田代 信

© 2018 SPIE. The ASTRO-H mission was designed and developed through an international collaboration of JAXA, NASA, ESA, and the CSA. It was successfully launched on February 17, 2016, and then named Hitomi. During the in-orbit verification phase, the on-board observational instruments functioned as expected. The intricate coolant and refrigeration systems for soft X-ray spectrometer (SXS, a quantum micro-calorimeter) and soft X-ray imager (SXI, an X-ray CCD) also functioned as expected. However, on March 26, 2016, operations were prematurely terminated by a series of abnormal events and mishaps triggered by the attitude control system. These errors led to a fatal event: the loss of the solar panels on the Hitomi mission. The X-ray Astronomy Recovery Mission (or, XARM) is proposed to regain the key scientific advances anticipated by the international collaboration behind Hitomi. XARM will recover this science in the shortest time possible by focusing on one of the main science goals of Hitomi,"Resolving astrophysical problems by precise high-resolution X-ray spectroscopy".1This decision was reached after evaluating the performance of the instruments aboard Hitomi and the mission's initial scientific results, and considering the landscape of planned international X-ray astrophysics missions in 2020's and 2030's. Hitomi opened the door to high-resolution spectroscopy in the X-ray universe. It revealed a number of discrepancies between new observational results and prior theoretical predictions. Yet, the resolution pioneered by Hitomi is also the key to answering these and other fundamental questions. The high spectral resolution realized by XARM will not offer mere refinements; rather, it will enable qualitative leaps in astrophysics and plasma physics. XARM has therefore been given a broad scientific charge: "Revealing material circulation and energy transfer in cosmic plasmas and elucidating evolution of cosmic structures and objects". To fulfill this charge, four categories of science objectives that were defined for Hitomi will also be pursued by XARM; these include (1) Structure formation of the Universe and evolution of clusters of galaxies; (2) Circulation history of baryonic matters in the Universe; (3) Transport and circulation of energy in the Universe; (4) New science with unprecedented high resolution X-ray spectroscopy. In order to achieve these scientific objectives, XARM will carry a 6 × 6 pixelized X-ray micro-calorimeter on the focal plane of an X-ray mirror assembly, and an aligned X-ray CCD camera covering the same energy band and a wider field of view. This paper introduces the science objectives, mission concept, and observing plan of XARM.

The Soft X-ray Spectrometer (SXS) onboard the Astro-H (Hitomi) orbiting x-ray observatory featured an array of 36 silicon thermistor x-ray calorimeters optimized to perform high spectral resolution x-ray imaging spectroscopy of astrophysical sources in the 0.3-12 keV band. Extensive pre-flight calibration measurements are the basis for our modeling of the pulse-height-energy relation and energy resolution for each pixel and event grade, telescope collecting area, detector efficiency, and pulse arrival time. Because of the early termination of mission operations, we needed to extract the maximum information from observations performed only days into the mission when the onboard calibration sources had not yet been commissioned and the dewar was still coming into thermal equilibrium, so our technique for reconstructing the per-pixel time-dependent pulse-height-energy relation had to be modified. The gain scale was reconstructed using a combination of an absolute energy scale calibration at a single time using a fiducial from an onboard radioactive source, and calibration of a dominant time-dependent gain drift component using a dedicated calibration pixel, as well as a residual time-dependent variation using spectra from the Perseus cluster of galaxies. The energy resolution was also measured using the onboard radioactive sources. It is consistent with instrument-level measurements accounting for the modest increase in noise due to spacecraft systems interference. We use observations of two pulsars to validate our models of the telescope area and detector efficiency, and to derive a more accurate value for the thickness of the gate valve Be window, which had not been opened by the time mission operations ceased. We use observations of the Crab pulsar to refine the pixel-to-pixel timing and validate the absolute timing.

