Numerical Construction of Magnetosphere with Relativistic Two-fluid Plasma Flows (2009)
Kojima, Yasufumi, Oogi, Junpei
We present a numerical model in which a cold pair plasma is ejected with relativistic speed through a polar cap region and flows almost radially outside the light cylinder. Stationary axisymmetric...
Ando, Masaki, Kawamura, Seiji, Sato, Shuichi, Nakamura, Takashi, Tsubono, Kimio, Araya, Akito, ...
DECIGO pathfinder (DPF) is a milestone satellite mission for DECIGO (DECi-hertz Interferometer Gravitational wave Observatory), which is a future space gravitational wave antenna. DECIGO is expected...
Collimation of a spherical collisionless particles stream in Kerr space-time (2009)
Takami, Kentaro, Kojima, Yasufumi
We examine the propagation of collisionless particles emitted from a spherical shell to infinity. The number distribution at infinity, calculated as a function of the polar angle, exhibits a small...
Kojima, Yasufumi, Saijo, Motoyuki
Nonlinear growth of the bar-mode deformation is studied for a differentially rotating star with supercritical rotational energy. In particular, the growth mechanism of some azimuthal modes with odd...
The correlation of black hole mass with metallicity index of host spheroid (2008)
Kisaka, Shota, Kojima, Yasufumi, Otani, Yosuke
We investigate the correlation between the mass of the supermassive black holes (SMBHs) and metal abundance, using existing data sets. The SMBH mass $M_{bh}$ is well correlated with integrated...
Ando, Masaki, Kawamura, Seiji, Nakamura, Takashi, Tsubono, Kimio, Tanaka, Takahiro, Funaki, Ikkoh, ...
DECIGO pathfinder (DPF) is a milestone satellite mission for DECIGO (DECi-hertz Interferometer Gravitational wave Observatory) which is a future space gravitational wave antenna. DECIGO is expected...
The Japanese space gravitational wave antenna; DECIGO (2008)
Kawamura, Seiji, Ando, Masaki, Nakamura, Takashi, Tsubono, Kimio, Tanaka, Takahiro, Funaki, Ikkoh, ...
DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is the future Japanese space gravitational wave antenna. DECIGO is expected to open a new window of observation for gravitational...
Faraday resonance in dynamical bar instability of differentially rotating stars (2008)
Saijo, Motoyuki, Kojima, Yasufumi
We investigate the nonlinear behaviour of the dynamically unstable rotating star for the bar mode by three-dimensional hydrodynamics in Newtonian gravity. We find that an oscillation along the...
Andersson, Nils, Kojima, Yasufumi, Kokkotas, Kostas D.
Abstract can be found in the full text link
On the Oscillation Spectra of Ultra Compact Stars (2006)
Kojima, Yasufumi, Andersson, Nils, Kokkotas, Kostas D.
Quasi-normal modes of ultra compact stars with uniform energy density have been calculated. For less compact stars, there is only one very slowly damped polar mode (corresponding to the Kelvin...
Joint LIGO and TAMA300 search for gravitational waves from inspiralling neutron star binaries (2006)
Abbott, B., Abbott, R., Adhikari, R., Ageev, A., Agresti, Juri, Ajith, P., ...
We search for coincident gravitational wave signals from inspiralling neutron star binaries using LIGO and TAMA300 data taken during early 2003. Using a simple trigger exchange method, we perform an...
Akutsu, Tomomi, Akutsu, Tomotadu, Ando, Masaki, Arai, Koji, Araya, Akito, Asada, H., ...
We analyze the data of the TAMA300 detector to search for gravitational waves from inspiraling compact star binaries with masses of the component stars in the range 1M[sun]–3M[sun]. In this...
The Japanese space gravitational wave antenna - DECIGO (2006)
Kawamura, Seiji, Nakamura, T., Ando, M., Seto, N., Tsubono, K., Numata, K., ...
DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is the future Japanese space gravitational wave antenna. It aims at detecting various kinds of gravitational waves between 1 mHz and...
Behavior of Torsional Alfven Waves and Field Line Resonance on Rotating Magnetars (2005)
Okita, Taishi, Kojima, Yasufumi
Torsional Alfven waves are likely excited with bursts in rotating magnetars. These waves are probably propagated through corotating atmospheres toward a vacuum exterior. We have studied the physical...
Tidal effects on magnetic gyration of a charged particle in Fermi coordinates (2005)
Kojima, Yasufumi, Takami, Kentaro
We examine the gyration motion of a charged particle, viewed from a reference observer falling along the Z axis into a Schwarzschild black hole. It is assumed that the magnetic field is constant and...
Resonant growth of stellar oscillations by incident gravitational waves (2005)
Kojima, Yasufumi, Tanimoto, Hajime
Stellar oscillation under the combined influences of incident gravitational wave and radiation loss is studied in a simple toy model. The star is approximated as a uniform density ellipsoid in the...
Upper limits from the LIGO and TAMA detectors on the rate of gravitational-wave bursts (2005)
Abbott, B., Abbott, R., Adhikari, R., Ageev, A., Agresti, Juri, Ajith, P., ...
Ando, M., Arai, K., Aso, Y., Beyersdorf, P. T., Hayama, K., Iida, Y., ...
