We present elemental abundances for ~10 huge solar flares with GOES classes larger than ~X3.0, by using Earth albedo data acquired with the X-ray Imaging Spectrometer (XIS) onboard Suzaku between 2005 and 2015. The albedo spectra with the XIS successfully resolved K shell line emission from Mg, Si, S, Ca, and Fe, allowing us to measure their relative abundances. Our preliminary analyses...
"The solar flares are one of the biggest energy-release phenomena drived by magnetic reconnections in the solar atmosphere. The electrons accelerated by magnetic reconnections radiate hard X-ray emissions via non-thermal bremsstrahlung at the flare foot-points and/or loop-top (Masuda et al. 1994). Observationally, the emission appears as power-law spectral shapes, which in turn represents that...
"The hard X-ray and gamma-ray continuum components in solar flares are considered as Bremsstrahlung emission by accelerated non-thermal electrons. The energy spectra are normally well described by the single power-law shape. However, several authors reported that some flares show hardening spectral shape at higher than 300 keV[1,2]. Such hardening shape is called as spectral ""break-up.""...
Although corona has been being well used in modelling accretion of XRBs, especially on aspects of the spectral state transitions and correlation with launching of a jet, so far its nature is still less known, especially on aspect of the formation mechanism. To probe this puzzle observationally, one has firstly to have a proper probe like the intense short soft X-ray shower, since the corona is...
Swift J0243.6+6124 is a new Galactic Be/X-ray binary pulsar discovered on 2017. The MAXI all-sky monitor triggered on the outburst of this X-ray source on September 29 but could not distinguish it from the nearby known object LS I +61 303. On October 3, Swift BAT on the source identified it as a new transient source. The pulsation with the 〜9.86 s period was detected by the Swift XRT follow...
"Magnetars are pulsars with extremely strong magnetic fields 10^(14-15) G and thought to be powered by dissipation of their magnetic energies. The mechanism of converting their magnetic energies to the X-ray radiations is still a mystery, so that X-ray observations of magnetars are very important.
We observed one of the famous magnetars SGR 1900+14 with NuSTAR and XMM-Newton simultaneously on...
"GRS 1915+105 is one of the brightest X-ray objects over 26 years since it was first detected by GRANAT/WATCH in 1992. Its variable behavior was classified to 12 different variability classes based on the analysis of the light curve and color-color diagram (Belloni et al. 2000). The variability is observed on different timescales from a few seconds to an hour. Later work suggests there are...
The accretion-induced pulse period changes of the Be/X-ray binary pulsar X Persei were investigated over the period of 1996 January to 2017 September. This study utilized the monitoring data acquired with the RXTE All-Sky Monitor in 1.5–12 keV and the MAXI Gas-Slit Camera in 2–20 keV. The source intensity changed by a factor of 5–6 over this period. The pulsar was spinning down for 1996–2002,...
A black-hole binary (BHB) consists of stellar-star mass black hole and companion star. The accretion disk around the black hole is formed with matter from the companion star, and shines brightly in X-ray due to the release of gravitational energy. Therefore, X-ray is suitable to study physics of accretion disk and black hole. The accretion disk shows two states depending on geometrical...
There is unresolved X-ray emission over the Galaxy, or Galactic diffuse X-ray emission (GDXE). The origin has been under investigation for a long time since the discovery in 1970's. Two major scenarios have been proposed. One is an integration of faint point sources such as active binaries (AB), magnetic or non-magnetic Cataclysmic Variables (mCV, non-mCV). The other is a truly diffuse...
"Runaway stars are massive OB-stars with high spatial velocities that can serve as particle acceleration sites on their bow shocks. Non-thermal X-ray and gamma-ray, which can constrain the efficiency of particle acceleration strongly, have not been detected clearly. Therefore, it is important to detect them from shocks of runaway stars and to constrain the maximum energy of accelerated...
Based on a detailed spectral analysis using Suzaku, we investigate an ionization structure of a accretion column plasma of EX Hya, a magnetic cataclysmic variable (mCV).Due to high density and high cooling rate, the plasma has been assumed to be in a collisional ionization equilibrium (CIE) state so far.Trying a fitting of the X-ray spectrum with a CIE model, we found large residuals at 9-10...
