Noriko YAMASAKI

Multiplexed readout of TES (Transition Edge Sensor) signals is one of the key technologies needed to realize large format arrays of microcalorimeters in future X-ray missions. In the FDM (Frequency-Domain Multiplexing) approach using MHz biasing frequencies, a wide band-width FLL (Flux Locked Loop) circuit is essential to compensate the phase delay between the TES sensor and the room temperature circuits. An analog feedback circuit using a lock-in amplifier technique and phase shifters with a very low noise pre-amplifier is being developed. This circuit will be tested with an actual TES array and an 8-input SQUID in the EURECA project.

The Soft X-ray Spectrometer (SXS) onboard the NeXT (New exploration X-ray Telescope) is an X-ray spectrometer utilizing an X-ray microcalorimeter array. Combined with the soft X-ray telescope of 6 m focal length, the instrument will have a ∼ 290cm2 effective at 6.7 keV. With the large effective area and the energy resolution as good as 6 eV (FWHM), the instrument is very suited for the high-resolution spectroscopy of iron K emission line. One of the major scientific objectives of SXS is to determine turbulent and/or macroscopic motions of the hot gas in clusters of galaxies of up to z ∼ 1. The instruments will use 6 × 6 or 8 × 8 format microcalorimeter array which is similar to that of Suzaku XRS. The detector will be cooled to a cryogenic temperature of 50 mK by multi-stage cooling system consisting of adiabatic demagnetization refrigerator, super fluid He, a 3He Joule Thomson cooler, and double-stage Stirling cycle cooler.

Spatially resolved X-ray spectroscopy with high spectral resolution allows the study of astrophysical processes in extended sources with unprecedented sensitivity. This includes the measurement of abundances, temperatures, densities, ionisation stages as well as turbulence and velocity structures in these sources. An X-ray calorimeter is planned for the Russian mission Spektr Rontgen-Gamma (SRG), to be launched in 2011. During the first half year (pointed phase) it will study the dynamics and composition of of the hot gas in massive clusters of galaxies and in supernova remnants (SNR). During the survey phase it will produce the first all sky maps of line-rich spectra of the interstellar medium (ISM). Spectral analysis will be feasible for typically every 5 degrees x 5 degrees region on the sky. Considering the very short time-scale for the development of this instrument it consists of a combination of well developed systems. For the optics an extra eROSITA mirror, also part of the Spektr-RG payload, will be used. The detector will be based on spare parts of the detector flown on Suzaku combined with a rebuild of the electronics and the cooler will be based oil the design for the Japanese mission NeXT, In this paper we will present the science and give an overview of the instrument.

X-ray reflectivity of an ultra light-weight X-ray optic using MEMS technologies was measured in two different energies (0.28 keV and 1.49 keV). The obtained reflectivities can be understood by considering the mirror surface structures.

The SXS (Soft X-ray Spectrometer) onboard the coming Japanese X-ray satellite NeXT (New Exploration Xray Telescope) and the SXC (Spectrum-RC X-ray Calorimeter) in Spectrum-RG mission are microcalorimeter array spectrometers which will achieve high spectral resolution of similar to 6 eV in 0.3-10.0 keV energy band. These spectrometers are well-suited to address key problems in high-energy astrophysics. To achieve these high spectral sensitivities, these detectors require to be operated under 50 mK by using very efficient cooling systems including adiabatic demagnetization refrigerator (ADR,). For both missions, we propose a two-stage series ADR as a cooling system below 1 K, in which two units of ADR consists of magnetic cooling material, a superconducting magnet, and a heat switch are operated step by step. Three designs of the ADR are proposed for SXS/SXC. In all three designs, ADR can attain the required hold time of 23 hours at 50 mK and cooling power of 0.4 mu W with a low magnetic fields (1.5/1.5 Tesla or 2.0/3.0 Tesla) in a small configuration (180 mm phi x 319 mm in length). We also fabricated a new portable refrigerator for a, technology investigation of two-stage ADR. Two units of ADR have been installed at the bottom of liquid He tank. By using this dewar, important technologies such as an operation of two-stage cooling cycle, tight temperature control less than 1 mu K (in rms) stability, a, magnetic shielding, saltpills, and gas-gap heat switches are evaluated.

The EURECA (EURopean-JapanEse Calorimeter Array) project aims to demonstrate the science performance and technological readiness of an imaging X-ray spectrometer based on a micro-calorimeter array for application in future X-ray astronomy missions, like Constellation-X and XEUS. The prototype instrument consists of a 5 x 5 pixel array of TES-based micro-calorimeters read out by by two SQUID-amplifier channels using frequency-domain-multiplexing (FDM). The SQUID-amplifiers are linearized by digital base-band feedback. The detector array is cooled in a cryogen-free cryostat consisting of a pulse tube cooler and a two stage ADR. A European-Japanese consortium designs, fabricates, and tests this prototype instrument. This paper describes the instrument concept, and shows the design and status of the various sub-units, like the TES detector array, LC-filters, SQUID-amplifiers, AC-bias sources, digital electronics, etc.

