824 research outputs found
Detection of X-ray line emission from the shell of SNR B0540-69.3 with XMM-Newton RGS
We present X-ray observations of PSR 0540-69.3 with the XMM-Newton
observatory. The spectra obtained with the Reflection Grating Spectrometer
reveal, for the first time, emission from ionized species of O, Ne and Fe
originating from the SNR shell. Analysis of the emission line spectrum allows
us to derive estimates of the temperature, ionization timescale, abundances,
location, and velocity of the emitting gas.Comment: 5 pages, 5 figures, accepted for publication in Astronomy and
Astrophysics, letters (XMM issue
Anomalous frequency and intensity scaling of collective and local modes in a coupled spin tetrahedron system
We report on the magnetic excitation spectrum of the coupled spin tetrahedral
system CuTeOCl using Raman scattering on single
crystals. The transition to an ordered state at T=18.2 K evidenced
from thermodynamic data leads to the evolution of distinct low-energy magnetic
excitations superimposed by a broad maximum. These modes are ascribed to
magnons with different degree of localization and a two-magnon continuum. Two
of the modes develop a substantial energy shift with decreasing temperature
similar to the order parameter of other Neel ordered systems. The other two
modes show only a negligible temperature dependence and dissolve above the
ordering temperature in a continuum of excitations at finite energies. These
observations point to a delicate interplay of magnetic inter- and
intra-tetrahedra degrees of freedom and an importance of singlet fluctuations
in describing a spin dynamics.Comment: 7pages, 6figures, 1tabl
Discovery of X-ray absorption features from the dipping low-mass X-ray binary XB 1916-053 with XMM-Newton
We report the discovery of narrow Fe XXV and Fe XXVI K alpha X-ray absorption
lines at 6.65 and 6.95 keV in the persistent emission of the dipping low-mass
X-ray binary (LMXB) XB 1916-053 during an XMM-Newton observation performed in
September 2002. In addition, there is marginal evidence for absorption features
at 1.48 keV, 2.67 kev, 7.82 keV and 8.29 keV consistent with Mg XII, S XVI, Ni
XXVII K alpha and Fe XXVI K beta transitions, respectively. Such absorption
lines from highly ionized ions are now observed in a number of high inclination
(ie. close to edge-on) LMXBs, such as XB 1916-053, where the inclination is
estimated to be between 60-80 degrees. This, together with the lack of any
orbital phase dependence of the features (except during dips), suggests that
the highly ionized plasma responsible for the absorption lines is located in a
cylindrical geometry around the compact object. Using the ratio of Fe XXV and
Fe XXVI column densities, we estimate the photo-ionization parameter of the
absorbing material to be 10^{3.92} erg cm s^{-1}. Only the Fe XXV line is
observed during dipping intervals and the upper-limits to the Fe XXVI column
density are consistent with a decrease in the amount of ionization during
dipping intervals. This implies the presence of cooler material in the line of
sight during dipping. We also report the discovery of a 0.98 keV absorption
edge in the persistent emission spectrum. The edge energy decreases to 0.87 keV
during deep dipping intervals. The detected feature may result from edges of
moderately ionized Ne and/or Fe with the average ionization level decreasing
from persistent emission to deep dipping. This is again consistent with the
presence of cooler material in the line of sight during dipping.Comment: 13 pages, accepted for publication in Astronomy and Astrophysic
Intrinsic Energy Localization through Discrete Gap Breathers in One-Dimensional Diatomic Granular Crystals
We present a systematic study of the existence and stability of discrete
breathers that are spatially localized in the bulk of a one-dimensional chain
of compressed elastic beads that interact via Hertzian contact. The chain is
diatomic, consisting of a periodic arrangement of heavy and light spherical
particles. We examine two families of discrete gap breathers: (1) an unstable
discrete gap breather that is centered on a heavy particle and characterized by
a symmetric spatial energy profile and (2) a potentially stable discrete gap
breather that is centered on a light particle and is characterized by an
asymmetric spatial energy profile. We investigate their existence, structure,
and stability throughout the band gap of the linear spectrum and classify them
into four regimes: a regime near the lower optical band edge of the linear
spectrum, a moderately discrete regime, a strongly discrete regime that lies
deep within the band gap of the linearized version of the system, and a regime
near the upper acoustic band edge. We contrast discrete breathers in anharmonic
FPU-type diatomic chains with those in diatomic granular crystals, which have a
tensionless interaction potential between adjacent particles, and highlight in
that the asymmetric nature of the latter interaction potential may lead to a
form of hybrid bulk-surface localized solutions
Implications of X-Ray Line Variations for 4U1822-371
4U 1822-371 is one of the proto-type accretion disk coronal sources with an
orbital period of about 5.6 hours. The binary is viewed almost edge-on at a
high inclination angle of 83 degrees, which makes it a unique candidate to
study binary orbital and accretion disk dynamics in high powered X-ray sources.
