969 research outputs found
On the light-bending model of X-ray variability of MCG-6-30-15
We apply the light bending model of X-ray variability to Suzaku data of the
Seyfert 1 galaxy MCG-6-30-15. We analyze the energy dependence of the root mean
square (rms) variability, and discuss conditions necessary for the model to
explain the characteristic decrease of the source variability around 5-8 keV. A
model, where the X-ray source moves radially rather than vertically close to
the disk surface, can indeed reproduce the reduced variability near the energy
of the Fe Kalpha line, although the formal fit quality is poor. The model then
predicts the energy spectra, which can be compared to observational data. The
spectra are strongly reflection dominated, and do not provide a good fit to
Suzaku spectral data of the source. The inconsistency of this result with some
previous claims can be traced to our using data in a broader energy band, where
effects of warm absorber in the spectrum cannot be neglected.Comment: 6 pages, PASJ, accepte
A Disk--Jet interaction model for the X--Ray Variability in Microquasars
We propose a simple dynamical model that may account for the observed
spectral and temporal properties of GRS 1915+105 and XTE J1550-5634. The model
is based on the assumption that a fraction of the radiation emitted by a hot
spot lying on the accreting disk is dynamically Comptonized by the relativistic
jet that typically accompanies the microquasar phenomenon. We show that
scattering by the jet produces a detectable modulation of the observed flux. In
particular, we found that the phase lag between hard and soft photons depends
on the radial position of the hot spot and, if the angle between the jet and
the line of sight is sufficiently large, the lags of the fundamental and its
harmonics may be either positive or negative.Comment: 14 pages, 4 figures, accepted for publication in ApJ Part
The Mixed State of Charge-Density-Wave in a Ring-Shaped Single Crystals
Charge-density-wave (CDW) phase transition in a ring-shaped crystals,
recently synthesized by Tanda et al. [Nature, 417, 397 (2002)], is studied
based on a mean-field-approximation of Ginzburg-Landau free energy. It is shown
that in a ring-shaped crystals CDW undergoes frustration due to the curvature
(bending) of the ring (geometrical frustration) and, thus, forms a mixed state
analogous to what a type-II superconductor forms under a magnetic field. We
discuss the nature of the phase transition in the ring-CDW in relation to
recent experiments.Comment: 6 pages, 4 figure
Resolving the Fe xxv Triplet with Chandra in Cen X-3
We present the results of a 45 ks Chandra observation of the high-mass X-ray
binary Cen X--3 at orbital phases between 0.13 and 0.40 (in the eclipse
post-egress phases). Here we concentrate on the study of discrete features in
the energy spectrum at energies between 6 and 7 keV, i.e. on the iron
K line region, using the High Energy Transmission Grating Spectrometer
on board the Chandra satellite. We clearly see a K neutral iron line
at keV and were able to distinguish the three lines of the
\ion{Fe}{25} triplet at 6.61 keV, 6.67 keV, and 6.72 keV, with an equivalent
width of 6 eV, 9 eV, and 5 eV, respectively. The equivalent width of the
K neutral iron line is 13 eV, an order of magnitude lower than
previous measures. We discuss the possibility that the small equivalent width
is due to a decrease of the solid angle subtended by the reflector.Comment: 11 pages, 2 figures, To appear in the Astrophysical Journal Letter
High-Energy sources before INTEGRAL -- INTEGRAL reference catalog --
We describe the INTEGRAL reference catalog which classifies previously known
bright X-ray and gamma-ray sources before the launch of INTEGRAL. These sources
are, or have been at least once, brighter than ~1 mCrab above 3 keV, and are
expected to be detected by INTEGRAL. This catalog is being used in the INTEGRAL
Quick Look Analysis to discover new sources or significantly variable sources.
