4,562 research outputs found
EUVE Observations of the Magnetic Cataclysmic Variable QQ Vulpeculae
We present simultaneous X-ray (lambda_peak ~ 44A) and EUV (lambda_peak = 89A)
light curves for the magnetic cataclysmic variable QQ Vulpeculae, obtained with
the EUVE satellite. We find that the unique shape of the X-ray light curve is
different from previously obtained X-ray light curves of QQ Vul and provides
evidence for two-pole accretion. Detailed examination of the photometric data
indicates that QQ Vul undergoes a stellar eclipse of the X-ray emitting region,
indicative of a high binary inclination. We discuss possible implications for
the nature of this system given the observed shape of its EUV and X-ray light
curves.Comment: 12 pages including 4 figures, accepted to PAS
Swift Observations of Hard X-ray Emitting White Dwarfs in Symbiotic Stars
The X-ray emission from most accreting white dwarfs (WDs) in symbiotic binary
stars is quite soft. Several symbiotic WDs, however, produce strong X-ray
emission at energies greater than ~20 keV. The Swift BAT instrument has
detected hard X-ray emission from 4 such accreting WDs in symbiotic stars: RT
Cru, T CrB, CD -57 3057, and CH Cyg. In one case (RT Cru), Swift detected
X-rays out to greater than 50 keV at a > 5 sigma confidence level. Combining
data from the XRT and BAT detectors, we find that the 0.3-150 keV spectra of RT
Cru, T CrB, and CD -57 3057 are well described by emission from a
single-temperature, optically thin thermal plasma, plus an unresolved 6.4-6.9
keV Fe line complex. The X-ray spectrum of CH Cyg contains an additional bright
soft component. For all 4 systems, the spectra suffer high levels of absorption
from material that both fully and partially covers the source of hard X-rays.
The XRT data did not show any of the rapid, periodic variations that one would
expect if the X-ray emission were due to accretion onto a rotating, highly
magnetized WD. The X-rays were thus more likely from the accretion-disk
boundary layer around a massive, non-magnetic WD in each binary. The X-ray
emission from RT Cru varied on timescales of a few days. This variability is
consistent with being due to changes in the absorber that partially covers the
source, suggesting localized absorption from a clumpy medium moving into the
line of sight. The X-ray emission from CD -57 3057 and T CrB also varied during
the 9 months of Swift observations, in a manner that was also consistent with
variable absorption.Comment: Accepted for publication in ApJ. 9 pages, 6 figure
Epitaxial designs for maximizing efficiency in resonant tunnelling diode based terahertz emitters
We discuss the modelling of high current density InGaAs/AlAs/InP resonant tunneling diodes to maximize their efficiency as THz emitters. A figure of merit which contributes to the wall plug efficiency, the intrinsic resonator efficiency, is used for the development of epitaxial designs. With the contribution of key parameters identified, we analyze the limitations of accumulated stress to assess the manufacturability of such designs. Optimal epitaxial designs are revealed, utilizing thin barriers, with a wide and shallow quantum well that satisfies the strained layer epitaxy constraint. We then assess the advantages to epitaxial perfection and electrical characteristics provided by devices with a narrow InAs sub-well inside a lattice-matched InGaAs alloy. These new structures will assist in the realization of the next-generation submillimeter emitters
X-ray Variability of the Magnetic Cataclysmic Variable V1432 Aql and the Seyfert Galaxy NGC 6814
V1432 Aquilae (=RX J1940.2-1025) is the X-ray bright, eclipsing magnetic
cataclysmic variable ~37' away from the Seyfert galaxy, NGC 6814. Due to a 0.3%
difference between the orbital (12116.3 s) and the spin (12150 s) periods, the
accretion geometry changes over the ~50 day beat period. Here we report the
results of an RXTE campaign to observe the eclipse 25 times, as well as of
archival observations with ASCA and BeppoSAX. Having confirmed that the eclipse
is indeed caused by the secondary, we use the eclipse timings and profiles to
map the accretion geometry as a function of the beat phase. We find that the
accretion region is compact, and that it moves relative to the center of white
dwarf on the beat period. The amplitude of this movement suggest a low-mass
white dwarf, in contrast to the high mass previously estimated from its X-ray
spectrum. The size of the X-ray emission region appears to be larger than in
other eclipsing magnetic CVs. We also report on the RXTE data as well as the
long-term behavior of NGC 6814, indicating flux variability by a factor of at
least 10 on time scales of years.Comment: 44 pages including 16 figures; ApJ, in pres
Symbiotic stars in X-rays II: faint sources detected with XMM-Newton and Chandra
We report the detection, with and XMM-, of
faint, soft X-ray emission from four symbiotics stars that were not known to be
X-ray sources. These four object show a -type X-ray spectrum, i.e. their
spectra can be modeled with an absorbed optically thin thermal emission with
temperatures of a few million degrees. Photometric series obtained with the
Optical Monitor on board XMM- from V2416 Sgr and NSV 25735
support the proposed scenario where the X-ray emission is produced in a
shock-heated region inside the symbiotic nebulae.Comment: 5 pages, 1 figure, 2 tables; A&A publishe
An XMM-Newton observation of the nova-like variable UX UMa: spatially and spectrally resolved two-component X-ray emission
In the optical and ultraviolet regions of the electromagnetic spectrum, UX
Ursae Majoris is a deeply eclipsing cataclysmic variable. However, no soft
X-ray eclipse was detected in ROSAT observations. We have obtained a 38 ksec
XMM-Newton observation to further constrain the origin of the X-rays. The
combination of spectral and timing information allows us to identify two
components in the X-ray emission of the system. The soft component, dominant
below photon energies of 2 keV, can be fitted with a multi-temperature plasma
model and is uneclipsed. The hard component, dominant above 3 keV, can be
fitted with a kT ~ 5 keV plasma model and appears to be deeply eclipsed. We
suggest that the most likely source of the hard X-ray emission in UX UMa, and
other systems in high mass transfer states, is the boundary layer.Comment: To appear in MNRAS Letter
Symbiotic stars in X-rays III: Suzaku observations
We describe the X-ray emission as observed with Suzaku from five symbiotic
stars that we selected for deep Suzaku observations after their initial
detection with ROSAT, ASCA and Swift. We find that the X-ray spectra of all
five sources can be adequately fit with absorbed, optically thin thermal plasma
models, with either single- or multi-temperature plasmas. These models are
compatible with the X-ray emission originating in the boundary layer between an
accretion disk and a white dwarf. The high plasma temperatures of kT keV
for all five targets were greater than expected for colliding winds. Based on
these high temperatures, as well as previous measurements of UV variability and
UV luminosity, and the large amplitude of X-ray flickering in 4 Dra, we
conclude that all five sources are accretion-powered through predominantly
optically thick boundary layers. Our X-ray data allow us to observe a small,
optically thin portion of the emission from these boundary layers. Given the
time between previous observations and these observations, we find that the
intrinsic X-ray flux and the intervening absorbing column can vary by factors
of three or more on a time scale of years. However, the location of the
absorber and the relationship between changes in accretion rate and absorption
are still elusive.Comment: 14 pages, 3 figures and 3 tables. Accepted to published 04/15/2016.
arXiv admin note: substantial text overlap with arXiv:1505.0063
A classification of some S3-bundles
Article信州大学理学部紀要 31(2): 55-58(1997)departmental bulletin pape
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