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The X-ray Astronomy Recovery Mission (XARM) is a recovery mission of ASTRO-H/Hitomi, which is expected to be launched in Japanese Fiscal Year of 2020 at the earliest. The Resolve instrument on XARM consists of an array of 6 × 6 silicon-thermistor microcalorimeters cooled down to 50 mK and a high-throughput X-ray mirror assembly with the focal length of 5.6 m. Hitomi was launched into orbit in February 2016 and observed several celestial objects, although the operation of Hitomi was terminated in April 2016. The soft X-ray spectrometer (SXS) on Hitomi demonstrated high-resolution X-ray spectroscopy of ~ 5 eV FWHM in orbit for most of the pixels. The Resolve instrument is planned to mostly be a copy of the Hitomi SXS and soft X-ray telescope designs, though several changes are planned based on the lessons learned from Hitomi. We report a brief summary of the SXS performance and the status of the Resolve instrument. [ABSTRACT FROM AUTHOR]

We present the latest update and progress on the future Japanese X-ray satellite mission Diffuse Intergalactic Oxygen Surveyor (DIOS). DIOS is proposed to JAXA as a small satellite mission, and would be launched with an Epsilon rocket. DIOS would carry on the legacy of ASTRO-H, which carries semiconductor-based microcalorimeters and is scheduled to be launched in 2016, in high-resolution X-ray spectroscopy. A 400-pixel array of transition-edge sensors (TESs) would be employed, so DIOS would also provide valuable lessons for the next ESA X-ray mission ATHENA on TES operation and cryogen-free cooling in space. We have been sophisticating the entire design of the satellite to meet the requirement for the Epsilon payload for the next call. The primary goal of the mission is to search for warm-hot intergalactic medium with high-resolution X-ray spectroscopy by detecting redshifted emission lines from OVII and OVIII ions. The results would have significant impacts on our understanding of the nature of 'dark baryons,' their total amount and spatial distribution, as well as their evolution over cosmological timescales. [ABSTRACT FROM AUTHOR]

Calorimetric X-ray detectors are very sensitive to their environment. The boundary conditions can have a profound effect on the gain including heat sink temperature, the local radiation temperature, bias, and the temperature of the readout electronics. Any variation in the boundary conditions can cause temporal variations in the gain of the detector and compromise both the energy scale and the resolving power of the spectrometer. Most production X-ray calorimeter spectrometers, both on the ground and in space, have some means of tracking the gain as a function of time, often using a calibration spectral line. For small gain changes, a linear stretch correction is often sufficient. However, the detectors are intrinsically non-linear and often the event analysis, i.e., shaping, optimal filters etc., add additional non-linearity. Thus for large gain variations or when the best possible precision is required, a linear stretch correction is not sufficient. Here, we discuss a new correction technique based on non-linear interpolation of the energy-scale functions. Using Astro-H/SXS calibration data, we demonstrate that the correction can recover the X-ray energy to better than 1 part in 10 $$^{4}$$ over the entire spectral band to above 12 keV even for large-scale gain variations. This method will be used to correct any temporal drift of the on-orbit per-pixel gain using on-board calibration sources for the SXS instrument on the Astro-H observatory. [ABSTRACT FROM AUTHOR]

A transition edge sensor (TES) microcalorimeter array as an X-ray sensor for a scanning transmission electron microscope system is being developed. The technical challenge of this system is a high count rate of $$\sim $$ 5000 counts/second/array. We adopted a 64 pixel array with a parallel readout. Common SQUID bias, and common TES bias are planned to reduce the number of wires and the resources of a room temperature circuit. The reduction rate of wires is 44 % when a 64 pixel array is read out by a common bias of 8 channels. The possible degradation of the energy resolution has been investigated by simulations and experiments. The bias fluctuation effects of a series connection are less than those of a parallel connection. Simple calculations expect that the fluctuations of the common SQUID bias and common TES bias in a series connection are $$10^{-7}$$ and $$10^{-3}$$ , respectively. We constructed 8 SQUIDs which are connected to 8 TES outputs and a room temperature circuit for common bias readout and evaluated experimentally. Our simulation of crosstalk indicates that at an X-ray event rate of 500 cps/pixel, crosstalk will broaden a monochromatic line by about 0.01 %, or about 1.5 eV at 15 keV. Thus, our design goal of 10 eV energy resolution across the 0.5-15 keV band should be achievable. [ABSTRACT FROM AUTHOR]

