Hirohiko Honda

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.

X-Ray Probing of the Central Regions of Clusters of Galaxies

The results on ASCA X-ray study of the central regions of medium-richness clusters of galaxies are summarized, while emphasizing the differences between cD and non-cD clusters. The intra-cluster medium (ICM) is likely to consist of two (hot and cool) phases within ∼ 100kpc of a cD galaxy, where the ICM metallicity is also enhanced. In contrast, the ICM in non-cD clusters appears to be isothermal with a small metallicity gradient right of the center. The gravitational potential exhibits a hierarchical nesting around cD galaxies, while a total mass-density profile with a central cusp is indicated for a non-cD cluster, Abell 1060. The iron-mass-to-light ratio of the ICM decreases toward the center in both types of clusters, although it is radially constant in peripheral regions. The silicon-toiron abundance ratio in the ICM increases with the cluster richness, but remains close to the solar ratio around cD galaxies. These overall results are interpreted without appealing to the popular cooling-flow hypothesis. Instead, an emphasis is put on the halo-in-halo structure formed around cD galaxies.

ASCA Observations of the Temperature Structure and Metal Distribution in the Perseus Cluster of Galaxies

Large-scale distributions of hot-gas temperature and Fe abundance in the Perseus cluster have been studied with multi-pointing observations by the GIS instrument onboard ASCA. Within a radius of 20 � from the cluster center, the energy spectra requires two temperature components, in which the cool component indicates kT ∼2keV and the hot-component temperature shows a significant decline from about 8 keV to 6 keV toward the center. In the outer region of the cluster, the temperature shows a fluctuation with an amplitude of about 2 keV, which suggest that a western region at ∼ 16 � from the cluster center is relatively hotter. As for the Fe abundance, a significant decline with radius is detected from 0.44 solar at the center to ∼ 0.1 solar at a 50 � offset region. If the observed Fe-K line intensity within 4 � from the center is suppressed by a factor of 2 due to the resonance scattering effect, the corrected

Temperature Variation in the Cluster of Galaxies Abell 115 Studied with ASCA

Abell 115 exhibits two distinct peaks in the surface brightness distribution. Observation with ASCA shows a significant temperature variation in this cluster, confirmed by a hardness ratio analysis and spectral fits. A linking region between the main cluster and subcluster shows a high temperature compared with other regions. Two possibilities are examined as the cause of the temperature variation: cooling flows in the main cluster and a shock heating due to the collision of the subcluster into the main system. Spectral fits with cooling flow models to the main-cluster data show a mass-deposition rate less than 419 M☉ yr-1. Temperatures in the main cluster, the linking region, and the subcluster are estimated by correcting for the effects of X-ray telescope response as 4.9, 11, and 5.2 keV, respectively. The high temperature in the linking region implies that Abell 115 is indeed a merger system, with possible contribution from cooling flows on the temperature structure.

Calibration of Astro-D telescope with an x-ray pencil beam

The x-ray optical properties of X-Ray Telescopes (XRTs) on board Asca were evaluated with an x-ray pencil beam at ISAS 30 m x-ray beam line. The total effective area of four XRTs is obtained to be about 1300 cm2, 800 cm2, and 450 cm2 at each energy of 1.5 keV, 4.5 keV, and 8.0 keV, respectively. These values are about 15% less than those calculated by ray tracing method in an ideal case. The shadow effect of closely packed foils might be the main reason for the degradation of effective area. The Point Spread Function of XRT was also measured by an x-ray CCD. We have also measured the contamination of stray light, which were caused by the one time reflected photons (by primary or secondary mirror) and photons reflected on the back side surface of the mirror shells. The stray light profile and intensity were consistent to the results simulated by the ray tracing.

Simulink based model realization for CDMA communication over power lines

This paper discusses a Simulink based model realization for many-to-one and one-to-many access CDMA communication over power lines through a 2-wire power line cord with neutral line cord (2WN). In addition, a hardware prototype with TCP/IP data link layer (IEEE802.3) that can send and receive video images at a speed of 1 Mbps through 2WN is introduced.

Canards in a slow-fast continuous piecewise linear vector field

Canards are phenomena which occur in slow-fast systems when the parameter, /spl epsiv/, is appropriately small. An RLC circuit with a five-segment piecewise linear resistor, namely a two-dimensional five region continuous piecewise linear (CPWL) vector field, is considered. The paper discusses rigorously the canard in the four region CPWL vector field, in the case of /spl epsiv//spl rarr/0, and verification of the boundary canard without head and canard with head in the four region.

Rigorous Verification of Poincaré Map Generated by a Continuous Piece-Wise Linear Vector Field and Its Application

This paper provides algorithms in order to solve an interval implicit function of the Poincare map generated by a continuous piecewise linear (CPWL) vector field, with the use of interval arithmetic. The algorithms are implemented with the use of MATLAB and INTLAB. We present an application to verification of canards in two-dimensional CPWL vector field appearing in nonlinear piecewise linear circuits frequently, and confirm that the algorithms are effective.

Rigorous verification of formal chaos produced by one-dimensional discrete dynamical system with use of interval arithmetic

Definitions of chaos and its observability for 1D mapping systems are briefly reviewed. This paper provides a theorem guaranteeing that formal chaos exists in 1D mapping system based on one dimensional horseshoe map geometrical structure, and also provides algorithms verifying the conditions in the theorem with the use of interval arithmetic. Further this paper discusses the effectiveness of the approach through an example of a transmission line circuit with nonlinear boundary conditions.

Error budgets for the image degradation of x-ray telescope on board Astro-E2

X-ray telescopes (XRTs) of nested thin foil mirrors were developed for Astro-E, the fifth Japanese x-ray astronomy satellite. Although the launch was not successful, the re-flight of Astro-E mission is approved as Astro-E2 and will carry the same XRTs. Ground-based calibration of Astro-E XRT revealed that its image quality and effective area are somewhat worse than what are expected from the original design. Conceivable causes of these defects of the XRT performance (i.e., surface roughness, waviness, misalignment of reflectors, and so on) are examined by X-rays and optical microscopic measurements. In this paper, we distinguish quantitatively these causes to limit the performance of the Astro-E XRT. Using the detail measurements, we can attribute both degradation of the image quality and a deficit of the effective area from the design values mainly to a slope error with a mm scale in each reflector and shadowing effects of neighboring reflectors due to various factors. There is still room for improvement in the support system of reflectors (i.e., alignment bars) in the XRT. One of the main aims of the mirror system calibration is to construct response function. Therefore, it is important that the development of a representative numerical model and its validation against extensive ground-based calibration. Taking account of the results of the pre-flight calibration and the microscopic measurements, we develop and tune a ray-tracing simulator which constructs the XRT response function for a point source at an arbitrary off-axis angle and spatial distributions of celestial X-ray sources.