257 research outputs found
Discovery of Gas Bulk Motion in the Galaxy Cluster Abell 2256 with Suzaku
The results from Suzaku observations of the galaxy cluster Abell2256 are
presented. This cluster is a prototypical and well-studied merging system,
exhibiting substructures both in the X-ray surface brightness and in the radial
velocity distribution of member galaxies. There are main and sub components
separating by 3'.5 in the sky and by about 2000 km s in radial velocity
peaks of member galaxies. In order to measure Doppler shifts of iron K-shell
lines from the two gas components by the Suzaku XIS, the energy scale of the
instrument was evaluated carefully and found to be calibrated well. A
significant shift of the radial velocity of the sub component gas with respect
to that of the main cluster was detected. All three XIS sensors show the shift
independently and consistently among the three. The difference is found to be
1500 (statistical) (systematic) km s. The X-ray
determined absolute redshifts of and hence the difference between the main and
sub components are consistent with those of member galaxies in optical. The
observation indicates robustly that the X-ray emitting gas is moving together
with galaxies as a substructure within the cluster. These results along with
other X-ray observations of gas bulk motions in merging clusters are discussed.Comment: Accepted for publication in PASJ in 2011-03-2
Slim Disk Model for Soft X-Ray Excess and Variability of Narrow-Line Seyfert 1 Galaxies
Narrow-line Seyfert 1 galaxies (NLS1s) exhibit extreme soft X-ray excess and
large variability. We argue that both features can be basically accounted for
by the slim disk model. We assume that a central black-hole mass in NLS1 is
relatively small, , and that a disk shines nearly at
the Eddington luminosity, . Then, the disk becomes a slim disk and
exhibits the following distinctive signatures: (1) The disk luminosity
(particularly of X-rays) is insensitive to mass-flow rates, , since the
generated energy is partly carried away to the black hole by trapped photons in
accretion flow. (2) The spectra are multi-color blackbody. The maximum
blackbody temperature is keV,
and the size of the blackbody emitting region is small, r_{\rm bb} \lsim 3
r_{\rm S} (with being Schwarzschild radius) even for a
Schwarzschild black hole. (3) All the ASCA observation data of NLS1s fall onto
the region of (with being the Eddington
luminosity) on the () plane, supporting our view that a
slim disk emits soft X-rays at in NLS1s. (4) Magnetic energy
can be amplified, at most, up to the equipartition value with the trapped
radiation energy which greatly exceeds radiation energy emitted from the disk.
Hence, energy release by consecutive magnetic reconnection will give rise to
substantial variability in soft X-ray emission.Comment: 9 pages LaTeX including 4 figures, accepted to PASJ. e-mail to
[email protected]
ASCA Observation of the Nearest Gravitational Lensing Cluster Candidate -- A 3408
We observed the nearest gravitational lensing cluster candidate, A 3408
(), with ASCA. The projected mass profile of A 3408 was
determined from the ICM temperature and the -model parameters obtained
with ASCA, assuming that the hot gas is spherically symmetric and in
hydrostatic equilibrium. The projected mass within an arc radius, , of 110 kpc is M(r_{\rm arc})=1.2^{+0.8}_{-0.4} \times10^{13} \MO. This
is 18 -- 45% of the mass previously derived from a lensing analysis by
Campusano et al. (1998, AAA 069.160.189) without any X-ray information.
The primary cause of this discrepancy is in their assumption that the center
of the cluster potential coincides with the position of the brightest cluster
galaxy (BCG), while we reveal the BCG position to be 60 outside of the
X-ray center. We further calculated a model for the source galaxy position and
the gravitational potential that can reproduce both the X-ray data and the arc
image. In this model, the magnification factor of the lens for the source
galaxy was evaluated to be 0.070.03 mag; i.e., the source
galaxy is slightly magnified by the lens cluster A 3408.Comment: 13 pages, 6 figures, to appear in PASJ vol. 5
Suzaku Observation of the Diffuse X-Ray Emission from the Open Cluster Westerlund 2: a Hypernova Remnant?
We present the analysis of Suzaku observations of the young open cluster
Westerlund 2, which is filled with diffuse X-ray emission. We found that the
emission consists of three thermal components or two thermal and one
non-thermal components. The upper limit of the energy flux of the non-thermal
component is smaller than that in the TeV band observed with H.E.S.S. This may
indicate that active particle acceleration has stopped in this cluster, and
that the accelerated electrons have already cooled. The gamma-ray emission
observed with H.E.S.S. is likely to come from high-energy protons, which hardly
cool in contrast with electrons. Metal abundances of the diffuse X-ray gas may
indicate the explosion of a massive star in the past.Comment: Accepted for publication in PAS
High Metallicity of the X-Ray Gas up to the Virial Radius of a Binary Cluster of Galaxies: Evidence of Galactic Superwinds at High-Redshift
We present an analysis of a Suzaku observation of the link region between the
galaxy clusters A399 and A401. We obtained the metallicity of the intracluster
medium (ICM) up to the cluster virial radii for the first time. We determine
the metallicity where the virial radii of the two clusters cross each other (~2
Mpc away from their centers) and found that it is comparable to that in their
inner regions (~0.2 Zsun). It is unlikely that the uniformity of metallicity up
to the virial radii is due to mixing caused by a cluster collision. Since the
ram-pressure is too small to strip the interstellar medium of galaxies around
the virial radius of a cluster, the fairly high metallicity that we found there
indicates that the metals in the ICM are not transported from member galaxies
by ram-pressure stripping. Instead, the uniformity suggests that the
proto-cluster region was extensively polluted with metals by extremely powerful
outflows (superwinds) from galaxies before the clusters formed. We also
searched for the oxygen emission from the warm--hot intergalactic medium in
that region and obtained a strict upper limit of the hydrogen density
(nH<4.1x10^-5 cm^-3).Comment: Typo corrected. The published version is available on-line free of
charge by the end of 2008. http://pasj.asj.or.jp/v60/sp1/60s133/60s133.pd
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