X-Ray Observation of Very High Energy Gamma-Ray Source, HESS J1745-303, with Suzaku (2008)
Bamba, Aya, Yamazaki, Ryo, Kohri, Kazunori, Matsumoto, Hironori, Wagner, Stefan, Puehlhofer, Gerd, ...
Suzaku observations of a TeV unidentified (unID) source, HESS J1745-303, are presented. A possible excess of neutral iron line emission is discovered, and is likely associated with the main part of...
Prior Emission Model for X-ray Plateau Phase of Gamma-Ray Burst Afterglows (2008)
The two-component emission model to explain the plateau phase of the X-ray afterglows of gamma-ray bursts (GRBs) is proposed. One component, which is responsible for the plateau and subsequent steep...
The Nature of a Cosmic-ray Accelerator CTB37B Observed with Suzaku and Chandra (2008)
Nakamura, Ryoko, Bamba, Aya, Ishida, Manabu, Nakajima, Hiroshi, Yamazaki, Ryo, Terada, Yukikatsu, ...
We report the Suzaku and Chandra observations of the young supernova remnant (SNR) CTB37B from which TeV-rays are detected by the H.E.S.S. Cherenkov telescope. The 80 ks Suzaku observation provided...
On the Gamma-Ray Spectrum of RX J1713.7-3946 in the GLAST era (2008)
Yamazaki, Ryo, Kohri, Kazunori, Katagiri, Hideaki
The recently launched GLAST satellite is expected to find out if cosmic-ray (CR) protons are generated at supernova remnants, especially at RX J1713.7-3946, by observing the GeV-to-TeV gamma-rays. We...
Umeda, Takayuki, Yamao, Masahiro, Yamazaki, Ryo
A two-dimensional (2D) shock-rest-frame model for particle simulations is developed. Then full kinetic dynamics of a perpendicular collisionless shock is examined by means of a 2D full particle...
Matsumoto, Hironori, Uchiyama, Hideki, Sawada, Makoto, Tsuru, Takeshi G., Koyama, Katsuji, Katagiri, Hideaki, ...
We report the Suzaku results of HESS J1614-518, which is the brightest extended TeV gamma-ray source discovered in the Galactic plane survey conducted using the H.E.S.S. telescope. We discovered...
The Suzaku Observation of RCW 86 Northeastern Shell (2007)
Yamaguchi, Hiroya, Koyama, Katsuji, Nakajima, Hiroshi, Bamba, Aya, Yamazaki, Ryo, Vink, Jacco, ...
This paper reports the Suzaku results on the northeast shell of RCW 86. With the spatial and spectral analysis, we separated the X-rays into three distinct components; low (kT_e~0.3keV) and high...
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...
Nonthermal Emission Associated with Strong AGN Outbursts at the Centers of Galaxy Clusters (2007)
Fujita, Yutaka, Kohri, Kazunori, Yamazaki, Ryo, Kino, Motoki
Recently, strong AGN outbursts at the centers of galaxy clusters have been found. Using a simple model, we study particle acceleration around a shock excited by an outburst and estimate nonthermal...
Takami, Kentaro, Yamazaki, Ryo, Sakamoto, Takanori, Sato, Goro
We show that the jet structure of gamma-ray bursts (GRBs) can be investigated with the tail emission of the prompt GRB. The tail emission which we consider is identified as a steep-decay component of...
A Unified Model of the Prompt Optical Emission of Gamma-Ray Bursts (2007)
Doi, Hirotsugu, Takami, Kentaro, Yamazaki, Ryo
The observational diversity of optical emission, which coincides with prompt gamma-ray bursts (GRBs), has been discovered in the recent Swift era. We show that on the assumption of the synchrotron...
Full particle simulation of a perpendicular collisionless shock: A shock-rest-frame model (2006)
Umeda, Takayuki, Yamazaki, Ryo
The full kinetic dynamics of a perpendicular collisionless shock is studied by means of a one-dimensional electromagnetic full particle simulation. The present simulation domain is taken in the shock...
The X-ray synchrotron emission of RCW 86 and the implications for its age (2006)
Vink, Jacco, Bleeker, Johan, Van Der Heyden, Kurt, Bykov, Andrei, Bamba, Aya, Yamazaki, Ryo
We report here X-ray imaging spectroscopy observations of the northeastern shell of the supernova remnant RCW 86 with Chandra and XMM-Newton. Along this part of the shell the dominant X-ray radiation...
