2,030 research outputs found
The Origin of Soft X-rays in DQ Herculis
DQ Herculis (Nova Herculis 1934) is a deeply eclipsing cataclysmic variable
containing a magnetic white dwarf primary. The accretion disk is thought to
block our line of sight to the white dwarf at all orbital phases due to its
extreme inclination angle. Nevertheless, soft X-rays were detected from DQ Her
with ROSAT PSPC. To probe the origin of these soft X-rays, we have performed
Chandra ACIS observations. We confirm that DQ Her is an X-ray source. The bulk
of the X-rays are from a point-like source and exhibit a shallow partial
eclipse. We interpret this as due to scattering of the unseen central X-ray
source, probably in an accretion disk wind. At the same time, we observe what
appear to be weak extended X-ray features around DQ Her, which we interpret as
an X-ray emitting knot in the nova shell.Comment: 18 pages including 4 figures, accepted for publication in
Astrphyisical Journa
Dynamic processes and kinetic structure of collisionless reconnection at the dayside magnetopause: comparison between GEOTAIL observations and computer simulations
International audienceIn this paper we report new kinetic features of ions and electrons observed in the vicinity of the reconnection layer on 10 January 1997. This event has a three-dimensional magnetic field topological structure, which is much more complex than the previously suggested two-dimensional magnetic configuration. The ion distributions are non-gyrotropic and electrons show non-Maxwellian distribution functions. Acceleration of multiple ion beams, both parallel and perpendicular to the local magnetic field, have been observed. The perpendicular acceleration of the multiple ion beams can be explained by plasma mixing between the meandering ions accelerated around the ion diffusion region and the cold ions convected directly from the magnetosheath without passing through the X-line region. The parallel acceleration of the multiple ion beams can be understood by the fact that high-velocity ions ejected from the vicinity of the X-line mix with the plasma flowing directly across the boundary. We observed the kinetic effect of the separation of the electron and ion edges due to the time-of-flight effect. It is stressed that kinetic processes are the key to understanding these new observations that cannot be adequately explained by magnetohydrodynamic (MHD) models
On the nature of the ultraluminous X-ray transient in Cen~A (NGC 5128)
We combine 9 ROSAT, 9 Chandra, and 2 XMM-Newton observations of the Cen~A
galaxy to obtain the X-ray light curve of 1RXH J132519.8-430312 (=CXOU
J132519.9430317) spanning 1990 to 2003. The source reached a peak 0.1-2.4
keV flux F_X>10^{-12} ergs cm^{-2} s^{-1} during a 10~day span in 1995 July.
The inferred peak isotropic luminosity of the source therefore exceeded 3
10^{39} ergs s^{-1}, which places the source in the class of ultra-luminous
X-ray sources. Coherent pulsations at 13.264 Hz are detected during a second
bright episode (F_X >3 times 10^{-13} ergs cm^{-2} s^{-1}) in 1999 December.
The source is detected and varies significantly within three additional
observations but is below the detection threshold in 7 observations. The X-ray
spectrum in 1999 December is best described as a cut-off power law or a
disk-blackbody (multi-colored disk). We also detect an optical source, m_F555W
~ 24.1 mag, within the Chandra error circle of 1RXH J132519.8-430312 in HST
images taken 195~days before the nearest X-ray observation. The optical
brightness of this source is consistent with a late O or early B star at the
distance of Cen A. If the optical source is the counterpart, then the X-ray and
optical behavior of 1RXH J132519.8-430312 are similar to the transient Be/X-ray
pulsar A 0538-66.Comment: 7 pages, 8 figures. ApJ (accepted
On the nature of the hard X-ray sources SWIFTJ1907.3-2050, IGRJ12123-5802 and IGRJ19552+0044
The INTEGRAL and Swift hard X-ray surveys have identified a large number of
new sources, among which many are proposed as Cataclysmic Variables (CVs). Here
we present the first detailed study of three X-ray selected CVs, Swift
J1907.3-2050, IGRJ12123-5802, and IGRJ19552+0044 based on XMM-Newton, Suzaku,
Swift observations and ground based optical and archival nIR/IR data. Swift
J1907.3-2050 is highly variable from hours to months-years at all wavelengths.
No coherent X-ray pulses are detected but rather transient features. The X-ray
spectrum reveals a multi-temperature optically thin plasma absorbed by complex
neutral material and a soft black body component arising from a small area.
These characteristics are remarkably similar to those observed in magnetic CVs.
