It is important to enhance a tight collaboration between Japan and China on the X-ray astronomy using our current-and-future X-ray observatories. The goals of the workshop are to review current status of X-ray missions in Japan and China and their science results, to summarize the knowledge on the instrument calibration, analyses software and user support, and to search for the collaboration plan between Japan and Chine on the data analyses and coordinated observations. The workshop also covers the lectures for beginners of the analyses of the Suzaku/Hitomi and the Insight-HXMT (慧眼) missions.
This workshop is supported by JAXA and Hiroshima University/CORE-U
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 indicate that the Ca abundance is generally enhanced compared with the other elements, which is consistent with a recent study using the Solar Assembly for X-rays on the Mercury MESSENGER spacecraft (Dennis et al. 2015). We also present flare-to-flare variations of elemental abundances. Finally, we briefly discuss future prospects for HXMT and XRISM.
"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 energy distribution of the accelerated electrons is also power-law type. In addition, Ishikawa et al. (2011) describes that the X-ray peak of a foot-point delays about 10 sec from that of the loop-top emission due to the transit time of the accelerated electrons from the loop-top to the foot-points. However, more careful treatments of the pile-up effect on finer time bins on the analyses are needed to investigate the detailed transfer of the accelerated electrons.
We performed time-resolved spectroscopy of the solar flares observed by the Suzaku HXD-WAM, which is the BGO scintillator surrounding the Suzaku hard X-ray detector and was used as all sky monitor in the 50-5000 keV (Yamaoka et al. 2009). In our analyses, we studied the time evolution of photon indexes and the flux every 1 second, after taking into account pile-up effects using the Geant4-based pile-up simulator (Yasuda et al. 2015). As a result, we found that the peak time of the flux in the high energy band (520-5000 keV) is later than that in the low energy band (50-110 keV). This result supports the picture described in Ishikawa et al. (2011) that the accelerated electrons at the loop-top precipitate into the foot-points after several seconds.
 Masuda et al. 1994, Nature, 371, 495
 Ishikawa et al. 2011, The Astrophysical Journal, 737, 48
 Yamaoka et al. 2009, Publications of the Astronomical Society of Japan, 61, 35
 Yasuda et al. 2015, Publications of the Astronomical Society of Japan, 67, 41"
"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 one of the reasons may be nuclear gamma-ray lines emmisions, the break-up is also found in electron-dominated events, i.e., flares showing no nuclear gamma-ray lines. Therefore, at least the spectral break-up of electron-dominated flares is caused by intrinsic feature of energy distribution of source electrons. In this presentaion, the results of analysis about spectrum break-up using the Suzaku Wide-band All-sky Monitor(WAM) are summarized. The Suzaku WAM is the BGO anti-coincidence shields of the Hard X-ray Detectors (HXD) facing four sides. The WAM is also used for the all sky monitor in the 50 to 5,000 keV band with the large effective area of 400 cm^2 at 1 MeV per side. Among 756 solar flares detected by WAM, 14 flares are found to have non-single power-law spectra, indicating electron break-up phenomena or contamination of gamma-ray lines. The properties of these flares will be presented.
 Share et al. 2003, Astrophysical Journal Letters, 595, L85
 Kong et al. 2013, Astrophysical Journal, 774, 140
 Li et al. 2013, Astrophysical Journal, 769, 22
 Yamaoka et al. 2009, Publications of Astronomical Society of Japan, 61, 35"
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 in definition less emissive and can only be lighted up with the incident soft X-rays. This probe, however, falls short in BH XRBs, but fits well the thermal nuclear flashes occurring on the NS surface. We therefore took the type-I burst to probe the accompanied disk/corona evolution and obtained an atoll sample which shows that corona can be cooled off by the burst shower. Further studies suggest that, a variety of issues apart from corona can be addressed as well by taking this probe. The current shortage in observations at hard X-rays is the relatively poor statistics of the data, which can be diminished by the HXMT mission.
