High-energy emission as a test of the prior emission model for gamma-ray burst afterglows (2009)
Murase, Kohta, Toma, Kenji, Yamazaki, Ryo, Nagataki, Shigehiro, Ioka, Kunihito
We study high-energy gamma-ray afterglow emission from gamma-ray bursts (GRBs) in the prior emission model, which is proposed to explain the plateau phase of the X-ray afterglow. This model predicts...
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...
Aoi, Junichi, Murase, Kohta, Takahashi, Keitaro, Ioka, Kunihito, Nagataki, Shigehiro
We revisit the high-energy spectral cutoff originating from the electron-positron pair creation in the prompt phase of gamma-ray bursts (GRBs) with numerical and analytical calculations. We show that...
Is the PAMELA anomaly caused by the supernova explosions near the Earth? (2009)
Fujita, Yutaka, Kohri, Kazunori, Yamazaki, Ryo, Ioka, Kunihito
We show that the anomaly of the positron fraction observed by the PAMELA experiment can be attributed to recent supernova explosion(s) in a dense gas cloud (DC) near the Earth. Protons are...
Kawanaka, Norita, Ioka, Kunihito, Nojiri, Mihoko M.
We investigate the observed spectrum of cosmic-ray electrons and positrons from astrophysical sources, especially pulsars, and the physical processes for making the spectrum spiky or smooth via...
Hypernova and Gamma-Ray Burst Remnants as TeV Unidentified Sources (2009)
Ioka, Kunihito, Meszaros, Peter
We investigate hypernova (hyper-energetic supernova) and gamma-ray burst (GRB) remnants in our Galaxy as TeV gamma-ray sources, particularly in the role of potential TeV unidentified sources, which...
A Gamma-Ray Burst/Pulsar for Cosmic-Ray Positrons with a Dark Matter-like Spectrum (2008)
We propose that a nearby gamma-ray burst (GRB) or GRB-like (old, single and short-lived) pulsar/microquasar about 10^{5-6} years ago may be responsible for the excesses of cosmic-ray positrons and...
Ohno, Masanori, Ioka, Kunihito, Yamaoka, Kazutaka, Tashiro, Makoto, Fukazawa, Yasushi, Nakagawa, Yujin E.
We perform a time-resolved spectral analysis of bright, long Gamma-ray burst GRB 061007 using Suzaku/WAM and Swift/BAT. Thanks to the large effective area of the WAM, we can investigate the time...
Statistical Properties of Gamma-Ray Burst Polarization (2008)
Toma, Kenji, Sakamoto, Takanori, Zhang, Bing, Hill, Joanne E., McConnell, Mark L., Bloser, Peter F., ...
The emission mechanism and the origin and structure of magnetic fields in gamma-ray burst (GRB) jets are among the most important open questions concerning the nature of the central engine of GRBs....
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...
Okuzumi, Satoshi, Ioka, Kunihito, Sakagami, Masa-aki
We investigate the nonlinear evolution of black hole ringdown in the framework of higher-order metric perturbation theory. By solving the initial-value problem of a simplified nonlinear field model...
Murase, Kohta, Ioka, Kunihito, Nagataki, Shigehiro, Nakamura, Takashi
Gamma-ray bursts (GRBs) are one of the candidates of ultra-high-energy (around 10^18.5 eV) cosmic-ray (UHECR) sources. We investigate high-energy cosmic-ray acceleration including heavy nuclei in...
Second order quasi-normal mode of the Schwarzschild black hole (2007)
Nakano, Hiroyuki, Ioka, Kunihito
Also archived in arXiv:0708.0450 v1 Aug 3, 2007
Toma, Kenji, Ioka, Kunihito, Nakamura, Takashi
The late-time optical/radio afterglows of $\gamma$-ray bursts (GRBs) are believed to be synchrotron emission of electrons accelerated in relativistic collisionless shocks propagating in the ambient...
