## About

46

Publications

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Introduction

**Skills and Expertise**

Additional affiliations

April 2017 - May 2018

## Publications

Publications (46)

We present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with low metallicities ($0.016-0.098\ Z_{\odot}$) and low stellar masses ($10^{4.7}-10^{7.6} M_{\odot}$). Taking deep medium-high resolution ($R\sim7500$) integral-field spectra with 8.2-m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with H$...

The primordial He abundance $Y_P$ is a powerful probe of cosmology. Currently, $Y_P$ is best determined by observations of metal-poor galaxies, while there are only a few known local extremely metal-poor ($<0.1 Z_\odot$) galaxies (EMPGs) having reliable He/H measurements with HeI$\lambda$10830 near-infrared (NIR) emission. Here we present deep Suba...

We present Keck/LRIS follow-up spectroscopy for 13 photometric candidates of extremely metal-poor galaxies (EMPGs) selected by a machine-learning technique applied to the deep (∼26 AB mag) optical and wide-area (∼500 deg ² ) Subaru imaging data in the EMPRESS survey. Nine out of the 13 candidates are EMPGs with an oxygen abundance (O/H) less than ∼...

We present the results of 3D hydrodynamic simulations of a gamma-ray burst (GRB) jet emanating from a massive star with a particular focus on the formation of high-velocity quasi-spherical ejecta and the jet-induced chemical mixing. Recent early-time optical observations of supernovae associated with GRBs (e.g., GRB 171205A/SN 2017iuk) indicate a c...

We present the results of 3D hydrodynamic simulations of gamma-ray burst (GRB) jet emanating from a massive star with a particular focus on the formation of high-velocity quasi-spherical ejecta and the jet-induced chemical mixing. Recent early-time optical observations of supernovae associated with GRBs (e.g., GRB 171205A/SN 2017iuk) indicate a con...

We present Keck/LRIS follow-up spectroscopy for 13 photometric candidates of extremely metal poor galaxies (EMPGs) selected by a machine-learning technique applied to the deep (~26 AB mag) optical and wide-area (~500 deg^2) Subaru imaging data in the EMPRESS survey. Nine out of the 13 candidates are EMPGs with an oxygen abundance (O/H) less than ~1...

We perform one-dimensional radiation-hydrodynamic simulations of energetic supernova ejecta colliding with a massive circumstellar medium (CSM) aiming at explaining SN 2016aps, likely the brightest supernova observed to date. SN 2016aps was a superluminous Type-IIn SN, which released as much as $\gtrsim 5\times 10^{51}$ erg of thermal radiation. Ou...

We present the results of two-dimensional radiation-hydrodynamic simulations of expanding supernova ejecta with a central energy source. As suggested in previous multi-dimensional hydrodynamic simulations, a sufficiently powerful central energy source can blow away the expanding supernova ejecta, leading to efficient mixing of stratified layers in...

Mixing of 56Ni, whose nuclear decay energy is a major luminosity source in stripped-envelope supernovae, is known to affect the observational properties of stripped-envelope supernovae such as light-curve and colour evolution. Here we systematically investigate the effect of 56Ni mixing on the photospheric velocity evolution in stripped-envelope su...

Mixing of 56Ni, whose nuclear decay energy is a major luminosity source in stripped-envelope supernovae, is known to affect the observational properties of stripped-envelope supernovae such as light-curve and color evolution. Here we systematically investigate the effect of 56Ni mixing on the photospheric velocity evolution in stripped-envelope sup...

A number of astrophyical transients originating from stellar explosions are powered by the collision of the ejected material with the circumstellar medium, which efficiently produces thermal radiation via shock dissipation. We investigate how such interaction-powered transients are distributed in the peak bolometric luminosity vs the rise time phas...

We perform a series of two-dimensional radiation-hydrodynamic simulations of the collision between supernova ejecta and circumstellar media (CSM). The hydrodynamic interaction of a fast flow and the surrounding media efficiently dissipates the kinetic energy of the fast flow and considered as a dominant energy source for a specific class of core-co...

We perform multiwavelength light-curve modeling of the recently discovered low-luminosity gamma-ray burst (GRB) 171205A. The emission model is based on the relativistic ejecta-circumstellar medium (CSM) interaction scenario. The collision of freely expanding spherical ejecta traveling at mildly relativistic velocities with the CSM produces the reve...

We perform multi-wavelength light curve modeling of the recently discovered low-luminosity gamma-ray burst (GRB) 171205A. The emission model is based on the relativistic ejecta-circumstellar medium (CSM) interaction scenario. The collision of freely expanding spherical ejecta traveling at mildly relativistic velocities with the CSM produces the rev...

We investigate broad-band emission from supernova ejecta powered by a relativistic wind from a central compact object. A recent two-dimensional hydrodynamic simulation studying the dynamical evolution of supernova ejecta with a central energy source has revealed that outermost layers of the ejecta are accelerated to mildly relativistic velocities b...

We investigate the properties of X-ray emission from shock breakout of a supernova in a stellar wind. We consider a simple model describing aspherical explosions, in which the shock front with an ellipsoidal shape propagates into the dense circumstellar matter. For this model, both X-ray light curves and spectra are simultaneously calculated using...

Recent observational studies of core-collapse supernovae suggest only stars with zero-age main sequence masses smaller than $16$-$18\ M_\odot$ explode when they are red supergiants, producing type IIP supernovae. This may imply that more massive stars produce other types of supernovae or they simply collapse to black holes without giving rise to br...

We investigate the relation between the emission properties of supernova shock breakout in the circumstellar matter (CSM) and the behavior of the shock. Using a Monte-Carlo method, we examine how the light curve and spectrum depends on the asphericity of the shock and bulk-Compton scattering, and compare the results with the observed properties of...

