arXiv subjects

T. Kotani

Publications and source records attributed to T. Kotani.

52 records · Page 3Linked to original sources

arXiv2007

MITSuME--Multicolor Imaging Telescopes for Survey and Monstrous Explosions

Development of MITSuME is reported. Two 50-cm optical telescopes have been built at Akeno in Yamanashi prefecture and at Okayama Astrophysical Observatory (OAO) in Okayama prefecture. Three CCD cameras for simultaneous g'RcIc photometry are to be mounted on each focal plane, covering a wide FOV of about 30" x 30". The limiting magnitude at V is fainter than 18. In addition to these two optical telescopes, a 91-cm IR telescope with a 1 deg x 1 deg field of view is being built at OAO, which performs photometry in YJHK bands. These robotic telescopes can start the observation of counterparts of a GRB within a minute from an alert. We aim to obtain photometric redshifts exceeding 10 with these telescopes. The performance and the current construction status of the telescopes are presented.

astro-ph↗

arXiv2007

Recent Radio Monitoring of Microquasars with RATAN-600 Radio Telescope

We report about the multi-frequency (1-30 GHz) daily monitoring of the radio flux variability of the three microquasars: SS433, GRS1915+105 and Cyg X-3 during the period from September 2005 to May 2006. 1. We detected clear correlation of the flaring radio fluxes and X-rays 'spikes' at 2-12 keV emission detected in RXTE ASM from GRS1915+105 during eight relatively bright (200-600 mJy) radio flares in October 2005. The 1-22 GHz spectra of these flares in maximum were optically thick at frequencies lower 2.3 GHz and optically thin at the higher frequencies. During the radio flares the spectra of the X-ray spikes become softer than those of the quiescent phase. Thus these data indicated the transitions from very high/hard states to high/soft ones during which massive ejections are probably happened. These ejections are visible as the detected radio flares. 2. After of the quiescent radio emission we have detected a drop down of the fluxes (~20 mJy) from Cyg X-3. That is a sign of the following bright flare. Indeed such a 1Jy-flare was detected on 3 February 2006 after 18 days of the quenched radio emission. The daily spectra of the flare in the maximum was flat from 1 to 100 GHz, using the quasi-simultaneous observations at 109 GHz with RT45m telescope and millimeter array (NMA) of Nobeyama Radio Observatory in Japan. The several bright radio flaring events (1-10 Jy) followed during this state of very variable and intensive 1-12 keV X-ray emission (~0.5 Crab), which being monitored in RXTE ASM program.

astro-ph↗

arXiv2006

Observation Campaign of SS 433 in April 2006

A radio-IR-optical-X-ray observation campaign of SS 433 has been performed in April 2006, when the jet axis is almost perpendicular to the line of sight. Five flares have been detected during the campaign by radio monitoring observation with RATAN-600. The X-ray astronomical satellite Suzaku observed the source in and out of eclipse. In the X-ray data out of eclipse, the flux shows a significant variation with a time scale of hours. The source seems to be in the active state during the campaign. The observation logs and preliminary results are presented.

astro-ph↗

arXiv2006

Monte-Carlo Simulator and Ancillary Response Generator of Suzaku XRT/XIS System for Spatially Extended Source Analysis

We have developed a framework for the Monte-Carlo simulation of the X-Ray Telescopes (XRT) and the X-ray Imaging Spectrometers (XIS) onboard Suzaku, mainly for the scientific analysis of spatially and spectroscopically complex celestial sources. A photon-by-photon instrumental simulator is built on the ANL platform, which has been successfully used in ASCA data analysis. The simulator has a modular structure, in which the XRT simulation is based on a ray-tracing library, while the XIS simulation utilizes a spectral "Redistribution Matrix File" (RMF), generated separately by other tools. Instrumental characteristics and calibration results, e.g., XRT geometry, reflectivity, mutual alignments, thermal shield transmission, build-up of the contamination on the XIS optical blocking filters (OBF), are incorporated as completely as possible. Most of this information is available in the form of the FITS (Flexible Image Transport System) files in the standard calibration database (CALDB). This simulator can also be utilized to generate an "Ancillary Response File" (ARF), which describes the XRT response and the amount of OBF contamination. The ARF is dependent on the spatial distribution of the celestial target and the photon accumulation region on the detector, as well as observing conditions such as the observation date and satellite attitude. We describe principles of the simulator and the ARF generator, and demonstrate their performance in comparison with in-flight data.

