515 research outputs found
A Chandra Observation of M51: Active Nucleus and Nuclear Outflows
We present a Chandra ACIS-S observation of the nuclear region of the nearby
spiral galaxy M51 (NGC 5194), which has a low-luminosity Seyfert 2 nucleus. The
X-ray image shows the nucleus, southern extranuclear cloud, and northern loop,
the morphology of the extended emission being very similar to those seen in
radio continuum and optical emission line images. The X-ray spectrum of the
nucleus is well represented by a model consisting of soft thermal plasma with
kT ~0.5 keV, a very hard continuum, and an Fe Kalpha emission line at 6.45 keV
with an equivalent width of >2 keV. The very strong Fe line and the flat
continuum indicate that the nucleus is obscured by a column density in excess
of 10^24 cm^-2 and the spectrum is dominated by reflected emission from cold
matter near the nucleus. The X-ray spectra of the extranuclear clouds are well
fitted by a thermal plasma model with kT ~0.5 keV. This spectral shape and
morphology strongly suggest that the clouds are shock heated by the bi-polar
outflow from the nucleus. The shock velocities of the extranuclear cloud and
northern loop inferred from the temperatures of the X-ray gas are 690 km/s and
660 km/s, respectively. By assuming a steady-state situation in which the
emission of the extranuclear clouds is powered by the jets, the mechanical
energy in the jets is found to be comparable to the bolometric luminosity of
the nucleus.Comment: 7 pages, 5 figures, Accepted for publication in the Astrophyscal
Jouna
Deep XMM-Newton survey of M33
In an XMM-Newton raster observation of the bright local group spiral galaxy
M33 we study the population of X-ray sources (X-ray binaries, supernova
remnants, super-shells) down to a 0.5-10 keV luminosity of 10^35 erg s^-1 --
more than a factor of 10 deeper than earlier ROSAT observations. EPIC spectra
and hardness ratios are used to distinguish between different source classes.
We confirmed the 3.45 d orbital light curve of the X-ray binary M33 X7,
detected a transient super-soft source in M33, and searched for short term
variability of the brighter sources. We characterize the diffuse X-ray
component that is correlated with the inner disk and spiral arms. We will
compare the results with other nearby galaxies.Comment: Proceedings of the "X-ray surveys, in the light of the new
observatories" workshop, Astronomische Nachrichten, in the press (4 pages, 5
figures, uses an.cls
Chandra View of the Dynamically Young Cluster of Galaxies A1367 I. Small-Scale Structures
The 40 ks \emph{Chandra} ACIS-S observation of A1367 provides new insights
into small-scale structures and point sources in this dynamically young
cluster. Here we concentrate on small-scale extended structures. A ridge-like
structure around the center (``the ridge'') is significant in the \chandra\
image. The ridge, with a projected length of 8 arcmin (or 300
h kpc), is elongated from northwest (NW) to southeast (SE), as is
the X-ray surface brightness distribution on much larger scales ( 2
h Mpc). The ridge is cooler than its western and southern
surroundings while the differences from its eastern and northern surroundings
are small. We also searched for small-scale structures with sizes
arcmin. Nine extended features, with sizes from 0.5 to 1.5, were
detected at significance levels above 4 . Five of the nine features are
located in the ridge and form local crests. The nine extended features can be
divided into two types. Those associated with galaxies (NGC 3860B, NGC 3860 and
UGC 6697) are significantly cooler than their surroundings (0.3 - 0.9 keV vs. 3
- 4.5 keV). The masses of their host galaxies are sufficient to bind the
extended gas. These extended features are probably related to thermal halos or
galactic superwinds of their host galaxies. The existence of these relatively
cold halos imply that galaxy coronae can survive in cluster environment (e.g.,
Vikhlinin et al. 2001). Features of the second type are not apparently
associated with galaxies. Their temperatures may not be significantly different
from those of their surroundings. This class of extended features may be
related to the ridge. We consider several possibilities for the ridge and the
second type of extended features. The merging scenario is preferred.Comment: To appear in ApJ, Vol 576, 2002, Sep., a high-resolution version is
in http://cfa160.harvard.edu/~sunm/a1367_a.ps.g
Diffuse X-ray emission in spiral galaxies
We compare the soft diffuse X-ray emission from Chandra images of 12 nearby
intermediate inclination spiral galaxies to the morphology seen in Halpha,
molecular gas, and mid-infrared emission. We find that diffuse X-ray emission
is often located along spiral arms in the outer parts of spiral galaxies but
tends to be distributed in a rounder morphology in the center. The X-ray
morphology in the spiral arms matches that seen in the mid-infrared or Halpha
and so implies that the X-ray emission is associated with recent active star
formation. We see no strong evidence for X-ray emission trailing the location
of high mass star formation in spiral arms. However, population synthesis
models predict a high mechanical energy output rate from supernovae for a time
period that is about 10 times longer than the lifetime of massive ionizing
