399 research outputs found
X-ray Diagnostics of Thermal Conditions of the Hot Plasmas in the Centaurus Cluster
X-ray data of the Centaurus cluster, obtained with {\it XMM-Newton} for 45
ksec, were analyzed. Deprojected EPIC spectra from concentric thin shell
regions were reproduced equally well by a single-phase plasma emission model,
or by a two-phase model developed by {\it ASCA}, both incorporating cool
(1.7--2.0 keV) and hot ( keV) plasma temperatures. However, EPIC
spectra with higher statistics, accumulated over 3-dimentional thick shell
regions, were reproduced better by the two-phase model than by the singe-phase
one. Therefore, hot and cool plasma phases are inferred to co-exist in the
cluster core region within kpc. The iron and silicon abundances of
the plasma were reconfirmed to increase significantly towards the center, while
that of oxygen was consistent with being radially constant. The implied
non-solar abundance ratios explains away the previously reported excess X-ray
absorption from the central region. Although an additional cool (
keV) emission was detected within kpc of the center, the RGS data
gave tight upper limits on any emission with a tempeartures below
keV. These results are compiled into a magnetosphere model, which interprets
the cool phase as confined within closed magnetic loops anchored to the cD
galaxy. When combined with so-called Rosner-Tucker-Vaiana mechanism which
applies to solar coronae, this model can potentially explain basic properties
of the cool phase, including its temperature and thermal stability.Comment: 53 pages, 11 figures, accepted for publication in Astrophysical
Journa
A second consensus sequence of ATP-requiring proteins resides in the 21-kDa C-terminal segment of myosin subfragment 1
AbstractPrevious comparisons of sequence homologies of ATP-requiring enzymes have defined three consensus sequences which appear to be involved in the binding of the nucleotide. One of these was identified in the N-terminal 27-kDa segment of the myosin heavy chain but the other two sequences have not hitherto been located in myosin. The present paper proposes that one of these other two consensus sequences is in the 21-kDa C-terminal portion of S1 and that it may contribute to the ATP binding domain
Parallelization of Markov chain generation and its application to the multicanonical method
We develop a simple algorithm to parallelize generation processes of Markov
chains. In this algorithm, multiple Markov chains are generated in parallel and
jointed together to make a longer Markov chain. The joints between the
constituent Markov chains are processed using the detailed balance. We apply
the parallelization algorithm to multicanonical calculations of the
two-dimensional Ising model and demonstrate accurate estimation of
multicanonical weights.Comment: 15 pages, 5 figures, uses elsart.cl
Electrically driven spin excitation in a ferroelectric magnet DyMnO_3
Temperature (5--250 K) and magnetic field (0--70 kOe) variations of the
low-energy (1--10 meV) electrodynamics of spin excitations have been
investigated for a complete set of light-polarization configurations for a
ferroelectric magnet DyMnO by using terahertz time-domain spectroscopy. We
identify the pronounced absorption continuum (1--8 meV) with a peak feature
around 2 meV, which is electric-dipole active only for the light -vector
along the a-axis. This absorption band grows in intensity with lowering
temperature from the spin-collinear paraelectric phase above the ferroelectric
transition, but is independent of the orientation of spiral spin plane ( or
), as shown on the original (ferroelectric polarization)
phase as well as the magnetic field induced phase. The possible origin of this electric-dipole active band is argued in
terms of the large fluctuations of spins and spin-current.Comment: New version, 11 pages including colored 8 figure
Discovery of a binary AGN in the ultraluminous infrared galaxy NGC 6240 using Chandra
Ultraluminous infrared galaxies (ULIRGs) are outstanding due to their huge
luminosity output in the infrared, which is predominantly powered by super
starbursts and/or hidden active galactic nuclei (AGN). NGC 6240 is one of the
nearest ULIRGs and is considered a key representative of its class.
