Takashi Nakamura

Kyoto University

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Kunihito Ioka

Kyoto University

Hiroyuki Nakano

Ryukoku University

Takahiro Tanaka

Kyoto University

Ryo Yamazaki

Shizuoka University

Takeshi Chiba

Nihon University

Daisuke Yonetoku

Kanazawa University

Keitaro Takahashi

Kumamoto University

Nobuyuki Kanda

Osaka City University

Tomoya Kinugawa

The University of Tokyo

Ken-ichi Oohara

Kavli Institute for the Physics and Mathematics of the Universe

Cooperative Institutions

The University of Tokyo

221

Kyoto University

143

National Astronomical Observatory of Japan

114

Osaka University

Japan Aerospace Exploration Agency

Institute of Space and Astronautical Science

Nagoya University

Tohoku University

High Energy Accelerator Research Organization

Kanazawa University

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Delayed Flash from Counter Jet of Gamma Ray Burst

arXiv (Cornell University) (2002)

Ryo Yamazaki Kunihito Ioka Takashi Nakamura

If X-ray flashes are due to the forward jet emissions from gamma ray bursts (GRBs) observed with large viewing angles, we show that a prompt emission from a counter jet should be observed as a delayed flash in the UV or optical band several hours to a day after the X-ray flash. Ultraviolet and Optical Telescope on Swift can observe the delayed flashes within ~13 Mpc, so that (double-sided) jets of GRBs may be directly confirmed. Since the event rate of delayed flashes detected by Swift may be as small as 6*10^{-5}events/yr, we require more sensitive detectors in future experiments.

Swift

Ultraviolet

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Conformal time slicing condition in three dimensional numerical relativity

Vistas in Astronomy (1993)

Masaru Shibata Takashi Nakamura

Special relativity

10.1016/0083-6656(93)90071-q

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Gravitational radiation from a particle with zero orbital angular momentum plunging into a Kerr black hole

Physics Letters A (1983)

Yasufumi Kojima Takashi Nakamura

Orbital motion

Black hole (networking)

10.1016/0375-9601(83)90003-8

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Citations (46)

Initial data of axisymmetric gravitational waves with a cosmological constant

Cambridge University Press eBooks (1992)

Ken-ichi Nakao Kei‐ichi Maeda Takashi Nakamura Ken-ichi Oohara

Gravitational constant

Cosmological constant

Constant (computer programming)

10.1017/cbo9780511524639.030

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A Possible Origin of Lognormal Distributions in Gamma-Ray Bursts

The Astrophysical Journal (2002)

Kunihito Ioka Takashi Nakamura

We show that if the intrinsic break energy of gamma-ray bursts (GRBs) is determined by the product of more than three random variables, the observed break energy distribution becomes almost lognormal including the redshift effect because of the central limit theorem. The excess from the lognormal distribution at the low break energy is possibly due to the high-redshift GRBs. The same argument may also apply to the pulse duration, the interval between pulses, and so on.

Log-normal distribution

10.1086/340815

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Citations (25)

Gravitational radiation from coalescing binary neutron stars

Cambridge University Press eBooks (1992)

K. Oohara Takashi Nakamura

. We present three-dimensional Newtonian and post-Newtonian codes, including the gravitational radiation damping effect, using a finite difference method. We follow the emission of gravitational radiation using the quadrupole approximation. Using these codes we calculate the coalescence of a neutron star binary. For Newtonian calculations the initial configuration is given as a hydrostatic equilibrium model of a close neutron-star binary. Calculations were performed for neutron stars of different masses as well as of the same masses. In order to evaluate general relativistic effects, we compare the results of the calculation of the coalescence of a binary comprising two spherical neutron stars using the post-Newtonian code with results using the Newtonian code.

10.1017/cbo9780511524639.018

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Citations (2)

Low frequency gravitational waves from black hole MACHO binaries

Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields (1999)

Kunihito Ioka Takahiro Tanaka Takashi Nakamura

The intensity of low frequency gravitational waves from black hole MACHO binaries is studied. First we estimate the gravitational wave background produced by black hole MACHO binaries in the Milky Way halo as well as the cosmological gravitational wave background produced by the extragalactic black hole MACHO binaries. It is found that the cosmological gravitational wave background due to black hole MACHO binaries is larger than the halo background unless an extreme model of the halo is assumed, while it is smaller than the background due to close white dwarf binaries at ${\ensuremath{\nu}}_{\mathrm{gw}}\ensuremath{\lesssim}{10}^{\ensuremath{-}2.5}$ Hz if the actual space density of white dwarfs is maximal. This cosmological background due to black hole MACHO binaries is well below the observational constraints from the pulsar timing, quasar proper motions and so on. We find that one year observation by LISA will be able to detect gravitational waves from at least several hundreds of nearby independent black hole MACHO binaries whose amplitudes exceed these backgrounds. This suggests that LISA will be able to pin down various properties of primordial black hole MACHOs together with the results of LIGO-VIRGO-TAMA-GEO network. Furthermore, it may be possible to draw a map of the mass distribution of our halo, since LISA can determine the position and the distance to individual sources consisting of black hole MACHO binaries. Therefore, LISA may open a new field of the gravitational wave astronomy.

Black hole (networking)

10.1103/physrevd.60.083512

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Citations (37)

A Unified Model for Gamma-Ray Bursts

tsra (2004)

Ryo Yamazaki Kunihito Ioka Takashi Nakamura Kenji Toma

A possible unified model of short and long gamma-ray bursts (GRBs), X-ray rich GRBs, and X-ray flashes is proposed. It is assumed that the jet of a GRB consists of many emitting sub-shells (i.e., an inhomogeneous jet model). The multiplicity of the sub-shells along a line of sight ns is an important parameter. If ns is large ( 1) the event looks like a long GRB, while if ns = 1, the event looks like a short GRB. Finally, when ns = 0, the event looks like an X-ray flash or an X-ray rich GRB. Furthermore, our model may also explain the bimodal distributions of T90 duration of BATSE-GRBs. Clearly, our model predicts that short GRBs should be associated with energetic SNe.

Line-of-sight

Unified Model

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A Possible Origin of Bimodal Distribution of Gamma‐Ray Bursts

The Astrophysical Journal (2005)

Kenji Toma Ryo Yamazaki Takashi Nakamura

We study the distribution of the durations of gamma-ray bursts (GRBs) in the unified model of short and long GRBs recently proposed by Yamazaki, Ioka, and Nakamura. Monte Carlo simulations show clear bimodal distributions, with lognormal-like shapes for both short and long GRBs, in a power-law as well as a Gaussian angular distribution of the subjets. We find that the bimodality comes from the existence of the discrete emission regions (subjets or patchy shells) in the GRB jet. To explain other temporal properties of short and long GRBs, the subjet parameters should depend on the angle in the whole jet.

Bimodality

Log-normal distribution

10.1086/427179

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Citations (14)

Introduction to plasma astrophysics characteristics of astrophysical plasma high density plasma.

Kakuyūgō kenkyū (1989)

Takashi Nakamura

Property of High Density Matter with density from 1g/cm3 to 1016g/cm3 is argued. Using the equation of state for high density matter, the equilibrium structure of high density star is discussed. There are two phases of high density stars. They are white dwarf and neutron star. Each has a maximum possible mass. The reason for the existence of the critical mass is simply explained.

10.1585/jspf1958.61.151

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