2,275 research outputs found
J-PARC kaon and muon programs
J-PARC has recently commenced operations. A variety of programs in particle and nuclear physics are planned to be conducted here. Among these, the kaon and muon programs are introduced in this presentation
ASCA Observations of the Seyfert 2 Galaxy NGC 7582: An Obscured and Scattered View of the Hidden Nucleus
ASCA observations of the Seyfert 2 galaxy NGC 7582 revealed it was highly
variable on the timescale of s in the hard X-ray (2-10 keV)
band, while the soft X-ray (0.5-2 keV) flux remained constant during the
observations.
The spectral analysis suggests that this object is seen through an obscuring
torus with the thickness of N. The
hard X-ray is an absorbed direct continuum from a hidden Seyfert 1 nucleus; the
soft X-ray is dominated by the scattered central continuum from an extended
spatial region. Thus we have an obscured/absorbed and a scattered view of this
source as expected from the unification model for Seyfert galaxies.
More interestingly, the inferred X-ray column was observed to increase by
from 1994 to 1996, suggesting a ``patchy''
torus structure, namely the torus might be composed of many individual clouds.
The observed iron line feature near 6.4 keV with the equivalent width of 170 eV
is also consistent with the picture of the transmission of nuclear X-ray
continuum through a non-uniform torus.Comment: 10 pages, 6 figures. To be appear in PASJ 50 No.5 (1998 Oct.25 issue
Completing the puzzle of the 2004-2005 outburst in V0332+53: the brightening phase included
Analysis of the data obtained with the RXTE observatory during a powerful
outburst of the X-ray pulsar V0332+53 in 2004-2005 is presented. Observational
data covering the outburst brightening phase are analysed in detail for the
first time. A comparison of source parameters and their evolution during the
brightening and fading phases shows no evidence for any hysteresis behaviour.
It is found that the dependences of the energy of the cyclotron absorption line
on the luminosity during the brightening and fading phases are almost
identical. The complete data sequence including the outburst brightening and
fading phases makes it possible to impose the more stringent constraints on the
magnetic field in the source. The pulse profile and pulsed fraction are studied
as functions of the luminosity and photon energy.Comment: 9 pages, 10 figures, accepted for publication in MNRA
Orbital phase resolved spectroscopy of 4U1538-52 with MAXI
4U 1538-52, an absorbed high mass X-ray binary with an orbital period of 3.73
days, shows moderate orbital intensity modulations with a low level of counts
during the eclipse. Several models have been proposed to explain the accretion
at different orbital phases by a spherically symmetric stellar wind from the
companion. The aim of this work is to study both the light curve and orbital
phase spectroscopy of this source in the long term. Particularly, the folded
light curve and the changes of the spectral parameters with orbital phase to
analyse the stellar wind of QV Nor, the mass donor of this binary system. We
used all the observations made from the Gas Slit Camera on board MAXI of 4U
1538-52 covering many orbits continuously. We obtained the good interval times
for every orbital phase range which were the input to extract our data. We
estimated the orbital period of the system and then folded the light curves and
we fitted the X-ray spectra with the same model for every orbital phase
spectrum. We also extracted the averaged spectrum of all the MAXI data
available. The MAXI spectra in the 2-20 keV energy range were fitted with an
absorbed Comptonization of cool photons on hot electrons. We found a strong
orbital dependence of the absorption column density but neither the
fluorescence iron emission line nor low energy excess were needed to fit the
MAXI spectra. The variation of the spectral parameters over the binary orbit
were used to examine the mode of accretion onto the neutron star in 4U 1538-52.
We deduce a best value of for QV Nor.Comment: 12 pages, 5 figures, accepted to be published by A&A, corrected typos
(changing bold font to normal one
Footprints in the wind of Vela X-1 traced with MAXI
The stellar wind around the compact object in luminous wind-accreting high
mass X-ray binaries is expected to be strongly ionized with the X-rays coming
from the compact object. The stellar wind of hot stars is mostly driven by
light absorption in lines of heavier elements, and X-ray photo-ionization
significantly reduces the radiative force within the so-called Stroemgren
region leading to wind stagnation around the compact object. In close binaries
like Vela X-1 this effect might alter the wind structure throughout the system.