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 up observation. This X-ray outburst of Swift J0243.6+6124 continued for about 4 months, and the flux reached over 5 Crab at the peak. The source distance was estimated to be 〜7kpc with the GAIA DR2. This suggests that the X-ray luminosity reached ten times the Eddington luminosity for a 1.4 solar mass neutron star. We present the result of MAXI-GSC data analysis around the flux peak. X-ray spectrum softened as the luminosity increased, and then hardened as it faded. The folded pulse profile exhibited energy dependence. We also investigated the relation between the luminosity and the spin-up rate and found that the positive correlation all the way up to ten times the Eddington luminosity. Assuming the power-laws accretion-torque model proposed by Ghosh & Lamb(1979), the surface magnetic filed is estimated to be about 10 to the 12th power Gauss.
"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 2016 October. In the timing analysis, we found the rotation period on 2016 October was 5.2267(1) s and the period derivative fluctuated more than 50 % in these 20 years. We also discovered the shape of pulse profiles changes at ~10 keV. In the spectral analysis, we determined the hard-tail photon index very precisely, Γ = 1.13(8), and also discovered the photon index varies depending on the rotation phase. Furthermore, we discuss the potentiality of HXMT to target SGR 1900+14, making full use of its broad-band observation up to 250 keV."
"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 two more classes (Klein-Wolt et al. 2002; Hannikanien et al. 2005). However, transitions among variability classes of GRS 1915+105 have not been well studied yet.
In this work, we classified 9 years’ activity of GRS 1915+105 into three branches in the hardness-intensity diagram drawn with the MAXI/GSC and Swift/BAT data. In the X-ray light curve, we identified the time periods that constitute each of these branches. We discuss the X-ray emission components present in these branches and transitions between them."
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, and has been spinning up since 2002, as already reported. The spin-up/down rate and the 3–12 keV flux, determined every 250 d, showed a clear negative correlation, which can be successfully explained by the accretion torque model proposed by Ghosh and Lamb (1979, ApJ, 234, 296). When the mass, radius, and distance of the neutron star were allowed to vary over a range of 1.0–2.4 solar masses, 9.5–15 km, and 0.77–0.85 kpc, respectively, the magnetic field strength of B = (4–25) × 10^13 G gave the best fits to the observations. In contrast, the observed results cannot be explained by the values of B ~ 10^12 G previously suggested for X Persei, as long as the mass, radius, and distance are required to take reasonable values. Assuming a distance of 0.81 ± 0.04 kpc as indicated by optical astrometry, the mass of the neutron star is estimated as M = 2.03 ± 0.17 solar masses.
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 structure and optical thickness, which are called as high/soft and low/hard states. LMC X-3 is a BHB with a low absorption column density and possible to study the emission of the accretion disk well below 1 keV. It was observed three times by X-ray satellite “Suzaku”. XIS and HXD detected the emission from 0.5-30 keV. We analyzed the three observations with referring to the previous method (Kubota et al. 2010). Among the three datasets, the luminosity changed from 2.3% to 13.5% of the Eddington luminosity. The brighter spectra show the dominant disk emission observed in the high/soft state, while the faintest one has the relatively bright power-law emission in the low/hard (or intermediate) state. With applying the multi-color disk model, we obtained that the disk inner radius moves away in the faintest dataset. In this presentation, we report the detail comparison of the three observations and discuss the deviation from the simple multi-color disk model.
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 emission. The most important feature of the GDXE is prominent lines of Fe at 6.40 (Ka), 6.68 (Hea), and 6.97 (Lya) keV. A Chandra deep observation at (l, b)=(0.0 deg, -1.4 deg) found that ~80% of the Fe emission is resolved into faint point sources, mainly magnetic Cataclysmic Variables (mCV). However, the fact was obtained only at the one position, which belongs to the bulge area, not to the center or ridge. And also detailed study on the Fe line band has not been performed yet. Therefore, using the Suzaku archive data, we have investigated the GDXE concentrating on the Fe line band by trying to fitting with spectral modeling of candidate point sources (AB, mCV, non-mCV). Although the bulge spectrum can be fitted by the point source model, non-mCVs dominate by ~70%. For the other areas (center and ridge), any combination of the point source models fail to fit the GDXE spectrum. Other origins than the candidate point sources should contribute to the GDXE. We will discuss origins of the GDXE.
"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 particles.
