Mio Murashima

Hard X-ray Detector (HXD) on board Suzaku

The Hard X-ray Detector (HXD) on board Suzaku covers a wide energy range from 10 keV to 600 keV by combination of silicon PIN diodes and GSO scintillators. The HXD is designed to achieve an extremely low in-orbit back ground based on a combination of new techniques, including the concept of well-type active shield counter. With an effective area of 142 cm^2 at 20 keV and 273 cm2 at 150 keV, the background level at the sea level reached ~1x10^{-5} cts s^{-1} cm^{-2} keV^{-1} at 30 keV for the PI N diodes, and ~2x10^{-5} cts s^{-1} cm^{-2} keV^{-1} at 100 keV, and ~7x10^{-6} cts s^{-1} cm^{-2} keV^{-1} at 200 keV for the phoswich counter. Tight active shielding of the HXD results in a large array of guard counters surrounding the main detector parts. These anti-coincidence counters, made of ~4 cm thick BGO crystals, have a large effective area for sub-MeV to MeV gamma-rays. They work as an excellent gamma-ray burst monitor with limited angular resolution (~5 degree). The on-board signal-processing system and the data transmitted to the ground are also described.

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 of the HXD-II wide-band all-sky monitor onboard Astro-E2

The hard X-ray detector (HXD-II) is one of the three scientific instruments onboard Japanese X-ray astronomy satellite Astro-E2 scheduled to be launched in 2005. This mission is very unique in a point of having a lower background than any other past missions in the 10-600 keV range. In the HXD-II, the large and thick BGO crystals are used as active shields for particle and gamma-ray background to the main detector. They have a wide field of view of ~2pi and a large effective area of 400 cm2 even at 1 MeV. Hence, the BGO shields have been developed as a wide-band all-sky monitor (WAM) with a broadband coverage of 50-5000 keV. In this paper, overall design and performance of the HXD-II/WAM based on the results of preflight calibration tests carried out in June 2004 are described. By irradiating various radio isotopes with the WAM flight model, we verified that it had comparable capabilities with other gamma-ray burst detectors

Improvements of the astro-E2 hard X-ray detector (HXD-II)

We summarize significant improvements which have been achieved 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/sup -6/ [cs/sup -1/ keV/sup -1/ cm/sup -2/].

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 a Monte Carlo Simulator for the Astro-E2 hard X-ray detector (HXD-II)

The Hard X-ray Detector (HXD-II) is one of the scientific payloads on board the fifth Japanese cosmic X-ray satellite Astro-E2 , scheduled for launch in 2005. The HXD-II is designed to cover a wide energy range of 10-600 keV with a high sensitivity of about 10/sup -5/ cnt/s/cm/sup 2//keV. In order to derive the energy response of the sensor and to estimate the background, a Monte Carlo simulator based on the Geant4 toolkit is currently being developed. This paper describes the design concept of the HXD-II software package, including the analysis tools and the Monte Carlo simulator, and its verification through a comparison with actual data taken by pre-flight radio-isotope irradiation experiments, together with calculated outputs that can demonstrate the in-orbit performance of the HXD-II.

Inflight calibration and performance of the hard X-ray detector (HXD) onboard Suzaku

The hard X-ray detector (HXD) onboard Suzaku covers an energy range of 8-700 keV, and thus in combination with the CCD camera (XIS) gives us an opportunity of wide-band X-ray observations of celestial sources with a good sensitivity over the 0.3-700 keV range. All of 64 Si-PIN photo diodes, 16 GSO/BGO phoswich scintillators, and 20 anti-coincidence BGO scintillators in the HXD are working well since the Suzaku launch on July 2005. The rejection of background events is confirmed to be as effective as expected, and accordingly the HXD achieved the lowest background level of the previously or currently operational missions sensitive in the comparable energy range. The energy and angular responses and timing have been continuously calibrated by the data from the Crab nebula, X-ray pulsars, and other sources, and at present several % accuracy is obtained. Even though the HXD does not perform simultaneous background observations, it detected weak sources with a flux as low as ~0.5 mCrab; stars, X-ray binaries, supernova remnants, active galactic nuclei, and galaxy clusters. Extensive studies of background subtraction enables us to study weaker sources.

In-orbit calibration of the hard x-ray detector (HXD-II) onboard Suzaku

The hard X-ray detector (HXD-II) is one of the scientific payloads onboard Suzaku, the 5th Japanese cosmic X-ray satellite. After the launch in July 2005, all the HXD-II components, including the sensors and analog/digital electronics, have been working normally. In order to archive the maximum performance of the HXD-II, especially the GSO/BGO well-type phoswich counters, extensive in-orbit qualification and calibration have been carried out utilizing the data acquired in early operations. Major items of these efforts include; to estimate the circuit dead time, calibrate energy scale, optimize the event selection criteria for background reduction, study the background, and examine the detector response. As a result of these in-orbit calibrations, the HXD-II background in the 10-600 keV range has been successfully lowered to (0.5-5.0) x 10-4 cs-1 keV-1 cm-2 This the lowest among the background ever achieved in orbit by cosmic hard x-ray detectors.

X-Ray Spectra of Narrow-Line Seyfert 1 Galaxies in Comparison with Galactic Black Holes

In order to study the origin of the soft excess of Narrow-Line Seyfertl Galaxies, 7 objects observed with XMM-Newton are analyzed. The soft excess is found to have mildly convex shape, which is successfully reproduced by a power-law with an exponential cutoff. It can be interpreted as disk Comptonization by cool and relatively optically thick plasma based on an analogy with Galactic black holes under high accretion rates.