Our recent development of transition-edge sensor (TES) microcalorimeters for future X-ray astronomical missions such as DIOS is reported. In-house micromaching processes has been established aiming at prompt fabrication of TES devices. With a single-pixel TES microcalorimeter and an Au absorber, the energy resolution of 4.8 eV at 5.9 keV is achieved. 16 x 16 pixel arrays of TES microcalorimeters are successfully fabricated by using deep dry etching technique. The energy resolution is 11 eV and 26 eV with and without all Au absorber; respectively. The worse energy resolution than a single-pixel TES is due to large decrease of TES sensitivity and increase of transition temperature after etching. The reason for these phenomena is under investigation. In parallel, mushroom-type Au absorber structures are being tested. Furthermore, to precisely measure TES sensitivities and heart capacity, an experimental setup for impedance measurements is established.

We present the current status of a small X-ray mission DIOS (Diffuse Intergalactic Oxygen Surveyor), consisting of a 4-stage X-ray telescope and an array of TES microcalorimeters, cooled with mechanical coolers, with a total weight of about 400 kg. The mission will perform survey observations of warm-hot intergalactic medium using OVII and OVIII emission lines. with the energy coverage Lip to 1.5 keV. The wide field of view of about. 50 ' diameter, superior energy resolution close to 2 eV FWHM, and very low background will together enable us a, wide range of science for diffuse X-ray sources. We briefly describe the. current status of the development of the satellite, and the subsystems.

The NeXT (New exploration X-ray Telescope). the new Japanese X-ray Astronomy Satellite following Suzaku, is all international X-ray mission which is currently planed for launch in 2013. NeXT is a combination of wide band X-ray spectroscopy (3-80 keV) provided by multi-layer coating, focusing hard X-ray mirror and hard X-ray imaging detectors, and high energy-resolution soft X-ray spectroscopy (0.3-10 keV) provided by thin-foil X-ray optics and a micro-calorimeter array. The mission will also carry an X-ray CCD camera as a focal plane detector for a soft, X-ray telescope and a non-focusing soft, gamma-ray detector. With these instruments, NeXT Covers very wide energy range from 0.3 keV to 600 keV. The micro-calorimeter system will be developed by international collaboration lead ISAS/JAXA and NASA. The simultaneous broad bandpass, coupled with high spectral resolution of Delta E similar to 7 eV by the micro-calorimeter will enable a wide variety of important, science themes to be pursued.

We studied the properties of the intra-cluster medium (ICM) in two clusters of galaxies (AWM 7 and Abell 1060) and two groups (HCG 62 and NGC 507) observed with the 5th Japanese X-ray astronomical satellite, Suzaku. We measured for the first time precise cumulative ICM metal masses and distributions for various elements, such as O, Ne, Mg, Si, S, Fe, within 0.1 and ∼0.3 r180. Because of the good XIS sensitivity to emission lines, especially below 2 keV, we directly measured O and Mg line intensities and obtained abundances. Comparing our results with supernova nucleosynthesis models, the number ratio of Type II (SNe II) to Type Ia (SNe Ia) is estimated to be ∼3.5, assuming the metal mass in the ICM is represented by the sum of products synthesized in SNe Ia and SNe II. Normalized by the K-band luminosities of present galaxies, and including the metals in stars, the integrated number of past SNe II explosions is estimated to be close to or somewhat higher than the star formation rate determined from Hubble Deep Field observations.

Status of the Suzaku survey for non-thermal hard X-ray emission from clusters of galaxies is reported. Utilizing the lowest and stable detector background of both the HXD and the XIS instruments, Suzaku achieved high sensitivity for hard X-ray diffuse emission survey. Deep (&gt 100 ks) observations of a merging cluster A3376 present an upper limit of ∼ 10 -11 erg cm-2 s_1 in the 15-50 keV band (Kawano et al. and this work). Other analyses using the HXD (Centaurus and A1060, Kitaguchi et al.) and the XIS (HCG 62, Tokoi et al.) are also briefly summarized.