We are developing the frequency-division multiplexing (FDM) readout system aimed to realize the 400-pixel transition edge sensor (TES) microcalorimeter array for the DIOS mission as well as large-format arrays with more than a thousand of TES for future space missions such as the ATHENA mission. The developed system consists of the low-power superconducting quantum interference device (SQUID), the digital FDM electronics, and the analog front-end to bridge the SQUID and the digital electronics. Using the developed readout system, we performed a TES readout experiment and succeeded to multiplex four TES signals with the single-staged cryogenic setup. We have experienced two issues during the experiment: an excess noise and crosstalk. The brief overview of the developed system and the details, results, and issues of the TES multiplexing readout experiment is discussed. [ABSTRACT FROM AUTHOR]

We are developing frequency-division multiplexing (FDM) systems with baseband feedback for TES X-ray microcalorimeter arrays for use with the DIOS mission. To meet the requirement of limited cooling capacity at cryogenic temperatures, we developed low-power and FDM-optmized dc-SQUIDs. To make maximum use of the SQUIDs, we also developed digital electronics using FPGA evaluation boards and ADC/DAC FMC daughter cards, and evaluated signal-to-noise ratios and gain-bandwidth products. [ABSTRACT FROM AUTHOR]

We have developed Ti/Au bilayer transition-edge sensor (TES) microcalorimeters for future X-ray astrophysical satellite missions such as DIOS. One possible concern on the space use of TES microcalorimeters is its radiation tolerance. We have evaluated the performance of a Ti/Au bilayer (30/40 nm thick) TES microcalorimeter with 1.5 $$\upmu $$ m thick Au absorber, before and after irradiation of 150 MeV proton beam with a total dose of 10 krad, corresponding to 10 years in the low Earth orbit. No significant changes on transition temperature, sensitivity, normal resistance, and critical current were observed. The energy resolution for 5.9 keV X-rays was 5.6 $$\pm $$ 0.3 eV (FWHM) after the irradiation, which was slightly worse than 5.1 $$\pm $$ 0.3 eV before the irradiation. We consider that our TES has sufficient radiation tolerance in orbit. [ABSTRACT FROM AUTHOR]

We have been improving our TEM-EDS for elemental microanalysis after a successful achievement of a high energy resolution (7.8 eV at 1.7 keV) using a TES microcalorimeter. The improvements fall into a 3D superconductive wiring and a high-speed processing (∼3,000 cps). We are implementing a 10-ch TES array for higher count rate and a broader dynamic range. The shape of a probe needs to be a small polygonal rod with an approximate size of 1 cm×1 cm×10 cm, and hence the placing and wiring of the TES array and read-out circuits at the cryogenic stage were very demanding. We overcame those difficulties by 3D photolithography and electrodeposition. With these new technologies, we developed the OFC probe with solder-plated 3D wiring, and successfully observed a superconductivity at the temperature of liquid helium. As a required count rate per channel is ∼300 cps, the overall system count rate is ∼3,000 cps, which is incomparably higher than before. In the last model, we used an embedded system to process waveforms from a 4-ch 14-bit 1 MS/s ADC due to a small signal bandwidth, but this time we parallelized three identical ADCs and transfer raw waveforms by Ethernet lines to a host to achieve the required system count rate. [ABSTRACT FROM AUTHOR]

