Mizuno, Yosuke, Zhang, Bing, Giacomazzo, Bruno, Nishikawa, Ken-Ichi, Hardee, Philip E., Nagataki, Shigehiro, ...
We solve the Riemann problem for the deceleration of an arbitrarily magnetized relativistic flow injected into a static unmagnetized medium in one dimension. We find that for the same initial Lorentz...
Detectability of Pair Echos from Gamma-Ray Bursts and Intergalactic Magnetic Fields (2008)
Takahashi, Keitaro, Murase, Kohta, Ichiki, Kiyotomo, Inoue, Susumu, Nagataki, Shigehiro
High-energy emission from gamma-ray bursts (GRBs) can give rise to pair echos, i.e. delayed inverse Compton emission from secondary $e^{\pm}$ pairs produced in $\gamma-\gamma$ interactions with...
Murase, Kohta, Takahashi, Keitaro, Inoue, Susumu, Ichiki, Kiyomoto, Nagataki, Shigehiro
More than a dozen blazars are known to be emitters of multi-TeV gamma rays, often with strong and rapid flaring activity. By interacting with photons of the cosmic microwave and infrared backgrounds,...
Murase, Kohta, Inoue, Susumu, Nagataki, Shigehiro
Accretion and merger shocks in clusters of galaxies are potential accelerators of high-energy protons, which can give rise to high-energy neutrinos through pp interactions with the intracluster gas....
Solar-type Theoretical Model for Magnetar Giant Flare (2008)
Masada, Youhei, Nagataki, Shigehiro, Shibata, Kazunari, Terasawa, Toshio
In the framework of solar flare/coronal mass ejection theory, we propose a theoretical model for magnetar giant flare, which can explain the flaring activity on 2004 December 27 from SGR1806-20...
Higher Order Terms of Kerr Parameter for Blandford-Znajek Monopole Solution (2008)
Tanabe, Kentarou, Nagataki, Shigehiro
Blandford-Znajek mechanism, by which the rotational energy of a black hole is extracted through electromagnetic fields, is one of the promising candidates as an essential process of the central...
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...
The effect of energy amplification variance on the shock-acceleration (2007)
Aoi, Junichi, Murase, Kohta, Nagataki, Shigehiro
The shock-acceleration theory predicts a power-law energy spectrum in the test particle approximation, and there are two ways to calculate a power-law index, Peacock's approximation and Vietri's...
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...
Cosmogenic neutrinos as a probe of the transition from Galactic to extragalactic cosmic rays (2007)
Takami, Hajime, Murase, Kohta, Nagataki, Shigehiro, Sato, Katsuhiko
Whether the ankle is the transition point of Galactic/extragalactic cosmic rays or the pair-creation dip is an widely-discussed problem for astroparticle physics. In this work, we discuss the...
Effects of Cosmic Infrared Background on High Energy Delayed Gamma-Rays from Gamma-Ray Bursts (2007)
Murase, Kohta, Asano, Katsuaki, Nagataki, Shigehiro
Regenerated high-energy emissions from gamma-ray bursts (GRBs) are studied in detail. If the intrinsic primary spectrum extends to the TeV range, these very high-energy photons are absorbed by the...
Numerical study of gamma-ray burst jet formation in collapsars (2007)
Nagataki, Shigehiro, Takahashi, Rohta, Mizuta, Akira, Takiwaki, Tomoya
Toward understanding the central engine of long GRBs (2007)
Nagataki, Shigehiro, Takahashi, Rohta, Mizuta, Akira, Takiwaki, Tomoya
Collimated Jet or Expanding Outflow: Possible Origins of GRBs and X-Ray Flashes (2006)
Mizuta, Akira, Yamasaki, Tatsuya, Nagataki, Shigehiro, Mineshige, Shin
We investigate the dynamics of an injected outflow propagating in a progenitor in the context of the collapsar model for gamma-ray bursts (GRBs) through two dimensional axisymmetric relativistic...
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...
High Energy Neutrino Flashes from Far-Ultraviolet and X-ray Flares in Gamma-Ray Bursts (2006)
Murase, Kohta, Nagataki, Shigehiro
The recent observations of bright optical and x-ray flares by the Swift satellite suggest these are produced by the late activities of the central engine. We study the neutrino emission from...
Sendouda, Yuuiti, Nagataki, Shigehiro, Sato, Katsuhiko
The mass spectrum of the primordial black holes formed by density perturbation in the radiation-dominated era of the Randall-Sundrum type-2 cosmology is given. The spectrum coincides with standard...
