125 research outputs found
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&
ROSAT and BeppoSAX evidence of soft X-ray excess emission in the Shapley supercluster: A3571, A3558, A3560 and A3562
Excess soft X-ray emission in clusters of galaxies has so far been detected
for sources that lie along lines-of-sight to very low Galactic HI column
density (such as Coma, A1795, A2199 and Virgo, N_H 0.9-2.0 10^{20} cm-2). We
show that the cluster soft excess emission can be investigated even at higher
N_H, which provides an opportunity for investigating soft X-ray emission
characteristics among a large number of clusters.
The ROSAT PSPC analysis of some members of the Shapley concentration (A3571,
A3558, A3560 and A3562, at N_H 4-4.5 10^{20} cm-2) bears evidence for excess
emission in the 1/4 keV band. We were able to confirm the finding for the case
of A3571 by a pointed SAX observation. Within the current sample the soft X-ray
flux is again found to be consistently above the level expected from a hot
virialized plasma. The data quality is however insufficient to enable a
discrimination between alternative models of the excess low energy flux.Comment: ApJL in press, 5 figure
High- and low energy nonthermal X-ray emission from the cluster of galaxies A 2199
We report the detection of both soft and hard excess X-ray emission in the
cluster of galaxies A 2199, based upon spatially resolved spectroscopy with
data from the BeppoSAX, EUVE and ROSAT missions. The excess emission is visible
at radii larger than 300 kpc and increases in strength relative to the
isothermal component. The total 0.1-100 keV luminosity of this component is 15
% of the cluster luminosity, but it dominates the cluster luminosity at high
and low energies. We argue that the most plausible interpretation of the excess
emission is an inverse Compton interaction between the cosmic microwave
background and relativistic electrons in the cluster. The observed spatial
distribution of the non-thermal component implies that there is a large halo of
cosmic ray electrons between 0.5-1.5 Mpc surrounding the cluster core. The
prominent existence of this component has cosmological implications, as it is
significantly changing our picture of a clusters's particle acceleration
history, dynamics between the thermal and relativistic media, and total mass
budgets.Comment: Accepted for publication in Astrophysical Journal, Letter
Unveiling the environment surrounding LMXB SAX J1808.4-3658
Low-mass X-ray binaries (LMXBs) are a natural workbench to study accretion
disk phenomena and optimal background sources to measure elemental abundances
in the Interstellar medium (ISM). In high-resolution XMM-Newton spectra, the
LMXB SAX J1808.4-3658 showed in the past a neon column density significantly
higher than expected given its small distance, presumably due to additional
absorption from a neon-rich circumstellar medium (CSM). It is possible to
detect intrinsic absorption from the CSM by evidence of Keplerian motions or
outflows. For this purpose, we use a recent, deep (100 ks long),
high-resolution Chandra/LETGS spectrum of SAX J1808.4-3658 in combination with
archival data. We estimated the column densities of the different absorbers
through the study of their absorption lines. We used both empirical and
physical models involving photo- and collisional-ionization in order to
determine the nature of the absorbers. The abundances of the cold interstellar
gas match the solar values as expected given the proximity of the X-ray source.
For the first time in this source, we detected neon and oxygen blueshifted
absorption lines that can be well modeled with outflowing photoionized gas. The
wind is neon rich (Ne/O>3) and may originate from processed, ionized gas near
the accretion disk or its corona. The kinematics (v=500-1000 km/s) are indeed
similar to those seen in other accretion disks. We also discovered a system of
emission lines with very high Doppler velocities (v~24000 km/s) originating
presumably closer to the compact object. Additional observations and UV
coverage are needed to accurately determine the wind abundances and its
ionization structure.Comment: 12 pages, 10 figures, accepted for publication on A&
Chemical Enrichment RGS cluster sample (CHEERS): Constraints on turbulence
Feedback from AGN, galactic mergers, and sloshing are thought to give rise to
turbulence, which may prevent cooling in clusters. We aim to measure the
turbulence in clusters of galaxies and compare the measurements to some of
their structural and evolutionary properties. It is possible to measure the
turbulence of the hot gas in clusters by estimating the velocity widths of
their X-ray emission lines. The RGS Spectrometers aboard XMM-Newton are
currently the only instruments provided with sufficient effective area and
spectral resolution in this energy domain. We benefited from excellent 1.6Ms
new data provided by the CHEERS project. The new observations improve the
quality of the archival data and allow us to place constraints for some
clusters, which were not accessible in previous work. One-half of the sample
shows upper limits on turbulence less than 500km/s. For several sources, our
data are consistent with relatively strong turbulence with upper limits on the
velocity widths that are larger than 1000km/s. The NGC507 group of galaxies
shows transonic velocities, which are most likely associated with the merging
phenomena and bulk motions occurring in this object. Where both low- and
high-ionization emission lines have good enough statistics, we find larger
upper limits for the hot gas, which is partly due to the different spatial
extents of the hot and cool gas phases. Our upper limits are larger than the
Mach numbers required to balance cooling, suggesting that dissipation of
turbulence may prevent cooling, although other heating processes could be
dominant. The systematics associated with the spatial profile of the source
continuum make this technique very challenging, though still powerful, for
current instruments. The ASTRO-H and Athena missions will revolutionize the
velocity estimates and discriminate between different spatial regions and
temperature phases.Comment: 16 pages, 18 figures, 3 tables, accepted for publications in
Astronomy and Astrophysic
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