833 research outputs found
A comprehensive analysis of the hard X-ray spectra of bright Seyfert galaxies
Hard X-ray spectra of 28 bright Seyfert galaxies observed with INTEGRAL were
analyzed together with the X-ray spectra from XMM-Newton, Suzaku and RXTE.
These broad-band data were fitted with a model assuming a thermal
Comptonization as a primary continuum component. We tested several model
options through a fitting of the Comptonized continuum accompanied by a complex
absorption and a Compton reflection. Both the large data set used and the model
space explored allowed us to accurately determine a mean temperature kTe of the
electron plasma, the Compton parameter y and the Compton reflection strength R
for the majority of objects in the sample. Our main finding is that a vast
majority of the sample (20 objects) is characterized by kTe < 100 keV, and only
for two objects we found kTe > 200 keV. The median kTe for entire sample is
48(-14,+57) keV. The distribution of the y parameter is bimodal, with a broad
component centered at ~0.8 and a narrow peak at ~1.1. A complex, dual absorber
model improved the fit for all data sets, compared to a simple absorption
model, reducing the fitted strength of Compton reflection by a factor of about
2. Modest reflection (median R ~0.32) together with a high ratio of Comptonized
to seed photon fluxes point towards a geometry with a compact hard X-ray
emitting region well separated from the accretion disc. Our results imply that
the template Seyferts spectra used in AGN population synthesis models should be
revised.Comment: 26 pages, 12 figures, accepted for publication in MNRA
The XMM Cluster Outskirts Project (X-COP): Physical conditions to the virial radius of Abell 2142
Context. Galaxy clusters are continuously growing through the accretion of
matter in their outskirts. This process induces inhomogeneities in the gas
density distribution (clumping) which need to be taken into account to recover
the physical properties of the intracluster medium (ICM) at large radii. Aims.
We studied the thermodynamic properties in the outskirts (R > R500) of the
massive galaxy cluster Abell 2142 by combining the Sunyaev Zel'dovich (SZ)
effect with the X-ray signal. Methods. We combined the SZ pressure profile
measured by Planck with the XMM-Newton gas density profile to recover radial
profiles of temperature, entropy and hydrostatic mass out to 2R500. We used a
method that is insensitive to clumping to recover the gas density, and we
compared the results with traditional X-ray measurement techniques. Results.
When taking clumping into account, our joint SZ/X-ray entropy profile is
consistent with the predictions from pure gravitational collapse, whereas a
significant entropy flattening is found when the effect of clumping is
neglected. The hydrostatic mass profile recovered using joint X-ray/SZ data
agrees with that obtained from spectroscopic X-ray measurements and with mass
reconstructions obtained through weak lensing and galaxy kinematics.
Conclusions. We found that clumping can explain the entropy flattening observed
by Suzaku in the outskirts of several clusters. When using a method insensitive
to clumping for the reconstruction of the gas density, the thermodynamic
properties of Abell 2142 are compatible with the assumption that the thermal
gas pressure sustains gravity and that the entropy is injected at accretion
shocks, with no need to evoke more exotic physics. Our results highlight the
need for X-ray observations with sufficient spatial resolution, and large
collecting area, to understand the processes at work in cluster outer regions.Comment: 22 pages, 32 figures, accepted in the journal A&
Prediction of pulse-to-pulse intensity fluctuation characteristics of high power ultrafast fiber amplifiers
Cataloged from PDF version of article.We report on the experimental characterization and theoretical prediction of pulse-to-pulse intensity fluctuations, namely, intensity noise, for ultrafast fiber amplifiers. We present a theoretical model with which the intensity noise of a Yb-doped fiber amplifier can be predicted with high accuracy, taking into account seed and pump noise, as well as generation of amplified spontaneous emission. Transfer of pump and seed signal modulations to the amplified output during fiber amplification are investigated thoroughly. Practically, our model enables design and optimization of fiber amplifiers with regards to their intensity noise performance. As a route to reducing noise imparted by pump diodes in a double-clad amplifier, we show the use of multiple, low-power diodes is more beneficial compared to a single, high-power diode due to the largely uncorrelated nature of their individual noise contributions. (C) 2014 AIP Publishing LLC
Multiwavelength campaign on Mrk 509. XIII. Testing ionized-reflection models on Mrk 509
Active Galactic Nuclei (AGN) are the most luminous persistent objects in the
universe. An excess of X-ray emission below about 2 keV, called soft-excess, is
very common in Type 1 AGN spectra. The origin of this feature remains debated.
