Discovery of Gas Bulk Motion in the Galaxy Cluster Abell 2256 with Suzaku

The results from Suzaku observations of the galaxy cluster Abell2256 are presented. This cluster is a prototypical and well-studied merging system, exhibiting substructures both in the X-ray surface brightness and in the radial velocity distribution of member galaxies. There are main and sub components separating by 3'.5 in the sky and by about 2000 km s$^{-1}$ in radial velocity peaks of member galaxies. In order to measure Doppler shifts of iron K-shell lines from the two gas components by the Suzaku XIS, the energy scale of the instrument was evaluated carefully and found to be calibrated well. A significant shift of the radial velocity of the sub component gas with respect to that of the main cluster was detected. All three XIS sensors show the shift independently and consistently among the three. The difference is found to be 1500 $\pm 300$ (statistical) $\pm 300$ (systematic) km s$^{-1}$. The X-ray determined absolute redshifts of and hence the difference between the main and sub components are consistent with those of member galaxies in optical. The observation indicates robustly that the X-ray emitting gas is moving together with galaxies as a substructure within the cluster. These results along with other X-ray observations of gas bulk motions in merging clusters are discussed.Comment: Accepted for publication in PASJ in 2011-03-2

Interferometric Measurement of Large Number Density of Metal Vapor in the Heat Pipe

A method is proposed which permits one to determine a large number density of metal atoms along the absorption path in a heat-pipe cell. The proposed method requires a measurement of the anomalous dispersion near the absorption lines with known oscillator strengths by the use of a Mach-Zehnder interferometer and a stigmatic spectrograph. The method is tested on the resonance line of calcium and the first doublet of sodium. Its advantage over the hook method and the method by Frich et al. is demonstrated, and its precision and validity are discussed

Competition of resonant and nonresonant paths in resonance-enhanced two-photon single ionization of He by an ultrashort extreme-ultraviolet pulse

We theoretically study the pulse-width dependence of the photoelectron angular distribution (PAD) from the resonance-enhanced two-photon single ionization of He by femtosecond ($\lesssim 20$ fs) extreme-ultraviolet pulses, based on the time-dependent perturbation theory and simulations with the full time-dependent Schr\"odinger equation. In particular, we focus on the competition between resonant and nonresonant ionization paths, which leads to the relative phase $\delta$ between the $S$ and $D$ wave packets distinct from the corresponding scattering phase shift difference. When the spectrally broadened pulse is resonant with an excited level, the competition varies with pulse width, and, therefore, $\delta$ and the PAD also change with it. On the other hand, when the Rydberg manifold is excited, $\delta$ and the PAD do not much vary with the pulse width, except for the very short pulse regime.Comment: 5 pages, 5 figures, 1 tabl

Observations of Collision-Induced Dipole Transitions Associated with High-Lying States of Calcium in Rare Gases

More than 20 collision-induced dipole (CID) transitions have been observed in the absorption spectrum of calcium below 2400 A in the presence of xenon or krypton. Some have also been observed in the presence of argon, neon or helium. The measured shifts and the effective oscillator strengths show a close correlation with the s-wave amplitude for the electron scattering by a rare-gas atom. This correlation leads us to the conclusion that the low-energy-electron-scattering process is responsible for the appearance of the CID transitions