Suzaku Observation of the Radio Halo Cluster Abell 2319: Gas Dynamics and Hard X-ray Properties

We present the results of Suzaku observation of the radio halo cluster Abell 2319. The metal abundance in the central cool region is found to be higher than the surrounding region, which was not resolved in the former studies. We confirm that the line-of-sight velocities of the intracluster medium in the observed region are consistent with those of the member galaxies of entire A2319 and A2319A subgroup for the first time, though any velocity difference within the region is not detected. On the other hand, we do not find any signs of gas motion relevant to A2319B subgroup. Hard X-ray emission from the cluster is clearly detected, but its spectrum is likely thermal. Assuming a simple single temperature model for the thermal component, we find that the upper limit of the non-thermal inverse Compton component becomes $2.6 \times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$ in the 10-40 keV band, which means that the lower limit of the magnetic field is 0.19 $\mu$G with the radio spectral index 0.92. Although the results slightly depend on the detailed spectral modeling, it is robust that the upper limit of the power-law component flux and lower limit of the magnetic field strength become $\sim 3 \times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$ and $\sim 0.2 \mu$G, respectively. Considering the lack of a significant amount of very hot ($\sim 20$ keV) gas and the strong bulk flow motion, it is more likely that the relativistic non-thermal electrons responsible for the radio halo are accelerated through the intracluster turbulence rather than the shocks.Comment: 12 pages, 15 figures, accepted for publication in PAS

The origin of an extended X-ray emission apparently associated with the globular cluster 47 Tucanae

Using the Suzaku X-ray Imaging Spectrometer, we performed a 130 ks observation of an extended X-ray emission, which was shown by ROSAT and Chandra observations to apparently associate with the globular cluster 47 Tucanae. The obtained $0.5-6$ keV spectrum was successfully fitted with a redshifted thin thermal plasma emission model whose temperature and redshift are $2.2^{+0.2}_{-0.3}$keV (at the rest frame) and $0.34\pm0.02$, respectively. Derived parameters, including the temperature, redshift, and luminosity, indicate that the extended X-ray source is a background cluster of galaxies, and its projected location falls, by chance, on the direction of the proper motion of 47 Tucanae.Comment: 9 pages, 9 figures, accepted for publication in PASJ Vol. 61 No.

Study of the Large-scale Temperature Structure of the Perseus Cluster with Suzaku

We report on a study of the large-scale temperature structure of the Perseus cluster with Suzaku, using the observational data of four pointings of 30' offset regions, together with the data from the central region. Thanks to the Hard X-ray Detector (HXD-PIN: 10 - 60 keV), Suzaku can determine the temperature of hot galaxy clusters. We performed the spectral analysis, by considering the temperature structure and the collimator response of the PIN correctly. As a result, we found that the upper limit of the temperature in the outer region is $\sim$ 14 keV, and an extremely hot gas, which was reported for RXJ 1347.5-1145 and A 3667, was not found in the Perseus cluster. This indicates that the Perseus cluster has not recently experienced a major merger.Comment: 17 pages, 25 figures, accepted for Publications of the Astronomical Society of Japan, references adde

X-Ray View of the Shock Front in the Merging Cluster Abell 3376 with Suzaku

We report on a Suzaku measurement of the shock feature associated with the western radio relic in the merging cluster A3376. The temperature profile is characterized by an almost flat radial shape with kT ~ 4 keV within 0.5 r200 and a rise by about 1 keV inside the radio relic. Across the relic region (0.6-0.8 r200), the temperature shows a remarkable drop from about 4.7 keV to 1.3 keV. This is a clear evidence that the radio relic really corresponds to a shock front possibly caused by a past major merger. The observed sharp changes of the temperature and electron density indicate the Mach number M~3. The radial entropy profile is flatter than the prediction (r^1.1) of numerical simulations within 0.5 r200}, and becomes steeper around the relic region. These observed features and time-scale estimation consistently imply that the ICM around the radio relic has experienced a merger shock and is in the middle of the process of dynamical and thermal relaxation.Comment: Accepted for publication in PASJ (12 pages, 6 figures

The Nature of the Stable Soft X-ray Emissions in Several Types of Active Galactic Nuclei Observed by Suzaku

To constrain the origin of the soft X-ray excess phenomenon seen in many active galactic nuclei, the intensity-correlated spectral analysis, developed by Noda et al. (2011b) for Markarian 509, was applied to wide-band (0.5-45 keV) Suzaku data of five representative objects with relatively weak reflection signature. They are the typical bare-nucleus type 1 Seyfert Fairall 9, the bright and typical type 1.5 Seyfert MCG-2-58-22, 3C382 which is one of the X-ray brightest broad line radio galaxies, the typical Seyfert-like radio loud quasar 4C+74.26, and the X-ray brightest radio quiet quasar MR2251-178. In all of them, soft X-ray intensities in energies below 3 keV were tightly correlated with that in 3-10 keV, but with significant positive offsets. These offsets, when calculated in finer energy bands, define a stable soft component in 0.5-3 keV. In each object, this component successfully explained the soft excess above a power-law fit. These components were interpreted in several alternative ways, including a thermal Comptonization component which is independent of the dominant power-law emission. This interpretation, considered physically most reasonable, is discussed from a viewpoint of Multi-Zone Comptonization, which was proposed for the black hole binary Cygnus X-1 (Makishima et al. 2008).Comment: 18 pages, 12 figures, 7 table

Implications of the mild gas motion found with Hitomi in the core of the Perseus cluster

Based mainly on X-ray observations, studies are made on interactions between the intra-cluster medium (ICM) in clusters of galaxies and their member galaxies. Through (magneto)hydrodynamic and gravitational channels, the moving galaxies are expected to drag the ICM around them, and transfer to the ICM some fraction of their dynamical energies on cosmological time scales. This hypothesis is in line with several observations, including the possible cosmological infall of galaxies towards the cluster center, found over redshifts of z~1 to z~0. Further assuming that the energy lost by the galaxies is first converted into ICM turbulence and then dissipated, this picture can explain the subsonic and uniform ICM turbulence, measured with Hitomi in the core region of the Perseus cluster. The scenario may also explain several other unanswered problems regarding clusters of galaxies, including what prevents the ICM from the expected radiative cooling, how the various mass components in nearby clusters have attained different radial distributions, and how a thermal stability is realized between hot and cool ICM components that co-exist around cD galaxies. This view is also considered to pertain to the general scenario of galaxy evolution, including their environmental effects.Comment: 15 pages, 3 figures, accepted for publication in A&

Suzaku Observation of Abell 1555 and Abell 1558: Searching for Non-thermal Emission from Large Scale Structure Formation

We report X-ray observations of two galaxy clusters Abell 1555 and Abell 1558 with Suzaku, which are included in a large scale filamentary structure and a supercluster, to search for non-thermal emission driven by shocks produced in structure formation. These two clusters are detected by Suzaku/XIS for the first time in the X-ray band of 0.5-7 keV. No significant flux is detected by HXD in the energy band of 13-40 keV, and upper limits are reported. From the analysis of the XIS data, we find that the spectrum of A1555 is fit by a thermal plus power-law model, significantly better than a single-temperature pure thermal spectrum. If this power-law component is due to inverse-Compton scattering, the fraction of total baryon energy imparted to non-thermal electrons is consistent with the typical value inferred from the observation of other clusters. However, other scenarios (e.g., under lying AGNs, multi-temperature thermal models) cannot be excluded and further investigation of this system is desired. Basic physical properties of A1555 (e.g., total mass) are also reported.Comment: 10 pages, 6 figures. Accepted for publication in the PAS