Molecular Clouds as a Probe of Cosmic-Ray Acceleration in a Supernova Remnant (2009)
Fujita, Yutaka, Ohira, Yutaka, Tanaka, Shuta J., Takahara, Fumio
We study cosmic-ray acceleration in a supernova remnant (SNR) and the escape from it. We model nonthermal particle and photon spectra for the hidden SNR in the open cluster Westerlund 2, and the...
Ohira, Yutaka, Terasawa, Toshio, Takahara, Fumio
H-alpha emission from supernova remnants (SNRs) implies the existence of neutral hydrogen in the circumstellar medium. Some of the neutral particles penetrating the shock are ionized by the charge...
Fujita, Yutaka, Hayashida, Kiyoshi, Takahashi, Hiroaki, Takahara, Fumio
We present the analysis of Suzaku observations of the young open cluster Westerlund 2, which is filled with diffuse X-ray emission. We found that the emission consists of three thermal components or...
Ohira, Yutaka, Reville, Brian, Kirk, John G., Takahara, Fumio
In supernova remnants, the nonlinear amplification of magnetic fields upstream of collisionless shocks is essential for the acceleration of cosmic rays to the energy of the "knee" at $10^{15.5}$ eV....
A Relativistic Electron-Positron Outflow from a Tepid Fireball (2008)
Asano, Katsuaki, Takahara, Fumio
Through detailed numerical simulations, we demonstrate that relativistic outflows (Lorentz factor $\Gamma \sim 7$) of electron-positron pairs can be produced by radiative acceleration even when the...
Ohira, Yutaka, Reville, Brian, Kirk, John G., Takahara, Fumio
In supernova remnants, the nonlinear amplification of magnetic fields upstream of collisionless shocks is essential for the acceleration of cosmic rays to the energy of the "knee" at 10^{15.5}eV. A...
Oblique Ion Two-Stream Instability in the Foot Region of a Collisionless Shock (2008)
Ohira, Yutaka, Takahara, Fumio
Electrostatic behavior of a collisionless plasma in the foot region of high Mach number perpendicular shocks is investigated through the two-dimensional linear analysis and electrostatic...
Gamma-Ray Emission From Blazars (2008)
I discuss implications of gamma-ray emission from blazars based on electron acceleration by shock waves in a relativistic jet. The number spectrum of electrons turns out to be a broken power law;...
Sergei Levshakov, Fumio Takahara, Irina I. Agafonova
We present a new method for recovering the kinetic temperature of the intervening di+use gas to an accuracy of 10%. The method is based on the comparison of unsaturated absorption-line proles of two...
Absence of Electron Surfing Acceleration in a Two-Dimensional Simulation (2007)
Ohira, Yutaka, Takahara, Fumio
Electron acceleration in high Mach number perpendicular shocks is investigated through two-dimensional electrostatic particle-in-cell (PIC) simulation. We simulate the shock foot region by modeling...
Generation of a Fireball in AGN Hot Plasmas (2006)
Asano, Katsuaki, Takahara, Fumio
Motivated by relativistic jets observed in active galactic nuclei (AGN), we simulate outflows of electron-positron pairs strongly coupled with photons from normal electron-proton plasmas. Using...
Energy and Momentum Transfer via Coulomb Frictions in Relativistic Two Fluids (2006)
Asano, Katsuaki, Iwamoto, Shizuo, Takahara, Fumio
We numerically calculate the energy and momentum transfer rates due to Coulomb scattering between two fluids moving with a relative velocity. The results are fitted by simple functions. The fitting...
A Structured Leptonic Jet Model of the "Orphan" TeV Gamma-Ray Flares in TeV Blazars (2006)
Kusunose, Masaaki, Takahara, Fumio
The emission spectra of TeV blazars extend up to tens of TeV and the emission mechanism of the TeV $\gamma$-rays is explained by synchrotron self-Compton scattering in leptonic models. In these...
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,...
The X-Ray Jet in Centaurus A: Clues to the Jet Structure and Particle Acceleration (2006)
Kataoka, Jun, Stawarz, Lucasz, Aharonian, Felix, Takahara, Fumio, Ostrowski, Michal, Edwards, Philip G.
We report detailed studies of the X-ray emission from the kiloparsec-scale jet in the nearest active galaxy, Centaurus A. By analyzing the highest quality X-ray data obtained with the Chandra ACIS-S,...
