Detection of Excess Hard X-ray Emission from the Group of Galaxies HCG62

From the group of galaxies HCG62, we detected an excess hard X-ray emission in energies above $\sim 4$ keV with \A SCA. The excess emission is spatially extended up to $\sim10'$ from the group center, and somewhat enhanced toward north. Its spectrum can be represented by either a power-law of photon index 0.8-2.7, or a Bremsstrahlung of temperature $>6.3$ keV. In the 2-10 keV range, the observed hard X-ray flux, $(1.0\pm0.3)\times10^{-12}$ erg cm$^{-2}$ s$^{-1}$, implies a luminosity of $(8.0\pm2.0)\times10^{41}$ erg 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 memb er galaxies. We discuss possible origin of the hard X-ray emission.Comment: 6 pages, 3 Postscript figures, uses emulateapj.sty. Accepted for publication in the Astrophysical Journal Letter

The Galaxy Cluster Luminosity-Temperature Relationship and Iron Abundances - A Measure of Formation History ?

Both the X-ray luminosity-temperature (L-T) relationship and the iron abundance distribution of galaxy clusters show intrinsic dispersion. Using a large set of galaxy clusters with measured iron abundances we find a correlation between abundance and the relative deviation of a cluster from the mean L-T relationship. We argue that these observations can be explained by taking into account the range of cluster formation epochs expected within a hierarchical universe. The known relationship of cooling flow mass deposition rate to luminosity and temperature is also consistent with this explanation. From the observed cluster population we estimate that the oldest clusters formed at z>~2. We propose that the iron abundance of a galaxy cluster can provide a parameterization of its age and dynamical history.Comment: 13 pages Latex, 2 figures, postscript. Accepted for publication in ApJ Letter

Suppression of Magnetic Order by Pressure in BaFe2As2

We performed the dc resistivity and the ZF 75As-NMR measurement of BaFe2As2 under high pressure. The T-P phase diagram of BaFe2As2 determined from resistivity anomalies and the ZF 75As-NMR clearly revealed that the SDW anomaly is quite robust against P.Comment: 2 pages, 2 figure

X-ray Measurements of the Gravitational Potential Profile in the Central Region of the Abell 1060 Cluster of Galaxies

X-ray spectral and imaging data from ASCA and ROSAT were used to measure the total mass profile in the central region of Abell 1060, a nearby and relatively poor cluster of galaxies. The ASCA X-ray spectra, after correcting for the spatial response of the X-ray telescope, show an isothermal distribution of the intra-cluster medium (ICM) within at least $\sim$ 12' (or $160h_{70}^{-1}$ kpc; $H_0 = 70 h_{70}$ km s$^{-1}$Mpc$^{-1}$) in radius of the cluster center. The azimuthally averaged surface brightness profile from the ROSAT PSPC exhibits a central excess above an isothermal $\beta$ model. The ring-sorted ASCA GIS spectra and the radial surface brightness distribution from the ROSAT PSPC were simultaneously utilized to constrain the gravitational potential profile. Some analytic models of the total mass density profile were examined. The ICM density profile was also specified by analytic forms. The ICM temperature distribution was constrained to satisfy the hydrostatic equilibrium, and to be consistent with the data. Then, the total mass distribution was found to be described better by the universal dark halo profile proposed by Navarro, Frenk, and White (1996;1997) than by a King-type model with a flat density core. A profile with a central cusp together with a logarithmic radial slope of $\sim 1.5$ was also consistent with the data. Discussions are made concerning the estimated dark matter distribution around the cluster center.Comment: 32 pages. Accepted: ApJ 2000, 35 pages, Title was correcte

Optical I-band Linear Polarimetry of the Magnetar 4U 0142+61 with Subaru

The magnetar 4U~0142+61 has been well studied at optical and infrared wavelengths and is known to have a complicated broad-band spectrum over the wavelength range. Here we report the result from our linear imaging polarimetry of the magnetar at optical $I$-band. From the polarimetric observation carried out with the 8.2-m Subaru telescope, we determine the degree of linear polarization $P=1.0\pm$3.4\%, or $P\leq$5.6\% (90\% confidence level). Considering models suggested for optical emission from magnetars, we discuss the implications of our result. The upper limit measurement indicates that different from radio pulsars, magnetars probably would not have strongly polarized optical emission if the emission arises from their magnetosphere as suggested.Comment: 5 pages, 1 figure, accepted for publication on Ap