寺田 幸功

WIDGET is a robotic telescope for rnonitoring the HETE-2 field-of-view to detect Gamma-Ray Burst optical flashes or possible optical precursors. The system has 62 degrees x 62 degrees wide field-of-view which covers about 80% of HETE-2 one with a, 2kx2k Apogee U10 CCD camera and a Canon EF 24 mm f/1.4 wide-angle lens without a bandpass filter. WIDGET has been in operation since June 2004 at Akeno observing site where is about 200 kin apart from Tokyo. Typical limiting magnitude with S/N=3 at the site is V = 10(mag) for 5 seconds exposure and V = 11(mag) for 30 seconds exposure. We had already six coincident observations with HETE-2 position alerts. It was, however, cloudy for all cases due to rainy season in Japan. The expected number of coincident observations under clear sky is about 5 events per year. We will extend the system in early 2005 for Swift era to monitor optical transients in wider field-of-view, multi-color or polarization modes.

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 × 10 -6 counts/s/keV/cm 2 at 200 keV for GSO and 1 × 10 -5 counts/s/keV/cm 2 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 ×10 -6 photons/s/keV/cm 2 . Anti-Counter units surrounding the HXD-II provide 50 keV-5 MeV information on gamma-ray bursts and bright X-ray transients.

Employing Fourier-synthesis optics and one-dimensional position-sensitive detectors, we are developing a novel hard X-ray imager which can work in the ∼10 keV to ∼200 keV range either as a telescope or a microscope. As the detection part of our imager, we have developed a strip detector made of Schottky CdTe diode, with its cathode divided into 64 channels of 150 μm pitch. Electrodes of all channels are gold-stud bonded to a fanout board, and connected to low noise analog ASIC. We read out signals from all channels simultaneously. As the grid optics elements, one-dimensional modulation collimator grids of 1 mm thick tungsten have been manufactured, with 10 grid pitches ranging from 0.2 mm to 2 mm with harmonic ratios. Combining the CdTe strip detector and the modulation collimators, we have verified hard X-ray imaging performance of this system. Specifically, by observing an241Am source, we have successfully obtained an image in the 10-70 keV range. © 2004 IEEE.

The Soft Gamma-ray Detector (SGD) on board NeXT (Japanese future high energy astrophysics mission) is a Compton telescope with narrow field of view (FOV), which utilizes Compton kinematics to enhance its background rejection capabilities. It is realized as a hybrid semiconductor gamma-ray detector which consists of silicon and CdTe (Cadmium Telluride) detectors. It can detect photons in a wide energy band (0.05-1 MeV) at a background level of 5 × 10-7counts/s/cm2/keV; the silicon layers are required to improve the performance at a lower energy band (<0.3 MeV). Excellent energy resolution is the key feature of the SGD, allowing to achieve both high angular resolution and good background rejection capability. An additional capability of the SGD, its ability to measure gamma-ray polarization opens up a new window to study properties of astronomical objects. We will present the development of key technologies to realize the SGD; high quality CdTe, low noise front-end ASIC and bump bonding tecnology. Energy resolutions of 1.7 keV (FWHM) for CdTe pixel detectors and 1.1 keV for Si strip detectors have been measured. We also present the validation of MC simulation used to evaluate the performance of the SGD. © 2004 IEEE.

We summarize significant improvements which have been achived in the development of Astro-E2 Hard X-ray Detector (HXD-II). An expanded energy range and better energy resolution have been achieved from progresses in device materials and redesigning of the front-end electronics. An improved estimation for the detector background in orbit has also been conducted based upon results from our proton irradiation experiment. The sensitivity of HXD-II can be expected to reach an order of 10(-6) [c s(-1) keV(-1) cm(-2)].

In addition to providing the initial gamma-ray burst trigger and location, the Swift Burst Alert Telescope (BAT) will also perform an all-sky hard x-ray survey based on serendipitous pointings resulting from the study of gamma-ray bursts. BAT was designed with a very wide field-of-view (FOV) so that it can observe roughly 1/7 of the sky at any time. Since gamma-ray bursts are uniformly distributed over the sky, the final BAT survey coverage is expected to be nearly uniform. BAT's large effective area and long sky exposures will produce a 15 - 150 keV survey with up to 30 times better sensitivity than any previous hard x-ray survey (e.g. HEAO A4). Since the sensitivity of deep exposures in this energy range is systematics limited, the ultimate survey sensitivity depends on the relative sizes of the statistical and systematic errors in the data. Many careful calibration experiments were performed at NASA/Goddard Space Flight Center to better understand the BAT instrument's response to 15-150 keV gamma-rays incident from any direction within the FOV. Using radioactive sources of gamma-rays with known locations and energies, the Swift team can identify potential systematic errors in the telescope's performance and estimate the actual Swift hard x-ray survey sensitivity in flight. These calibration results will be discussed and a preliminary parameterization of the BAT instrument response will be presented. While the details of the individual BAT CZT detector response will be presented elsewhere in these proceedings, this talk will focus on the translation of the calibration experimental data into overall hard x-ray survey sensitivity.