Kato, Tomohiro, Kusunose, Masaaki, Takahara, Fumio
H1426+428 is one of blazars that are observed by $\gamma$-rays in the TeV region. Because TeV $\gamma$-rays from distant sources are subject to attenuation by the extragalactic background light (EBL)...
The X-ray Jet in Centaurus A: Clues on the Jet Structure and Particle Acceleration (2005)
Kataoka, Jun, Stawarz, Lukasz, Aharonian, Felix, Takahara, Fumio, Ostrowski, Michal, Edwards, Philip G.
We report detailed studies of the X-ray emission from the kpc scale jet in the nearest active galaxy, Cen A. 41 compact sources were found within the jet, 13 of which were newly identified. We...
Coherent Curvature Radiation and Proton Counterflow in the Pulsar Magnetosphere (2005)
Asano, Katsuaki, Takahara, Fumio
In the proton counterflow model of a pulsar magnetosphere that we have recently proposed, non-relativistic protons are supplied from the magnetosphere to flow toward the pulsar surface and screen an...
Compton scattering in the Klein-Nishina Regime Revisited (2005)
Kusunose, Masaaki, Takahara, Fumio
In blazars such as 3C 279, GeV gamma-rays are thought to be produced by inverse Compton scattering of soft photons injected from external sources into the jet. Because of the large bulk Lorentz...
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...
Electric field screening by a proton counterflow in the pulsar polar cap (2004)
Asano, Katsuaki, Takahara, Fumio
We propose a new mechanism to screen the electric field in the pulsar polar cap. Previous studies have shown that if an electron beam from the stellar surface is accelerated to energies high enough...
Electrostatic Instability in Electron-Positron Pairs Injected in an External Electric Field (2004)
Asano, Katsuaki, Takahara, Fumio
Motivated by the particle acceleration problem in pulsars, we numerically investigate electrostatic instability of electron-positron pairs injected in an external electric field. The electric field...
Constraints on the energetics and plasma composition of relativistic jets in FR II sources (2003)
We explore the energetics and plasma composition in FR II sources using a new simple method of combining shock dynamics and radiation spectrum. The hot spots are identified with the reverse shocked...
The Electron Spectrum in 3C279 and the Observed Emission Spectrum (2003)
Kusunose, Masaaki, Takahara, Fumio, Kato, Tomohiro
The emission mechanisms of the blazar 3C 279 are studied by solving the kinetic equations of electrons and photons in a relativistically moving blob. The gamma-ray spectral energy distribution (SED)...
Asano, Katsuaki, Takahara, Fumio
Gamma-ray bursts are generally considered to be the result of internal shocks generated in an inhomogeneous relativistic outflow that arises from a fireball. In such shocks, the Fermi acceleration of...
Kato, Tsunehiko N., Takahara, Fumio
We give a new coherent description of the first-order Fermi acceleration of particles in shock waves from the point of view of stochastic process of the individual particles, under the test particle...
Chandra Detection of Hotspot and Knots of 3C 303 (2002)
Kataoka, Jun, Edwards, Philip, Georganopoulos, Markos, Takahara, Fumio, Wagner, Stefan
We report the detection at X-rays of the radio/optical hotspot and knots of 3C 303 from a short (15 ksec) Chandra exposure in 2001 March. The X-ray morphology is similar to that of the radio/optical...
Properties of the Brightest Cluster Galaxy and Its Host Cluster (2002)
Katayama, Haruyoshi, Hayashida, Kiyoshi, Takahara, Fumio, Fujita, Yutaka
We investigate the relation between the properties of Brightest Cluster Galaxies (BCGs) and those of their host clusters. To quantify the properties of cluster hot gas, we employ the parameter $Z$ of...
RXTE Observations of 3C273 between 1996 and 2000:Variability Timescale and Jet Power (2002)
Kataoka, Jun, Tanihata, Chiharu, Kawai, Nobuyuki, Takahara, Fumio, Takahashi, Tadayuki, Edwards, Philip G., ...
We present the results of a long-look monitoring of 3C273 with RXTE between 1996 and 2000. A total of 230 observations amounts to a net exposure of 845ksec, with this spectral and variability...
