16 research outputs found
EUVE Spectroscopy of the Accretion Region in AM Herculis
Progress in determining the gravitational energy conversion balance in accreting white dwarf stars is reported. Detailed photospheric spectra of the white dwarf stars in the brightest magnetic cataclysmic binaries, in the region where most of the energy is radiated by the stellar atmosphere - in the extreme ultraviolet band is obtained
Resolving the Effects of Resonant X-ray Line Scattering in Cen X-3 with Chandra
The massive X-ray binary Cen X-3 was observed over approximately one quarter
of the system's 2.08 day orbit, beginning before eclipse and ending slightly
after eclipse center with the Chandra X-ray Observatory using its High-Energy
Transmission Grating Spectrometer. The spectra show K shell emission lines from
hydrogen- and helium-like ions of magnesium, silicon, sulfur, and iron as well
as a K-alpha fluorescence emission feature from near-neutral iron. The
helium-like n=2->1 triplet of silicon is fully resolved and the analogous
triplet of iron is partially resolved. The helium-like triplet component flux
ratios outside of eclipse are consistent with emission from recombination and
subsequent cascades (recombination radiation) from a photoionized plasma. In
eclipse, however, the w (resonance) lines of silicon and iron are stronger than
that expected for recombination radiation, and are consistent with emission
from a collisionally ionized plasma. The triplet line flux ratios at both
phases can be explained more naturally, however, as emission from a
photoionized plasma if the effects of resonant line scattering are included in
addition to recombination radiation. We show that the emissivity due to
resonant scattering depends sensitively on the line optical depth and, in the
case of winds in X-ray binaries, this allows constraints on the wind velocity
even when Doppler shifts cannot be resolved.Comment: 31 pages, 8 figures, ApJ accepted, abridged in accord with referee's
Comment
X-ray Spectral Study of the Photoionized Stellar Wind in Vela~X-1
We present results from quantitative modeling and spectral analysis of the
high mass X-ray binary Vela X-1 obtained with the Chandra HETGS. The spectra
exhibit emission lines from H-like and He-like ions driven by photoionization,
as well as fluorescent emission lines from several elements in lower charge
states. In order to interpret and make full use of the high-quality data, we
have developed a simulator, which calculates the ionization and thermal
structure of a stellar wind photoionized by an X-ray source, and performs Monte
Carlo simulations of X-ray photons propagating through the wind. The emergent
spectra are then computed as a function of the viewing angle accurately
accounting for photon transport in three dimensions including dynamics. From
comparisons of the observed spectra with the simulation results, we are able to
find the ionization structure and the geometrical distribution of material in
Vela X-1 that can reproduce the observed spectral line intensities and
continuum shapes at different orbital phases remarkably well. It is found that
a large fraction of X-ray emission lines from highly ionized ions are formed in
the region between the neutron star and the companion star. We also find that
the fluorescent X-ray lines must be produced in at least three distinct regions
--(1)the extended stellar wind, (2)reflection off the stellar photosphere, and
(3)in a distribution of dense material partially covering and possibly trailing
the neutron star, which may be associated with an accretion wake. Finally, from
detailed analysis of the emission lines, we demonstrate that the stellar wind
is affected by X-ray photoionization.Comment: 22 pages, 7 tables, 24 figures, accepted for publication in The
Astrophysical Journa
Non-Detection of Gravitationally Redshifted Absorption Lines in the X-ray Burst Spectra of GS 1826-24
During a 200 ks observation with the XMM-Newton Reflection Grating
Spectrometer, we detected 16 type-I X-ray bursts from GS 1826-24. We combined
the burst spectra in an attempt to measure the gravitational redshifts from the
surface of the neutron star. We divided the composite GS 1826-24 burst spectrum
into three groups based on the blackbody temperature during the bursts. The
spectra do not show any obvious discrete absorption lines. We compare our
observations with those of EXO 0748-676.Comment: 4 pages, 4 figures; accepted for publication in ApJ
Interstellar X-Ray Absorption Spectroscopy of Oxygen, Neon, and Iron with the Chandra LETGS Spectrum of X0614+091
We find resolved interstellar O K, Ne K, and Fe L absorption spectra in the Chandra X-Ray Observatory Low-Energy Transmission Grating Spectrometer (LETGS) spectrum of the low-mass X-ray binary X0614+091. We measure the column densities in O and Ne and find direct spectroscopic constraints on the chemical state of the interstellar O. These measurements probably probe a low-density line of sight through the Galaxy, and we discuss the results in the context of our knowledge of the properties of interstellar matter in regions between the spiral arms
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Monte Carlo Simulator to Study High Mass X-Ray Binary System
We have developed a Monte Carlo simulator for astrophysical objects, which incorporate the transportation of X-ray photons in photoionized plasma. We applied the code to X-ray spectra of high mass X-ray binaries, Vela X-1 and GX 301-2, obtained with Chandra HETGS. By utilizing the simulator, we have successfully reproduced many emission lines observed from Vela X-1. The ionization structure and the matter distribution in the Vela X-1 system are deduced. For GX 301-2, we have derived the physical parameters of material surrounding the neutron star from fully resolved shape of the Compton shoulder in the iron K{alpha} line
The ASTRO-H mission
The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the high-energy universe by performing high-resolution, high-throughput spectroscopy with moderate angular resolution. ASTRO-H covers very wide energy range from 0.3 keV to 600 keV. ASTRO-H allows a combination of wide band X-ray spectroscopy (5-80 keV) provided by multilayer coating, focusing hard X-ray mirrors and hard X-ray imaging detectors, and high energy-resolution soft X-ray spectroscopy (0.3-12 keV) provided by thin-foil X-ray optics and a micro-calorimeter array. The mission will also carry an X-ray CCD camera as a focal plane detector for a soft X-ray telescope (0.4-12 keV) and a non-focusing soft gamma-ray detector (40-600 keV) . The micro-calorimeter system is developed by an international collaboration led by ISAS/JAXA and NASA. The simultaneous broad bandpass, coupled with high spectral resolution of ΔE ~7 eV provided by the micro-calorimeter will enable a wide variety of important science themes to be pursued