210 research outputs found
Suzaku and XMM-Newton Observations of the North Polar Spur: Charge Exchange or ISM Absorption?
By revisiting the Suzaku and XMM-Newton data of the North Polar Spur, we
discovered that the spectra are inconsistent with the traditional model
consisting of pure thermal emission and neutral absorption. The most prominent
discrepancies are the enhanced O VII and Ne IX forbidden-to-resonance ratios,
and a high O VIII Ly line relative to other Lyman series. A
collisionally ionized absorption model can naturally explain both features,
while a charge exchange component can only account for the former. By including
the additional ionized absorption, the plasma in the North Polar Spur can be
described by a single-phase CIE component with temperature of 0.25 keV, and
nitrogen, oxygen, neon, magnesium, and iron abundances of solar. The
abundance pattern of the North Polar Spur is well in line with those of the
Galactic halo stars. The high nitrogen-to-oxygen ratio reported in previous
studies can be migrated to the large transmission of the O VIII Ly
line. The ionized absorber is characterized by a balance temperature of
keV and a column density of cm. Based
on the derived abundances and absorption, we speculate that the North Polar
Spur is a structure in the Galactic halo, so that the emission is mostly
absorbed by Galactic ISM in the line of sight.Comment: Accepted for publication in Astronomy and Astrophysic
Contrasting the UV and X-ray O VI Column Density Inferred for the Outflow in NGC 5548
We compare X-ray and UV spectroscopic observations of NGC 5548. Both data
sets show O VI absorption troughs associated with the AGN outflow from this
galaxy. We find that the robust lower limit on the column density of the O VI
X-ray trough is seven times larger than the column density found in a study of
the O VI UV troughs. This discrepancy suggests that column densities inferred
for UV troughs of Seyfert outflows are often severely underestimated. We
identify the physical limitations of the UV Gaussian modeling as the probable
explanation of the O VI column density discrepancy. Specifically, Gaussian
modeling cannot account for a velocity dependent covering fraction, and it is a
poor representation for absorption associated with a dynamical outflow.
Analysis techniques that use a single covering fraction value for each
absorption component suffer from similar limitations. We conclude by suggesting
ways to improve the UV analysis.Comment: 16 pages, 1 figure, accepted for publication in Ap
Abundance and temperature distributions in the hot intra-cluster gas of Abell 4059
Using the EPIC and RGS data from a deep (~200 ks) XMM-Newton observation, we
investigate the temperature structure (kT and sigma_T ) and the abundances of 9
elements (O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni) of the intra-cluster medium
(ICM) in the nearby (z=0.046) cool-core galaxy cluster Abell 4059. Next to a
deep analysis of the cluster core, a careful modelling of the EPIC background
allows us to build radial profiles up to 12' (~650 kpc) from the core. Probably
because of projection effects, the temperature ICM is found not to be in single
phase, even in the outer parts of the cluster. The abundances of Ne, Si, S, Ar,
Ca and Fe, but also O are peaked towards the core. Fe and O are still
significantly detected in the outermost annuli; suggesting that the enrichment
by both type Ia and core-collapse SNe started in the early stages of the
cluster formation. However, the particularly high Ca/Fe ratio that we find in
the core is not well reproduced by the standard SNe yield models. Finally, 2-D
maps of temperature and Fe abundance are presented and confirm the existence of
a denser, colder, and Fe-rich ridge southwest of the core, previously observed
by Chandra. The origin of this asymmetry in the hot gas of the cluster core is
still unclear, but might be explained by a past intense ram-pressure stripping
event near the central cD galaxy.Comment: 17 pages, 13 figures, accepted for publication in A&
X-ray spectroscopy of galaxy clusters: beyond the CIE modeling
X-ray spectra of galaxy clusters are dominated by the thermal emission from
the hot intracluster medium. In some cases, besides the thermal component,
spectral models require additional components associated, e.g., with resonant
scattering and charge exchange. The latter produces mostly underluminous fine
spectral features. Detection of the extra components therefore requires high
spectral resolution. The upcoming X-ray missions will provide such high
resolution, and will allow spectroscopic diagnostics of clusters beyond the
current simple thermal modeling. A representative science case is resonant
scattering, which produces spectral distortions of the emission lines from the
dominant thermal component. Accounting for the resonant scattering is essential
for accurate abundance and gas motion measurements of the ICM. The high
resolution spectroscopy might also reveal/corroborate a number of new spectral
components, including the excitation by non-thermal electrons, the deviation
from ionization equilibrium, and charge exchange from surface of cold gas
clouds in clusters. Apart from detecting new features, future high resolution
spectroscopy will also enable a much better measurement of the thermal
component. Accurate atomic database and appropriate modeling of the thermal
spectrum are therefore needed for interpreting the data.Comment: published in Space Science Review
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