Explosive Nucleosynthesis in GRB Jets Accompanied by Hypernovae (2006)
Nagataki, Shigehiro, Mizuta, Akira, Sato, Katsuhiko
Two-dimensional hydrodynamic simulations are performed to investigate explosive nucleosynthesis in a collapsar using the model of MacFadyen and Woosley (1999). It is shown that 56Ni is not produced...
Collimated jet or expanding outflow: possible origins of gamma-ray bursts and X-ray flashes (2006)
Mizuta, Akira, Yamasaki, Tatsuya, Nagataki, Shigehiro, Mineshige, Shin
Murase, Kohta, Nagataki, Shigehiro
High energy neutrino emission from GRBs is discussed. In this paper, by using the simulation kit GEANT4, we calculate proton cooling efficiency including pion-multiplicity and proton-inelasticity in...
Effects of Magnetic Fields on Proto-Neutron Star Winds (2005)
Ito, Hirotaka, Yamada, Shoichi, Sumiyoshi, Kohsuke, Nagataki, Shigehiro
We discuss effects of magnetic fields on proto-neutron star winds by performing numerical simulation. We assume that the atmosphere of proto-neutron star has a homogenous magnetic field (ranging from...
Alfven Wave-Driven Proto-Neutron Star Winds And R-Process Nucleosynthesis (2004)
Suzuki, Takeru K., Nagataki, Shigehiro
We propose magnetic proto-neutron star (PNS) winds driven by \Alfven waves as well as the neutrino heating as an appropriate site for the r-process nucleosynthesis. \Alfven waves excited by surface...
Magneto-driven Shock Waves in Core-Collapse Supernova (2004)
Takiwaki, Tomoya, Kotake, Kei, Nagataki, Shigehiro, Sato, Katsuhiko
We perform a series of two-dimensional magnetohydrodynamic simulations of the rotational core-collapse of a magnetized massive star. We employ a realistic equation of state and take into account the...
Sendouda, Yuuiti, Kohri, Kazunori, Nagataki, Shigehiro, Sato, Katsuhiko
We investigate cosmic-ray antiprotons emitted from the galactic primordial black holes in the Randall-Sundrum type-2 braneworld. The recent results of the BESS antiproton observation implies the...
Matsuura, Shunji, Dolgov, Alexander. D., Nagataki, Shigehiro, Sato, Katsuhiko
We study the impact of possible high density baryonic bubbles on the early formed QSO, IGM, and metal poor stars. Such bubbles could be created, under certain conditions, in Affleck-Dine model of...
Yoshiguchi, Hiroyuki, Nagataki, Shigehiro, Sato, Katsuhiko
Recently, the High Resolution Fly's Eye (HiRes) experiment claims that there is no small scale anisotropy in the arrival distribution of ultra-high energy cosmic rays (UHECRs) above $E>10^{19}$ eV...
Sendouda, Yuuiti, Nagataki, Shigehiro, Sato, Katsuhiko
We investigate the spectral shape of a high-energy diffuse photon emitted by evaporating primordial black holes (PBHs) in the Randall-Sundrum type II (RS2) braneworld. In their braneworld scenario,...
Arrival Distribution of Ultra-High Energy Cosmic Rays: Prospects for the Future (2003)
Yoshiguchi, Hiroyuki, Nagataki, Shigehiro, Sato, Katsuhiko
We predict the arrival distribution of UHECRs above $4 \times 10^{19}$ eV with the event number expected by future experiments in the next few years. We perform event simulations with the source...
Nagataki, Shigehiro, Takahashi, Keitaro
We estimate the fluxes of very high energy (VHE) gamma-rays and neutrinos from the Galactic Center which are by-products of the hadronic interactions between primary protons which are accelerated up...
Explosive Nucleosynthesis in Axisymmetrically Deformed Type II Supernovae (1997)
Nagataki, Shigehiro, Hashimoto, Masa-aki, Sato, Katsuhiko, Yamada, Shoichi
Explosive nucleosynthesis under the axisymmetric explosion in Type II supernova has been performed by means of two dimensional hydrodynamical calculations. We have compared the results with the...
Matter Mixing in Axisymmetric Supernova Explosion (1997)
Nagataki, Shigehiro, Shimizu, Tetsuya, Sato, Katsuhiko
Growth of Rayleigh-Taylor (R-T) instabilities under the axisymmetric explosion are investigated by two-dimensional hydrodynamical calculations. The degree of the axisymmetric explosion and amplitude...
Effects of axisymmetric explosion in collapse-driven supernovae / (1997)
Thesis (Ph. D.?)--University of Tokyo, 1997