We are developing a Compton camera based on Si and CdTe semiconductor imaging devices with high energy resolution. In this paper, results from the most recent prototype are reported. The Compton camera consists of six stacked double-sided Si Strip detectors and CdTe pixel detectors, which are read out with low noise analog ASICs, VA32TAs. We obtained Compton reconstructed images and spectra of line gamma-rays from 80 keV to 662 keV. The energy resolution (FWHM) is 10 keV and 16 keV at 356 keV and 511 keV, respectively. © 2004 IEEE.

Compton telescopes based on semiconductor technologies are being developed to explore the gamma-ray universe in an energy band 0.1-20 MeV, which is not well covered by the present or near-future gamma-ray telescopes. The key feature of such Compton telescopes is the high energy resolution that is crucial for high angular resolution and high background rejection capability. The energy resolution around 1 keV is required to approach physical limit of the angular resolution due to Doppler broadening. We have developed a low noise front-end ASIC, VA32TA, to realize this goal for the readout of Double-sided Silicon Strip Detector (DSSD) and Cadmium Telluride (CdTe) pixel detector which are essential elements of the semiconductor Compton telescope. We report on the design and test results of the VA32TA. We have reached an energy resolution of 1.3 keV (FWHM) for 60 keV and 122 keV at 0̊ Cwith a DSSD and 1.7 keV (FWHM) with a CdTe detector.

To bring a breakthrough in the observation of the gamma-ray universe, we are working on the development of Semiconductor Multi-Compton Telescope(SMCT). In the SMCT, all the energy, positional and timing resolution must be high to ensure high sensitivity. The imaging device based on the high resolution CdTe diode and Si, such as CdTe pixel detectors and Double-sided Si Strip Detectors (DSSDs), are promising candidates for the components of the SMCT. Here we report the results of a CdTe pixel detector connected with a low noise analog ASIC. We obtained an energy resolution of 2.5 keV(FWHM) at 122 keV, with a positional resolution of 2 mm. Performance of the first prototype Compton Camera using a DSSD and two CdTe pixel detectors is also described. We irradiated 100% linearly polarised 170 keV γ-ray line to the system and obtained the polarimetric modulation factor of 43%.

A Semiconductor Multiple-Compton Telescope (SMCT) is being developed to explore the gamma-ray universe in an energy band 0.1-20 MeV, which is not well covered by the present or near-future gamma-ray telescopes. The key feature of the SMCT is the high energy resolution that is crucial for high angular resolution and high background rejection capability. We have developed prototype modules for a low noise Double-sided Silicon Strip Detector (DSSD) system which is an essential element of the SMCT. The geometry of the DSSD is optimized to achieve the lowest noise possible. A new front-end VLSI device optimized for low noise operation is also developed. We report on the design and test results of the prototype system. We have reached an energy resolution of 1.3 keV (FWHM) for 60 keV and 122 keV at 0°C.

We have studied the rapid X-ray variability of four TeV blazars, Mrk 421, Mrk 501, PKS 2155-304 and 1ES 2344+514. Analyzing the X-ray light curves obtained from ASCA and/or RXTE observations, we have investigated the variability in the time domain from 103 to 107 sec. The structure functions show a roll-over around 1 day, which can be interpreted as the typical time-scale of day-by-day flare events. On time-scales shorter than 1 day, variability is significantly suppressed, indicating a steep power spectrum density (PSD) of f-2~-3. This is very different from other types of mass-accreting black-hole systems for which the short timescale variability is well characterized by a fractal, flickering noise (f-1~-2). Importantly, the steep PSD index and the characteristic time-scale of day-by-day flares imply that the X-ray emitting site in the jet is of limited spatial extent; D~=1017-18 cm distant from the base of the jet, which corresponds to ~=102-4Rg for 107-9Msolar black-hole systems.