9 research outputs found
Evidence for the importance of resonance scattering in X-ray emission line profiles of the O star Puppis
We fit the Doppler profiles of the He-like triplet complexes of \ion{O}{7}
and \ion{N}{6} in the X-ray spectrum of the O star Puppis, using
XMM-Newton RGS data collected over ks of exposure. We find that they
cannot be well fit if the resonance and intercombination lines are constrained
to have the same profile shape. However, a significantly better fit is achieved
with a model incorporating the effects of resonance scattering, which causes
the resonance line to become more symmetric than the intercombination line for
a given characteristic continuum optical depth . We discuss the
plausibility of this hypothesis, as well as its significance for our
understanding of Doppler profiles of X-ray emission lines in O stars.Comment: 29 pages, 8 figures, revised version accepted by Ap
Measurements and analysis of helium-like triplet ratios in the X-ray spectra of O-type stars
We discuss new methods of measuring and interpreting the
forbidden-to-intercombination line ratios of helium-like triplets in the X-ray
spectra of O-type stars, including accounting for the spatial distribution of
the X-ray emitting plasma and using the detailed photospheric UV spectrum.
Measurements are made for four O stars using archival Chandra HETGS data. We
assume an X-ray emitting plasma spatially distributed in the wind above some
minimum radius R_0. We find minimum radii of formation typically in the range
of 1.25 < R_0 / R_* < 1.67, which is consistent with results obtained
independently from line profile fits. We find no evidence for anomalously low
f/i ratios and we do not require the existence of X-ray emitting plasmas at
radii that are too small to generate sufficiently strong shocks.Comment: 52 pages, 24 figures. Accepted in Ap
XMM-Newton Reflection Grating Spectrometer Observations of Discrete Soft-X-ray Emission Features from NGC 1068
We present the first high-resolution, soft-X-ray spectrum of the prototypical
Seyfert 2 galaxy, NGC 1068. This spectrum was obtained with the XMM-Newton
Reflection Grating Spectrometer. Emission lines from H-like and He-like low-Z
ions (from C to Si) and Fe-L-shell ions dominate the spectrum. Strong, narrow
radiative recombination continua (RRC) for several ions are also present,
implying that most of the observed soft-X-ray emission arises in
low-temperature (few eV) plasma. This plasma is photoionized by the inferred
nuclear continuum (obscured along our line of sight), as in the unified model
of active galactic nuclei (AGN). We find excess emission (compared with pure
recombination) in all resonance lines (np to 1s) up to the photoelectric edge,
demonstrating the importance of photoexcitation as well. We introduce a simple
model of a cone of plasma irradiated by the nuclear continuum; the line
emission we observe along our line of sight perpendicular to the cone is
produced through recombination/radiative cascade following photoionization and
radiative decay following photoexcitation. A remarkably good fit is obtained to
the H-like/He-like ionic line series, with inferred radial ionic column
densities consistent with recent observations of warm absorbers in Seyfert 1
galaxies. Previous Chandra imaging revealed a large (extending out to 500 pc)
ionization cone containing most of the X-ray flux, implying that the warm
absorber in NGC 1068 is a large-scale outflow. To explain the ionic column
densities, a broad, flat distribution in the logarithm of the ionization
parameter () is necessary, spanning --3. This
suggests either radially-stratified ionization zones or the existence of a
broad density distribution (spanning a few orders of magnitude) at each radius.Comment: 23 pages, 16 figures, ApJ (accepted). XSPEC local model "photo" is
available at http://xmm.astro.columbia.edu/research.htm