Originally modeled with a blackbody, there are now several possibilities to
model the soft-excess, including warm Comptonization and blurred ionized
reflection. In this paper, we test ionized-reflection models on Mrk 509, a
bright Seyfert 1 galaxy for which we have a unique data set, in order to
determine whether it can be responsible for the strong soft-excess. We use ten
simultaneous XMM-Newton and INTEGRAL observations performed every four days. We
present here the results of the spectral analysis, the evolution of the
parameters and the variability properties of the X-ray emission. The
application of blurred ionized-reflection models leads to a very strong
reflection and an extreme geometry, but fails to reproduce the broad-band
spectrum of Mrk 509. Two different scenarios for blurred ionized reflection are
discussed: stable geometry and lamp-post configuration. In both cases we find
that the model parameters do not follow the expected relations, indicating that
the model is fine-tuned to fit the data without physical justification. A
large, slow variation of the soft-excess without counterpart in the hard X-rays
could be explained by a change in ionization of the reflector. However, such a
change does not naturally follow from the assumed geometrical configuration.
Warm Comptonization remains the most probable origin of the soft-excess in this
object. Nevertheless, it is possible that both ionized reflection and warm
Comptonization mechanisms can explain the soft-excess in all objects, one
dominating the other one, depending on the physical conditions of the disk and
the corona.Comment: 12 pages, A&A accepte
The search for decaying Dark Matter
We propose an X-ray mission called Xenia to search for decaying superweakly
interacting Dark Matter particles (super-WIMP) with a mass in the keV range.
The mission and its observation plan are capable of providing a major break
through in our understanding of the nature of Dark Matter (DM). It will
confirm, or reject, predictions of a number of particle physics models by
increasing the sensitivity of the search for decaying DM by about two orders of
magnitude through a wide-field imaging X-ray spectrometer in combination with a
dedicated observation program.
The proposed mission will provide unique limits on the mixing angle and mass
of neutral leptons, right handed partners of neutrinos, which are important
Dark Matter candidates. The existence of these particles is strongly motivated
by observed neutrino flavor oscillations and the problem of baryon asymmetry of
the Universe.
In super-WIMP models, the details of the formation of the cosmic web are
different from those of LambdaCDM. The proposed mission will, in addition to
the search for decaying Dark Matter, provide crucial insight into the nature of
DM by studying the structure of the "cosmic web". This will be done by
searching for missing baryons in emission, and by using gamma-ray bursts as
backlight to observe the warm-hot intergalactic media in absorption.Comment: A white paper submitted in response to the Fundamental Physics
Roadmap Advisory Team (FPR-AT) Call for White Paper
Multiwavelength campaign on Mrk 509 XV. A global modeling of the broad emission lines in the Optical, UV and X-ray bands
We model the broad emission lines present in the optical, UV and X-ray
spectra of Mrk 509, a bright type 1 Seyfert galaxy. The broad lines were
simultaneously observed during a large multiwavelength campaign, using the
XMM-Newton-OM for the optical lines, HST-COS for the UV lines and
XMM-Newton-RGS and Epic for the X-ray lines respectively. We also used FUSE
archival data for the broad lines observed in the far-ultra-violet. The goal is
to find a physical connection among the lines measured at different wavelengths
and determine the size and the distance from the central source of the emitting
gas components. We used the "Locally optimally emission Cloud" (LOC) model
which interprets the emissivity of the broad line region (BLR) as regulated by
powerlaw distributions of both gas density and distances from the central
source. We find that one LOC component cannot model all the lines
simultaneously. In particular, we find that the X-ray and UV lines likely may
originate in the more internal part of the AGN, at radii in the range
~5x10^{14}-3x10^{17} cm, while the optical lines and part of the UV lines may
likely be originating further out, at radii ~3x10^{17}-3x^{18} cm. These two
gas components are parametrized by a radial distribution of the luminosities
with a slope gamma of ~1.15 and ~1.10, respectively, both of them covering at
least 60% of the source. This simple parameterization points to a structured
broad line region, with the higher ionized emission coming from closer in,
while the emission of the low-ionization lines is more concentrated in the
outskirts of the broad line region.Comment: 10 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
XMM-Newton observations of four high mass X-ray binaries and IGR J17348-2045
We present the results of the XMM-Newton observations of five hard X-ray
emitters: IGR J08262-3736, IGR J17354-3255, IGR J16328-4726, SAX J1818.6-1703,
and IGR J17348-2045. The first source is a confirmed supergiant high mass X-ray
binary, the following two are candidates supergiant fast X-ray transients, SAX
J1818.6-1703 is a confirmed supergiant fast X-ray transient and IGR J17348-2045
is one of the still unidentified objects discovered with INTEGRAL. The
XMM-Newton observations permitted the first detailed soft X-ray spectral and
timing study of IGR J08262-3736 and provided further support in favor of the
association of IGR J17354-3255 and IGR J16328-4726 with the supergiant fast
X-ray transients. SAX J1818.6-1703 was not detected by XMM-Newton, thus
supporting the idea that this source reaches its lowest X-ray luminosity
(~10^32 erg/s) around apastron. For IGR J17348-2045 we identified for the first
time the soft X-ray counterpart and proposed the association with a close-by
radio object, suggestive of an extragalactic origin.Comment: 9 pages, 9 figures. Accepted for publication in A&
Multiwavelength campaign on Mrk 509 XIV. Chandra HETGS spectra
We present in this paper the results of a 270 ks Chandra HETGS observation in
the context of a large multiwavelength campaign on the Seyfert galaxy Mrk 509.
