K. Mitsuda

Energy Spectra of the Soft X-Ray Diffuse Emission in Fourteen Fields Observed with Suzaku

The soft diffuse X-ray emission of twelve fields observed with Suzaku are presented together with two additional fields from previous analyses. All have galactic longitudes 65 deg < l < 295 deg to avoid contributions from the very bright diffuse source that extends at least 30 deg from the Galactic center. The surface brightnesses of the Suzaku nine fields for which apparently uncontaminated ROSAT All Sky Survey (RASS) were available were statistically consistent with the RASS values, with an upper limit for differences of 17 x 10^{-6} c s^{-1} amin^{-2} in R45}-band. The Ovii and Oviii intensities are well correlated to each other, and Ovii emission shows an intensity floor at ~2 photons s^{-1} cm^{-2 str^{-1} (LU). The high-latitude Oviii emission shows a tight correlation with excess of Ovii emission above the floor, with (Oviii intensity) = 0.5 x [(Ovii intensity) -2 LU], suggesting that temperatures averaged over different line-of-sight show a narrow distribution around ~0.2 keV. We consider that the offset intensity of Ovii arises from the Heliospheric solar wind charge exchange and perhaps from the local hot bubble, and that the excess Ovii (2-7 LU) is emission from more distant parts of the Galaxy. The total bolometric luminosity of this galactic emission is estimated to be 4 x 10^{39} erg s^{-1}, and its characteristic temperature may be related to the virial temperature of the Galaxy.

X-Ray and Ultraviolet Spectroscopy of Galactic Diffuse Hot Gas Along the Large Magellanic Cloud X-3 Sight Line

We present Suzaku spectra of X-ray emission in the fields just off the LMC X-3 sight line. O VII, O VIII, and Ne IX emission lines are clearly detected, suggesting the presence of an optically thin thermal plasma with an average temperature of 2.4 ? 106 K. This temperature is significantly higher than that inferred from existing X-ray absorption line data obtained with Chandra grating observations of LMC X-3, strongly suggesting that the gas is not isothermal. We then jointly analyze these data to characterize the spatial and temperature distributions of the gas. Assuming a vertical exponential Galactic disk model, we estimate the gas temperature and density at the Galactic plane and their scale heights as 3.6(2.9, 4.7) ? 106 K and 1.4(0.3, 3.4) ? 10?3 cm?3 and 1.4(0.2, 5.2) kpc and 2.8(1.0, 6.4) kpc, respectively. This characterization can account for all the O VI line absorption, as observed in a Far Ultraviolet Spectroscopy Explorer spectrum of LMC X-3, but only predicts less than one-tenth of the O VI line emission intensity typically detected at high Galactic latitudes. The bulk of the O VI emission most likely arises at interfaces between cool and hot gases.

LiteBIRD: a small satellite for the study of B-mode polarization and inflation from cosmic background radiation detection

LiteBIRD [Lite (Light) satellite for the studies of B-mode polarization and Inflation from cosmic background Radiation Detection] is a small satellite to map the polarization of the cosmic microwave background (CMB) radiation over the full sky at large angular scales with unprecedented precision. Cosmological inflation, which is the leading hypothesis to resolve the problems in the Big Bang theory, predicts that primordial gravitational waves were created during the inflationary era. Measurements of polarization of the CMB radiation are known as the best probe to detect the primordial gravitational waves. The LiteBIRD working group is authorized by the Japanese Steering Committee for Space Science (SCSS) and is supported by JAXA. It has more than 50 members from Japan, USA and Canada. The scientific objective of LiteBIRD is to test all the representative inflation models that satisfy single-field slow-roll conditions and lie in the large-field regime. To this end, the requirement on the precision of the tensor-to-scalar ratio, r, at LiteBIRD is equal to or less than 0.001. Our baseline design adopts an array of multi-chroic superconducting polarimeters that are read out with high multiplexing factors in the frequency domain for a compact focal plane. The required sensitivity of 1.8μKarcmin is achieved with 2000 TES bolometers at 100mK. The cryogenic system is based on the Stirling/JT technology developed for SPICA, and the continuous ADR system shares the design with future X-ray satellites.

ASCA Observations of GRO J1744–28

We report the ASCA results of the bursting X-ray pulsar GRO J1744-28, which was observed in 1996 February and 1997 March. The source flux in the 2-10 keV band was 2.0 × 10-8 ergs s-1 cm2 in 1996 and 5.0 × 10-9 ergs s-1 cm2 in 1997. We detected 12 and 17 type II bursts during the two observations, with mean bursting intervals of about 27 min and 37 min. Each burst is followed by an intensity dip with the depleted flux depending on the burst fluence. The energy spectra are approximated by an absorbed power law with additional structure around 6-7 keV. The constant absorption column, (5-6) × 1022 cm-2, independent of the observation dates and emission phases (persistent, burst, and dip) is interpreted as an interstellar absorption. The source may be actually located near the Galactic center, at a distance of 8.5 kpc. The structure in the energy spectrum at 6-7 keV is most probably due to iron and may be reproduced by a disk line model with additional broadening mechanism.