How structures of various scales formed and evolved from the early Universe up to present time is a fundamental question of astrophysics. EDGE1will trace the cosmic history of the baryons from the early generations of massive stars by Gamma-Ray Burst (GRB) explosions, through the period of galaxy cluster formation, down to the very low redshift Universe, when between a third and one half of the baryons are expected to reside in cosmic filaments undergoing gravitational collapse by dark matter (the so-called warm hot intragalactic medium). In addition EDGE, with its unprecedented capabilities, will provide key results in many important fields. These scientific goals are feasible with a medium class mission using existing technology combined with innovative instrumental and observational capabilities by: (a) observing with fast reaction Gamma-Ray Bursts with a high spectral resolution (R - 500). This enables the study of their (star-forming) environment and the use of GRBs as back lights of large scale cosmological structures (b) observing and surveying extended sources (galaxy clusters, WHIM) with high sensitivity using two wide field of view X-ray telescopes (one with a high angular resolution and the other with a high spectral resolution). The mission concept includes four main instruments: a Wide-field Spectrometer with excellent energy resolution (3 eV at 0.6 keV), a Wide-Field Imager with high angular resolution (HPD 15") constant over the full 1.4 degree field of view, and a Wide Field Monitor with a FOV of 1/4 of the sky, which will trigger the fast repointing to the GRB. Extension of its energy response up to 1 MeV will be achieved with a GRB detector with no imaging capability. This mission is proposed to ESA as part of the Cosmic Vision call. We will briefly review the science drivers and describe in more detail the payload of this mission.

We carried out observations of the central and 20′ east offset regions of the cluster of galaxies Abell 1060 with Suzaku. Spatially resolved X-ray spectral=analysis has revealed temperature and abundance profiles of Abell 1060 out to 27′ ≃ 380 h70 -1kpc, which corresponded to ∼0.3 rvir. The temperature decrease of the intra cluster medium from 3.4 keV at the center to 2.2 keV in the outskirt region are clearly observed. Si, S and Fe abundances also decrease by more than 50% from the center to the outer parts, while Mg shows a fairly constant abundance of ∼ 0.7 solar within r &lt 17′. O shows a lower abundance of ∼0.3 solar in the central region (r &lt 6′), and indicates a similar feature with Mg, however it is sensitive to the estimated contribution of the Galactic components at the outer annuli (r &gt 13′). Results on temperature and abundances of Si, S, and Fe are consistent with those derived by XMM-Newton at r &lt 13′ The formation and metal enrichment of the cluster are discussed based on implications of our results. © 2007 Springer-Verlag Berlin Heidelberg.

We present our proposal for a small X-ray mission DIOS (Diffuse Intergalactic Oxygen Surveyor), consisting of a 4-stage X-ray telescope and an array of TES microcalorimeters, cooled with mechanical coolers, with a total weight of about 400 kg. The mission will perform survey observations of warm-hot intergalactic medium using OVII and OVIII emission lines, with the energy coverage up to 1.5 keV. The wide field of view of about 50' diameter, superior energy resolution close to 2 eV FWHM, and very low background will together enable us a wide range of science for diffuse X-ray sources. We briefly describe the design of the satellite, performance of the subsystems and the expected results.

EURECA (EURopean-JapanEse Calorimeter Array) comprises a 5 x 5 pixel imaging TES-based micro-calorimeter array read-out by SQUID-based frequency-domain-multiplexed electronics and cooled down by an adiabatic demagnetization refrigerator. A European-Japanese consortium designs, fabricates, and tests this prototype instrument with the aim to show within about 2 years technology readiness of a TES-based X-ray imaging micro-calorimeter array in anticipation of future X-ray astronomy missions, like XEUS (ESA), Constellation-X (NASA), NEXT (JAXA), DIOS (JAXA), ESTREMO (ASI), and NEW (Dutch-multinational). This paper describes the instrument concept, and shows the design of the various sub-units, like the TES detector array, LC-filters, SQUID-amplifiers, flux-locked-loop electronics, AC-bias sources, etc.

We are developing a superconducting transition-edge sensor (TES) microcalorimeter array for the Diffuse Intergalactic Oxygen Surveyor (DIOS) mission. DIOS is a relatively small Japanese X-ray mission which will study large-scale distribution of the warm-hot intergalactic medium (WHIM) using OVII and OVIII emission lines. The satellite weighs about 400 kg equipped with a four-reflection X-ray telescope (FXT) and a TES microcalorimeter array (XSA). The design goal of the observing system is an effective area larger than 100 cm2 at the oxygen line energy, a field of view about 50 arcmin square, and an energy resolution about 2 eV in the energy range of 0.3-1 keV. The TES microcalorimeter array provides the large field of view and good energy resolution at the same time. We plan to install an array comprising 16 × 16 pixels with an overall size of 1 cm square, which is cooled with a cryogen-free cooler. Pixels are readout by multiplexing signals using a multi-input SQUID amplifier, with each input connected to a TES microcalorimeter which is AC biased with a different frequency. We report the design and present status of the XSA system development.