Second and higher-order quasi-normal modes in binary black hole mergers (2007)
Ioka, Kunihito, Nakano, Hiroyuki
Also archived in arXiv:0704.3467 v3 Aug 3, 2007
Closure Relations for Electron-Positron Pair-Signatures in Gamma-Ray Bursts (2007)
We present recipes to diagnose the fireball of gamma-ray bursts (GRBs) by combining observations of electron-positron pair-signatures (the pair-annihilation line and the cutoff energy due to the...
Unstable GRB photospheres and electron-positron annihilation lines (2007)
Ioka, Kunihito, Murase, Kohta, Toma, Kenji, Nagataki, Shigehiro, Nakamura, Takashi
We propose an emission mechanism of prompt gamma-ray bursts (GRBs) that can reproduce the observed non-thermal spectra with high radiative efficiencies, >50%. Internal dissipation below a photosphere...
Second Order Quasi-Normal Mode of the Schwarzschild Black Hole (2007)
Nakano, Hiroyuki, Ioka, Kunihito
We formulate and calculate the second order quasi-normal modes (QNMs) of a Schwarzschild black hole (BH). Gravitational wave (GW) from a distorted BH, so called ringdown, is well understood as QNMs...
Urata, Yuji, Yamazaki, Ryo, Sakamoto, Takanori, Huang, Kuiyun, Zheng, Weikang, Sato, Goro, ...
We study the ``normal'' decay phase of the X-ray afterglows of gamma-ray bursts (GRBs), which follows the shallow decay phase, using the events simultaneously observed in the R-band. The classical...
A multi band study of the optically dark GRB 051028 (2007)
Urata, Yuji, Huang, Kui-Yun, Kuo, Ping-Hung, Ip, Wing-Huen, Qiu, Yulei, Masuno, Keisuke, ...
Observations were made of the optical afterglow of GRB 051028 with the Lulin observatory's 1.0 m telescope and the WIDGET robotic telescope system. R band photometric data points were obtained on...
Second and higher-order quasi-normal modes in binary black hole mergers (2007)
Ioka, Kunihito, Nakano, Hiroyuki
Black hole (BH) oscillations known as quasi-normal modes (QNMs) are one of the most important gravitational wave (GW) sources. We propose that higher perturbative order of QNMs, generated by...
Toma, Kenji, Ioka, Kunihito, Sakamoto, Takanori, Nakamura, Takashi
The gamma-ray burst (GRB) 060218 has ~ 10^5 times lower luminosity than typical long GRBs, and is associated with a supernova (SN). The radio afterglow displays no jet break, so that this burst might...
High Energy Neutrinos and Cosmic-Rays from Low-Luminosity Gamma-Ray Bursts? (2006)
Murase, Kohta, Ioka, Kunihito, Nagataki, Shigehiro, Nakamura, Takashi
The recently discovered gamma-ray burst (GRB) GRB 060218/SN 2006aj is classified as an X-ray Flash with very long duration driven possibly by a neutron star. Since GRB 060218 is very near about 140...
Ioka, Kunihito, Toma, Kenji, Yamazaki, Ryo, Nakamura, Takashi
Most X-ray afterglows of gamma-ray bursts (GRBs) observed by the Swift satellite have a shallow decay phase t^{-1/2} in the first few hours. This is not predicted by the standard afterglow model and...
Shallow Decay of Early X-ray Afterglows from Inhomogeneous Gamma-Ray Burst Jets (2005)
Toma, Kenji, Ioka, Kunihito, Yamazaki, Ryo, Nakamura, Takashi
Almost all the X-ray afterglows of gamma-ray bursts (GRBs) observed by the Swift satellite have a shallow decay phase in the first thousands of seconds. We show that in an inhomogeneous jet...
Tail Emission of Prompt Gamma-Ray Burst Jets (2005)
Yamazaki, Ryo, Toma, Kenji, Ioka, Kunihito, Nakamura, Takashi
Tail emission of the prompt gamma-ray burst (GRB) is discussed using a multiple emitting sub-shell (inhomogeneous jet, sub-jets or mini-jets) model, where the whole GRB jet consists of many emitting...
