61 research outputs found
Suzaku and XMM-Newton Observations of the Fornax cluster: Temperature and Metallicity Distribution
Suzaku observed a central region and five offset regions within 0.2 r180 in
the Fornax cluster, a nearby poor cluster, and XMM-Newton mapped the cluster
with 15 pointings out to 0.3 r180. The distributions of O, Mg, Si, S, and Fe in
the intracluster medium (ICM) were studied with Suzaku, and those of Fe and
temperature were studied with XMM. The temperature of the ICM gradually
decreases with radius from 1.3 keV at 0.04 r180 to 1 keV at 0.2-0.3 r180. If
the new solar abundances of Lodders et al. (2003) and a single-temperature
plasma model are adopted, O, Mg, Si, S, and Fe show similar abundances: 0.4-0.6
solar within 0.02-0.2 r180. This Fe abundance is similar to those at 0.1-0.2
r180 in rich clusters and other groups of galaxies. At 0.2-0.3 r180, the Fe
abundance becomes 0.2-0.3 solar. A two-temperature plasma model yields ICM
abundances that are higher by a factor of 1.2-1.5, but gives similar abundance
ratios among O, Mg, Si, S, and Fe. The northern region has a lower ICM
temperature and higher brightness and Fe abundance, whereas the southern region
has a higher ICM temperature and lower brightness and Fe abundance. These
results indicate that the cD galaxy may have traveled from the north because of
recent dynamical evolution. The cumulative oxygen- and iron-mass-to-light
ratios within 0.3 r180 are more than an order of magnitude lower than those of
rich clusters and some relaxed groups of galaxies. Past dynamical evolution
might have hindered the strong concentration of hot gas in the Fornax cluster's
central region. Scatter in the IMLR and similarity in the element abundances in
the ICM of groups and clusters of galaxies indicate early metal synthesis.Comment: 15 pages, 13 figures, accepted for publication in PAS
Soft and Hard X-Ray Emissions from the Anomalous X-ray Pulsar 4U 0142+61 Observed with Suzaku
The anomalous X-ray pulsar 4U 0142+61 was observed with Suzaku on 2007 August
15 for a net exposure of -100 ks, and was detected in a 0.4 to ~70 keV energy
band. The intrinsic pulse period was determined as 8.68878 \pm 0.00005 s, in
agreement with an extrapolation from previous measurements. The broadband
Suzaku spectra enabled a first simultaneous and accurate measurement of the
soft and hard components of this object by a single satellite. The former can
be reproduced by two blackbodies, or slightly better by a resonant cyclotron
scattering model. The hard component can be approximated by a power-law of
photon index \Gamma h ~0.9 when the soft component is represented by the
resonant cyclotron scattering model, and its high-energy cutoff is constrained
as >180 keV. Assuming an isotropic emission at a distance of 3.6 kpc, the
unabsorbed 1-10 keV and 10-70 keV luminosities of the soft and hard components
are calculated as 2.8e+35 erg s^{-1} and 6.8e+34 erg s^{-1}, respectively.
Their sum becomes ~10^3 times as large as the estimated spin-down luminosity.
On a time scale of 30 ks, the hard component exhibited evidence of variations
either in its normalization or pulse shape.Comment: 24 pages, 8 figures, accepted for publication in Publications of the
Astronomical Society of Japa
Metallicity of the Fossil Group NGC 1550 Observed with Suzaku
We studied the temperature and metal abundance distributions of the
intra-cluster medium (ICM) in a group of galaxies NGC 1550 observed with
Suzaku. The NGC 1550 is classified as a fossil group, which have few bright
member galaxies except for the central galaxy. Thus, such a type of galaxy is
important to investigate how the metals are enriched to the ICM. With the
Suzaku XIS instruments, we directly measured not only Si, S, and Fe lines but
also O and Mg lines and obtained those abundances to an outer region of ~0.5
r_180 for the first time, and confirmed that the metals in the ICM of such a
fossil group are indeed extending to a large radius. We found steeper gradients
for Mg, Si, S, and Fe abundances, while O showed almost flat abundance
distribution. Abundance ratios of alpha-elements to Fe were similar to those of
the other groups and poor clusters. We calculated the number ratio of type II
to type Ia supernovae for the ICM enrichment to be 2.9 +- 0.5 within 0.1 r_180,
and the value was consistent with those for the other groups and poor clusters
observed with Suzaku. We also calculated metal mass-to-light ratios (MLRs) for
Fe, O and Mg with B-band and K-band luminosities of the member galaxies of NGC
1550. The derived MLRs were comparable to those of NGC 5044 group in the r<0.1
r_180 region, while those of NGC 1550 are slightly higher than those of NGC
5044 in the outer region.Comment: 11 pages, 7 figures, accepted for publication in PAS