A supra-solar abundance of nitrogen could arise from nuclear processed material
from the donor star. Swift J1907.3-2050 could be a peculiar magnetic CV with
the second longest (20.82 h) binary period. IGRJ12123-5802 is variable in the
X-rays on a timescale of ~7.6 h. No coherent pulsations are detected, but its
spectral characteristics suggest that it could be a magnetic CV of the
Intermediate Polar (IP) type. IGRJ19552+0044 shows two X-ray periods, 1.38 h
and 1.69 h and a X-ray spectrum characterized by a multi-temperature plasma
with little absorption.We derive a low accretion rate, consistent with a CV
below the orbital period gap. Its peculiar nIR/IR spectrum suggests a
contribution from cyclotron emission. It could either be a pre-polar or an IP
with the lowest degree of asynchronism.Comment: Accepted for publication in MNRAS. 14 pages, 11 figures, 5 table
Phase noise of four‐wave mixing in semiconductor lasers
This is the published version. Copyright © 1992 American Institute of PhysicsA simple theoreticalanalysis shows that the linewidth of the conjugate wave produced in four‐wave mixing in semiconductor lasers is equal to the linewidth of the probe plus four times the linewidth of the pump. Experimental results in good agreement with the theory are presented. This result implies an enormous enhancement in the phase noise of the conjugate wave and sets a limitation on some practical applications of four‐wave mixing
Three embeddings of the Klein simple group into the Cremona group of rank three
We study the action of the Klein simple group G consisting of 168 elements on
two rational threefolds: the three-dimensional projective space and a smooth
Fano threefold X of anticanonical degree 22 and index 1. We show that the
Cremona group of rank three has at least three non-conjugate subgroups
isomorphic to G. As a by-product, we prove that X admits a Kahler-Einstein
metric, and we construct a smooth polarized K3 surface of degree 22 with an
action of the group G.Comment: 43 page
Obscuration in the Host Galaxies of Soft X-ray Selected Seyferts
We define a new sample of 96 low-redshift (z<0.1), soft X-ray selected
Seyferts from the catalog of the Einstein Slew Survey (Elvis etal. 1992,
Plummer et al. 1994). We probe the geometry and column depth of obscuring
material in the host-galaxy disks using galaxian axial ratios determined mainly
from the Digitized Sky Survey. The distribution of host-galaxy axial ratios
clearly shows a bias against edge-on spirals, confirming the existence of a
geometrically thick layer of obscuring material in the host-galaxy planes. Soft
X-ray selection recovers some of the edge-on objects missed in UV and visible
surveys but still results in 30% incompleteness for Type 1's. We speculate that
thick rings of obscuring material like the ones we infer for these Seyferts
might be commonly present in early type spirals, sitting at the Inner Lindblad
Resonances of the nonaxisymmetric potentials of the host galaxies.Comment: 14 pages including 2 tables and 3 eps figures, aas2pp4.sty, to appear
in Ap
The Peculiar Multi-Wavelength Evolution Of V1535 Sco
We present multi-wavelength observations of the unusual nova V1535 Sco
throughout its outburst in 2015. Early radio observations were consistent with
synchrotron emission, and early X-ray observations revealed the presence of
high-energy (>1 keV) photons. These indicated that strong shocks were present
during the first ~2 weeks of the nova's evolution. The radio spectral energy
distribution was consistent with thermal emission from week 2 to week 6.
Starting in week 7, the radio emission again showed evidence of synchrotron
emission and there was an increase in X-ray emission, indicating a second shock
event. The optical spectra show evidence for at least two separate outflows,
with the faster outflow possibly having a bipolar morphology. The optical and
near infrared light curves and the X-ray measurements of the hydrogen column
density indicated that the companion star is likely a K giant.Comment: 20 pages, 13 figures, under review at ApJ, updated to match the most
recent version submitted to the refere
The curve of lines on a prime Fano threefold of genus 8
We show that a general prime Fano threefold X of genus 8 can be reconstructed
from the pair , where is its Fano curve of lines and
is the theta-characteristic which gives a natural embedding
\Gamma \subset \matbb{P}^5.Comment: 24 pages, misprints corrected, to appear in International Journal of
Mathematic
New Measurements of the Motion of the Zodiacal Dust
Using the Wisconsin H-Alpha Mapper (WHAM), we have measured at high spectral
resolution and high signal-to-noise the profile of the scattered solar Mg I
5184 absorption line in the zodiacal light. The observations were carried out
toward 49 directions that sampled the ecliptic equator from solar elongations
of 48\dg (evening sky) to 334\dg (morning sky) plus observations near +47\dg
and +90\dg ecliptic latitude. The spectra show a clear prograde kinematic
signature that is inconsistent with dust confined to the ecliptic plane and in
circular orbits influenced only by the sun's gravity. In particular, the
broadened widths of the profiles, together with large amplitude variations in
the centroid velocity with elongation angle, indicate that a significant
population of dust is on eccentric orbits. In addition, the wide, flat-bottomed
line profile toward the ecliptic pole indicates a broad distribution of orbital
inclinations extending up to about 30\dg - 40\dg with respect to the ecliptic
plane. The absence of pronounced asymmetries in the shape of the profiles
limits the retrograde population to less than 10% of the prograde population
and also places constraints on the scattering phase function of the particles.
These results do not show the radial outflow or evening--morning velocity
amplitude asymmetry reported in some earlier investigations. The reduction of
the spectra included the discovery and removal of extremely faint, unidentified
terrestrial emission lines that contaminate and distort the underlying Mg I
profile. This atmospheric emission is too weak to have been seen in earlier,
lower signal-to-noise observations, but it probably affected the line centroid
measurements of previous investigations.Comment: 24 pages, 8 figures, 1 table, to appear in ApJ v612; figures appear
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