Using the spectral data from Monitor of All-sky X-ray Image (MAXI), we study
the observed dependence of the photoelectric absorption as function of orbital
phase in Vela X-1, and find that it is inconsistent with expectations for a
spherically-symmetric smooth wind. Taking into account previous investigations
we develop a simple model for wind structure with a stream-like photoionization
wake region of slower and denser wind trailing the neutron star responsible for
the observed absorption curve.Comment: 5 pages, 3 figures, accepted in A&
V0332+53 in the outburst of 2004--2005: luminosity dependence of the cyclotron line and pulse profile
We present results of observations of the transient X-ray pulsar V0332+53
performed during a very powerful outburst in Dec, 2004 -- Feb, 2005 with the
INTEGRAL and RXTE observatories in a wide (3-100 keV) energy band. A cyclotron
resonance scattering line at an energy of ~26 keV has been detected in the
source spectrum together with its two higher harmonics at ~50 and ~73 keV,
respectively. We show that the energy of the line is not constant but linearly
changes with the source luminosity. Strong pulse profile variations, especially
near the cyclotron line, are revealed for different levels of the source
intensity. We discuss the obtained results in terms of the theoretical models
of X-ray pulsars.Comment: Accepted for publication in MNRAS. 10 pages, 9 figure
Gamma-Ray Burst Polarimeter - GAP - aboard the Small Solar Power Sail Demonstrator IKAROS
The small solar power sail demonstrator "IKAROS" is a Japanese engineering
verification spacecraft launched by H-IIA rocket on May 21, 2010 at JAXA
Tanegashima Space Center. IKAROS has a huge sail with 20 m in diameter which is
made of thin polyimide membrane. This sail converts the solar
radiation-pressure into the propulsion force of IKAROS and accelerates the
spacecraft. The Gamma-Ray Burst Polarimeter (GAP) aboard IKAROS is the first
polarimeter to observe the gamma-ray polarization of Gamma-Ray Bursts (GRBs)
during the IKAROS cruising phase. GAP is a tinny detector of 3.8 kg in weight
and 17 cm in size with an energy range between 50-300 keV. The GAP detector
also plays a role of the interplanetary network (IPN) to determine the GRB
direction. The detection principle of gamma-ray polarization is the anisotropy
of the Compton scattering. GAP works as the GRB polarimeter with the full
coincidence mode between the central plastic and the surrounding CsI detectors.
GAP is the first instrument, devoted for the observation of gamma-ray
polarization in the astronomical history. In this paper, we present the GAP
detector and its ground and onboard calibrations.Comment: Submitted to Publications of the Astronomical Society of Japan
(PASJ), 23 pages, 14 figure
The broad band spectral properties of binary X-ray pulsars
The X-ray telescopes on board BeppoSAX are an optimal set of instruments to
observe bright galactic binary pulsars. These sources emit very hard and quite
complex X-ray spectra that can be accurately measured with BeppoSAX between 0.1
and 200 keV. A prototype of this complexity, the source Her X-1, shows at least
seven different components in its spectrum. A broad band measure is therefore
of paramount importance to have a thorough insight into the physics of the
emitting region. Moreover the detection of cyclotron features, when present,
allows a direct and highly significant measure of the magnetic field intensity
in the emission region. In this paper we briefly report the results obtained
with BeppoSAX on this class of sources, with emphasis on the detection and on
the measured properties of the cyclotron lines.Comment: 10 Latex pages, 4 figures, uses psfig.sty. Accepted for publication
in Advances in Space Research, in Proceedings of 32nd Scientific Assembly of
COSPAR - Symposium E1.1: "Broad-Band X-ray Spectroscopy of Cosmic Sources
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
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