The bow shocks of runaway stars with strong stellar winds of over 2000 km s(-1) can serve as particle acceleration sites. The conversion from stellar wind luminosity into particle acceleration power has an efficiency of the same order of magnitude as those in supernova remnants, based on the radio emission from the bow shock region of runaway star BD +43 3654 (Benaglia et al. 2010, A&A, 517, L10). If this object exhibits typical characteristics, then runaway star systems can contribute a non-negligible fraction of Galactic cosmic-ray electrons. To constrain the maximum energy of accelerated particles from measurements of possible non-thermal emissions in the X-ray band, Suzaku observed BD +43 3654 in 2011 April with an exposure of 99 ks. Because the onboard instruments have a stable and low background level, Suzaku detected a possible enhancement over the background of 7.6 +/- 3.4 counts arcmin(-2) at the bow shock region, where the error represents the 3 a statistics only. However, the excess is not significant within the systematic errors of non-X-ray and cosmic-ray backgrounds of the X-ray Imaging Spectrometer, which are +/- 6.0 and +/- 34 counts arcmin(-2), respectively, and the 3 sigma upper limit in the X-ray luminosity from the shock region, which is 1.1 x 10(32) erg s(-1) per 41.2 arcmin(2) in the 0.5 to 10 keV band. This result leads to three conclusions: (1) a shock-heating process is inefficient on this system; (2) the maximum energy of electrons does not exceed similar to 10 TeV, corresponding to a Lorentz factor of less than 10(7); and (3) the magnetic field in the shock acceleration site might not be as turbulent as those in pulsar wind nebulae and supernova remnants.

We present the development status of the Pulse Shape Processor (PSP), which is the on-board digital electronics responsible for the signal processing of the X-ray microcalorimeter spectrometer instrument (the Soft X-ray Spectrometer; SXS) for the ASTRO-H satellite planned to be launched in 2014. We finished the design and fabrication for the engineering model, and are currently undertaking a series of performance verification and environmental tests. In this report, we summarize the results obtained in a part of the tests completed in the first half of this year. © 2012 SPIE.

We report the design and the performance of the engineering model of the digital signal processing system called the Pulse Shape Processor (PSP) for the Soft X-ray Spectrometer (SXS) onboard the ASTRO-H satellite. The SXS employs an X-ray microcalorimeter system, in which X-ray photons are detected as a heat pulse due to photoelectric absorption. The pixelized HgTe absorbers are cooled down to 50 mK. The required energy resolution is 7 eV (FWHM) at 6 keV. Since the data link to the satellite data recorder is limited to 200 kbit s -1, the onboard digital processor PSP plays a critical role in achieving the required resolution. The PSP is also the rate-limiting factor for other performance of the SXS, such as maximum count rate and energy range. In this paper, we show the design of the PSP, and show the performance based on a series of laboratory tests performed with the engineering models of the detector and the analog readout electronics. We found that (1) the PSP can register energy in the 0.07-18 keV band [energy range], (2) the energy resolution of the engineering model system, including the detector, analog electronics, and the PSP, is 4.8-5.7 eV at 5.9 keV [energy resolution], and (3) the PSP has sufficient processing power to handle a point-like source fainter than 0.3 Crab [maximum count rate]. These results are expected to be quite similar to those with the flight model, thus the results will be useful for the observation planning using the SXS. © 2012 IEEE.

The Pulse Shape Processor is a digital signal processing electronics for the microcalorimeter instrument onboard ASTRO-H. Receiving digitized waveform (14 bit, 12.5 kHz sample) from 2×18 channels, two identical units of PSP-A and -B trigger X-ray events, assign five kinds of event grade, and perform optimal filtering to measure energy deposit on the 6 × 6 microcalorimeter pixels. One unit of PSP is composed of one FPGA board and two CPU boards. This paper describes the event processing algorithm to fulfill requirements for the signal processing, and task sharing between FPGA and CPU. © Springer Science+Business Media, LLC 2012.

