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Performance of microcalorimeters with a Ti/Au transition-edge sensor (TES) and an electrodeposited absorber has been investigated. The absorbers are in a mushroom-shape made of Sn or Bi. With an Sn absorber we observed a long time scale component of 1.8 ms for X-ray pulses, which is due presumably to recombination of quasiparticles into phonons. As a result, the energy resolution is not good with the Sn absorber. Better energy resolution of 28±1 eV was obtained with an incomplete-shaped Bi absorber, although the long component was also seen with smaller level. A calorimeter with only a neck of the Au seed layer for the electrodeposition had the best energy resolution of 6.3±0.4 eV in spite of saturated pulses and relatively high transition temperature of 210 mK. [Copyright &y& Elsevier]

We examined the performance of a single pixel Ti/Au transition-edge sensor (TES) calorimeter for incident X-ray energies of Al-Kα, Cr-Kα, and Fe-Kα, as a function of the TES resistance. We find that the energy resolution does not always degrade with increasing energy. The best energy resolution of 5.7±0.9 eV at 6.4 keV is obtained, which is possibly even better than the baseline width of 6.5±0.2 eV. Assuming that the noise level is determined by the noise spectrum NS(f;R∼R+dR(E)) considering the resistance change of dR(E), instead of NS(f;R) at the operating point, these results may be explained by the fact that the noise decreases at the higher TES resistance. The pulse variation appears to have a minimum at a certain resistance of R+dR(E)≃48 mΩ, and the best energy resolution for each line is obtained at such an operating point, respectively. The pulse variation could be enhanced when the fluctuation of the TES sensitivity α is large at R+dR(E). [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]

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: Background counts on the XRS calorimeter spectrometer of the Suzaku Observatory (formerly Astro-E2) have several sources, including primary cosmic rays and secondary particles interacting with the pixels and with the silicon structure of the array. Using ground data, we identified the types of correlations between events on different pixels, and between pixel pulses and the signal from the anti-coincidence detector behind the calorimeter. In this paper, we present details of the ground background events and the rejection criteria required to remove them while minimizing deadtime. We also present the in-orbit background measured during the time that XRS was functioning in orbit. [Copyright &y& Elsevier]

Abstract: The X-ray Spectrometer (XRS) is a high resolution, non-dispersive cryogenic detector on board the X-ray satellite, Suzaku (Astro-E2), which was successfully launched on July 10, 2005. The XRS achieves an energy resolution of 6eV at 6keV (FWHM) and covers a broad energy range of –10keV. The XRS will enable powerful plasma diagnostics of a variety of astrophysical objects such as the dynamics of gas in clusters of galaxies. The XRS was integrated to the spacecraft in September 2004, and underwent a series of spacecraft tests until April 2005. We describe results of the XRS performance verification in the spacecraft configuration. First, the noise level was extremely low on the spacecraft, and most of the pixels achieved an energy resolution of 5–6eV at 5.9keV. Microphonic noise from the mechanical cooler was one of the concerns, but this was not a problem, when the dewar was integrated to the spacecraft and filled with solid neon. To attain the best energy resolution, however, correction of gain drift is mandatory. The XRS has a dedicated calibration pixel for that purpose, and drift correction using the calibration pixel is very effective when the gain variation is due to changes in the heat sink temperature. On the other hand, the calibration pixel and the other pixels do not respond in the same way to variations of the helium and neon bath temperatures, and this effect requires further study. [Copyright &y& Elsevier]