We observed the X-ray source in 4U 1822-371 with the Chandra High Energy
Transmission Grating Spectrometer (HETGS) for almost nine binary orbits. X-ray
eclipse times provide an update of the orbital ephemeris. We find that our
result follows the quadratic function implied by previous observations;
however, it suggests a flatter trend. Detailed line dynamics also confirm a
previous suggestion that the observed photo-ionized line emission originates
from a confined region in the outer edge of the accretion disk near the hot
spot. Line properties allow us to impose limits on the size of accretion disk,
the central corona, and the emission region. The photo-ionized plasma is
consistent with ionization parameters of log(xi) > 2, and when combined with
disk size and reasonable assumptions for the plasma density, this suggests
illuminating disk luminosities which are over an order of magnitude higher than
what is actually observed. That is, we do not directly observe the central
emitting X-ray source. The spectral continua are best fit by a flat power law
with a high energy cut-off and partial covering absorption (N_H ranging from
5.4-6.3x10^{22} cm^{-2}) with a covering fraction of about 50%. We discuss some
implications of our findings with respect to the photo-ionized line emission
for the basic properties of the X-ray source.Comment: Submitted to the Astrophysical Journa
High Resolution Spectroscopy of the X-ray Photoionized Wind in Cygnus X-3 with the Chandra High Energy Transmission Grating Spectrometer
We present a preliminary analysis of the 1--10 keV spectrum of the massive
X-ray binary Cyg X-3, obtained with the High Energy Transmission Grating
Spectrometer on the Chandra X-ray Observatory. The source reveals a richly
detailed discrete emission spectrum, with clear signatures of
photoionization-driven excitation.
Among the spectroscopic novelties in the data are the first astrophysical
detections of a number of He-like 'triplets' (Si, S, Ar) with emission line
ratios characteristic of photoionization equilibrium, fully resolved narrow
radiative recombination continua of Mg, Si, and S, the presence of the H-like
Fe Balmer series, and a clear detection of a ~ 800 km/s large scale velocity
field, as well as a ~1500 km/s FWHM Doppler broadening in the source. We
briefly touch on the implications of these findings for the structure of the
Wolf-Rayet wind.Comment: 11 pages, 3 figures; Accepted for publication in ApJ Letter
Asymmetric spin-wave dispersion due to Dzyaloshinskii-Moriya interaction in an ultrathin Pt/CoFeB film
Employing Brillouin spectroscopy, strong interfacial Dzyaloshinskii-Moriya
interactions have been observed in an ultrathin Pt/CoFeB film. Our
micromagnetic simulations show that spin-wave nonreciprocity due to asymmetric
surface pinning is insignificant for the 0.8nmthick CoFeB film studied. The
observed high asymmetry of the monotonic spin wave dispersion relation is thus
ascribed to strong Dzyaloshinskii-Moriya interactions present at the Pt/CoFeB
interface. Our findings should further enhance the significance of CoFeB as an
important material for magnonic, spintronic and skyrmionic applications.Comment: 12 pages, 4 figure
High-Resolution spectroscopy of the low-mass X-ray binary EXO 0748-67
We present initial results from observations of the low-mass X-ray binary EXO
0748-67 with the Reflection Grating Spectrometer on board the XMM-Newton
Observatory. The spectra exhibit discrete structure due to absorption and
emission from ionized neon, oxygen, and nitrogen. We use the quantitative
constraints imposed by the spectral features to develop an empirical model of
the circumsource material. This consists of a thickened accretion disk with
emission and absorption in the plasma orbiting high above the binary plane.
This model presents challenges to current theories of accretion in X-ray binary
systems.Comment: 5 pages, 4 figures, accepted by A&A letters, XMM special issu
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