"Radio galaxies are good objects for studying jet periphery emission. NGC 1275(3C 84) is the brightest radio galaxy in the gamma-ray band. Recently, the gamma-ray flux of NGC 1275 has increased gradually. The gamma-ray emission originated from the jet, however it is still under debate whether the optical/UV and X-ray emission is coming from the jet or accretion disk/corona.
In the present...
"The accretion disk and the super-massive black hole in the active galactic nucleus (AGN) are thought to be surrounded by an optically thick, dusty torus, which should have an essential role for the unification scheme of the AGN, the star formation history around the torus and the mass supply to central black hole. Observed X-ray spectra contain important information for revealing the torus...
"Blazars are one type of active galactic nuclei (AGN) whose jet is directed toward us, and especially, Flat Spectrum Radio Quasars (FSRQs) are the particularly bright blazars. We can research the evolution of super massive black hole about its jet and accretion disk. By modeling spectral energy distributions (SEDs) of FSRQs, physical parameters of relativistic jets can be estimated to the...
Clusters of galaxies carry important astrophysical and cosmological information on the formation history of the large scale structure and the estimates of cosmological parameters. Among others, mass of clusters is the most fundamental quantities. In this work, assuming spherical symmetry and hydrostatic equilibrium, we present the surface brightness, hydrostatic mass and gas mass fraction of...
"Galaxy clusters are formed by the gravitational collapse of the universe. In order to understand the evolution of the large-scale structure of the universe, it is necessary to study the merging process of galaxy clusters. We analyze XMM-Newton data of the merging cluster MCXC J0157.4-0550 and derive the 2-dimensional temperature, density, pressure and entropy maps from the hardness ratio map....
Gamma-ray spectra of GRB prompt emission are often described with the Band function consisting of smoothly connected two power-law functions at a break energy . The break energy is recognized as the typical energy of each GRB prompt emission. Since the break energy varies in time and distributes in the wide range --- from keV-band to MeV-band, the wide band spectroscopy is necessary to...
Accurately measuring the interstellar medium (ISM) gas distribution is important to study the structure and evolution of the Milky Way. Usually, the ISM gas is traced by HI 21-cm line surveys and CO 2.6-mm surveys.However, a significant amount of gas not properly traced by these surveys has been reported recently (dark gas). Although the emission from dust mixed with the ISM gas is usually...
The FORCE (Focusing On Relativistic universe and Cosmic Evolution) mission is a 1t-class X-ray observatory proposed for launch in late 2020s, using Japanese Epsilon rocket. The mission features, 1-80 keV wide-band coverage including hard X-rays, <15'' good angular resolution, and low background X-ray imaging spectroscopy. By utilizing the good angular resolution, and low instrumental...
"We are developing a fleet of nano-satellites to perform the accurate position determination of short gamma-ray bursts (SGRBs) by measuring the arrival time differences for the proposing CAMELOT (Cubesats Applied for MEasuring and LOcalising Transients) mission. To measure the arrival time precisely and achieve sufficient photon statistics under the severe limitation of size, mass and power...
We have been developing a compact X-ray imaging system with coded aperture for future missions. We evaluated performance of image reconstruction with several aperture patterns, including URA, MURA, and random patterns, based on theoretical discussion and numerical simulations. We will also show demonstration of the image reconstruction by using an optical imaging sensor.
"The Hard X-ray Imager (HXI) onboard Hitomi achieved the best background performance ever in the hard X-ray band. The main focal plane camera of the HXI consisted of four layers of Si imaging detectors and a CdTe imager. In order to
improve the sensitivity in future observations, it is indispensable to reduce non-X-ray background, which is especially important for observations of diffuse...
"X-ray polarization measurement is a powerful tool for investigating the geometric and magnetic structure of compact stars. However, there are few observations of X-ray polarization because of the difficulty of developing the accurate X-ray polarimeter.
We are now jointly developing the novel hard X-ray (15-40 keV) polarimeter X-Calibur with Washington University in St. Louis.
X-Calibur is a...
We introduce a new concept of astronominal X-ray interferometer consisting simply of grating and pixel detector. We show our latest results reaching subarcsecond resolution with very compact size. The system is highly scalable. We show some examples of application to future missions.
