Extended Thermal X-ray Emission from the Spiral-Dominant Group of Galaxies HCG 57

We observed a group of galaxies, HCG 57, with ASCA. Regardless that their member galaxies are dominated by spiral galaxies, we detected extended thermal X-ray emission that is attributed to hot gas with a temperature of $1.04\pm0.10$ keV. This is the second clear detection of thermal X-ray emission from a spiral-dominant group of galaxies after HCG 92. The luminosity of the thermal emission is about $5\times10^{41}$ erg s$^{-1}$ in the 0.5--10 keV band, which is higher than that of HCG 92, but relatively less luminous among groups of galaxies. The X-ray emission is extended over several member galaxies, and is thus associated with the group rather than an individual galaxy. The metal abundance cannot be well constrained with a lower limit of 0.08 solar. The gas-to-stellar mass ratio is $\sim0.3$. Although this is relatively low among groups, the hot gas is also a significant component even in the spiral-dominant group. We suggest that the X-ray faintness of spiral-dominant groups is due to the low surface brightness and somewhat low gas mass, at least in the case of HCG 57.Comment: 12 pages, 4 figures, to appear in PASJ 54 No.

Chandra X-Ray Spectral Analysis of Cooling Flow Clusters, 2A 0335+096 and Abell 2199

We report on a spatially resolved analysis of Chandra X-ray data on a nearby typical cooling flow cluster of galaxies 2A 0335+096, together with A 2199 for a comparison. As recently found in the cores of other clusters, the temperature around the central part of 2A 0335+096 is 1.3--1.5 keV, which is higher than that inferred from the cooling flow picture. Furthermore, the absorption column density is almost constant against the radius in 2A 0335+096; there is no evidence of excess absorption up to 200--250 kpc. This indicates that no significant amount of cold material, which has cooled down, is present. These properties are similar to those of A 2199. Since the cooling time in the central part is much shorter than the age of the clusters, a heating mechanism, which weakens the effect of radiative cooling, is expected to be present in the central part of both clusters of galaxies. Both 2A 0335+096 and A 2199 have radio jets associated with their cD galaxy. We discuss the possibility of heating processes caused by these radio jets by considering the thermal conduction and the sound velocity together with the observed disturbance of the ICM temperature and density. We conclude that the observed radio jets can produce local heating and/or cooling, but do not sufficiently reduce the overall radiative cooling. This implies that much more violent jets, whose emission has now decayed, heated up the cooling gas $>10^9$ years ago.Comment: 13 pages, 7 figures, to appear in PASJ 55 No.

Influence of mechanical reinforcement of MgB2 wires on the superconducting properties

Monofilamentary MgB2-wires with a mechanical tough Nb/Cu/steel or Fe/steel sheath were prepared and characterized. The steel content was varied to investigate the reinforcement effect and the consequences for the superconducting properties of the wires, which were heat treated to achieve dense and homogeneous filaments. The use of Nb as first sheath layer, having a smaller thermal expansion coefficient than MgB2, requires the application of higher amounts of steel to achieve compressive pre-stress on the filament in comparison to Fe as first wall material. With raised steel content in the sheath the critical transport currents show field dependent significant critical current and irreversibility field degradations. First Ic vs. axial stress and strain experiments confirmed this observation of pre-stress induced degradations. Consequences for improved wires and for future applications will be discussed.Comment: 14 pages, 7 figures, 1 table; Submitted to Physica C; presentation at ISS-2001, Kobe Japa