stars, conflicting with the narrow appearance of the arms in X-rays. The
fraction of supernova energy that goes into heating the ISM must depend on
environment and is probably higher near sites of active star formation. The
X-ray estimated emission measures suggest that the volume filling factors and
scale heights are high in the galaxy centers but low in the outer parts of
these galaxies. The differences between the X-ray properties and morphology in
the centers and outer parts of these galaxies suggest that galactic fountains
operate in outer galaxy disks but that winds are primarily driven from galaxy
centers.Comment: 28 pages, 4 figures, to be submitted to Ap
AGN behind the SMC selected from radio and X-ray surveys
The XMM-Newton survey of the Small Magellanic Cloud (SMC) revealed 3053 X-ray
sources with the majority expected to be active galactic nuclei (AGN) behind
the SMC. However, the high stellar density in this field often does not allow
assigning unique optical counterparts and hinders source classification. On the
other hand, the association of X-ray point sources with radio emission can be
used to select background AGN with high confidence, and to constrain other
object classes like pulsar wind nebula. To classify X-ray and radio sources, we
use clear correlations of X-ray sources found in the XMM-Newton survey with
radio-continuum sources detected with ATCA and MOST. Deep radio-continuum
images were searched for correlations with X-ray sources of the XMM-Newton
SMC-survey point-source catalogue as well as galaxy clusters seen with extended
X-ray emission. Eighty eight discrete radio sources were found in common with
the X-ray point-source catalogue in addition to six correlations with extended
X-ray sources. One source is identified as a Galactic star and eight as
galaxies. Eight radio sources likely originate in AGN that are associated with
clusters of galaxies seen in X-rays. One source is a PWN candidate. We obtain
43 new candidates for background sources located behind the SMC. A total of 24
X-ray sources show jet-like radio structures.Comment: 9 pages, 6 figures, accepted for publication in A&
The dust-scattering X-ray rings of the anomalous X-ray pulsar 1E 1547.0-5408
On 2009 January 22 numerous strong bursts were detected from the anomalous
X-ray pulsar 1E 1547.0-5408. Swift/XRT and XMM-Newton/EPIC observations carried
out in the following two weeks led to the discovery of three X-ray rings
centered on this source. The ring radii increased with time following the
expansion law expected for a short impulse of X-rays scattered by three dust
clouds. Assuming different models for the dust composition and grain size
distribution, we fit the intensity decay of each ring as a function of time at
different energies, obtaining tight constrains on the distance of the X-ray
source. Although the distance strongly depends on the adopted dust model, we
find that some models are incompatible with our X-ray data, restricting to 4-8
kpc the range of possible distances for 1E 1547.0-5408. The best-fitting dust
model provides a source distance of 3.91 +/- 0.07 kpc, which is compatible with
the proposed association with the supernova remnant G 327.24-0.13, and implies
distances of 2.2 kpc, 2.6 kpc and 3.4 kpc for the dust clouds, in good
agreement with the dust distribution inferred by CO line observations towards
1E 1547.0-5408. However, dust distances in agreement with CO data are also
obtained for a set of similarly well-fitting models that imply a source
distance of about 5 kpc. A distance of about 4-5 kpc is also favored by the
fact that these dust models are already known to provide good fits to the
dust-scattering halos of bright X-ray binaries.Comment: Accepted for publication in The Astrophysical Journal; 10 pages in
emulate-apj style, 3 tables, 5 color figures. Note: abstract truncated; full
abstract in the pape
The population of X-ray supernova remnants in the Large Magellanic Cloud
We present a comprehensive X-ray study of the population of supernova
remnants (SNRs) in the LMC. Using primarily XMM-Newton, we conduct a systematic
spectral analysis of LMC SNRs to gain new insights on their evolution and the
interplay with their host galaxy. We combined all the archival XMM observations
of the LMC with those of our Very Large Programme survey. We produced X-ray
images and spectra of 51 SNRs, out of a list of 59. Using a careful modelling
of the background, we consistently analysed all the X-ray spectra and measure
temperatures, luminosities, and chemical compositions. We investigated the
spatial distribution of SNRs in the LMC and the connection with their
environment, characterised by various SFHs. We tentatively typed all LMC SNRs
to constrain the ratio of core-collapse to type Ia SN rates in the LMC. We
compared the X-ray-derived column densities to HI maps to probe the
three-dimensional structure of the LMC. This work provides the first
homogeneous catalogue of X-ray spectral properties of LMC SNRs. It offers a
complete census of LMC SNRs exhibiting Fe K lines (13% of the sample), or
revealing contribution from hot SN ejecta (39%). Abundances in the LMC ISM are
found to be 0.2-0.5 solar, with a lower [/Fe] than in the Milky Way.
The ratio of CC/type Ia SN in the LMC is , lower than in local SN surveys and galaxy clusters.