astro-ph↗

arXiv2006

Adequacy of Approximations in GW Theory

We use an all-electron implementation of the GW approximation to analyze several possible sources of error in the theory and its implementation. Among these are convergence in the polarization and Green's functions, the dependence of QP levels on choice of basis sets, and differing approximations for dealing with core levels. In all GW calculations presented here, G and W are generated from the local-density approximation (LDA), which we denote as the \GLDA\WLDA approximation. To test its range of validity, the \GLDA\WLDA approximation is applied to a variety of materials systems. We show that for simple sp semiconductors, \GLDA\WLDA always underestimates bandgaps; however, better agreement with experiment is obtained when the self-energy is not renormalized, and we propose a justification for it. Some calculations for Si are compared to pseudopotential-based \GLDA\WLDA calculations, and some aspects of the suitability of pseudopotentials for GW calculations are discussed.

cond-mat.mtrl-sci↗

arXiv2006

Cyclotron resonance energies at a low X-ray luminosity: A0535+262 observed with Suzaku

The binary X-ray pulsar A0535+262 was observed with the Suzaku X-ray observatory, on 2005 September 14 for a net exposure of 22 ksec. The source was in a declining phase of a minor outburst, exhibiting 3--50 keV luminosity of about $3.7 \times 10^{35}$ ergs s$^{-1}$ at an assumed distance of 2 kpc. In spite of the very low source intensity (about 30 mCrab at 20 keV), its electron cyclotron resonance was detected clearly with the Suzaku Hard X-ray Detector, in absorption at about 45 keV. The resonance energy is found to be essentially the same as those measured when the source is almost two orders of magnitude more luminous. These results are compared with the luminosity-dependent changes in the cyclotron resonance energy, observed from 4U 0115+63 and X 0331+53.

astro-ph↗

arXiv2006

Quasiparticle Self-Consistent GW Theory

In past decades the scientific community has been looking for a reliable first-principles method to predict the electronic structure of solids with high accuracy. Here we present an approach which we call the quasiparticle self-consistent GW approximation (QpscGW). It is based on a kind of self-consistent perturbation theory, where the self-consistency is constructed to minimize the perturbation. We apply it to selections from different classes of materials, including alkali metals, semiconductors, wide band gap insulators, transition metals, transition metal oxides, magnetic insulators, and rare earth compounds. Apart some mild exceptions, the properties are very well described, particularly in weakly correlated cases. Self-consistency dramatically improves agreement with experiment, and is sometimes essential. Discrepancies with experiment are systematic, and can be explained in terms of approximations made.

cond-mat.mtrl-sci↗

arXiv2005

A Massive Jet Ejection Event from the Microquasar SS 433 Accompanying Rapid X-Ray Variability

Microquasars occasionally exhibit massive jet ejections which are distinct from the continuous or quasi-continuous weak jet ejections. Because those massive jet ejections are rare and short events, they have hardly been observed in X-ray so far. In this paper, the first X-ray observation of a massive jet ejection from the microquasar SS 433 with the Rossi X-ray Timing Explorer (RXTE) is reported. SS 433 undergoing a massive ejection event shows a variety of new phenomena including a QPO-like feature near 0.1 Hz, rapid time variability, and shot-like activities. The shot-like activity may be caused by the formation of a small plasma bullet. A massive jet may be consist of thousands of those plasma bullets ejected from the binary system. The size, mass, internal energy, and kinetic energy of the bullets and the massive jet are estimated.

astro-ph↗

arXiv2005

Chandra Observation of the Interaction between the Hot Plasma Nebula RCW89 and the Pulsar Jet of PSR B1509-58

We present a Chandra observation of the H II region RCW89. The nebula lies on 10' north from the central pulsar PSR B1509-58, and it has been suggested that the nebula is irradiated by the pulsar jet. We performed a spectral analysis of the seven brightest emitting regions aligned in a ``horse-shoe'' shape, and found that the temperature of the knots increases along the ``horse-shoe'' in the clockwise direction, while, in contrast, the ionization parameter decreases. This strongly supports a picture of energy transfer via the precessing pulsar jet. We examined the energy budget assuming that RCW89 is powered by the pulsar jet, and confirmed that the pulsar rotational energy loss is sufficient to drive the nebula. The rate of energy injection into RCW89 by the jet was estimated from the synchrotron radiation flux. We obtained a heating time-scale of 1400 yr, which is consistent with the pulsar characteristic age of 1700 yr. To explain the temperature gradient, we discuss the cooling process for plasma clouds in RCW89. We argue that the plasma clouds can be cooled down by the adiabatic expansion within 70 yr, and form the temperature gradient reflecting the sequential heating by the precessing pulsar jet. We also determined the velocities of the individual plasma clouds by spectral fitting. The plasma clouds in RCW89 are moving away at 240 ~ 860 km/s, which constrains the inclination angle of the pulsar spin axis i > 50 degree and the expanding velocity of the shell as v > 1100 km/s.

