1,222 research outputs found
Broad Band X-Ray Observations of the Narrow Line X-Ray Galaxy NGC 5506
We present a detailed analysis of broad band X-ray data of the Seyfert 2
galaxy NGC5506. 2-10 keV band are detected during a 1-day ASCA observation,
while no significant change in the 2-10 keV continuum shape is found. The ASCA
spectrum consists of an absorbed power-law, a 'soft excess' below 2 keV, and an
Fe K emission line at 6.4 keV. The 'soft excess' can be well described
by either thermal emission from very low abundance material at a temperature
kT0.8 keV, or scattered/leaking flux from the primary power-law plus a
small amount of thermal emission. Analysis of ROSAT HRI data reveals that the
soft X-ray emission is extended on kpc scales in this object, and the extended
component may account for most of the soft X-ray excess observed by the ASCA.
The result suggests that in this type 2 AGN, the 'soft excess' at least partly
comes from an extended region, imposing serious problem for the model in which
the source is partially covered. Fe K profile is complex and can not be
satisfactorily modeled by a single gaussian. Models of either double gaussians,
or a narrow gaussian plus a line from a relativistic accretion disk viewed at
an inclination of about 40 provide good fits to the data. However,
the inclination of the disk can be substantially larger if there is a small
amount of excessive Fe K edge absorption. The intermediate inclinations for
NLXGs are consistent with the ideas that the inner accretion disk is aligned
with the outer obscuring torus.Comment: 8 pages, 5 postscript figures. to appear in Astrophy. J., 1999, April
2
Numerical Study of the Ghost-Gluon Vertex in Landau gauge
We present a numerical study of the ghost-gluon vertex and of the
corresponding renormalization function \widetilde{Z}_1(p^2) in minimal Landau
gauge for SU(2) lattice gauge theory. Data were obtained for three different
lattice volumes (V = 4^4, 8^4, 16^4) and for three lattice couplings \beta =
2.2, 2.3, 2.4. Gribov-copy effects have been analyzed using the so-called
smeared gauge fixing. We also consider two different sets of momenta (orbits)
in order to check for possible effects due to the breaking of rotational
symmetry. The vertex has been evaluated at the asymmetric point (0;p,-p) in
momentum-subtraction scheme. We find that \widetilde{Z}_1(p^2) is approximately
constant and equal to 1, at least for momenta p > ~ 1 GeV. This constitutes a
nonperturbative verification of the so-called nonrenormalization of the Landau
ghost-gluon vertex. Finally, we use our data to evaluate the running coupling
constant \alpha_s(p^2).Comment: 19 pages, 6 figures, 9 tables, using axodraw.sty; minor modifications
in the abstract, introduction and conclusion
Test of the Conserved Vector Current Hypothesis by beta-ray Angular Distribution Measurement in the Mass-8 System
The beta-ray angular correlations for the spin alignments of 8Li and 8B have
been observed in order to test the conserved vector current (CVC) hypothesis.
The alignment correlation terms were combined with the known beta-alpha-angular
correlation terms to determine all the matrix elements contributing to the
correlation terms. The weak magnetism term, 7.5\pm0.2, deduced from the
beta-ray correlation terms was consistent with the CVC prediction 7.3\pm0.2,
deduced from the analog-gamma-decay measurement based on the CVC hypothesis.
However, there was no consistent CVC prediction for the second-forbidden term
associated with the weak vector current. The experimental value for the
second-forbidden term was 1.0 \pm 0.3, while the CVC prediction was 0.1 \pm 0.4
or 2.1 \pm 0.5.Comment: 31 pages, 12 figures, Accepted for publication in Phys. Rev.
Peculiar outburst of A 0535+26 observed with INTEGRAL, RXTE and Suzaku
A normal outburst of the Be/X-ray binary system A0535+26 has taken place in
August 2009. It is the fourth in a series of normal outbursts that have occured
around the periastron passage of the source, but is unusual by starting at an
earlier orbital phase and by presenting a peculiar double-peaked light curve. A
first "flare" (lasting about 9 days from MJD 55043 on) reached a flux of 440
mCrab. The flux then decreased to less than 220 mCrab, and increased again
reaching 440 mCrab around the periastron at MJD 55057. Target of Opportunity
observations have been performed with INTEGRAL, RXTE and Suzaku. First results
of these observations are presented, with special emphasis on the cyclotron
lines present in the X-ray spectrum of the source, as well as in the pulse
period and energy dependent pulse profiles of the source.Comment: 6 pages, Accepted for publication on PoS, Proceedings of "The Extreme
sky: Sampling the Universe above 10 keV", held in Otranto (Italy) in October
200
Rapidly variable Fe K line in NGC 4051
We present a detailed analysis on the variability of the Fe K emission line
in NGC 4051 using ASCA data. Through simple Gaussian line fits, we find not
only obvious Fe K line variability with no significant difference in the X-ray
continuum flux between two ASCA observations which were separated by 440
days, but also rapid variability of Fe K line on time scales s
within the second observation. During the second observation, the line is
strong (EW = 733 eV) and broad (
keV) when the source is brightest, and become weaker (EW = 165
eV) and narrower ( keV) whilst the source is weakest. The
equivalent width of Fe K line correlates positively with the continuum flux,
which shows an opposite trend with another Seyfert 1 galaxy MCG --6-30-15.Comment: 12 pages with 5 figures, to appear in ApJ Vol. 516, L6
Discovery of a flux-related change of the cyclotron line energy in Her X-1
We present the results of ten years of repeated measurements of the Cyclotron
Resonance Scattering Feature (CRSF) in the spectrum of the binary X-ray pulsar