For future X-ray astronomy, a microcalorimeter array that has both mega-pixel imaging capability and eV-level high energy-resolution is desirable. In order to realize it, thermometers with negligible self-heating, multiplexing readout and close packing are essential components. We propose a novel detector concept, a dielectric microcalorimeter (DMC) and present current design studies. The DMC uses dielectric pixels as thermometers which form LC resonators in GHz band. The signals from many pixels can be easily multiplexed in a similar way to kinetic inductance detectors. The dielectric pixels are easy to be integrated into large and dense arrays. However, dielectrics with temperature-dependent permittivity below 2 K were not known. We evaluated quantum ferroelectric strontium titanate (STO) used in a capacitive thermometer higher than 2 K as a suitable dielectric for the DMC pixels. We fabricated STO capacitors and measured their capacitance from 2 K down to 80 mK. As a result, we found that their capacitive thermometer sensitivity at 100 mK are dlog C/ dlog T∼10, and they can be sensitive enough to detect X-ray with a resonator. We report the concepts, the measurement details, expected response to X-ray irradiation and our designs of the DMC. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We assess the possibility of detecting the warm-hot intergalactic medium in emission and characterizing its physical conditions and spatial distribution through spatially resolved X-ray spectroscopy, in the framework of the recently proposed DIOS, EDGE, Xenia, and ORIGIN missions, all of which are equipped with microcalorimeter-based detectors. For this purpose, we analyze a large set of mock emission spectra, extracted from a cosmological hydrodynamical simulation. These mock X-ray spectra are searched for emission features showing both the O VII Kα triplet and O VIII Lyα line, which constitute a typical signature of the warm-hot gas. Our analysis shows that 1 Ms long exposures and energy resolution of 2.5 eV will allow us to detect about 400 such features per deg2 with a significance ≥5σ and reveals that these emission systems are typically associated with density ∼100 above the mean. The temperature can be estimated from the line ratio with a precision of ∼20%. The combined effect of contamination from other lines, variation in the level of the continuum, and degradation of the energy resolution reduces these estimates. Yet, with an energy resolution of 7 eV and all these effects taken into account, one still expects about 160 detections per deg2. These line systems are sufficient for tracing the spatial distribution of the line-emitting gas, which constitute an additional information, independent from line statistics, to constrain the poorly known cosmic chemical enrichment history and the stellar feedback processes. [ABSTRACT FROM AUTHOR]

Fully utilizing the benefit of strong electrothermal feedback, we achieved the energy resolution of 6.6 eV (FWHM) at 5.9 keV and a fast response time of 74 μs with our bridge-type Ti/Au transition-edge sensor (TES) microcalorimeter. The energy resolution of this device was limited by a noise that was larger than the intrinsic noise and the readout noise. This noise only appeared when the current through the TES was large (≳10 μA), and its level, defined as a fluctuation amplitude of the current through the TES, was in proportion to the inverse of the TES resistance. We also found that the TES sensitivity depended on the current through the TES, normalized with the critical current of the TES. When the current exceeded about 1% of the critical current, the TES sensitivity was significantly degraded. The critical current clearly correlated with the TES sensitivity, and hence the signal-to-noise ratio at the optimal operating point, among devices with different TES size and thickness. Thus, the critical current is one of the key parameters to determine the performance of the TES microcalorimeter. [Copyright &y& Elsevier]

We are developing transition edge sensor (TES) microcalorimeter arrays for future Japanese astronomy missions. Although 6.6 eV energy resolution for 5.9 keV and 74 μs decay time are achieved, our energy resolution was limited by the excess noise of unknown origin. The dominant noise showed 1/R dependence and it only appeared when the current through the TES, I, is larger than 10 μA. This is explained if we assume a constant voltage noise source with a level of ∼2(4kTCRn)1/2. We also investigated the influence of I on the TES performance and found the TES sensitivity α is reduced when the ratio of current to the critical current I/IC is large. It can explain the reduction of α observed when operated without a magnetic shield. We also found a strong correlation between IC and α or the baseline width. Thus, we conclude that IC is an essential parameter for the TES performance. [Copyright &y& Elsevier]

Abstract: We present the latest results of the performance of micro-calorimeters based on transition edge sensors (TESs) for space applications. Sensors based on TiAu superconductive layers with Cu/Bi absorbers are discussed and have been characterized. Different coupling schemes between absorber and TES have been tested leading to an optimal (preferred) design for a new batch of arrays. We discuss the progress on array development for the International X-ray Observatory (IXO) in terms of pixel uniformity and filling factor. Inter-pixel cross-talk is discussed as well. [Copyright &y& Elsevier]

An X-ray microcalorimeter is a high performance X-ray spectrometer that can achieve both high energy resolution of conventional wavelength dispersive spectrometers (WDS) and high quantum efficiency of energy dispersive spectrometers (EDS). The energy resolution can be theoretically improved to about 1 eV, which value is 120 times better than that of conventional Si(Li) spectrometers and nearly 100% of quantum efficiency can be achieved using microabsorbers. In order to realize high energy-resolution X-ray imaging using an array of X-ray microcalorimeters, two types of 2×2 X-ray microcalorimeter arrays were fabricated and tested. Using an X-ray microabsorber so-called “mushroom-shaped” X-ray microabsorber, the filling factor was enhanced to about 70%. We tested Sn and Bi as an X-ray microabsorber. Consequently, the Sn absorber degrades the energy resolution because of the long time constant. This problem was cleared using the Bi microabsorber. The achievable energy resolution was also investigated. As a result, the energy resolution of 6.3 eV was obtained with the test device. [Copyright &y& Elsevier]