astro-ph↗

arXiv2002

Gamma Ray Large Area Space Telescope (GLAST) Balloon Flight Data Handling Overview

The GLAST Balloon Flight Engineering Model (BFEM) represents one of 16 towers that constitute the Large Area Telescope (LAT), a high-energy (>20 MeV) gamma-ray pair-production telescope being built by an international partnership of astrophysicists and particle physicists for a satellite launch in 2006. The prototype tower consists of a Pb/Si pair-conversion tracker (TKR), a CsI hodoscopic calorimeter (CAL), an anti-coincidence detector (ACD) and an autonomous data acquisition system (DAQ). The self-triggering capabilities and performance of the detector elements have been previously characterized using positron, photon and hadron beams. External target scintillators were placed above the instrument to act as sources of hadronic showers. This paper provides a comprehensive description of the BFEM data-reduction process, from receipt of the flight data from telemetry through event reconstruction and background rejection cuts. The goals of the ground analysis presented here are to verify the functioning of the instrument and to validate the reconstruction software and the background-rejection scheme.

astro-ph↗

arXiv2002

A Massive Jet-Ejection from SS433

The detection of a massive jet-ejection event from SS433 with RXTE is reported. SS433 in its high state has been monitored with RXTE from 2001/11/09 (MJD = 52222) to 2001/11/25 (MJD = 52238), following a radio flare on 2001/11/02 (MJD = 52215). An irregular temporal variation with time scales of 100-1000 s appears in the light curve, and the amplitude increases day by day. This is the first detection of such a fast variation from the source. In addition to the fast variations, the daily light curve scatters with a time scale of ~day from 2001/11/17 (MJD = 52230). Following the scatter, another radio flare has been detected on 2001/11/22 (MJD = 52235), which has been obviously formed during the X-ray scatter. This is a preliminary report on a massive jet-ejection event witnessed in X-ray band for the first time.

astro-ph↗

arXiv2002

Study of the Largest Multiwavelength Campaign of the Microquasar GRS 1915+105

We present the results from a multiwavelength campaign of GRS 1915+105 performed from 2000 April 16 to 25. This is one of the largest coordinated set of observations ever performed for this source, covering the wide energy band in radio (13.3-0.3 cm), near-infrared (J-H-K), X-rays and Gamma-rays (from 1 keV to 10 MeV). During the campaign GRS 1915+105 was predominantly in the "plateau" (or low/hard) state but sometimes showed soft X-ray oscillations: before April 20.3, rapid, quasi-periodic (~= 45 min) flare-dip cycles were observed. The radio flares observed on April 17 shows frequency- dependent peak delay, consistent with an expansion of synchrotron-emitting region starting at the transition from the hard-dip to the soft-flare states in X-rays. On the other hand, infrared flares on April 20 appear to follow (or precede) the beginning of X-ray oscillations with an inconstant time delay of ~= 5-30 min. This implies that the infrared emitting region is located far from the black hole by >~ 10E13 cm, while its size is <~ 10E12 cm constrained from the time variability. We find a good correlation between the quasi-steady flux level in the near-infrared band and in the X-ray band. From this we estimate that the reprocessing of X-rays, probably occurring in the outer parts of the accretion disk, accounts for about 20-30% of the observed K magnitude in the plateau state. The OSSE spectrum in the 0.05-10 MeV band is represented by a single power law with a photon index of 3.1 extending to ~1 MeV with no cutoff. The power-law slope above ~30 keV is found to be very similar between different states in spite of large flux variations in soft X-rays, implying that the electron energy distribution is not affected by the change of the state in the accretion disk.

astro-ph↗

arXiv2000

X-ray Energy Spectra of the Super-soft X-ray Sources CAL87 and RXJ0925.7-4758 Observed with ASCA

