磯部 直樹

The ASTRO-E hard X-ray detector utilizes GSO(Gd2SiO5:Ce 0.5% mol)-BGO(Bi4Ge3O12) well-type phoswich counters [1] in compound-eye configuration to achieve an extremely low background level of about a few times 10-5 counts s-1 cm-2 keV-1. The GSO scintillators placed at the bottom of the BGO well observe photons in the energy range 30-600 keV. To cover the lower energy range of 10-60 keV, silicon p-i-n diodes of 2 mm in thickness and 21.5×21.5 mm2 in size were newly developed and placed in front of the GSO scintillators. The p-i-n diode exhibits complex spectral responses, including subpeak and low energy tail components. To examine the origin of these components, we measured the spatially resolved response of the p-i-n diode and confirmed that the subpeak and the low energy tail are related to the electrode structures and electric fields in the p-i-n diode, respectively.

We detected an excess of hard X-ray emission at energies above similar to 4 keV from the group of galaxies HCG 62 using data from the ASCA satellite. The excess emission is spatially extended up to similar to 10' from the group center and somewhat enhanced toward the north. Its spectrum can be represented by either a power law of photon index 0.8-2.7 or a bremsstrahlung of temperature greater than 6.3 keV. In the 2-10 keV range, the observed hard X-ray flux, (1.0 +/- 0.3) x 10(-12) ergs cm(-2) s(-1), implies a luminosity of (8.0 +/- 2.0) x 10(41) ergs s(-1) for a Hubble constant of 50 km s(-1) Mpc(-1). The emission is thus too luminous to be attributed to X-ray binaries in the member galaxies. We discuss possible origins of the hard X-ray emission.

ASCA results are presented of extended X-rays from radio lobes of PKS B2356-601 and surrounding the cluster of galaxies Abell 4067. Obtained X-ray spectrum from the lobes allows two possibilities as its origin, those are a thin thermal plasma emission associated with one of lobes or an inverse-Compton (IC) emission by the relativistic electrons in the lobe. The paper presents a discussion on the origin and pressures of the lobe electrons and the surrounding intra-cluster medium.

The energy densities of electrons and magnetic fields, u(e) and u(m) respectively, are calculated for lobes of four radio galaxies from which the inverse Compton X-rays are detected. A tendency of u(e) > u(m) is found. Relations are examined between the core luminosity of radio galaxies and u(e) or u(m) in the lobes. We found that the ratio of u(e) to u(m) increases when the core becomes more active.

The ASTRO-E Hard X-ray Detector utilizes GSO/BGO well-type phoswich counters in compound-eye configuration, to achieve an extremely low background level of about a few times 10-5 counts s-1 cm-2 keV-1. The GSO scintillators placed at the bottom of the BGO well observe photons in the energy range 30-600 keV. To cover the lower energy range of 10-60 keV, silicon PIN diodes of 2 mm in thickness and 21.5 × 21.5mm2 in size were newly developed, and placed in front of the GSO scintillators. The PIN diode exhibits complex spectral responses, including subpeak and low energy tail components. To examine the origin of these components, we measured spatially-resolved response of the PIN diode, and confirmed that the subpeak and the low energy tail are related to the electrode structures and electric fields in the PIN diode, respectively.

The Bard X-ray Detector (HXD) is one of the three instruments on the fifth Japanese cosmic X-ray satellite ASTROE , scheduled for launch in January, 2000. The HXD covers a wide energy range of 10-600 keV, using 16 identical GSO/BGO phoswich-counter modules, of which the low-energy efficiency is greatly improved by adding 2 mm-thick silicon PIN diodes. Production of the HXD between completed and pre-flight calibration is now in progress. The design concept of the HXD sensor, detail of the production process, and a brief summary of the measured performance is reported.

A summary is presented of ASCA (Tanaka ct al. 1994) results on inverse-Comptonized X-rays from lobes of radio galaxies, which are emitted when relativistic electrons constructing synchrotron radio lobes boost up the cosmic microwave background photons to the X-ray and gamma-ray energy. By comparing the two radiation fluxes, we derived the energy distribution between magnetic fields and the relativistic electrons, assuming the same relativistic electrons in the lobes produce the emissions. This method is essentially free from the energy equipartition assumption. A study on spatial distributions of the field and particle energy densities is also presented. Based on the results presented in this paper, we suggest particle domination in the lobes and at the formation of the lobe.

The Hard X-ray Detector (HXD) is one of the three experiments of the Astro-E mission, the fifth Japanese X-ray satellite devoted to studies of high energy phenomena in the universe in the X-ray to soft gamma-ray region. Prepared for launch at the beginning of 2000 via the newly developed M-V launch vehicle of the Institute of Space and Astronautical Science, the Astro-E is to be thrown into a near-circular orbit of 550 km altitude, with an inclination of 31 degrees. The flight model has been finished assembled this year, and we carried out various tests to verify the performance. We acquired the background spectrum at sea level, and confirmed that our system is operating effectively in reducing the background level. The HXD will observe photons in the energy range of 10-600 keV, and the calculations based on the preflight calibration suggest that the HXD will have the highest sensitivity ever achieved in this energy range. We also verified that our electronic system will maintain its performance against charged particle events expected in orbit.

Hard X-ray Detector (HXD) is one of three instruments on the fifth Japanese X-ray astronomy satellite, Astro-E, scheduled for launch in 2000. The sensitivity of the Astro-E HXD will be higher by more than one order of magnitude than that of any previous instrument between 10 keV and several 100 keV. The electronic system is designed to handle many independent data channels from the HXD within the limitation of size and power consumption required in Astro-E. In this paper, we will present the design and the preliminary performance of the processing electronic system.