-ray Emission of the Gamma-ray Binary LS 5039

We propose a model for the gamma-ray binary LS 5039 in which the X-ray emission is due to the inverse Compton (IC) process instead of the synchrotron radiation. Although the synchrotron model has been discussed in previous studies, it requires a strong magnetic field which leads to a severe suppression of the TeV gamma-ray flux in conflict with H.E.S.S. observations. In this paper, we calculate the IC emission by low energy electrons (γ_e \lesssim 10^3) in the Thomson regime. We find that IC emission of the low energy electrons can explain the X-ray flux and spectrum observed with Suzaku if the minimum Lorentz factor of injected electrons γ_min is around 10^3. In addition, we show that the Suzaku light curve is well reproduced if γ_min varies in proportion to the Fermi flux when the distribution function of injected electrons at higher energies is fixed. We conclude that the emission from LS 5039 is well explained by the model with the IC emission from electrons whose injection properties are dependent on the orbital phase. Since the X-ray flux is primarily determined by the total number of cooling electrons, this conclusion is rather robust, although some mismatches between the model and observations at the GeV band remain in the present formulation.

astro-ph.HE↗