Her X-1 and report the discovery of a positive correlation of the centroid
energy of this absorption feature in pulse phase averaged spectra with source
luminosity.Our results are based on a uniform analysis of observations bythe
RXTE satellite from 1996 to 2005, using sufficiently long observations of 12
individual 35-day Main-On states of the source. The mean centroid energy E_c of
the CRSF in pulse phase averaged spectra of Her X-1 during this time is around
40 keV, with significant variations from one Main-On state to the next. We find
that the centroid energy of the CRSF in Her X-1 changes by ~5% in energy for a
factor of 2 in luminosity. The correlation is positive, contrary to what is
observed in some high luminosity transient pulsars. Our finding is the first
significant measurement of a positive correlation between E_c and luminosity in
any X-ray pulsar. We suggest that this behaviour is expected in the case of
sub-Eddington accretion and present a calculation of a quantitative estimate,
which is very consistent with the effect observed in Her X-1.We urge that Her
X-1 is regularly monitored further and that other X-ray pulsars are
investigated for a similar behaviour.Comment: 4 pages, 2 figures, accepted by A&A Letter
Negative Differential Resistivity and Positive Temperature Coefficient of Resistivity effect in the diffusion limited current of ferroelectric thin film capacitors
We present a model for the leakage current in ferroelectric thin- film
capacitors which explains two of the observed phenomena that have escaped
satisfactory explanation, i.e. the occurrence of either a plateau or negative
differential resistivity at low voltages, and the observation of a Positive
Temperature Coefficient of Resistivity (PTCR) effect in certain samples in the
high-voltage regime. The leakage current is modelled by considering a
diffusion-limited current process, which in the high-voltage regime recovers
the diffusion-limited Schottky relationship of Simmons already shown to be
applicable in these systems
The X-ray CCD camera of the MAXI Experiment on the ISS/JEM
MAXI, Monitor of All-sky X-ray Image, is the X-ray observatory on the
Japanese experimental module (JEM) Exposed Facility (EF) on the International
Space Station (ISS). MAXI is a slit scanning camera which consists of two kinds
of X-ray detectors: one is a one-dimensional position-sensitive proportional
counter with a total area of , the Gas Slit Camera (GSC), and
the other is an X-ray CCD array with a total area , the
Solid-state Slit Camera (SSC). The GSC subtends a field of view with an angular
dimension of 1 while the SSC subtends a field of view
with an angular dimension of 1 times a little less than 180. In
the course of one station orbit, MAXI can scan almost the entire sky with a
precision of 1 and with an X-ray energy range of 0.5-30 keV. We have
developed the engineering model of CCD chips and the analogue electronics for
the SSC. The energy resolution of EM CCD for Mn K has a full-width at
half maximum of 182 eV. Readout noise is 11 e^- rms.Comment: 10 pages, 4 figures Accepted for Nuclear Instruments and Method in
Physics Researc
INTEGRAL observation of the high-mass X-ray transient V 0332+53 during the 2005 outburst decline
The decline of the high mass X-ray transient V 0332+53 during the Dec. 2004 to Feb. 2005 outburst is analysed from the data recorded by INTEGRAL. The flux is shown to decrease exponentially until 2005 Feb. 10, with a decay time scale of âŒ30 days above 20 keV and âŒ20 days at lower energies, and to decrease linearly thereafter.
The energy spectrum is well modelled throughout the decay by a power law with a folding energy of âŒ7.5 keV, and with two cyclotron absorption features. The folding energy does not vary significantly over the decay, but the spectrum becomes harder with time. Most importantly, we show that the parameters describing the fundamental cyclotron line around 27 keV do vary with time: its energy and depth increase (by about 17% for the energy in âŒ6 weeks), while its width decreases. These changes of the cyclotron line parameters are interpreted as resulting from a change in the extent of the cyclotron scattering region.
Two quasi-periodic oscillations are also observed at various times during the observations, one at 0.05 Hz and another one near the pulsation frequency around 0.23 Hz
4U 0115+63 from RXTE and INTEGRAL Data: Pulse Profile and Cyclotron Line Energy
We analyze the observations of the transient X-ray pulsar 4U 0115+63 with the
RXTE and INTEGRAL observatories in a wide X-ray (3-100 keV) energy band during
its intense outbursts in 1999 and 2004. The energy of the fundamental harmonic
of the cyclotron resonance absorption line near the maximum of the X-ray flux
from the source (luminosity range 5x10^{37} - 2x10^{38} erg/s) is ~11 keV. When
the pulsar luminosity falls below ~5x10^{37} erg/s, the energy of the
fundamental harmonic is displaced sharply toward the high energies, up to ~16
keV. Under the assumption of a dipole magnetic field configuration, this change
in cyclotron harmonic energy corresponds to a decrease in the height of the
emitting region by ~2 km, while other spectral parameters, in particular, the
cutoff energy, remain essentially constant. At a luminosity ~7x10^{37} erg/s,
four almost equidistant cyclotron line harmonics are clearly seen in the
spectrum. This suggests that either the region where the emission originates is
compact or the emergent spectrum from different (in height) segments of the
accretion column is uniform. We have found significant pulse profile variations
with energy, luminosity, and time. In particular, we show that the profile
variations from pulse to pulse are not reduced to a simple modulation of the
accretion rate specified by external conditions.Comment: 30 pages, 13 figures, Astronomy Letters, 33, 368 (2007
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