193 research outputs found
Constraints on the Velocity and Spatial Distribution of Helium-like Ions in the Wind of SMC X-1 from Observations with XMM-Newton/RGS
We present here X-ray spectra of the HMXB SMC X-1 obtained in an observation
with the XMM observatory beginning before eclipse and ending near the end of
eclipse. With the Reflection Grating Spectrometers (RGS) on board XMM, we
observe emission lines from hydrogen-like and helium-like ions of nitrogen,
oxygen, neon, magnesium, and silicon. Though the resolution of the RGS is
sufficient to resolve the helium-like n=2->1 emission into three line
components, only one of these components, the intercombination line, is
detected in our data. The lack of flux in the forbidden lines of the
helium-like triplets is explained by pumping by ultraviolet photons from the B0
star and, from this, we set an upper limit on the distance of the emitting ions
from the star. The lack of observable flux in the resonance lines of the
helium-like triplets indicate a lack of enhancement due to resonance line
scattering and, from this, we derive a new observational constraint on the
distribution of the wind in SMC X-1 in velocity and coordinate space. We find
that the solid angle subtended by the volume containing the helium-like ions at
the neutron star multiplied by the velocity dispersion of the helium-like ions
must be less than 4pi steradians km/s. This constraint will be satisfied if the
helium-like ions are located primarily in clumps distributed throughout the
wind or in a thin layer along the surface of the B0 star.Comment: 22 pages, 17 figures, ApJ accepted, discussion of relevant other work
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X-ray Spectral Diagnostics of Gamma-Ray Burst Environments
Recently, the detection of discrete features in the X-ray afterglow spectra
of GRB970508 and GRB970828 was reported. The most natural interpretation of
these features is that they are redshifted Fe K emission complexes. The
identification of the line emission mechanism has drastic implications for the
inferred mass of radiating material, end hence the nature of the burst site.
X-ray spectroscopy provides a direct observational constraint on these
properties of gamma-ray bursters. We briefly discuss how these constraints
arise, in the context of an application to the spectrum of GRB970508.Comment: 11 pages, 2 figures, accepted for publication in ApJ Letter
High-Resolution Chandra Spectroscopy Of Tau Scorpii: A Narrow-Line X-Ray Spectrum From A Hot Star
Long known to be an unusual early-type star by virtue of its hard and strong X-ray emission, tau Scorpii poses a severe challenge to the standard picture of O-star wind-shock X-ray emission. The Chandra HETGS spectrum now provides significant direct evidence that this B0.2 star does not fit this standard wind-shock framework. The many emission lines detected with the Chandra gratings are significantly narrower than what would be expected from a star with the known wind properties of tau Sco, although they are broader than the corresponding lines seen in late-type coronal sources. While line ratios are consistent with the hot plasma on this star being within a few stellar radii of the photosphere, from at least one He-like complex there is evidence that the X-ray emitting plasma is located more than a stellar radius above the photosphere. The Chandra spectrum of Sco is harder and more variable than those of other hot stars, with the exception of the young magnetized O star theta(1) Ori C. We discuss these new results in the context of wind, coronal, and hybrid wind-magnetic models of hot-star X-ray emission
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
The Chandra High Energy Transmission Grating Observation of an X-ray Ionization Cone in Markarian 3
We present a preliminary analysis of the first high-resolution X-ray spectrum
of a Seyfert 2 galaxy, Mkn 3, obtained with the High Energy Transmission
Grating Spectrometer onboard the Chandra X-ray Observatory. The high-energy
spectrum (lambda < 4 Ang) is dominated by reflection of the AGN continuum
radiation in a cold optically thick medium and contains bright K-alpha
fluorescent lines from iron and silicon, as well as weak, blended lines from
sulfur and magnesium. The soft X-ray emission (4 < lambda < 23 Ang) is
spatially extended along the [O III] ionization cone and shows discrete
signatures of emission following recombination and photoexcitation produced in
a warm photoionized region. The measured iron L line fluxes indicate that
emission from collisionally ionized plasma is almost completely negligible, and
does not contribute significantly to the total energy budget of the X-ray
emission. We find that significant fractions of the H- and He-like resonance
lines, as well as the observed iron L lines are produced through re-emission
from the warm absorbing medium observed in Seyfert 1 galaxies. Its X-ray
spectral properties are qualitatively consistent with those of a typical
Seyfert 1 galaxy viewed at a different orientation, and provide further
convincing evidence for the existence of an obscured Seyfert 1 nucleus in Mkn
3.Comment: 16 pages, including 1 table and 2 figure
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