We present the results of new Suzaku observations of the Coma Cluster, the X-ray brightest, nearby, merging system hosting a well-studied, typical giant radio halo. It has been previously shown that, ...on the western side of the cluster, the radio brightness shows a much steeper gradient compared to other azimuths. XMM-Newton and Planck revealed a shock front along the southern half of the region associated with this steep radio gradient, suggesting that the radio emission is enhanced by particle acceleration associated with the shock passage. Suzaku demonstrates for the first time that this shock front extends northwards, tracing the entire length of the western edge of the Coma radio halo. The shock is detected both in the temperature and X-ray surface brightness distributions and has a Mach number of around $\mathcal {M}\sim 1.5$. The locations of the surface brightness edges align well with the edge of the radio emission, while the obtained temperature profiles seem to suggest shocks located 125–185 kpc further out in radius. In addition, the shock strengths derived from the temperature and density jumps are in agreement when using extraction regions parallel to the radio halo edge, but become inconsistent with each other when derived from radial profiles centered on the Coma Cluster core. It is likely that, beyond mere projection effects, the geometry of the shock is more complex than a front with a single, uniform Mach number and an approximately spherically symmetric shape.
Abstract
We report properties of the intracluster medium (ICM) in Abell 1246 to the virial radius (r200) and further outside as observed with Suzaku. The ICM emission is clearly detected to r200, and ...we derive profiles of electron temperature, density, entropy, and cluster mass based on the spectral analysis. The temperature shows variation from ∼ 7 keV at the central region to ∼ 2.5 keV around r200. The total mass in r500 is (4.3 ± 0.4) × 1014 M⊙, assuming hydrostatic equilibrium. At r > r500, the hydrostatic mass starts to decline and we therefore employ the total mass within r200 based on a weak-lens mass profile obtained from a sample of lower-mass clusters. This yields a gas mass fraction at r200 consistent with the cosmic baryon fraction, i.e., ∼ 17%. The entropy profile indicates a flatter slope than that of the numerical simulation, particularly in r > r500. These tendencies are similar to those of other clusters observed with Suzaku. We detect no significant ICM emission outside of r200, and 2 σ upper limits of redshifted O vii and O viii line intensities are constrained to be less than 2.9 and 5.6 × 10−7 photons cm−2 s−1 arcmin−2, respectively. The O vii line upper limit indicates nH < 4.7 × 10−5 cm−3 (Z/0.2 Z⊙)−1/2 (L/20 Mpc)−1/2, which corresponds to an overdensity, δ < 160 (Z/0.2 Z⊙)−1/2 (L/20 Mpc)−1/2.
Abstract
We conduct a joint X-ray and weak-lensing study of four relaxed galaxy clusters (Hydra A, A 478, A 1689, and A 1835) observed by both Suzaku and Subaru out to virial radii, with the aim of ...understanding recently discovered unexpected features of the intracluster medium (ICM) in cluster outskirts. We show that the average hydrostatic-to-lensing total mass ratio for the four clusters decreases from ∼ 70% to ∼ 40% as the overdensity contrast decreases from 500 to the virial value. The average gas mass fraction from lensing total mass estimates increases with cluster radius and agrees with the cosmic mean baryon fraction within the virial radius, whereas the X-ray-based gas fraction considerably exceeds the cosmic values due to underestimation of the hydrostatic mass. We also develop a new advanced method for determining normalized cluster radial profiles for multiple X-ray observables by simultaneously taking into account both their radial dependence and multivariate scaling relations with weak-lensing masses. Although the four clusters span a range of halo mass, concentration, X-ray luminosity, and redshift, we find that the gas entropy, pressure, temperature, and density profiles are all remarkably self-similar when scaled with the weak-lensing M200 mass and r200 radius. The entropy monotonically increases out to ∼ 0.5 r200 ∼ r1000 following the accretion shock heating model K(r) ∝ r1.1, and flattens at ≳ 0.5 r200. The universality of the scaled entropy profiles indicates that the thermalization mechanism over the entire cluster region (> 0.1 r200) is controlled by gravitation in a common way for all clusters, although the heating efficiency in the outskirts needs to be modified from the standard r1.1 law. The bivariate scaling functions of the gas density and temperature reveal that the flattening of the outskirts entropy profile is caused by the steepening of the temperature, rather than the flattening of the gas density.
The results from Suzaku observations of the central region of the Perseus cluster are presented. Deep exposures with the X-ray Imaging Spectrometer provide high-quality X-ray spectra from the ...intracluster medium. X-ray lines from helium-like Cr and Mn have been detected significantly for the first time in clusters. In addition, elemental abundances of Ne, Mg, Si, S, Ar, Ca, Fe, and Ni are accurately measured within 10' (or 220 kpc) from the cluster center. The relative abundance ratios are found to be within a range of 0.8-1.5 times the solar value. These abundance ratios are compared with previous measurements, those in extremely metal-poor stars in the Galaxy, and theoretical models.