Here, we report the first high-resolution imaging spectroscopy of NGC 6240 in
X-rays. The observation, performed with the ACIS-S detector aboard the Chandra
X-ray observatory, led to the discovery of two hard nuclei, coincident with the
optical-IR nuclei of NGC 6240. The AGN character of both nuclei is revealed by
the detection of absorbed hard, luminous X-ray emission and two strong neutral
Fe_K_alpha lines. In addition, extended X-ray emission components are present,
changing their rich structure in dependence of energy. The close correlation of
the extended emission with the optical Halpha emission of NGC 6240, in
combination with the softness of its spectrum, clearly indicates its relation
to starburst-driven superwind activity.Comment: ApJ Letters in press, 7 colour figures included; preprint and related
papers on NGC 6240 also available at http://www.xray.mpe.mpg.de/~skomossa
On the Flux-Across-Surfaces Theorem
The quantum probability flux of a particle integrated over time and a distant
surface gives the probability for the particle crossing that surface at some
time. We prove the free Flux-Across-Surfaces Theorem, which was conjectured by
Combes, Newton and Shtokhamer, and which relates the integrated quantum flux to
the usual quantum mechanical formula for the cross section. The integrated
quantum flux is equal to the probability of outward crossings of surfaces by
Bohmian trajectories in the scattering regime.Comment: 13 pages, latex, 1 figure, very minor revisions, to appear in Letters
in Mathematical Physics, Vol. 38, Nr.
Scattering by a toroidal coil
In this paper we consider the Schr\"odinger operator in with
a long-range magnetic potential associated to a magnetic field supported inside
a torus . Using the scheme of smooth perturbations we construct
stationary modified wave operators and the corresponding scattering matrix
. We prove that the essential spectrum of is an
interval of the unit circle depending only on the magnetic flux across
the section of . Additionally we show that, in contrast to the
Aharonov-Bohm potential in , the total scattering cross-section
is always finite. We also conjecture that the case treated here is a typical
example in dimension 3.Comment: LaTeX2e 17 pages, 1 figur
Detection of an X-Ray Hot Region in the Virgo Cluster of Galaxies with ASCA
Based on mapping observations with ASCA, an unusual hot region with a spatial
extent of 1 square degree was discovered between M87 and M49 at a center
coordinate of R. A. = 12h 27m 36s and Dec. = (J2000). The X-ray
emission from the region has a 2-10 keV flux of ergs
s cm and a temperature of keV, which is
significantly higher than that in the surrounding medium of keV. The
internal thermal energy in the hot region is estimated to be ergs with a gas density of cm. A power-law
spectrum with a photon index is also allowed by the data. The hot
region suggests there is an energy input due to a shock which is probably
caused by the motion of the gas associated with M49, infalling toward the M87
cluster with a velocity km s.Comment: 12 pages, 3 figures, accepted to ApJ
Heavy X-ray Absorption in Soft X-ray Weak Active Galactic Nuclei
Recent ROSAT studies have identified a significant population of Active
Galactic Nuclei (AGN) that are notably faint in soft X-rays relative to their
optical fluxes. Are these AGN intrinsically X-ray weak or are they just highly
absorbed? Brandt, Laor & Wills have systematically examined the optical and UV
spectral properties of a well-defined sample of these soft X-ray weak (SXW) AGN
drawn from the Boroson & Green sample of all the Palomar Green AGN with z<0.5.
We present ASCA observations of three of these SXW AGN: PG 1011-040, PG
1535+547 (Mrk 486), and PG 2112+059. In general, our ASCA observations support
the intrinsic absorption scenario for explaining soft X-ray weakness; both PG
1535+547 and PG 2112+059 show significant column densities (N_H~10^22-10^23
cm^-2) of absorbing gas. Interestingly, PG 1011-040 shows no spectral evidence
for X-ray absorption. The weak X-ray emission may result from very strong
absorption of a partially covered source, or this AGN may be intrinsically
X-ray weak. PG 2112+059 is a Broad Absorption Line (BAL) QSO, and we find it to
have the highest X-ray flux known of this class. It shows a typical power-law
X-ray continuum above 3 keV; this is the first direct evidence that BAL QSOs
indeed have normal X-ray continua underlying their intrinsic absorption.
Finally, marked variability between the ROSAT and ASCA observations of PG
1535+547 and PG 2112+059 suggests that the soft X-ray weak designation may be
transient, and multi-epoch 0.1-10.0 keV X-ray observations are required to
constrain variability of the absorber and continuum.Comment: 30 pages, 10 figures, LaTeX, uses aaspp4.sty; submitted to Ap
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