Coherent Radiation in Gamma-Ray Bursts and Relativistic Collisionless Shocks (2005)
We suggest that coherent radiation may occur in relativistic collisionless shocks via two-stream Weibel instabilities. The coherence amplifies the radiation power by many orders [$\sim 10^{12}$ in...
TeV-PeV Neutrinos from Giant Flares of Magnetars and the Case of SGR 1806-20 (2005)
Ioka, Kunihito, Razzaque, Soebur, Kobayashi, Shiho, Meszaros, Peter
We estimate the high energy neutrino flux from the giant flare of SGR 1806-20 on December 27, 2004, which irradiated Earth with a gamma-ray flux ~10^4 times larger than the most luminous gamma-ray...
A Unified Model for Gamma-Ray Bursts (2005)
Yamazaki, Ryo, Ioka, Kunihito, Nakamura, Takashi, Toma, Kenji
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...
Ioka, Kunihito, Meszaros, Peter
We consider the spatial clustering of massive black hole (MBH) mergers, and discuss possible ways to use gravitational wave observations in the LISA and DECIGO/BBO range for obtaining cosmological...
Giant flare of SGR 1806-20 from a relativistic jet (2005)
Yamazaki, Ryo, Ioka, Kunihito, Takahara, Fumio, Shibazaki, Noriaki
Japanese magnetospheric explorer GEOTAIL recorded a detailed light curve during the initial 600 msec of a giant flare from SGR 1806-20 on December 27, 2004. We show that the observed light curve is...
Yamazaki, Ryo, Ioka, Kunihito, Nakamura, Takashi, Toma, Kenji
We propose a possible unified model of short and long gamma-ray bursts (GRBs), X-ray rich GRBs, and X-ray flashes. The jet of a GRB is assumed to consist of multiple sub-jets or sub-shells (i.e., an...
Ioka, Kunihito, Kobayashi, Shiho, Zhang, Bing
We show that simple kinematic arguments can give limits on the timescale and amplitude of variabilities in gamma-ray burst (GRB) afterglows, especially when the variability timescale is shorter than...
Ioka, Kunihito, Meszaros, Peter
We investigate the radio afterglows of gamma-ray bursts (GRBs) and hypernovae (HNe) at high redshifts and quantify their detectability, as well as their potential usefulness for 21 cm absorption line...
Extended GeV-TeV Emission around Gamma-Ray Burst Remnants, and the Case of W49B (2004)
Ioka, Kunihito, Kobayashi, Shiho, Meszaros, Peter
We investigate the high-energy photon emission around Gamma-Ray Burst (GRB) remnants caused by ultrahigh-energy cosmic rays (UHECRs) from the GRBs. We apply the results to the recent report that the...
Gravitational Wave Memory of Gamma-Ray Burst Jets (2004)
Sago, Norichika, Ioka, Kunihito, Nakamura, Takashi, Yamazaki, Ryo
Gamma-Ray Bursts (GRBs) are now considered as relativistic jets. We analyze the gravitational waves from the acceleration stage of the GRB jets. We show that (i) the point mass approximation is not...
Yamazaki, Ryo, Ioka, Kunihito, Nakamura, Takashi
Taking into account the recent suggestion that a short gamma-ray burst (GRB) looks like the first 1 sec of a long GRB, we propose that the jet of a GRB consists of multiple sub-jets or sub-shells...
Peak Energy-Isotropic Energy Relation in the Off-Axis Gamma-Ray Burst Model (2004)
Yamazaki, Ryo, Ioka, Kunihito, Nakamura, Takashi
Using a simple uniform jet model of prompt emissions of gamma-ray bursts (GRBs), we reproduce the observed peak energy--isotropic energy relation. A Monte Carlo simulation shows that the...
Cosmological X-Ray Flashes from Off-Axis Jets (2003)
Yamazaki, Ryo, Ioka, Kunihito, Nakamura, Takashi
The of the cosmological X-ray flashes detected by WFC/BeppoSAX is calculated theoretically in a simple jet model. The total emission energy from the jet is assumed to be constant. We find that if...
