Ken-ichi Tamura

In-orbit performance of the hard X-ray detector on board Suzaku

The in-orbit performance and calibration of the Hard X-ray Detector (HXD) on board the X-ray astronomy satellite Suzaku are described. Its basic performances, including a wide energy bandpass of 10–600keV, energy resolutions of ∼ 4keV (FWHM) at 40keV and ∼ 11% at 511keV, and a high background rejection efficiency, have been confirmed by extensive in-orbit calibrations. The long-term gains of PIN-Si diodes have been stable within 1% for half a year, and those of scintillators have decreased by 5–20%. The residual non-X-ray background of the HXD is the lowest among past non-imaging hard X-ray instruments in energy ranges of 15–70 and 150–500keV. We provide accurate calibrations of energy responses, angular responses, timing accuracy of the HXD, and relative normalizations to the X-ray CCD cameras using multiple observations of the Crab Nebula.

Development and qualification of the HXD-II onboard Astro-E2

The Hard X-ray Detector (HXD-II), one of instruments onboard the Astro-E2 satellite to be launched in February 2005, is in the final stage of its development. The HXD-II probes the universe in the energy range of 10-600 keV with a sensitivity by an order of magnitude better than those of previous missions. The assembly of the HXD-II completed in January 2004, followed by a series of pre-launch qualification tests. As a result, the design goals of the HXD-II have been met. These include; a background level of 5 x 10-6 counts/s/keV/cm2 at 200 keV for GSO and 1 x 10-5 counts/s/keV/cm2 at 30 keV for PIN; energy resolutions of 2.9 keV (PIN diode, at 59.5 keV) and 10% (GSO scintillator, at 662 keV); and low energy thresholds of 10 keV for PIN diodes and 30 keV for GSO scintillators. The measured background predicts a continuum sensitivity of a few x 10-6 photons/s/keV/cm2. Anti-Counter units surrounding the HXD-II provide 50 keV-5 MeV information on gamma-ray bursts and bright X-ray transients.

Development of an Si/CdTe semiconductor Compton telescope

We are developing a Compton telescope based on high resolution Si and CdTe imaging devices in order to obtain a high sensitivity astrophysical observation in sub-MeV gamma-ray region. In this paper, recent results from the prototype Si/CdTe semiconductor Compton telescope are reported. The Compton telescope consists of a double-sided Si strip detector (DSSD) and CdTe pixel detectors, combined with low noise analog LSI, VA32TA. With this detector, we obtained Compton reconstructed images and spectra from line gamma-rays ranging from 81 keV up to 356 keV. The energy resolution is 3.8 keV and 7.9 keV at 122 keV and 356 keV, respectively, and the angular resolution is 9.9° and 5.7° at 122 keV and 356 keV, respectively.

Hirschsprung's disease associated with Ondine's curse: A special subgroup?

The authors report a case of the rare occurrence of congenital central hypoventilation syndrome (Ondines curse) and long segmental colonic aganglionosis (Hirschsprungs disease). A review of 24 reported cases showed that the proportion of females having this concurrence is higher than for ordinary Hirschsprungs disease. It also appears that the aganglionic segment is much longer in these cases than in ordinary Hirschsprungs disease.

Suzaku Detection of Extended/Diffuse Hard X-Ray Emission from the Galactic Center

Five on-plane regions within ˙0: i 8o ft he galactic center were observed with the Hard X-ray Detector (HXD) and the X-ray Imaging Spectrometer (XIS) aboard Suzaku. From all regions, significant hard X-ray emission was detected with HXD-PIN up to 40 keV, in addition to the extended plasma emission which is dominant in the XIS band. The hard X-ray signals are inferred to come primarily from a spatially extended source, rather than from as mall number of bright discrete objects. Contributions to the HXD data from catalogued X-ray sources, typically brighter than 1 mCrab, were estimated and removed using information from Suzaku and other satellites. Even after this removal, the hard X-ray signals remained significant, exhibiting a typical 12-40 keV surface brightness of 4 � 10 � 10 erg cm � 2 s � 1 deg � 2 and power-law-like spectra with a photon index of 1.8. Combined fittings to the XIS and HXD-PIN spectra confirm that a separate hard tail component is superposed onto the hot thermal emission, confirming a previous report based on the XIS data. Over the 5-40 keV band, the hard tail is spectrally approximated by a power law of photon index � 2, but better by those with somewhat convex shapes. Possible origins of the extended hard X-ray emission are discussed.

Performance of Prototype Hard X-ray Polarimeter Utilizing Compton Scattering

In X-ray astronomy, various kinds of information on stellar objects have been obtained from energy spectrum, time variabilities, and images. Although the observation of polarization is also important, it has not been carried out for 25 years, because of the difficulty of developing a polarimeter with a high sensitivity. Thus, we have been developing a Compton-scattering-type hard X-ray polarimeter sensitive to the energy range from 40 to 300 keV, employing segmented plastic and CsI(Tl) scintillators mounted on a flat-panel multianode photomutiplier (MAPMT). Constructing the prototype polarimeter and using polarized hard X rays of 80 keV, we carried out basic experiments to investigate the performance of our polarimeter. Moreover, we carried out computer simulations and confirmed that the results obtained by computer simulation are in good agreement with those obtained by experiment. Finally, it was found that the prototype polarimeter can obtain a modulation factor and a detection efficiency of ~40 and ~20%, respectively.

Development of a low-noise analog front-end ASIC for CdTe detectors

We developed a low-noise analog front-end ASIC for CdTe detectors. The ASIC was designed on the basis of Open- IP, an LSI circuit library, and fabricated with a TSMC 0.35- mum CMOS technology. The ASIC contains eight identical channels, each of which consists of a charge-sensitive amplifier, slow and fast CR-RC shapers, comparator, and sample-and-hold circuit. The initial evaluations were performed with the ASIC packaged in a plastic mold and held in a burn-in socket. The equivalent noise level of a typical channel reached 188 e + 7.5 e /pF (rms). In order to minimize a parasitic capacitance from an assembly issue and demonstrate further low-noise performance, we designed a front-end carrier board and evaluated the performance of the bare ASIC. As a result, the typical noise level for the input capacitance of OpF improved to 130 e and the minimum noise level reached 110 e (rms) at -20degC. We also combined the ASIC with a Shottky CdTe diode detector and obtained a gamma- ray spectrum. The energy resolutions were 2.43 keV (FWHM) for 60 keV gamma-rays and 2.26 keV (FWHM) for 17.6 keV gamma-rays at -20degC.