We targeted 3FGL J2004.4+3338, Fermi-LAT unidentified gamma-ray source with the shell-like radio morphology with VLA and a B-star, so it can be a runaway star.
In this study, the shell-like X-ray morphology with a radius of 15"" was found with Chandra. In this paper, we report on the spectral information of the source and possible observations with XRISM and HXMT."
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 keV, which is consistent with a radiative recombination continuum generated by free-bound transition of electron capture by fully ionized Fe (Fe XXVI RRC).The Fe XXVI RRC indicates the plasma has larger fraction of Fe XXVII ions than that of CIE, suggesting recombining plasma (RP).A possible scenario is photoionization; X-rays from high-temperature plasma ionize low-temperature plasma.We construct a RP model based on the photo-ionization scenario to fit the X-ray spectrum. Then, the 9-10 keV residuals are improved significantly.This is the first discovery of the RP from mCVs.
"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 work, using the optical/UV and X-ray data from Swift UVOT and XRT we have performed PSF photometry in optical/UV to estimate the contribution of AGN and host galaxy in the total observed emission. From the long-term observations, the optical/UV and X-ray fluxes gradually increase as gamma-ray emission and reddening which mean that those components could be contributed to the jet emission. Additionally, the observed steep peak in the optical/UV SED may suggest an accretion disk origin of the emission. Similar observed correlation of optical and UV flux with the X-ray flux indicates that the X-rays can be attributed to the accretion disk and or corona."
"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 structure and its physical condition because we observe not only a direct component but also a reprocessed component caused by the torus. Characteristics of the Compton shoulder, which is a Compton scattered broad structure adjacent to the emission lines, is a powerful tool to investigate the structure of the torus. Hence, developing a precise spectral model to reproduce the structure of the Compton shoulder and X-ray observations with an enough high spectral resolution are crucial.
We analyzed the spectral shape of the Compton shoulder around the neutral Fe-Kα line of the Compton-thick type Ⅱ Seyfert nucleus of the Circinus galaxy. We applied our X-ray reflection spectral model based on Monte Carlo method to Chandra High Energy Transmission Grating data, and we successfully reproduced the structure of the Compton shoulder and constrained various spectral parameters, such as a column density, inclination angle and metal abundance independently, using the spectral data only around the Fe-Kα emission line. The obtained column density and inclination angle are consistent with that of reported by previous studies. In addition, we could put a constraint on the metal abundance of the torus for the smooth and clumpy torus cases to be 1.75 (+0.19, -0.17) and 1.74 (±0.16) solar abundance, respectively, which could give useful information for the star formation history around 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 mechanism of jet ejection. SEDs of FSRQ are usually modeled by synchrotron self Compton model plus external Compton model. However, the model calculation takes much time and thus parameter estimation has some problems. Therefore, in order to calculate the model as fast as possible, we referred to the approximation formula of Finke et al. 2016. Fast calculation enables us to perform Markov chain Monte-Carlo (MCMC), which is a powerful approach to constrain model parameters.
We applied our MCMC modeling to a famous FSRQ 3C279 which shows a change of SED around flares as shown in Hayashida et al. 2015. In this poster, we report emission model of FSRQs, calculation technique and some preliminary result of how changing jets parameters."
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 the cool-core cluster Abell 1437 observed with XMM-Newton.
"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. From the entropy maps, we find that this galaxy cluster merged 3 billion years ago. This galaxy cluster has a rare swirl structure in the X-ray band. Our results confirm that this structure is related to ram pressure stripping.
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 investigate the prompt emission systematically. Additionally, it is thought that the prompt emission may include the thermal radiation from the explosion in the photosphere, however existence of the thermal component in the prompt emission have been largely uncertain yet. In this study, we carried out the timing analysis of Swift/XRT -Swift/BAT -SUZAKU/WAM joint spectra of GRB100725B. The data has enough statistics to determine spectrum parameters of the Band function. Most of the spectra was well described by Band function, but some of them deviate from typical Band function; their high energy spectral index (β) is larger than -2. Therefore, we examined additional thermal component in order to search for the radiation component from the photosphere. In this paper, we showed the broad band XRT-BAT-WAM joint spectra analysis and derived physics of the prompt emission, and discuss possible joint observation and expected results with Swift/XRT-Swift/BAT and HXMT.