Energetics of Tev Blazars and Physical Constraints on their Emission Regions (2001)
Kino, Motoki, Takahara, Fumio, Kusunose, Masaaki
Using multi-frequency spectra from TeV blazars in quiescent states, we obtain the physical parameters of the emission region of blazars within the framework of the one-zone synchrotron self-Compton...
Kataoka, Jun, Takahashi, Tadayuki, Wagner, Stefan J., Iyomoto, Naoko, Edwards, Philip G., Hayashida, Kiyoshi, ...
We have studied the rapid X-ray variability of three extragalactic TeV gamma-ray sources; Mrk 421, Mrk 501 and PKS 2155-304. Analyzing the X-ray light curves obtained from ASCA and/or RXTE...
Enoki, Motohiro, Takahara, Fumio, Fujita, Yutaka
We investigate statistical properties of galaxy clusters in the context of hierarchical clustering scenario, taking account of their formation epoch distribution, motivated by the recent finding by...
The Variation of Gas Mass Distribution in Galaxy Clusters: Effects of Preheating and Shocks (2000)
Fujita, Yutaka, Takahara, Fumio
We investigate the origin of the variation of the gas mass fraction in the core of galaxy clusters, which was indicated by our work on the X-ray fundamental plane. The adopted model supposes that the...
Global Relationships among Physical Properties of Galaxy Cluster Cores (1999)
Fujita, Yutaka, Takahara, Fumio
Using X-ray data, we investigate interrelations between gas density rho_0, virial density rho_vir, core radius R, temperature T, entropy S_gas, and metal abundance Z in the core region of clusters of...
The X-ray Fundamental Plane and $L_X-T$ Relation of Clusters of Galaxies (1999)
Fujita, Yutaka, Takahara, Fumio
We analyze the relations among central gas density, core radius, and temperature of X-ray clusters by plotting the observational data in the three-dimensional ($\log \rho_0$, $\log R$, and $\log T$)...
Cosmological Implications of the Fundamental Relations of X-ray Clusters (1999)
Fujita, Yutaka, Takahara, Fumio
Based on the two-parameter family nature of X-ray clusters of galaxies obtained in a separate paper, we discuss the formation history of clusters and cosmological parameters of the universe....
Levshakov, Sergei A., Takahara, Fumio, Agafonova, Irina I.
We present a new method for recovering the kinetic temperature of the intervening diffuse gas to an accuracy of 10%. The method is based on the comparison of unsaturated absorption-line profiles of...
The D/H ratio at z = 3.57 toward Q 1937-1009 (1998)
Levshakov, Sergei A., Kegel, Wilhelm H., Takahara, Fumio
Deuterium abundance re-measurements by Burles and Tytler (1998; hereafter BT) yielded D/H = (3.3 +/- 0.3) 10^{-5} and the robust upper limit D/H < 3.9 10^{-5} from the z_a = 3.572 system toward...
The D/H ratio at z=0.7 toward Q 1718+4807 (1998)
Levshakov, Sergei A., Kegel, Wilhelm H., Takahara, Fumio
The apparent discrepancy between low and high D abundances derived from QSO spectra may be caused by spatial correlations in the stochastic velocity field. If one accounts for such correlations, one...
Primordial Deuterium Abundance Measurements (1997)
Levshakov, Sergei A., Kegel, Wilhelm H., Takahara, Fumio
Deuterium abundances measured recently from QSO absorption-line systems lie in the range from 3 10^{-5} to 3 10^{-4}, which shed some questions on standard big bang theory. We show that this...
The primordial deuterium abundance : problems and prospects (1997)
Levshakov, Sergei A., Takahara, Fumio, Kegel, Wilhelm H.
The current status of extragalactic deuterium abundance is discussed using two examples of `low' and `high' D/H measurements. We show that the discordance of these two types of D abundances may be a...
How Accurately Can the Deuterium Abundance Be Determined ? (1997)
Sergei Levshakov, Wilhelm H. Kegel, Fumio Takahara, N Hi
h respect to the H+D absorption observed in QSO spectra. The hydrogen absorbers with N HI ΒΈ 10 17 \Gamma 10 18 cm \Gamma2 (which are especially useful for deuterium observations) are usually...
Implications on the Ionizing Background Radiation from HST Heii Gunn-Peterson Test (1994)
Recently, Jakobsen et al. reported that the HeII Gunn-Peterson optical depth is greater than 1.7 at $ z=3.3$. When we consider this observation combined with the HI Gunn-Peterson optical depths and...