Yasushi Fukazawa

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.

Scaling Mass Profiles around Elliptical Galaxies Observed with Chandra and XMM-Newton

We investigated the dynamical structure of 53 elliptical galaxies using the Chandra archival X-ray data. In X-ray-luminous galaxies, temperature increases with radius and gas density is systematically higher at the optical outskirts, indicating the presence of a significant amount of the group-scale hot gas. In contrast, X-ray-dim galaxies show a flat or declining temperature profile against radius and the gas density is relatively lower at the optical outskirts. Thus, it is found that X-ray-bright and faint elliptical galaxies are clearly distinguished by the temperature and gas density profile. The mass profile is well scaled by a virial radius r200 rather than an optical half-radius re, is quite similar at (0.001-0.03)r200 between X-ray-luminous and dim galaxies, and smoothly connects to those profiles of clusters of galaxies. At the inner region of (0.001-0.01)r200 or (0.1-1)re, the mass profile well traces a stellar mass with a constant mass-to-light ratio of M/LB = 3-10 M☉/L☉. The M/LB ratio of X-ray-bright galaxies rises up steeply beyond 0.01r200 and thus requires a presence of massive dark matter halo. From the deprojection analysis combined with the XMM-Newton data, we found that X-ray-dim galaxies NGC 3923, NGC 720, and IC 1459 also have a high M/LB ratio of 20-30 at 20 kpc, comparable to that of X-ray-luminous galaxies. Therefore, dark matter is indicated to be common in elliptical galaxies; their dark matter distribution, as well as that of galaxy clusters, almost follows the NFW profile.

ASCA Measurements of Silicon and Iron Abundances in the Intracluster Medium

We analyzed the ASCA X-ray data of 40 nearby Clusters of galaxies, whose intracluster-medium temperature distributes in the range of 0.9-10 keV. We measured the Si and Fe abundances of the intracluster medium, spatially averaging over each Cluster, but excluding the central ~ 0.15/I^Q1 Mpc region in order to avoid any possible abundance gradients and complex temperature structures. The Fe abundances of these Clusters are 0.2-0.3 solar, with only weak dependence on the temperature of the intracluster medium, hence on the Cluster richness. In contrast, the Si abundance is observed to increase from 0.3 to 0.6-0.7 solar from the poorer to richer Clusters. These results suggest that the Supernovae of both type-Ia and type-II significantly contribute to the metal enrichment of the intracluster medium, with the relative contribution of type-II Supernovae increasing towards richer Clusters. We suggest a possibility that a considerable fraction of type-II Supernova products escaped from poorer Systems.

Discovery of Spectral Transitions from Two Ultraluminous Compact X-Ray Sources in IC 342

Two ASCA observations were made of two ultraluminous compact X-ray sources (ULXs) in the spiral galaxy IC 342. In the 1993 observation, source 2 showed a 0.5-10 keV luminosity of 6 × 1039 ergs s-1 (assuming a distance of 4.0 Mpc) and a hard power-law spectrum of photon index ~1.4. As already reported, source 1 was ~3 times brighter on that occasion and exhibited a soft spectrum represented by a multicolor disk model with an inner-disk temperature of ~1.8 keV. The second observation, made in 2000 February, revealed that source 1 had made a transition into a hard spectral state, while source 2 made a transition into a soft spectral state. The ULXs are therefore inferred to exhibit two distinct spectral states, and they sometimes make transitions between them. These results significantly reinforce the scenario that describes ULXs as mass-accreting black holes.

Early Phase Obserbations of Extermely Luminous Type Ia Supernova 2009dc

We present early phase observations in optical and near-infrared wavelengths for the extremely luminous Type Ia supernova (SN Ia) 2009dc. The decline rate of the light curve is ?m 15(B) = 0.65 ? 0.03, which is one of the slowest among SNe Ia. The peak V-band absolute magnitude is estimated to be MV = ?19.90 ? 0.15?mag if no host extinction is assumed. It reaches MV = ?20.19 ? 0.19?mag if we assume the host extinction of AV = 0.29?mag. SN 2009dc belongs to the most luminous class of SNe Ia, like SNe 2003fg and 2006gz. Our JHKs -band photometry shows that this SN is also one of the most luminous SNe Ia in near-infrared wavelengths. We estimate the ejected 56Ni mass of 1.2 ? 0.3 M ? for the no host extinction case (and of 1.6 ? 0.4 M ? for the host extinction of AV = 0.29?mag). The C II ?6580 absorption line remains visible until a week after the maximum brightness, in contrast to its early disappearance in SN 2006gz. The line velocity of Si II ?6355 is about 8000?km?s?1 around the maximum, being considerably slower than that of SN 2006gz. The velocity of the C II line is similar to or slightly less than that of the Si II line around the maximum. The presence of the carbon line suggests that the thick unburned C+O layer remains after the explosion. Spectropolarimetric observations by Tanaka et?al. indicate that the explosion is nearly spherical. These observational facts suggest that SN 2009dc is a super-Chandrasekhar mass SN Ia.