We compiled several published X-ray and gamma-ray catalogs, and surveyed recent
publications for new sources. Consequently, there are 1122 sources in our
INTEGRAL reference catalog. In addition to the source positions, we show an
approximate spectral model and expected flux for each source, based on which we
derive expected INTEGRAL counting rates. Assuming the default instrument
performances and at least ~10^5 sec exposure time for any part of the sky, we
expect that INTEGRAL will detect at least ~700 sources below 10 keV and ~400
sources above 20 keV over the mission life.Comment: Accepted to A&A Letter INTEGRAL special issu
Anti-correlated hard X-ray time lags in Galactic black hole sources
We investigate the accretion disk geometry in Galactic black hole sources by
measuring the time delay between soft and hard X-ray emissions. Similar to the
recent discoveries of anti-correlated hard X-ray time lags in Cyg X-3 and GRS
1915+105, we find that the hard X-rays are anti-correlated with soft X-rays
with a significant lag in another source: XTE J1550-564. We also find the
existence of pivoting in the model independent X-ray spectrum during these
observations. We investigate time-resolved X-ray spectral parameters and find
that the variation in these parameters is consistent with the idea of a
truncated accretion disk. The QPO frequency, which is a measure of the size of
truncated accretion disk, too changes indicating that the geometric size of the
hard X-ray emitting region changes along with the spectral pivoting and soft
X-ray flux. Similar kind of delay is also noticed in 4U 1630-47.Comment: 14 pages, 7 figures, accepted for publication in Ap
ASCA Observation of the New Transient X-ray Pulsar XTE J0111.2-7317 in the Small Magellanic Cloud
The new transient X-ray pulsar XTE J0111.2-7317 was observed with Advanced
Satellite for Cosmology and Astrophysics (ASCA) on 1998 November 18, a few days
after its discovery with the Proportional Counter Array onboard the Rossi X-ray
Timing Explorer. The source was detected at a flux level of 3.6x10^-10 erg
cm^-2 s^-1 in the 0.7--10.0 keV band, which corresponds to the X-ray luminosity
of 1.8x10^38 erg s^-1, if a distance of 65 kpc for this pulsar in the Small
Magellanic Cloud is assumed. Nearly sinusoidal pulsations with a period of
30.9497 +/- 0.0004 s were unambiguously detected during the ASCA observation.
The pulsed fraction is low and slightly energy dependent with average value of
\~27%. The energy spectrum shows a large soft excess below ~2 keV when fitted
to a simple power-law type model. The soft excess is eliminated if the spectrum
is fitted to an ``inversely broken power-law'' model, in which photon indices
below and above a break energy of 1.5 keV are 2.3 and 0.8, respectively. The
soft excess can also be described by a blackbody or a thermal bremsstrahlung
when the spectrum above ~2 keV is modeled by a power-law. In these models,
however, the thermal soft component requires a very large emission zone, and
hence it is difficult to explain the observed pulsations at energies below 2
keV. A bright state of the source enables us to identify a weak iron line
feature at 6.4 keV with an equivalent width of 50 +/- 14 eV. Pulse phase
resolved spectroscopy revealed a slight hardening of the spectrum and marginal
indication of an increase in the iron line strength during the pulse maximum.Comment: 8 pages, 5 Figures, to be published in ApJ. Also available at
http://www-cr.scphys.kyoto-u.ac.jp/member/jun/job
M 33 X-7: ChASeM33 reveals the first eclipsing black hole X-ray binary
The first observations conducted as part of the Chandra ACIS survey of M 33
(ChASeM33) sampled the eclipsing X-ray binary M 33 X-7 over a large part of the
3.45 d orbital period and have resolved eclipse ingress and egress for the
first time. The occurrence of the X-ray eclipse allows us to determine an
improved ephemeris of mid-eclipse and binary period as HJD (2453639.119+-0.005)
+- N x (3.453014+-0.000020) and constrain the eclipse half angle to (26.5+-1.1)
degree. There are indications for a shortening of the orbital period. The X-ray
spectrum is best described by a disk blackbody spectrum typical for black hole
X-ray binaries in the Galaxy. We find a flat power density spectrum and no
significant regular pulsations were found in the frequency range of 10^{-4} to
0.15 Hz. HST WFPC2 images resolve the optical counterpart, which can be
identified as an O6III star with the help of extinction and colour corrections
derived from the X-ray absorption. Based on the optical light curve, the mass
of the compact object in the system most likely exceeds 9 M_sun. This mass, the
shape of the X-ray spectrum and the short term X-ray time variability identify
M 33 X-7 as the first eclipsing black hole high mass X-ray binary.Comment: 14 pages, 5 figures, ApJ accepte
Proposal for measuring the quantum states of neutrons in the gravitational field with a CCD-based pixel sensor
An experimental setup is proposed for the precise measurement of the quantum
states of ultracold neutrons bound in the earth's gravitational field. The
experiment utilizes a CCD-based pixel sensor and magnification system to
observe the fine structure of the neutron distribution. In this work, we
analyzed the sensor's deposited energy measurement capability and found that
its spatial resolution was 5.3 um. A magnifying power of two orders of
magnitude was realized by using a cylindrical rod as a convex mirror.Comment: Accepted for publication in NIMA; 13 pages, 8 figure
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