Comparison of X-ray luminosity functions of SNRs in Local Group galaxies
reveals an intriguing excess of bright objects in the LMC. We confirm that 30
Doradus and the LMC Bar are offset from the main disc of the LMC, to the far
and near sides, respectively. (abridged)Comment: Accepted for publication in Astronomy and Astrophysics. 54 pages, 18
figures, 12 tables. The resolution of the figures has been reduced compared
to the journal version; v2: New title, minor text edits; v3: Correct version
A Chandra Observation of Abell 13: Investigating the Origin of the Radio Relic
We present results from the Chandra X-ray observation of Abell 13, a galaxy
cluster that contains an unusual noncentral radio source, also known as a radio
relic. This is the first pointed X-ray observation of Abell 13, providing a
more sensitive study of the properties of the X-ray gas. The X-ray emission
from Abell 13 is extended to the northwest of the X-ray peak and shows
substructure indicative of a recent merger event. The cluster X-ray emission is
centered on the bright galaxy H of Slee et al. 2001. We find no evidence for a
cooling flow in the cluster. A knot of excess X-ray emission is coincident with
the other bright elliptical galaxy F. This knot of emission has properties
similar to the enhanced emission associated with the large galaxies in the Coma
cluster.
With these Chandra data we are able to compare the properties of the hot
X-ray gas with those of the radio relic from VLA data, to study the interaction
of the X-ray gas with the radio emitting electrons. Our results suggest that
the radio relic is associated with cooler gas in the cluster. We suggest two
explanations for the coincidence of the cooler gas and radio source. First, the
gas may have been uplifted by the radio relic from the cluster core.
Alternatively, the relic and cool gas may have been displaced from the central
galaxy during the cluster merger event.Comment: 11 pages, 9 figures, Accepted for Publication in the Astrophysical
Journal, higher-resolution figures can be found at
http://www.astro.virginia.edu/~amj3r/Abell13
XMM-Newton survey of the Local Group galaxy M 33
In an XMM-Newton raster observation of the bright Local Group spiral galaxy M
33 we study the population of X-ray sources (X-ray binaries, supernova
remnants) down to a 0.2--4.5 keV luminosity of 10^35 erg/s -- more than a
factor of 10 deeper than earlier ROSAT observations. EPIC hardness ratios and
optical and radio information are used to distinguish between different source
classes. The survey detects 408 sources in an area of 0.80 square degree. We
correlate these newly detected sources with earlier M 33 X-ray catalogues and
information from optical, infra-red and radio wavelengths. As M 33 sources we
detect 21 supernova remnants (SNR) and 23 SNR candidates, 5 super-soft sources,
and 2 X-ray binaries (XRBs). There are 267 sources classified as hard, which
may either be XRBs or Crab-like SNRs in M 33 or background AGN. The 44
confirmed and candidate SNRs more than double the number of X-ray detected SNRs
in M 33. 16 of these are proposed as SNR candidates from the X-ray data for the
first time. On the other hand, there are several sources not connected to M 33:
five foreground stars, 30 foreground star candidates, 12 active galactic
nucleus candidates, one background galaxy and one background galaxy candidate.
Extrapolating from deep field observations we would expect 175 to 210
background sources in this field. This indicates that about half of the sources
detected are sources within M 33.Comment: 14 pages, 6 figures, accepted for publication in A&A, the images of
Figs. 1,2,3,4,6 are available in jpg format, a full version of the paper is
available at ftp://ftp.xray.mpe.mpg.de/people/fwh/docs/M33_AA0068.p
High-resolution X-ray spectroscopy and imaging of the nuclear outflow of the starburst galaxy NGC 253
Aims: Using XMM-Newton data, we have aimed to study the nuclear outflow of
the nearby starburst galaxy NGC 253 in X-rays with respect to its morphology
and to spectral variations along the outflow. Methods: We analysed XMM-Newton
RGS spectra, RGS brightness profiles in cross-dispersion direction, narrow band
RGS and EPIC images and EPIC PN brightness profiles of the nuclear region and
of the outflow of NGC 253. Results: We detect a diversity of emission lines
along the outflow of NGC 253. This includes the He-like ions of Si, Mg, Ne and
O and their corresponding ions in the next higher ionisation state.
Additionally transitions from Fe XVII and Fe XVIII are prominent. The derived
temperatures from line ratios along the outflow range from 0.21+/-0.01 to
0.79+/-0.06 keV and the ratio of Fe XVII lines indicates a predominantly
collisionally ionised plasma. Additionally we see indications of a recombining
or underionized plasma in the Fe XVII line ratio. Derived electron densities
are 0.106+/-0.018 cm^-3 for the nuclear region and 0.025+/-0.003 cm^-3 for the
outflow region closest to the centre. The RGS image in the O VIII line energy
clearly shows the morphology of an outflow extending out to ~750 pc along the
south-east minor axis, while the north-west part of the outflow is not seen in
O VIII due to the heavy absorption by the galactic disc. This is the first time
that the hot wind fluid has been detected directly. The limb brightening seen
in Chandra and XMM-Newton EPIC observations is only seen in the energy range
containing the Fe XVII lines (550-750 eV). In all other energy ranges between
400 and 2000 eV no clear evidence of limb brightening could be detected.Comment: 14 pages, 7 figures, 3 tables, accepted for publication on A&A, v2:
typos corrected, electron densities and table with emission line flux added,
discussion improve
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