The hydrodynamical interaction between freely expanding supernova ejecta and a relativistic wind injected from the central region is studied in analytic and numerical ways. As a result of the collision between the ejecta and the wind, a geometrically thin shell surrounding a hot bubble forms and expands in the ejecta. We use a self-similar solution...

Hydrodynamical interaction of spherical ejecta freely expanding at mildly relativistic speeds into an ambient cold medium is studied in semi-analytical and numerical ways to investigate how ejecta produced in energetic stellar explosions dissipate their kinetic energy through the interaction with the surrounding medium. We especially focus on the c...

A two-dimensional special relativistic radiation-hydrodynamics code is developed and applied to numerical simulations of supernova shock breakout in bipolar explosions of a blue supergiant. Our calculations successfully simulate the dynamical evolution of a blast wave in the star and its emergence from the surface. Results of the model with spheric...

We report the late-time evolution of Type IIb Supernova (SN IIb) 2013df. SN
2013df showed a dramatic change in its spectral features at ~1 year after the
explosion. Early on it showed typical characteristics shared by SNe IIb/Ib/Ic
dominated by metal emission lines, while later on it was dominated by broad and
flat-topped Halpha and He I emissions....

We investigate the hydrodynamical evolution of an ultra-relativistic fireball
colliding with a freely expanding gas. The hydrodynamical interaction of the
fireball and the gas results in the formation of a geometrically thin shell. We
study the dynamical evolution of the shell by an analytical way and perform a
numerical simulation equipped with an...

We investigate effects of cosmic-rays on the linear growth of the
Kelvin-Helmholtz instability. Cosmic-rays are treated as an adiabatic gas and
allowed to diffuse along magnetic field lines. We calculated the dispersion
relation of the instability for various sets of two free parameters, the ratio
of the cosmic-ray pressure to the thermal gas press...

We present theoretical expectations for non-thermal emission due to the bulk
Comptonization at the ultra-relativistic shock breakout. We calculate the
transfer of photons emitted from the shocked matter with a Monte Carlo code
fully taking into account special relativity. As a hydrodynamical model, we use
a self-similar solution of Nakayama & Shige...

We performed a series of hydrodynamical calculations of an ultra-relativistic
jet propagating through a massive star and the circumstellar matter to
investigate the interaction between the ejecta and the circumstellar matter. We
succeed in distinguishing two qualitatively different cases in which the ejecta
are shocked and adiabatically cool. To ex...

We present a new self-similar solution describing early evolution of an
ultra-relativistic flow resulting from a collision of homologously expanding
spherical ejecta with the circumstellar matter, in which a shock wave
propagates in the circumstellar matter while a weak discontinuity propagates in
the ejecta at the sound speed

We consider supernova shock breakout in aspherical core-collapse supernovae. We perform hydrodynamical calculations to investigate the propagation of a strong shock wave in a compact star and the subsequent emergence from the surface. Using the results combined with a simple emission model based on blackbody radiation, we clarify how aspherical ene...

We investigate effects of the bulk comptonization process on emissions from a radiative shock wave propagating in a stellar envelope. At the shock, photons diffuse out from the front and are scattered back to the downstream by electron scattering. Consequently, these photons have a power-law energy spectrum. In this study, to model the circumstance...

To account for the non-thermal emission from the classical nova V2491 Cygni, we perform a series of numerical calculations of radiative transfer of γ-ray photons from the radioactive isotope 22Na in the matter ejected from a white dwarf. Using a simple wind model for the dynamical evolution of the ejecta and a Monte Carlo code, we calculate radiati...

We investigate roles of the bulk comptonization process in the propagation of thermal photons emitted at the shock breakout of a supernova explosion. We use a hydrodynamical model based on a self-similar solution for the shock breakout. The propagation of photons is treated by a Monte-Carlo technique. Results of the simulations successfully reprodu...

We investigate effects of aspherical energy deposition in core-collapse
supernovae on the light curve of the supernova shock breakout. We performed
two-dimensional hydrodynamical calculations of an aspherical supernova
explosion to obtain the time when a shock wave generated in the stellar
interior reaches the stellar surface in each radial directi...

Results of a simulation of the wakefield acceleration, which is a plasma process thought to operate in the upstream region of a relativistic collisionless shock, are presented. A power-law energy spectrum with index −2 is reproduced as previous works claim.

A new scheme for numerical integration of the 1D2V relativistic Vlasov-Maxwell system is proposed. Assuming that all particles in a cell of the phase space move with the same velocity as that of the particle located at the center of the cell at the beginning of each time step, we successfully integrate the system with no artificial loss of particle...

We present results of a 2D3V kinetic Vlasov simulation of the Weibel
instability. The kinetic Vlasov simulation allows us to investigate the
velocity distribution of dilute plasmas, in which the effect of collisions
between particles is negligible, and has the advantage that the accuracy of the
calculated velocity distribution does not depend on th...

A method to derive stationary solutions of the relativistic Vlasov-Maxwell system is explored. In the non-relativistic case, a method using the Hermite polynomial series to describe the deviation from the Maxwell-Boltzmann distribution is found to be successful in deriving a few stationary solutions including two dimensional one. Instead of the Her...

A novel method to derive stationary solutions of the Vlasov-Maxwell system is established. This method is based on the assumption that the deviation of the velocity distribution from the Maxwell-Boltzmann distribution can be expanded by the Hermite polynomials. By applying our method, a new two-dimensional equilibrium is derived, which may provide...

We present a self-similar solution to describe the propagation of a shock wave whose energy is deposited or lost at the front. Both of the propagation of the shock wave in a medium having a power-law density profile and the expansion of the medium to a vacuum after the shock breakout are described with a Lagrangian coordinate. The Chapman-Jouguet d...

## Projects

Project (1)