The detector subsystem for the SXS instrument on the ASTRO-H Observatory

The Soft X-ray Spectrometer (SXS) instrument on the Astro-H observatory is based on a 36 pixel x-ray calorimeter array cooled to 50 mK in a sophisticated spaceflight cryostat. The SXS is a true spatial-spectral instrument, where each spatially discrete pixel functions as a high-resolution spectrometer. Here we discuss the SXS detector subsystem that includes the detector array, the anticoincidence detector, the first stage amplifiers, the thermal and mechanical staging of the detector, and the cryogenic bias electronics. The design of the SXS detector subsystem has significant heritage from the Suzaku/XRS instrument but has some important modifications that increase performance margins and simplify the focal plane assembly. Notable improvements include x-ray absorbers with significantly lower heat capacity, improved load resistors, improved thermometry, and a decreased sensitivity to thermal radiation. These modifications have yielded an energy resolution of 3.5-4.0 eV FWHM at 6 keV for representative devices in the laboratory, giving considerable margin against the 7 eV instrument requirement. We expect similar performance in flight.

Filters and calibration sources for the Soft X-ray Spectrometer (SXS) instrument on ASTRO-H

The SXS instrument is the Soft X-ray micro-calorimeter Spectrometer planned for the Japanese ASTRO-H satellite, scheduled to be launched in 2014. In this paper, the trade off and modelling for the X-ray absorption and optical blocking filters will be described. The X-ray absorption filter will optimize the efficiency for high spectral resolution observations for bright sources at higher energies (notably around the Fe-K line at 6.4 KeV), given the characteristics of the instrument while the optical blocking filter allows X-ray observations of optically bright sources. For this mission a novel type of on-off-switchable X-ray calibration source, using light sensitive photo-cathodes, is being developed, which will be used for gain calibration and contamination monitoring. These sources will be used by both the SXS and SXI (Soft X-ray Imager) instruments and have the capability to be pulsed at millisecond intervals. Details of these sources will also be discussed.

X-Ray Spectrum of Supernova 1993J Observed with ASCA and Its Evolution 8-572 Days after the Explosion

ASCA observations of the supernova in M81, SN 1993J, 8-572 days after the explosion are presented. Utilizing a one-dimensional image-fitting to the Solid-State Imaging Spectrometer (SIS) data, energy spectra of the supernova in 0.5-8 keV are obtained. The spectrum showed drastic softening with a power-law photon index of 0.3-4, while the X-ray intensity decreased from 0.03 to 0.008 counts s-1 SIS-1. The early phase of spectra requires two thermal emission components of different absorption columns if they are fitted with thermal models. The temperatures of two emission components cannot be well constrained with ASCA continuum spectra. However, the detection of an iron K emission line with ASCA and the hard X-ray spectra observed by OSSE on the Compton Gamma-Ray Observatory suggest that the two components have different temperatures: a few keV and about 100 keV. The properties of the two emission components are consistent with emissions from the front and reverse shocks of the supernova explosion. The drastic softening of the X-ray spectra is explained by the decrease of the absorption column density of the reverse shock component and the change of the major contributor to the soft X-ray band from the front to the reverse shocks.

The Digital Processing System for the Soft X-Ray Spectrometer Onboard ASTRO-H —The Design and the Performance—

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.

Calibration sources for the soft x-ray spectrometer instrument on ASTRO-H

The SXS instrument is the Soft X-ray micro-calorimeter Spectrometer planned for the Japanese ASTRO-H satellite, scheduled to be launched in 2014. In this paper we describe the X-ray calibration sources used in this instrument. These sources use light sensitive photo-cathodes to generate electrons, which in turn generate the X-rays. This design has the unique property to allow for fast discrete pulsations of the generated X-rays. This enables the energy scale calibration of the instrument simultaneously with astronomical observations, without adding to the background in the astronomical data. Flight-model sources have been made, and a number of them have been operating in the past several months to monitor their behaviour. Here we report on the characterisation and performance of these sources. In addition, we will elaborate on the nature and expected accuracy of the energy calibration, in relation to the expected stability of the instrument, given the calibration source strength and its mode of operation.

Delays of Optical Bursts in Simultaneous Optical and X-Ray Observations of MXB 1636-53

Observations of simultaneous optical and X-ray bursts from 4U/MXB 1636-53 were made using the Hakucho burst monitor system and optical telescopes at the European Southern Observatory during 1979 and 1980. The six best cases among the 10 coinciding observations are analyzed in terms of a model in which the optical emission is the result of reprocessing of X-rays (through blackbody heating). From this analysis, the temperature (spatially averaged) and size of a reprocessor, and the smearing and delay of the optical bursts are obtained. For the maximum temperatures of the optical reprocessor, the values differ from burst to burst, ranging from about 3 x 10 to the 4th to about 10 to the 5th K. The present analysis suggests that the size of the reprocessor varies by a factor of a few. For the smearing of the optical bursts an upper limit of a few seconds is derived. The most important result of this analysis is that the delay times are not the same for all bursts. The possible constraints which these results put on a low-mass binary model of this burst source are discussed.