A digital signal processing system for the X-ray microcalorimeter array (SXS) is being developed for the next Japanese X-ray astronomy satellite, ASTRO-H. The SXS digital signal processing system evaluates each pulse by an optimal filtering process. For the ASTRO-H project, we decided to employ digital electronics hardware, which includes a digital I/O board based upon FPGAs, and a separate CPU board. It is crucially important for the FPGA to be able to detect the presence of an "secondary" pulses on the tail of an initial pulse. In order to detect the contaminating pulses, we have developed a new finite impulse response filter, to compensate for the undershoot in the derivative. By employing the filter it is possible for FPGA to detect the secondary pulse very close the first pulse, and to reduce the load of the CPU in the secondary pulse searching process. © 2009 American Institute of Physics.

A Suzaku observation of a giant radio galaxy, 3C 326, which has a physical size of about 2 Mpc, was conducted on 2008 January 19-21. In addition to several X-ray sources, diffuse emission was significantly detected and associated with its west lobe, but the east lobe was contaminated by an unidentified X-ray source WARP J1552.4+2007. After careful evaluation of the X-ray and non-X-ray background, the 0.4-7 keV X-ray spectrum of the west lobe is described by a power-law model modified with the Galactic absorption. The photon index and 1 keV flux density were derived as Gamma = 1.82(-0.24)(+0.26) +/- 0.04 and S-X = 19.4(-3.2)(+3.3) +/- 3.0 nJy, respectively, where the first and second errors represent the statistical and systematic ones. The diffuse X-rays were attributed to be inverse Compton (IC) radiation by the synchrotron radio electrons scattering off the cosmic microwave background photons. This radio galaxy is the largest among those with lobes detected through IC X-ray emission. A comparison of the radio to X-ray fluxes yields the energy densities of electron and magnetic field as u(e) = (2.3 +/- 0.3 +/- 0.3) x 10(-13) erg cm(-3) and u(m) = (1.2(-0.1)(+0.2) +/- 0.2) x 10(-14) erg cm(-3), respectively. The galaxy is suggested to host a low-luminosity nucleus with an absorption-corrected 2-10 keV luminosity of < 2 x 10(42) erg s(-1), together with a relatively weak radio core. The energetics in the west lobe of 3C 326 were compared with those of moderate radio galaxies with a size of similar to 100 kpc. The west lobe of 3C 326 is confirmed to agree with the correlations for the moderate radio galaxies, u(e) proportional to D-2.2 +/- 0.4 and u(m) proportional to D-2.4 +/- 0.4, where D is their total physical size. This implies that the lobes of 3C 326 are still being energized by the jet, despite the current weakness of the nuclear activity.

One of the most prominent, yet controversial associations derived from the ensemble of prompt-phase observations of gamma-ray bursts (GRBs) is the apparent correlation in the source frame between the peak energy (E-peak) of the nu F(nu) spectrum and the isotropic radiated energy, E-iso. Since most GRBs have E-peak above the energy range (15-150 keV) of the Burst Alert Telescope (BAT) on Swift, determining accurate E-peak values for large numbers of Swift bursts has been difficult. However, by combining data from Swift/BAT and the Suzaku Wideband All-Sky Monitor (WAM), which covers the energy range from 50 to 5000 keV, for bursts which are simultaneously detected, one can accurately fit E-peak and E-iso and test the relationship between them for the Swift sample. Between the launch of Suzaku in 2005 July and the end of 2009 April, there were 48 GRBs that triggered both Swift/BAT and WAM, and an additional 48 bursts that triggered Swift and were detected by WAM, but did not trigger. A BAT-WAM team has cross-calibrated the two instruments using GRBs, and we are now able to perform joint fits on these bursts to determine their spectral parameters. For those bursts with spectroscopic redshifts, we can also calculate the isotropic energy. Here, we present the results of joint Swift/BAT-Suzaku/WAM spectral fits for 91 of the bursts detected by the two instruments. We show that the distribution of spectral fit parameters is consistent with distributions from earlier missions and confirm that Swift bursts are consistent with earlier reported relationships between E-peak and isotropic energy. We show through time-resolved spectroscopy that individual burst pulses are also consistent with this relationship.