Propagation and Transmission of Alfven Waves in Rotating Magnetars (2004)
Kojima, Yasufumi, Okita, Taishi
We study the propagation and transmission of Alfven waves in the context of cylindrical geometry. This approximates the polar cap region of aligned pulsar with strong magnetic fields. Non-propagating...
Kojima, Yasufumi, Matsunaga, Norihito, Okita, Taishi
We investigate the electromagnetic fields in the vacuum exterior of a rotating relativistic star endowed with a magnetic dipole moment, and with the stellar surface behaving as a perfect conductor....
Some Properties of an Axisymmetric Pulsar Magnetosphere Constructed by Numerical Calculation (2003)
We have explored the magnetosphere described by a numerical solution for an axisymmetric rotating field satisfying the force-free and ideal MHD conditions everywhere. The electric current...
Discrimination of Quark Stars from Neutron Stars in Quadrupole Oscillations (2002)
Kojima, Yasufumi, Sakata, Koh-ichi
The frequencies and damping times due to gravitational radiation are calculated for self-bound quark star models. The results are compared with those for neutron star models. They are markedly...
General Relativistic Modification of a Pulsar Electromagnetic Field (2000)
Konno, Kohkichi, Kojima, Yasufumi
We consider an exterior electromagnetic field surrounding a rotating star endowed with a dipole magnetic field in the context of general relativity. The analytic solution for a stationary...
Profiles and Polarization Properties of Emission Lines from Relativistic Disks (2000)
Ogura, Jun, Ohuo, Nobuyori, Kojima, Yasufumi
We examined the profiles and polarization properties of emission lines originating from the extremely relativistic region of Kepler disks. Because the emission region is more localized to the inner...
Approximate equation relevant to axial oscillations on slowly rotating relativistic stars (2000)
Kojima, Yasufumi, Hosonuma, Masayasu
Axial oscillations relevant to the r-mode instability are studied with slow rotation formalism in general relativity. The approximate equation governing the oscillations is derived with second-order...
Stability of Relativistic Blast Waves (2000)
A spherical blast wave with relativistic velocity can be described by a similarity solution, that is used for theoretical models of gamma-ray bursts. We consider the linear stability of such a...
Gravitational Waves from Relativistic Stars (2000)
Stellar pulsations in rotating relativistic stars are reviewed. Slow rotation approximation is applied to solving the Einstein equations. The rotational effects on the non-axisymmetric oscillations...
The R-Mode Oscillations in Relativistic Rotating Stars (1999)
Kojima, Yasufumi, Hosonuma, Masayasu
The axial mode oscillations are examined for relativistic rotating stars with uniform angular velocity. Using the slow rotation formalism and the Cowling approximation, we have derived the equations...
Asymmetry in Microlensing-Induced Light Curves (1999)
Konno, Kohkichi, Kojima, Yasufumi
We discuss distortion in microlensing-induced light curves which are considered to be curves due to single-point-mass lenses at a first glance. As factors of the distortion, we consider close binary...
Quasi-toroidal oscillations in rotating relativistic stars (1997)
Quasi-toroidal oscillations in slowly rotating stars are examined in the framework of general relativity. The oscillation frequency to first order of the rotation rate is not a single value even for...
Accuracy of the relativistic Cowling approximation in slowly rotating stars (1997)
Yoshida, Shijun, Kojima, Yasufumi
We have calculated the non-radial oscillation in slowly rotating relativistic stars with the Cowling approximation. The frequencies are compared with those based on the complete linearized equations...
Quasi-Toroidal Oscillations in Rotating Relativistic Stars (1997)
Quasi-toroidal Oscillations, Yasufumi Kojima
Quasi-toroidal oscillations in slowly rotating stars are examined in the framework of general relativity. The oscillation frequency to first order of the rotation rate is not a single value even for...
Gravitational Correction in Neutrino Oscillations (1996)
We investigate the quantum mechanical oscillations of neutrinos propagating in weak gravitational field. The correction to the result in the flat space-time is derived.
Nils Andersson, Yasufumi Kojima, Kostas D. Kokkotas
An extensive survey of gravitational-wave modes for uniform density stars is presented. The study covers stars ranging in compactness from R=M = 100 to the limit of stability in general relativity:...
Andersson, Nils, Kojima, Yasufumi, Kokkotas, Kostas D.
An extensive survey of gravitational-wave modes for uniform density stars is presented. The study covers stars ranging in compactness from $R/M=100$ to the limit of stability in general relativity:...
ON THE OSCILLATION SPECTRA OF ULTRA COMPACT STARS (1995)
Kojima, Yasufumi, Andersson, Nils, Kokkotas, Kostas D.
Quasinormal modes of ultra compact stars with uniform energy density have been calculated. For less compact stars, there is only one very slowly damped polar mode (corresponding to the Kelvin f-mode)...
High-overtone normal modes of Schwarzschild black holes (1990)
Guinn, J. W., Will, Clifford M., Kojima, Yasufumi, Schutz, Bernard F.
The frequencies of normal-mode oscillations of Schwarzschild black holes are studied using a higher-order WKB approach. The method is mathematically equivalent to locating the poles in the...
Quasi-toroidal oscillations in rotating relativistic stars
Quasi-toroidal oscillations in slowly rotating stars are examined in the framework of general relativity. The oscillation frequency to first order of the rotation rate is not a single value even for...