TeV Gamma-Rays from Old Supernova Remnants (2006)
Yamazaki, Ryo, Kohri, Kazunori, Bamba, Aya, Yoshida, Tatsuo, Tsuribe, Toru, Takahara, Fumio
We study the emission from an old supernova remnant (SNR) with an age of around 10^5 yrs and that from a giant molecular cloud (GMC) encountered by the SNR. When the SNR age is around 10^5 yrs,...
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...
Matsubayashi, Tatsushi, Yamazaki, Ryo, Yonetoku, Daisuke, Murakami, Toshio, Ebisuzaki, Toshikazu
Using the luminosity function and the apparent GRB rate inferred from the spectral peak energy-luminosity relation, we investigate the absolute GRB formation rate, taking into account the effects of...
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...
Bamba, Aya, Yamazaki, Ryo, Hiraga, Junko S.
A galactic supernova remnant (SNR) Vela Jr. (RX J0852.0$-$4622, G266.6$-$1.2) shows sharp filamentary structure on the north-western edge of the remnant in the hard X-ray band. The filaments are so...
Ep-Eiso Correlation in a Multiple Subjet Model of Gamma-Ray Bursts (2005)
Toma, Kenji, Yamazaki, Ryo, Nakamura, Takashi
We perform Monte Carlo simulations to study Ep-Eiso correlation in the context of a multiple subjet model (or inhomogeneous jet model) for gamma-ray bursts (GRBs), X-ray--rich GRBs (XRRs), and X-ray...
Yonetoku, Daisuke, Yamazaki, Ryo, Nakamura, Takashi, Murakami, Toshio
We propose a method to estimate the pseudo jet opening half-angle of GRBs using the spectral peak energy ($\Ep$)--peak luminosity relation (so called Yonetoku relation) as well as the...
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...
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...
Bamba, Aya, Yamazaki, Ryo, Yoshida, Tatsuo, Terasawa, Toshio, Koyama, Katsuji
The outer shells of young supernova remnants (SNRs) are the most plausible acceleration sites of high-energy electrons with the diffusive shock acceleration (DSA) mechanism. We studied spatial and...
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...
A Possible Origin of Bimodal Distribution of Gamma-Ray Bursts (2004)
Toma, Kenji, Yamazaki, Ryo, Nakamura, Takashi
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...
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...
GRB980425 in the Off-Axis Jet Model of the Standard GRBs (2003)
Yamazaki, Ryo, Yonetoku, Daisuke, Nakamura, Takashi
Using a simple off-axis jet model of GRBs, we can reproduce the observed unusual properties of the prompt emission of GRB980425, such as the extremely low isotropic equivalent gamma-ray energy, the...
Yamazaki, Ryo, Yoshida, Tatsuo, Terasawa, Toshio, Bamba, Aya, Koyama, Katsuji
Characteristic scale lengths of nonthermal X-rays from the SN1006 NE rim, which are observed by Chandra, are interpreted in the context of the diffusive shock acceleration on the assumption that the...
Near-Infrared Colors of Gamma-Ray Burst Afterglows and Cosmic Reionization History (2003)
Inoue, Akio K., Yamazaki, Ryo, Nakamura, Takashi
Using the near-infrared (NIR) observations of the afterglows of the high redshift ($5 \la z \la 25$) gamma-ray bursts (GRBs) which will be detected by the {\it Swift} satellite, we discuss a way to...
An Off-Axis Jet Model For GRB980425 and Low Energy Gamma-Ray Bursts (2003)
Yamazaki, Ryo, Yonetoku, Daisuke, Nakamura, Takashi
Using a simple off-axis jet model of GRBs, we can reproduce the observed unusual properties of the prompt emission of GRB980425, such as the extremely low isotropic equivalent gamma-ray energy, the...
Fine Structures of Shock of SN 1006 with the Chandra Observation (2003)
Bamba, Aya, Yamazaki, Ryo, Ueno, Masaru, Koyama, Katsuji
The north east shell of SN 1006 is the most probable acceleration site of high energy electrons (up to ~ 100 TeV) with the Fermi acceleration mechanism at the shock front. We resolved non-thermal...
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....
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...
Black holes in three-dimensional Einstein-Born-Infeld-dilaton theory (2001)
The three-dimensional static and circularly symmetric solution of the Einstein-Born-Infeld-dilaton system is derived. The solutions corresponding to low energy string theory are investigated in...
Thick Domain Walls Intersecting a Black Hole (2000)
Morisawa, Yoshiyuki, Yamazaki, Ryo, Ida, Daisuke, Ishibashi, Akihiro, Nakao, Ken-ichi
We discuss the gravitationally interacting system of a thick domain wall and a black hole. We numerically solve the scalar field equation in the Schwarzschild spacetime and show that there exist...