We show a possible way to measure the column density of free electrons along the light path, the so-called Dispersion Measure (DM), from the early $[\sim 415 (\nu/1 {\rm GHz})^{-2} ({\rm DM}/10^{5}...
Circular Polarization from Gamma-ray Burst Afterglows (2003)
Matsumiya, Makoto, Ioka, Kunihito
We investigate the circular polarization (CP) from Gamma-Ray Burst (GRB) afterglows. We show that a tangled magnetic field cannot generate CP without an ordered magnetic field because there is always...
Relativistic stars with poloidal and toroidal magnetic fields and meridional flow (2003)
We investigate stationary axisymmetric configurations of magnetized stars in the framework of general relativistic ideal magnetohydrodynamics. Our relativistic stellar model incorporates a toroidal...
Grad-Shafranov equation in noncircular stationary axisymmetric spacetimes (2003)
A formulation is developed for general relativistic ideal magnetohydrodynamics in stationary axisymmetric spacetimes. We reduce basic equations to a single second-order partial differential equation,...
Cosmological X-ray Flashes in the Off-Axis Jet Model (2002)
Yamazaki, Ryo, Ioka, Kunihito, Nakamura, Takashi
The of the cosmological X-ray flashes detected by Wide Field Cameras on BeppoSAX is calculted theoretically in a simple jet model. The total emission energy from the jet is assumed to be constant....
Ultra Fast Self-Compton Cooling (2002)
We investigate the synchrotron self-Compton process in a planar shell taking the shock structure into account. We find that the energy density of the seed photons could deviate from the one-zone...
Delayed Flashes from Counter Jets of Gamma Ray Bursts (2002)
Yamazaki, Ryo, Ioka, Kunihito, Nakamura, Takashi
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...
X-ray Flashes from Off-axis Gamma-Ray Bursts (2002)
Yamazaki, Ryo, Ioka, Kunihito, Nakamura, Takashi
Ioka and Nakamura (2001) proposed a simple jet model that is compatible with the peak luminosity-spectral lag relation, the peak luminosity-variability relation and various other relations in the...
Possible Origin of Lognormal Distributions in Gamma-Ray Bursts (2002)
Ioka, Kunihito, Nakamura, Takashi
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...
Ioka, Kunihito, Nakamura, Takashi
We compute the kinematical dependence of the peak luminosity, the pulse width and the spectral lag of the peak luminosity on the viewing angle $\theta_v$ of a jet. For appropriate model parameters we...
Microlensing of collimated Gamma-Ray Burst afterglows (2001)
Ioka, Kunihito, Nakamura, Takashi
We investigate stellar microlensing of the collimated gamma-ray burst afterglows. A spherical afterglow appears on the sky as a superluminally expanding thin ring (``ring-like'' image), which is...
Magnetic Deformation of Magnetars for the Giant Flares of the Soft Gamma-Ray Repeaters (2000)
We present one possible mechanism for the giant flares of the Soft Gamma-Ray Repeaters (SGRs) within the framework of magnetar, i.e., superstrongly magnetized neutron star model, motivated by the...
Gravitational waves from inspiralling compact binaries with magnetic dipole moments (2000)
Ioka, Kunihito, Taniguchi, Keisuke
We investigate the effects of the magnetic dipole-dipole coupling and the electromagnetic radiation on the frequency evolution of gravitational waves from inspiralling binary neutron stars with...
Ioka, Kunihito, Tanaka, Takahiro, Nakamura, Takashi
Under the assumption that the Milky Way's dark halo consists of primordial black hole MACHOs (PBHMACHOs), the mass density of the halo can be measured by the low frequency gravitational waves...
Low frequency gravitational waves from black hole MACHO binaries (1998)
Ioka, Kunihito, Tanaka, Takahiro, Nakamura, Takashi
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...
Ioka, Kunihito, Chiba, Takeshi, Tanaka, Takahiro, Nakamura, Takashi
We study black hole MACHO binary formation through three-body interactions in the early universe at $t\sim 10^{-5}$s. The probability distribution functions of the eccentricity and the semimajor axis...