Yoh Takei

Baryons at the Edge of the X-ray–Brightest Galaxy Cluster

The Suzaku satellite provides a census of the gas, metals, and dark matter out to the outskirts of the Perseus Cluster. Studies of the diffuse x-ray–emitting gas in galaxy clusters have provided powerful constraints on cosmological parameters and insights into plasma astrophysics. However, measurements of the faint cluster outskirts have become possible only recently. Using data from the Suzaku x-ray telescope, we determined an accurate, spatially resolved census of the gas, metals, and dark matter out to the edge of the Perseus Cluster. Contrary to previous results, our measurements of the cluster baryon fraction are consistent with the expected universal value at half of the virial radius. The apparent baryon fraction exceeds the cosmic mean at larger radii, suggesting a clumpy distribution of the gas, which is important for understanding the ongoing growth of clusters from the surrounding cosmic web.

Energy Spectra of the Soft X-Ray Diffuse Emission in Fourteen Fields Observed with Suzaku

The soft diffuse X-ray emission of twelve fields observed with Suzaku are presented together with two additional fields from previous analyses. All have galactic longitudes 65 deg < l < 295 deg to avoid contributions from the very bright diffuse source that extends at least 30 deg from the Galactic center. The surface brightnesses of the Suzaku nine fields for which apparently uncontaminated ROSAT All Sky Survey (RASS) were available were statistically consistent with the RASS values, with an upper limit for differences of 17 x 10^{-6} c s^{-1} amin^{-2} in R45}-band. The Ovii and Oviii intensities are well correlated to each other, and Ovii emission shows an intensity floor at ~2 photons s^{-1} cm^{-2 str^{-1} (LU). The high-latitude Oviii emission shows a tight correlation with excess of Ovii emission above the floor, with (Oviii intensity) = 0.5 x [(Ovii intensity) -2 LU], suggesting that temperatures averaged over different line-of-sight show a narrow distribution around ~0.2 keV. We consider that the offset intensity of Ovii arises from the Heliospheric solar wind charge exchange and perhaps from the local hot bubble, and that the excess Ovii (2-7 LU) is emission from more distant parts of the Galaxy. The total bolometric luminosity of this galactic emission is estimated to be 4 x 10^{39} erg s^{-1}, and its characteristic temperature may be related to the virial temperature of the Galaxy.

O and Ne K Absorption Edge Structures and Interstellar Abundance toward Cygnus X-2

We have studied the O and Ne absorption features in the X-ray spectrum of Cyg X-2, observed with the Chandra LETG. The O absorption edge is represented by the sum of three absorption edge components within the limit of the energy resolution and the photon counting statistics. Two of them are due to the atomic O; their energies correspond to two distinct spin states of photoionized O atoms. The remaining edge component is considered to represent compound forms of oxide dust grains. Since Cyg X-2 is about 1.4 kpc above the Galactic disk, the H column densities can be determined by radio (21 cm and CO emission line) and Hα observations, with relatively small uncertainties. Thus, the O abundance relative to H can be determined from the absorption edges. We found that the dust scattering can affect the apparent depth of the edge of the compound forms. We determined the amplitude of the effect, which we consider to be the largest possible correction factor. The ratio of column densities of O in atomic to compound forms and the total abundance of O were determined to be in the ranges 1.7 to 2.8 (ratio) and 0.63 ± 0.12 to 0.74 ± 0.14 solar (abundance), taking into account the uncertainties in the dust-scattering correction and in the ionized H column density. We also determined the Ne abundance from the absorption edge to be 0.75 ± 0.20 solar. These abundance values are smaller than the widely used solar values, but consistent with the latest estimates of solar abundance.

Azimuthally Resolved X-Ray Spectroscopy to the Edge of the Perseus Cluster

We present the results from extensive, new observations of the Perseus Cluster of galaxies, obtained as a Suzaku Key Project. The 85 pointings analyzed span eight azimuthal directions out to 2 degrees = 2.6 Mpc, to and beyond the virial radius r_200 ~ 1.8 Mpc, offering the most detailed X-ray observation of the intracluster medium (ICM) at large radii in any cluster to date. The azimuthally averaged density profile for r>0.4r_200 is relatively flat, with a best-fit power-law index of 1.69+/-0.13 significantly smaller than expected from numerical simulations. The entropy profile in the outskirts lies systematically below the power-law behavior expected from large-scale structure formation models which include only the heating associated with gravitational collapse. The pressure profile beyond ~0.6r_200 shows an excess with respect to the best-fit model describing the SZ measurements for a sample of clusters observed with Planck. The inconsistency between the expected and measured density, entropy, and pressure profiles can be explained primarily by an overestimation of the density due to inhomogeneous gas distribution in the outskirts; there is no evidence for a bias in the temperature measurements within the virial radius. We find significant differences in thermodynamic properties of the ICM at large radii along the different arms. Along the cluster minor axis, we find a flattening of the entropy profiles outside ~0.6r_200, while along the major axis, the entropy rises all the way to the outskirts. Correspondingly, the inferred gas clumping factor is typically larger along the minor than along the major axis.