Properties of Transition-Edge Sensor (TES) microcalorimeters operated with AC bias are studied utilizing the calorimeter Wheatstone bridge circuit called Calorimeter Bridge Biased by an AC Generator (CABBAGE). The CABBAGE eliminates the AC carrier significantly, thus enables us to study the AC responses of the TES with high sensitivity. We tested two kinds of TES devices operating at 110 and 440 mK, respectively. With the 110 mK device biased with 25 kHz, an energy resolution of 28 eV is obtained for Mn Kα line. On the other hand, we multiplexed the signals from two 440 mK device biased with 50 and 20 kHz, respectively, and obtained 167 and 271 eV energy resolutions. Even at the balance point of the bridge, AC signal did not disappear and odd-order harmonics were observed. They are considered to arise from the current dependence of the TES resistance, which is characterized by β≡d log R/d log I. Numerical solution for the CABBAGE response can reproduce the experimental results well if β=0.24±0.02. Since the harmonics may cause severe problem in the SQUID operation even after attenuated by a band-pass filter, especially at high bias frequency operation such as several hundred kHz, it is important to make β small. [Copyright &y& Elsevier]

We have developed multi-pixel TES microcalorimeters in order to realize high-energy resolution and X-ray imaging. A Sn absorber and a Bi absorber were formed on Si3N4 and SiO2 membrane using two-step exposure photolithography and electrodeposition. A FEM analysis was carried out to investigate the performance of the X-ray microabsorbers. In addition, a superconducting through-wafer interconnection was demonstrated considering the future X-ray imager using microcalorimeters. Detail of the fabrication techniques, characteristics and simulation results of two types of the microabsorbers, as well as those of the calorimeters are described. [Copyright &y& Elsevier]

We are developing a Ti/Au TES microcalorimeter array for future Japanese X-ray astronomy missions. The goal is an energy resolution of 2–5 eV at 6 keV, and an array of 100–1000 pixels to achieve a geometrical area of >1 cm2 and a moderate spatial resolution simultaneously. The energy resolution was improved to ∼6 eV at 6 keV with a very fast time constant (<100 μs). To achieve a high coverage fraction, it is necessary to fabricate mushroom-shaped X-ray microabsorbers. We are developing an electrodeposition fabrication technique that is suitable for our process. Sn was used as absorber material, but the energy resolution was not good due to the existence of long-lived quasiparticles. Bi is also used, and the process is under optimization now. The readout strategy is to multiplex signals in the frequency domain, using a bridge circuit. So far, we succeeded in multiplexing two pixels modulated with 50 and 20 kHz at 440 mK. The energy resolution obtained at 110 mK was 33 eV (25 kHz). [Copyright &y& Elsevier]

Abstract: The XRS microcalorimeter was launched in July 2005 as part of the Suzaku mission. It covers the energy band from 0.3 to 10keV with a nearly constant energy resolution of 6eV and a peak effective area of 200cm2 at 1.5keV. The XRS will provide unprecedented throughput and resolving power, particularly at high energies and for extended sources. The XRS has undergone extensive instrument-level ground calibration prior to integration into the spacecraft. In this presentation, we will describe our pre-launch characterization of the instrument. We will include discussions of the energy scale, the line spread function, and the efficiency of the various components that make up the effective area. [Copyright &y& Elsevier]

Abstract: We succeeded in fabricating 256-pixel arrays of Ti/Au transition edge sensor (TES) microcalorimeters with electrodeposited microabsorbers made of Bi, and report on their test results. We confirmed all pixels tested so far were alive, however most of the microabsorbers were stripped off during cooling cycles. We investigated some pixels by irradiating with 5.9keV X-rays, and confirmed that they actually worked as microcalorimeters. The X-ray pulses are represented by a sum of two components with different decay times. The ratio of the two components fluctuates from pulse to pulse, which limits the energy resolution to . We discuss the pulse shape of two decay-time components considering thermal conductivities, i.e., inside microabsorbers, between microabsorbers and TES. [Copyright &y& Elsevier]