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&
Galaxy Infall by Interacting with its Environment: a Comprehensive Study of 340 Galaxy Clusters
To study systematically the evolution on the angular extents of the galaxy,
ICM, and dark matter components in galaxy clusters, we compiled the optical and
X-ray properties of a sample of 340 clusters with redshifts , based on
all the available data with the Sloan Digital Sky Survey (SDSS) and {\it
Chandra}/{\it XMM-Newton}. For each cluster, the member galaxies were
determined primarily with photometric redshift measurements. The radial ICM
mass distribution, as well as the total gravitational mass distribution, were
derived from a spatially-resolved spectral analysis of the X-ray data. When
normalizing the radial profile of galaxy number to that of the ICM mass, the
relative curve was found to depend significantly on the cluster redshift; it
drops more steeply towards outside in lower redshift subsamples. The same
evolution is found in the galaxy-to-total mass profile, while the ICM-to-total
mass profile varies in an opposite way. We interpret that the galaxies, the
ICM, and the dark matter components had similar angular distributions when a
cluster was formed, while the galaxies travelling interior of the cluster have
continuously fallen towards the center relative to the other components, and
the ICM has slightly expanded relative to the dark matter although it suffers
strong radiative loss. This cosmological galaxy infall, accompanied by an ICM
expansion, can be explained by considering that the galaxies interact strongly
with the ICM while they are moving through it. The interaction is considered to
create a large energy flow of erg per cluster from
the member galaxies to their environment, which is expected to continue over
cosmological time scales.Comment: 55 pages, 22 figures, accepted for publication in Astrophysical
Journa
Spectral transitions of an ultraluminous X-ray source, NGC 2403 Source 3
Suzaku observation of an ultraluminous X-ray source, NGC 2403 Source 3,
performed on 2006 March 16--17, is reported. The Suzaku XIS spectrum of Source
3 was described with a multi-color black-body-like emission from an optically
thick accretion disk. The innermost temperature and radius of the accretion
disk was measured to be keV and km, respectively, where with being the disk inclination. The bolometric
luminosity of the source was estimated to be ergs s. Archival Chandra and XMM-Newton data of the source were
analyzed for long-term spectral variations. In almost all observations, the
source showed multi-color black-body-like X-ray spectra with parameters similar
to those in the Suzaku observation. In only one Chandra observation, however,
Source 3 was found to exhibit a power-law-like spectrum, with a photon index of
, when it was fainter by about than in the
Suzaku observation. The spectral behavior is naturally explained in terms of a
transition between the slim disk state and the "very high" states, both found
in Galactic black hole binaries when their luminosity approach the Eddington
limit. These results are utilized to argue that ultraluminous X-ray sources
generally have significantly higher black-hole masses than ordinary
stellar-mass black holes.Comment: Accepted for PASJ 3nd Suzaku special issu
Hard X-ray Properties of the Merging Cluster Abell 3667 as Observed with Suzaku
Wide-band Suzaku data on the merging cluster Abell 3667 were examined for
hard X-ray emission in excess to the known thermal component. Suzaku detected
X-ray signals in the wide energy band from 0.5 to 40 keV. The hard X-ray (> 10
keV) flux observed by the HXD around the cluster center cannot be explained by
a simple extension of the thermal emission with average temperature of ~7 keV.
The emission is most likely an emission from a very hot (kT > 13.2 keV) thermal
component around the cluster center, produced via a strong heating process in
the merger. In the north-west radio relic, no signature of non-thermal emission
was observed. Using the HXD, the overall upper-limit flux within a 34'x34'
field-of-view around the relic is derived to be 5.3e-12 erg s-1 cm-2 in the
10-40 keV band, after subtracting the ICM contribution estimated using the XIS
or the XMM-Newton spectra. Directly on the relic region, the upper limit is
further tightened by the XIS data to be less than 7.3e-13 erg s-1 cm-2, when
converted into the 10--40 keV band. The latter value suggest that the average
magnetic field within the relic is higher than 1.6 uG. The non-thermal pressure
due to magnetic fields and relativistic electrons may be as large as ~20% of
the thermal pressure in the region.Comment: 18 pages, 13 figures, to be appeared in PASJ 200
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