We performed simultaneous spectral analyses of Chandra (26.6 ks) and Suzaku (102.3 ks) X-ray data of the starburst galaxy NGC 3079. The spectra were extracted from four regions: 0
$ .\!\!'$
5 (2.25 ...kpc) circle, an inner 0
$ .\!\!'$
5–1
$ '$
(2.25–4.5 kpc) ring, and an outer 1
$ '$
–2
$ '$
(4.5–9 kpc) ring from Chandra, and 4
$ '$
(18 kpc) circle from Suzaku, all centered on the nucleus. Fittings of thermal plasma models yield interstellar medium (ISM) temperatures of 0.65
$ ^{+0.05}_{-0.04}$
(0
$ .\!\!'$
5 circle), 0.45
$ ^{+0.07}_{-0.06}$
(0
$ .\!\!'$
5–1
$ '$
ring), and 0.24
$ ^{+0.03}_{-0.02}$
(1
$ '$
–2
$ '$
ring) keV in the three regions. The combination of Chandra's high angular resolution and Suzaku's high spectral sensitivity enabled us to spatially resolve and measure the abundances of the metals O, Ne, Mg, Si, and Fe within the hot ISM. In particular, the abundance patterns of O
$ /$
Fe, Ne
$ /$
Fe, Mg
$ /$
Fe, and Si
$ /$
Fe in the central region (
$ \lt$
4.5 kpc) are consistent with those expected from a supernova (SN) II synthesis. On the other hand, the pattern in the region beyond 4.5 kpc is closer to solar. The central region is also where copious polycyclic aromatic hydrocarbon infrared emission related to the recent starburst activity is known to occur. This suggests that we are seeing starburst-related SN II metal enrichment in the hot X-ray-emitting nuclear ISM. The spatial extent of SN II-like abundance patterns is consistent with that of NGC 3079 being in a relatively-early phase of starburst activity.
Variable ultraluminous X-ray sources (ULXs), which are considered to be black hole binaries (BHBs), are known to show state transitions similar to Galactic BHBs. However, the relation between the ULX ...states and the Galactic BHB states is still unclear, primarily due to the less well-understood behaviors of ULXs in contrast to the Galactic BHBs. Here, we report a statistical X-ray spectral study of 34 energy spectra from seven bright ULXs in the interacting galaxy systems M 51 and NGC 4490/85, using archive data from multiple Chandra and XMM-Newton observations spanning a few years. In order to compare them with Galactic BHB states, we applied representative spectral models of BHBs-a power-law (PL), a multi-color disk blackbody (MCD), and a slim-disk model-to all the ULX spectra. We found a hint of a bimodal structure in the luminosity distribution of the samples, suggesting that ULXs have two states that respectively have typical luminosities of (3-6)x 10{sup 39} and (1.5-3)x 10{sup 39} ergs s{sup -1}. Most spectra in the brighter state are explained by the MCD or the slim-disk model, whereas those in the fainter state are explained by the PL model. In particular, the slim-disk model successfully explains the observed spectral variations of NGC 4490/85 ULX-6 and ULX-8 by changes of the mass accretion rate to a black hole of an estimated mass of <40 M{sub sun}. From the best-fit model parameters of each state, we speculate that the brighter state in these two ULXs corresponds to the brightest state of Galactic BHBs, which is often called the 'apparently standard state'. The fainter state of the ULXs has a PL-shaped spectrum, but the photon index range is much wider than that seen in any single state of Galactic BHBs. We thus speculate that it is a state unique to ULXs. Some sources show much fainter and steeper spectra than the faint state, which we identified as yet another state.
We report on Suzaku observations of the northern half of the Hydra A cluster out to
$ \sim$
1.4 Mpc, reaching the virial radius. There are the first Suzaku observations of a medium-size (
$ kT$
$ ...\sim$
3 keV) cluster out to the virial radius. Two observations were conducted, north-west and north-east offsets, which continue in a filament direction and a void direction of the large-scale structure of the Universe, respectively. The X-ray emission and distribution of galaxies elongate in the filament direction. The temperature profiles in the two directions are mostly consistent with each other within the error bars, and drop to 1.5 keV at 1.5
$ r_{500}$
. As observed by Suzaku in hot clusters, the entropy profile becomes flatter beyond
$ r_{500}$
, in disagreement with the
$ r^{1.1}$
relationship, which is expected from accretion shock heating models. When scaled with the average intracluster medium (ICM) temperature, the entropy profiles of clusters observed with Suzaku are universal, and do not depend on the system mass. The hydrostatic mass values in the void and filament directions are in good agreement, and the Navarro, Frenk, and White universal mass profile represents the hydrostatic mass distribution up to
$ \sim$
2
$ r_{500}$
. Beyond
$ r_{500}$
, the ratio of the gas mass to the hydrostatic mass exceeds the result of the Wilkinson microwave anisotropy probe, and at
$ r_{100}$
, these ratios in the filament and void directions reach 0.4 and 0.3, respectively. We discuss possible deviations from the hydrostatic equilibrium at cluster outskirts. We derived radial profiles of the gas-mass-to-light ratio and the iron-mass-to-light ratio out to the virial radius. Within
$ r_{500}$
, the iron-mass-to-light ratio of the Hydra A cluster was compared with those in other clusters observed with Suzaku.
We performed spectral analysis of Suzaku data of the galactic disk and outflow regions of the starburst galaxy M 82. Thermal modeling of the central disk regions requires at least three temperature ...components. The Ly
$\beta $
line fluxes of O VIII and Ne X exceed those expected from a plasma in collisional ionization equilibrium. The ratios of the Ly
$\beta/$
Ly
$\alpha$
lines for O VIII and Ne X are higher than those of collisional ionization equilibrium, which may be caused by the process of charge exchange. In the outflow wind region, the spectra are well reproduced with two-temperature thermal models, and we have derived the metal abundances of O, Ne, Mg, and Fe in the outflow. The ratios of O
$/$
Fe, Ne
$/$
Fe, and Mg
$/$
Fe are about 2, 3, and 2, respectively, relative to the solar value determined by Lodders (2003, ApJ, 591, 1220). Since there is no evidence of charge exchange in the outflow region, the metal abundances should be more reliable than those in the central region. This abundance pattern indicates that starburst activity enriches the outflow through SN II metal ejection into intergalactic space.
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