Search

A TES microcalorimeter array is a promising spectrometer with excellent energy resolution and a moderate imaging capability. To realize a large format array in space, multiplexing the TES signals at the low tempersture stage is mandatory. We are developing frequency division multiplexing (FDM) based on baseband feedback technique. In FDM, each TES is AC-biased with a different carrier frequency. Signals from several pixels are summed and then read out by one SQUID. The maximum number of multiplexed pixels are limited by the frequency band in which the SQUID can be operated in a flux-locked loop, which is ∼1 MHz with standard flux-locked loop circuit. In the baseband feedback, the signal (∼10 kHz band) from the TES is once demodulated. Then a reconstructed copy of the modulated signal with an appropriate phase is fed back to the SQUID input coil to maintain an approximately constant magnetic flux. This can be implemented even for large cable delays and automatically suppresses the carrier. We developed a prototype electronics for the baseband feedback based on an analog phase sensitive detector (PSD) and a multiplier. Combined with Seiko 80-SSA SQUID amp, open-loop gain of 8 has been obtained for 10 kHz baseband signal at 5 MHz carrier frequency, with a moderate noise contribution of [formula] at input. [ABSTRACT FROM AUTHOR]

To understand the so-called excess noise, we measured the complex impedance of a TES microcalorimeter, and derived the hernial sensitivity α, current sensitivity β, and heat capacity C. Making use of the obtained parameters, we found that the excess noise can be represented by two types of extra noise having similar spectra as Johnson and phonon noise. The contribution of the Johnson-like, usually expressed by the M factor, depended on α [formula] which is consistent with the behavior of the excess noise studied in other groups. Pursuing the better energy resolution, we suppressed the dominant noise components by introducing a Si collimator to irradiate X-rays only to the Au absorber, increasing the ADC resolution, and improving the temperature stability. So far, the energy resolution has been improved from 4.8 eV to 2.8 eV (FWHM). [ABSTRACT FROM AUTHOR]

We are developing Frequency Domain Multiplexing (FDM) for the read-out of TES imaging microcalorimeter arrays for future X-ray missions like IXO. In the FDM configuration the TES is AC voltage biased at a well defined frequencies (between 0.3 to 10 MHz) and acts as an AM modulating element. In this paper we will present a full comparison of the performance of a TES microcalorimeter under DC bias and AC bias at a frequency of 370 kHz. In both cases we measured the current-to-voltage characteristics, the complex impedance, the noise, the X-ray responsivity, and energy resolution. The behaviour is very similar in both cases, but deviations in performances are observed for detector working points low in the superconducting transition (R/RN<0.5). The measured energy resolution at 5.89 keV is 2.7 eV for DC bias and 3.7 eV for AC bias, while the baseline resolution is 2.8 eV and 3.3 eV, respectively. [ABSTRACT FROM AUTHOR]

For the next generation of astronomical X-ray imaging detectors, arrays with large numbers of microstructures (∼1000 pixels) will be required. To meet this requirement, a tin absorber for an X-ray microcalorimeter, which has a so-called "mushroom" shape, is fabricated by electrodeposition and polishing. This method enables the fabrication of a large number of arrayed microcalorimeters. Details of the fabrication process, the characteristics of the absorber and the fabricated microcalorimeters are reported. [ABSTRACT FROM AUTHOR]

We present a detailed structural study of the hot ISM in the Galactic halo along the sight line toward the bright active galactic nucleus Mkn 421. The O VII and O VIII absorption lines were measured with the Low Energy Transmission Grating Spectrograph aboard Chandra toward Mkn 421, and the O VII and O VIII emission lines were observed in the vicinities of the sight line with the X-ray Imaging Spectrometer aboard Suzaku. We jointly analyzed the absorption and the emission spectra assuming exponential distributions of the gas temperature and density from the Galactic plane, and constrained the temperature and density at the plane to be 2.7(+0.6,-0.5)×106 K and 1.5(+0.7,-0.5)×10-3 cm-3, with the scale heights of 1.6(+3.6,-0.9)kpc and 5.1(> 1.2)kpc respectively. The results are consistent with those obtained in the LMC X-3 direction and the PKS 2155-304 direction, describing a thick disk-like hot gas with its height of a few kpc from the Galactic plane. [ABSTRACT FROM AUTHOR]