838 research outputs found
Why does the intermediate polar V405 Aurigae show a double-peaked spin pulse?
V405 Aurigae is an intermediate polar showing a double-peaked pulsation in
soft X-rays and a single-peaked pulsation in harder X-rays. From XMM-Newton
observations we find that the soft band is dominated by blackbody emission from
the heated white-dwarf surface. Such emission is at a maximum when either
magnetic pole points towards us, explaining the double-peaked pulsation. The
symmetry of the pulses requires that the angle between the magnetic and spin
axes be high.
The single-peaked pulsation in harder X-rays is explained in the usual way,
as a result of opacity in the accretion curtains. However, the high dipole
inclination means that the accretion curtains are nearly in the plane. Thus the
outer regions of the curtains do not cross the line of sight to the accretion
footprints, explaining the absence of the deep absorption dip characteristic of
many intermediate polars. The sawtooth profile of this pulsation requires that
the magnetic axis be offset from the white-dwarf centre.
We remark also on the double-peaked optical emission in this star. We suggest
that the difference between V405 Aur's spin pulse and those of other
intermediate polars is the result of its high dipole inclination.Comment: 7 pages, 6 figures, accepted for publication in MNRA
Inelastic final-state interaction
The final-state interaction in multichannel decay processes is sytematically
studied with application to B decay in mind. Since the final-state inteaction
is intrinsically interwoven with the decay interaction in this case, no simple
phase theorem like "Watson's theorem" holds for experimentally observed final
states. We first examine in detail the two-channel problem as a toy-model to
clarify the issues and to remedy common mistakes made in earlier literature.
Realistic multichannel problems are too challenging for quantitative analysis.
To cope with mathematical complexity, we introduce a method of approximation
that is applicable to the case where one prominant inelastic channel dominates
over all others. We illustrate this approximation method in the amplitude of
the decay B to pi K fed by the intermediate states of a charmed meson pair.
Even with our approximation we need more accurate information of strong
interactions than we have now. Nonethless we are able to obtain some insight in
the issue and draw useful conclusions on general fearyres on the strong phases.Comment: The published version. One figure correcte
The lower boundary of the accretion column in magnetic cataclysmic variables
Using a parameterised function for the mass loss at the base of the
post-shock region, we have constructed a formulation for magnetically confined
accretion flows which avoids singularities, such as the infinity in density, at
the base associated with all previous formulations. With the further inclusion
of a term allowing for the heat input into the base from the accreting white
dwarf we are able also to obtain the hydrodynamic variables to match the
conditions in the stellar atmosphere. (We do not, however, carry out a mutually
consistent analysis for the match). Changes to the emitted X-ray spectra are
negligible unless the thickness of mass leakage region at the base approaches
or exceeds one percent of the height of the post-shock region. In this case the
predicted spectra from higher-mass white dwarfs will be harder, and fits to
X-ray data will predict lower white-dwarf masses than previous formulations.Comment: 13 pages, 6 figures, accepted for publication in MNRA
On the iron Kalpha complex in magnetic cataclysmic variables
We present a compilation of spectra of the iron Kalpha region in magnetic
cataclysmic variables, using data from the Chandra-HETG. The H-like, He-like
and fluorescent components are clearly resolved, and there are hints of the
structure within each component. The different shape of the He-like component
in AM Her might be related to greater cyclotron cooling in this star. A
surprising absence of Doppler shifts in the H-like and He-like components
implies that the X-ray emission is predominantly from the denser,
lower-velocity base of the accretion columns. This absence will allow ASTRO-E2
to resolve the structure in each component, leading to temperature diagnostics.
We do not confirm the report that the H-like and He-like components of AO Psc
are Compton broadened; however we do detect a Compton-downshifted shoulder to
the fluorescent line of GK Per. Further, a Doppler-shifted wing of this line
arises in the high-velocity, pre-shock flow.Comment: To appear in MNRAS; 5 page
Accretion physics of AM Herculis binaries, I. Results from one-dimensional stationary radiation hydrodynamics
We have solved the one-dimensional stationary two-fluid hydrodynamic
equations for post-shock flows on accreting magnetic white dwarfs simultaneous
with the fully frequency and angle-dependent radiative transfer for cyclotron
radiation and bremsstrahlung. Magnetic field strengths B = 10 to 100 MG are
considered. At given B, this theory relates the properties of the emission
region to a single physical parameter, the mass flow density (or accretion rate
per unit area). We present the normalized temperature profiles and fit formulae
for the peak electron temperature, the geometrical shock height, and the column
density of the post-shock flow. The results apply to pillbox-shaped emission
regions. With a first-order temperature correction they can also be used for
narrower columns provided they are not too tall.Comment: 10 pages with 10 Postscript figures, accepted for publication in
Astronomy & Astrophysics. The source file contains Table 1a/b in ASCII forma
High sensitive X-ray films to detect electron showers in 100 GeV region
Nonscreen type X-ray films were used in emulsion chamber experiments to detect high energy showers in cosmic rays. Ranges of the detection threshold is from about 1 to 2 TeV depending on the exposure conditions. Different types of X-ray films and sheets i.e. high sensitive screen type X-ray films and luminescence sheets were tested. The threshold of the shower detection is found to be about 200 GeV, which is much lower than that of nonscreen type X-ray films. These films are useful to detect showers in the medium energy range, a few hundred GeV, of the cosmic ray electrons
High energy electrons beyond 100 GEV observed by emulsion chamber
Much efforts have been expended to observe the spectrum of electrons in the high energy region with large area emulsion chambers exposed at balloon altitudes, and now 15 electrons beyond 1 TeV have been observed. The observed integral flux at 1 TeV is (3.24 + or - 0.87)x10(-5)/sq m sec sr. The statistics of the data around a few hundred GeV are also improving by using new shower detecting films of high sensitivity. The astrophysical significance of the observed spectrum are discussed for the propagation of electrons based on the leaky box and the nested leaky box model
Twin wall of cubic-tetragonal ferroelastics
We derive solutions for the twin wall linking two tetragonal variants of the
cubic-tetragonal ferroelastic transformation, including for the first time the
dilatational and shear energies and strains. Our solutions satisfy the
compatibility relations exactly and are obtained at all temperatures. They
require four non-vanishing strains except at the Barsch-Krumhansl temperature
TBK (where only the two deviatoric strains are needed). Between the critical
temperature and TBK, material in the wall region is dilated, while below TBK it
is compressed. In agreement with experiment and more general theory, the twin
wall lies in a cubic 110-type plane. We obtain the wall energy numerically as a
function of temperature and we derive a simple estimate which agrees well with
these values.Comment: 4 pages (revtex), 3 figure
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