We report observation results of the super-soft X-ray sources (SSS) CAL87 and RXJ0925.7-4758 with the X-ray CCD cameras (Solid-state Imaging Spectrometer; SIS) on-board the ASCA satellite. We have applied theoretical spectral models to CAL87, and constrained the white dwarf mass and intrinsic luminosity as 0.8 - 1.2 M_solar and 4 x 10^{37}- 1.2 x 10^{38} erg s^{-1}, respectively. However, we have found the observed luminosity is an order of magnitude smaller than the theoretical estimate, which indicates the white dwarf is permanently blocked by the accretion disk, and we are observing a scattering emission by a fully ionized accretion disk corona (ADC) whose column density is ~ 1.5 x 10^{23} cm^{-2}. Through simulation, we have shown that the orbital eclipse can be explained by the ADC model, such that a part of the extended X-ray emission from the ADC is blocked by the companion star filling its Roche lobe. We have found that very high surface gravity and temperature, ~ 10^{10} cm s^{-2} and ~ 100 eV respectively, as well as a strong absorption edge at ~ 1.02 keV, are required to explain the X-ray energy spectrum of RXJ0925.7-4758. These values are only possible for an extremely heavy white dwarf near the Chandrasekhar limit. Although the super soft source luminosity should be ~ 10^{38} erg s^{-1} at the Chandrasekhar limit, the observed luminosity of RXJ0925.7-4758 is nearly two orders of magnitude smaller even assuming an extreme distance of ~10 kpc. To explain the luminosity discrepancy, we propose a model that very thick matter which was previously ejected from the system, as a form of jets, intervenes the line of sight, and reduces the luminosity significantly due to Thomson scattering.

astro-ph↗

arXiv2000

ASCA Observations of the Jet Source XTE J1748-288

XTE J1748-288 is a new X-ray transient with a one-sided radio jet. It was observed with ASCA on 1998/09/06 and 1998/09/26, 100 days after the onset of the radio-X-ray outburst. The spectra were fitted with an attenuated power-law model, and the 2-6-keV flux was 4.6 * 10^{-11} erg s^{-1} cm^{-2} and 2.2 * 10^{-12} on 09/06 and 09/26, respectively. The light curve showed that the steady exponential decay with an e-folding time of 14 days lasted over 100 days and 4 orders of magnitude from the peak of the outburst. The celestial region including the source had been observed with ASCA on 1993/10/01 and 1994/09/22, years before the discovery. In those period, the flux was < 10^{-13} erg s^{-1} cm^{-2}, below ASCA's detection limit. The jet blob colliding to the environmental matter was supposedly not the X-ray source, although the emission mechanism has not been determined. A possible detection of a K line from highly ionized iron is discussed.

astro-ph↗

arXiv1999

The X-ray CCD camera of the MAXI Experiment on the ISS/JEM

MAXI, Monitor of All-sky X-ray Image, is the X-ray observatory on the Japanese experimental module (JEM) Exposed Facility (EF) on the International Space Station (ISS). MAXI is a slit scanning camera which consists of two kinds of X-ray detectors: one is a one-dimensional position-sensitive proportional counter with a total area of $\sim 5000 cm^2$, the Gas Slit Camera (GSC), and the other is an X-ray CCD array with a total area $\sim 200 cm^2$, the Solid-state Slit Camera (SSC). The GSC subtends a field of view with an angular dimension of 1$^\circ\times 180^\circ$ while the SSC subtends a field of view with an angular dimension of 1$^\circ$ times a little less than 180$^\circ$. In the course of one station orbit, MAXI can scan almost the entire sky with a precision of 1$^\circ$ and with an X-ray energy range of 0.5-30 keV. We have developed the engineering model of CCD chips and the analogue electronics for the SSC. The energy resolution of EM CCD for Mn K$α$ has a full-width at half maximum of $\simeq$ 182 eV. Readout noise is $\simeq$ 11 e^- rms.

physics.ins-det↗

arXiv1996

ASCA observations of the iron K complex of Circinus X-1 near zero phase: spectral evidence for partial covering

We report on ASCA energy spectra of Cir X-1 taken near its zero phase on 1994 August 4-5. The ASCA SIS detectors allow a more detailed study of the iron K complex than has been possible before. We find that prior to a sudden upward flux transition the dominant iron K feature appears to consist of a large edge from neutral or nearly-neutral iron. The depth of the edge corresponds to an absorption column of about 1.5E24 cm^{-2}, while little absorption over that expected from the Galaxy is seen at lower X-ray energies. The differential absorption at high and low X-ray energies combined with the iron edge energy are strong evidence that partial covering is a crucial determinant of the behaviour observed from Cir X-1. The continuum spectral variability observed by ASCA can also be understood naturally in terms of partial covering column changes. There is evidence for a relatively weak emission line from neutral iron with an equivalent width of only about 65 eV. After the flux transition, the strength of the edge feature is greatly reduced, suggesting a large reduction in the amount of partial covering. For a large region of statistically acceptable chi-squared parameter space, the luminosity of Cir X-1, after correction for partial covering, need not change during the transition. We discuss models for the partial covering and suggest that X-ray scattering by electrons may be important. Aspects of the Cir X-1 spectrum are very similar to those of Seyfert 2 galaxies with Compton-thin tori.

astro-ph↗