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 used to trace the dark gas, the procedure has not been established yet, introducing the uncertainty of the ISM gas distribution. Therefore, we aim to accurately estimate the column density distribution of the ISM gas in the Milky Way using Gamma-Ray Burst (GRB) afterglow data. Because the X-ray absorption of the afterglow does not depend on the gas states such as the temperature, we can accurately estimate the ISM gas column density. For this purpose, we analyzed GRB afterglow data by Swift/XRT toward various directions of the Milky Way and measured the total column density. We then compared several models of the Galactic ISM gas column density with the intrinsic column density (total minus Galactic ISM gas column density); the intrinsic column density should not depend on the Galactic gas column density.Compared to the previous study (Willingale et al. 2013), we employed newly available dust emission models (radiance and optical depth at 353 GHz) by Planck satellite and increased the number of GRB events by more than a factor of two(about 1000 in total).We divided GRB data into several groups by their position and the GRB type (short-GRB or long-GRB), and applied a correction on the Galactic column density model with the dust temperature if necessary.In this contribution, we report details of the analysis and obtained results.
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 background as shown by the Hitomi Hard X-ray Imager (HXI), FORCE will provide 1-order of magnitude better sensitivity in 10-80 keV compared to NuSTAR and Hitomi/HXI. In this talk, we will present current status of the mission development, as well as driving science case studies, such as, search for deeply obscured AGNs and isolated black holes, SNRs' and clusters of galaxies' shock structures, and particle accelerations therein.
"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 consumption, we synchronize time information of each satellite by using a global positioning system, and plan to use large-area CsI(Tl) scintillators which provide a high light output and readout by multi-pixel photon counters (MPPC). We plan to use one of the latest-model MPPCs provided by Hamamatsu Photonics, namely, S13360-6050CS, which have an active area of 6×6 mm^2.
We compared the performance of two scintillators of different sizes (150×75×5 mm^3, 100×75×5 mm^3); the bigger one is the maximum size that can be mounted on a three-unit satellite we are planning to apply. We found that the difference of light yield was only ~13 %. We also tested two-MPPC readout to improve the energy threshold and uniformity, and confirmed the almost same energy threshold as one-MPPC readout of ~10 keV at 25 ℃ and energy resolution got better by 7 % thanks to the improved uniformity. Then we investigated the optimum position of two-MPPCs on the scintitllator by using ray-tracing Monte Carlo simulator, and found that symmetrical configurations against to the center of the scintillator gives the best performance of light yield. In this contribution, we will present a detail of experimental and simulation studies about the detectors for our CAMELOT mission."
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 sources. In this work, we investigated background produced by atmospheric neutrons, which has a significant contribution to the entire non-X-ray background but has been poorly understood, by using data during the earth occultations and blank sky
observations. We found that the background rate had positive correlation with the cosmic-ray flux in orbit, suggesting that the background was dominated by the atmospheric neutrons. Using this correlation, we extracted the flux, the spectrum and their spatial variations of the neutron background. We also made a comparison between the extracted neutron background measurement and estimates by our Monte-Carlo simulations."
"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 balloon-borne Compton-based polarimeter with high-sensitivity by attaching the X-ray telescope and launched from McMurdo (Antarctic) in Dec. 2018. We can observe the X-ray polarization by detecting the photons that undergo Compton scattering in a beryllium with a subsequent photoelectric absorption in a CZT detector.
At the flight in 2018, we are planning to observe the high mass X-ray binary Vela X-1 and will investigate the radiation direction of X-ray for the magnetic field.
We are also planning to launch the upgraded X-Calibur in 2021 by using the X-ray telescope that originally developed by Japan for the FFAST mission.
The detection efficiency is expected to be improved up to a factor of 10 by this upgrade. The IXPE satellite that observes the soft X-ray (2-8keV) image with polarization is planned for launch in 2021 and we will observe the same object in the same time.
In our poster, we present estimation of the improvement of minimum detectable polarization for X-Calibur 2018 to 2021 flight."
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.