548 research outputs found
Detection of Iron Emission Line from the Galaxy Cluster Including the Radio Galaxy 3C220.1 at z=0.62
We have detected an emission line feature at 4 keV in the X-ray emission from
a sky region including the distant radio galaxy 3C220.1(z=0.62) obtained with
ASCA. The line energy is 6.1 - 7.0 keV (90% confidence) in the rest frame of
3C220.1. Within the present statistics, the observed spectra are consistent
with two different models: a non-thermal model consisting of a power-law
continuum plus a 6.4 keV iron emission line, and a Raymond-Smith thin-thermal
emission model of kT ~6 keV with a metal abundance of ~0.5 solar. However,
because of the large (~ 500 eV) equivalent width of the line, a significant
fraction of the X-ray emission is likely to arise from the hot intracluster gas
associated with the galaxy cluster that includes 3C220.1. The spectral
parameters of the thermal emission are consistent with the
luminosity-temperature relation of nearby clusters.Comment: 15 pages, 5 ps figures, accepted for publication in the Astrophysical
Journa
Gas, Iron and Gravitational Mass in Galaxy Clusters: The General Lack of Cluster Evolution at z < 1.0
We have analyzed the ASCA data of 29 nearby clusters of galaxies
systematically, and obtained temperatures, iron abundances, and X-ray
luminosities of their intracluster medium (ICM). We also estimate ICM mass
using the beta model, and then evaluate iron mass contained in the ICM and
derive the total gravitating mass. This gives the largest and most homogeneous
information about the ICM derived only by the ASCA data. We compare these
values with those of distant clusters whose temperatures, abundances, and
luminosities were also measured with ASCA, and find no clear evidence of
evolution for the clusters at z<1.0. Only the most distant cluster at z=1.0,
AXJ2019.3+1127, has anomalously high iron abundance, but its iron mass in the
ICM may be among normal values for the other clusters, because the ICM mass may
be smaller than the other clusters. This may suggest a hint of evolution of
clusters at z ~ 1.0.Comment: 23 pages including 5 figures. Using PASJ2.sty, and PASJ95.sty.
Accepted by PAS
A possible route to spontaneous reduction of the heat conductivity by a temperature gradient driven instability in electron-ion plasmas
We have shown that there exists low-frequency growing modes driven by a
global temperature gradient in electron and ion plasmas, by linear perturbation
analysis within the frame work of plasma Kinetic theory. The driving force of
the instability is the local deviation of the distribution function from the
Maxwell-Boltzmann due to global temperature gradient. Application to the
intracluster medium shows that scattering of the particles due to waves excited
by the instability is possible to reduce mean free paths of electron and ion
down to five to seven order of magnitude than the mean free paths due to
Coulomb collisions. This may provide a hint to explain why hot and cool gas can
co-exist in the intracluster medium in spite of the very short evaporation time
scale due to thermal conduction if the conductivity is the classical Spitzer
value. Our results suggest that the realization of the global thermal
equilibrium is postponed by the local instability which is induced for quicker
realization of local thermal equilibrium state in plasmas. The instability
provides a new possibility to create and grow cosmic magnetic fields without
any seed magnetic field.Comment: Accepted for publication in ApJ: 16 pages, 1figur
A method to measure a relative transverse velocity of source-lens-observer system using gravitational lensing of gravitational waves
Gravitational waves propagate along null geodesics like light rays in the
geometrical optics approximation, and they may have a chance to suffer from
gravitational lensing by intervening objects, as is the case for
electromagnetic waves. Long wavelength of gravitational waves and compactness
of possible sources may enable us to extract information in the interference
among the lensed images. We point out that the interference term contains
information of relative transverse velocity of the source-lens-observer system,
which may be obtained by possible future space-borne gravitational wave
detectors such as BBO/DECIGO.Comment: 27 pages, 9 figures. Accepted for publication in Physical Review
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