SUZAKU OBSERVATIONS OF THE DIFFUSE X-RAY EMISSION ACROSS THE FERMI BUBBLES' EDGES

We present SuzakuX-ray observations along two edge regions of the Fermi Bubbl es, with eight≃ 20 ksec pointings across the northern part of the North Polar Spur (N PS) surrounding the north bubble and six across the southernmost edge of the south bubble. After removing co mpact X-ray features, diffuse X-ray emission is clearly detected and is well reproduced by a three-componen t sp ctral model consisting of unabsorbed thermal emission (temperature kT ≃ 0.1 keV) from the Local Bubble (LB), absorbed kT ≃ 0.3 keV thermal emission related to the NPS and/or Galactic Halo (GH), and a power-law component at a level consistent with the cosmic X-ray background. The emission measure (EM) of the 0. 3 keV plasma decreases by ≃ 50% toward the inner regions of the north-east bubble, with no accompan ying temperature change. However, such a jump in the EM is not clearly seen in the south bubble data. While it is unclear if the NPS originates from a nearby supernova remnant or is related to previous activity wi hin/around the Galactic Center, our Suzaku observations provide evidence suggestive of the latter sce nario. In the latter framework, the presence of a large amount of neutral matter absorbing the X-ray emission as wel l as the existence of the kT ≃ 0.3 keV gas can be naturally interpreted as a weak shock driven by the bubble s’ expansion in the surrounding medium, with velocityvexp ∼ 300 km s (corresponding to shock Mach number M ≃ 1.5), compressing the GH gas to form the NPS feature. We also derived an upper limit for any non-th ermal X-ray emission component associated with the bubbles and demonstrate, that in agreement with the findings above, the non-thermal pressure and energy estimated from a one-zone leptonic model of its broad -band spectrum, are in rough equilibrium with that of the surrounding thermal plasma. Subject headings: acceleration of particles — cosmic rays — Galaxy: center — Ga laxy: halo — X-rays: ISM

The Astro-H High Resolution Soft X-Ray Spectrometer

We present the overall design and performance of the Astro-H (Hitomi) Soft X-Ray Spectrometer (SXS). The instrument uses a 36-pixel array of x-ray microcalorimeters at the focus of a grazing-incidence x-ray mirror Soft X-Ray Telescope (SXT) for high-resolution spectroscopy of celestial x-ray sources. The instrument was designed to achieve an energy resolution better than 7 eV over the 0.3-12 keV energy range and operate for more than 3 years in orbit. The actual energy resolution of the instrument is 4-5 eV as demonstrated during extensive ground testing prior to launch and in orbit. The measured mass flow rate of the liquid helium cryogen and initial fill level at launch predict a lifetime of more than 4 years assuming steady mechanical cooler performance. Cryogen-free operation was successfully demonstrated prior to launch. The successful operation of the SXS in orbit, including the first observations of the velocity structure of the Perseus cluster of galaxies, demonstrates the viability and power of this technology as a tool for astrophysics.

LARGE-SCALE MOTIONS IN THE PERSEUS GALAXY CLUSTER

By combining large-scale mosaics of ROSAT PSPC, XMM-Newton, and Suzaku X-ray observations, we present evidence for large-scale motions in the intracluster medium of the nearby, X-ray bright Perseus Cluster. These motions are suggested by several alternating and interleaved X-ray bright, low-temperature, low-entropy arcs located along the east-west axis, at radii ranging from ~10 kpc to over a Mpc. Thermodynamic features qualitatively similar to these have previously been observed in the centers of cool-core clusters, and were successfully modeled as a consequence of the gas sloshing/swirling motions induced by minor mergers. Our observations indicate that such sloshing/swirling can extend out to larger radii than previously thought, on scales approaching the virial radius.

X-Ray Study of the Outer Region of Abell 2142 with Suzaku

We observed outer regions of a bright cluster of galaxies A2142 with Suzaku. Temperature and brightness structures were measured out to the virial radius (

Detection of Highly Ionized O and Ne Absorption Lines in the X-Ray Spectrum of 4U 1820–303 in the Globular Cluster NGC 6624

r_{200}

Soft x-ray spectrometer (SXS): The high-resolution cryogenic spectrometer onboard ASTRO-H

) with good sensitivity. We confirmed the temperature drop from 9 keV around the cluster center to about 3.5 keV at