Structure of the X-Ray-emitting Gas in the Hydra A Cluster of Galaxies

The temperature and abundance structure in the intracluster medium (ICM) of the Hydra A Cluster of galaxies is studied with ASCA and ROSAT. The effect of the large extended outskirts in the point-spread function of the X-ray telescope on ASCA is included in this analysis. In the X-ray brightness profile, the strong central excess above a single β model, identified in the Einstein and ROSAT data, is also found in the harder energy band (>4 keV). A simultaneous fit of five annular spectra taken with the GIS instrument shows a radial distribution of the temperature and metal abundance. A significant central enhancement in the abundance distribution is found, while the temperature profile suggests that the ICM is approximately isothermal, with a temperature of ~3.5 keV. The ROSAT position-sensitive proportional counter (PSPC) spectrum in the central 15 region indicates a significantly lower temperature than the GIS result. A joint analysis of the GIS and PSPC data reveals that the spectra can be described by a two-temperature model as well as by a cooling flow model. In both cases, the hot-phase gas with a temperature of ~3.5 keV occupies more than 90% of the total emission measure within 15 from the cluster center. The estimated mass of the cooler (0.5-0.7 keV) component is ~(2-6) × 109 M☉, which is comparable to the mass of hot halos seen in non-cD ellipticals. The cooling flow model gives the mass deposition rate of 60 ± 30 M☉ yr-1, an order of magnitude lower than the previous estimation.

Detections of hard X-ray emissions from bright early-type galaxies with ASCA

Five bright elliptical galaxies in the Virgo Cluster, NGC 4365, NGC 4374 (M84), NGC 4406 (M86), NGC 4472 (M49), and NGC 4636, were observed with ASCA. In addition to the extended thermal X-ray emission of temperature kT approximately 1 keV, harder X-rays with color temperature kT greater than or equal to 2 keV were detected from all of them. The 2-10 keV luminosities of this hard component for the five galaxies, integrated within 5 min, are distributed within a relatively narrow range of (1-4) x 10(exp 40) ergs/s. The hard X-ray component is primarily attributed to the integrated emission from discrete X-ray sources. In NGC 4406 and NGC 4374 the data indicate that the hard component is contributed additionally by foreground/background emission from the hot intracluster medium (ICM) of the Virgo Cluster. The hard component of NGC 4472 seems also contributed by the Virgo ICM emission, but in this case there is evidence that the ICM brightness is locally enhanced within approximately 10 min of NGC 4472.

High resolution CdTe detectors for the next-generation multi-Compton gamma-ray telescope

A multi-Compton gamma-ray telescope based on high resolution semiconductor materials (Semiconductor Multi-Compton Telescope (SMCT) or Advanced Compton Telescope (ACT)) is a promising approach to achieve high sensitivity for gamma-rays with energies from several hundred keV up to several MeV. A SMCT utilizing several tens of layers of thin CdTe (Cadmium Telluride) detector is an attractive concept to obtain higher detection efficiency in comparison with Si-based SMCT. Recently we have developed high energy-resolution CdTe diode detectors. A large-area detector with dimensions of 2.15 × 2.15 cm2 with a thickness of 0.5mm shows an energy resolution of better than 3 keV (FWHM) at 60 keV. In order to extend the application of CdTe diodes to the detection of MeV gamma-rays, we have constructed a stacked detector consisting of 40 layers of large CdTe diodes. Here we report the recent progress on the high-resolution CdTe diode and describe the conceptual design of new Multi-Compton Gamma-ray telescopes based on Monte Carlo simulation. An idea of active pair production telescope is briefly described.

Temperature Dependence of Scintillation Properties of Bright Oxide Scintillators for Well-Logging

Scintillation characteristics such as the pulse height, energy resolution, and decay time of single crystals of Tl-doped NaI (Tl:NaI), Ce-doped Lu2SiO5 (Ce:LSO), Ce-doped YAlO3 (Ce:YAP), Ce-doped Gd3(Al,Ga)5O12 (Ce:GAGG), Pr-doped Lu3Al5O12 (Pr:LuAG), undoped LuAG, and Ce-doped Y3Al5O12 (Ce:YAG) transparent ceramics were compared at 25–150 °C to simulate well logging conditions. For increasing temperature, the light output of the scintillators decreased, mostly because of thermal quenching. Among these samples, Pr:LuAG demonstrated the highest scintillation performance at 150 °C.