The HETGS spectrum allows us to study the high ionisation warm absorber and the
Fe-K complex in Mrk 509. We search for variability in the spectral properties
of the source with respect to previous observations in this campaign, as well
as for evidence of ultra-fast outflow signatures. The Chandra HETGS X-ray
spectrum of Mrk 509 was analysed using the SPEX fitting package. We confirm the
basic structure of the warm absorber found in the 600 ks XMM-Newton RGS
observation observed three years earlier, consisting of five distinct
ionisation components in a multikinematic regime. We find little or no
variability in the physical properties of the different warm absorber phases
with respect to previous observations in this campaign, except for component D2
which has a higher column density at the expense of component C2 at the same
outflow velocity (-240 km/s). Contrary to prior reports we find no -700 km/s
outflow component. The O VIII absorption line profiles show an average covering
factor of 0.81 +/- 0.08 for outflow velocities faster than -100 km/s, similar
to those measured in the UV. This supports the idea of a patchy wind. The
relative metal abundances in the outflow are close to proto-solar. The narrow
component of the Fe Kalpha emission line shows no changes with respect to
previous observations which confirms its origin in distant matter. The narrow
line has a red wing that can be interpreted to be a weak relativistic emission
line. We find no significant evidence of ultra-fast outflows in our new
spectrum down to the sensitivity limit of our data.Comment: 12 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
Variability of Active Galactic Nuclei from the Optical to X-ray Regions
Some progress in understanding AGN variability is reviewed. Reprocessing of
X-ray radiation to produce significant amounts of longer-wavelength continua
seems to be ruled out. In some objects where there has been correlated X-ray
and optical variability, the amplitude of the optical variability has exceeded
the amplitude of X-ray variability. We suggest that accelerated particles
striking material could be linking X-ray and optical variability (as in
activity in the solar chromosphere). Beaming effects could be significant in
all types of AGN. The diversity in optical/X-ray relationships at different
times in the same object, and between different objects, might be explained by
changes in geometry and directions of motion relative to our line of sight.
Linear shot-noise models of the variability are ruled out; instead there must
be large-scale organization of variability. Variability occurs on
light-crossing timescales rather than viscous timescales and this probably
rules out the standard Shakura-Sunyaev accretion disk. Radio-loud and
radio-quiet AGNs have similar continuum shapes and similar variability
properties. This suggests similar continuum origins and variability mechanisms.
Despite their extreme X-ray variability, narrow-line Seyfert 1s (NLS1s) do not
show extreme optical variability.Comment: Invited talk given at Euro Asian Astronomical Society meeting in
Moscow, June 2002. 20 pages, 4 figures. References update
Multiwavelength campaign on Mrk 509 XII. Broad band spectral analysis
(Abridged) The simultaneous UV to X-rays/gamma rays data obtained during the
multi-wavelength XMM/INTEGRAL campaign on the Seyfert 1 Mrk 509 are used in
this paper and tested against physically motivated broad band models. Each
observation has been fitted with a realistic thermal comptonisation model for
the continuum emission. Prompted by the correlation between the UV and soft
X-ray flux, we use a thermal comptonisation component for the soft X-ray
excess. The UV to X-rays/gamma-rays emission of Mrk 509 can be well fitted by
these components. The presence of a relatively hard high-energy spectrum points
to the existence of a hot (kT~100 keV), optically-thin (tau~0.5) corona
producing the primary continuum. On the contrary, the soft X-ray component
requires a warm (kT~1 keV), optically-thick (tau~15) plasma. Estimates of the
amplification ratio for this warm plasma support a configuration close to the
"theoretical" configuration of a slab corona above a passive disk. An
interesting consequence is the weak luminosity-dependence of its emission, a
possible explanation of the roughly constant spectral shape of the soft X-ray
excess seen in AGNs. The temperature (~ 3 eV) and flux of the soft-photon field
entering and cooling the warm plasma suggests that it covers the accretion disk
down to a transition radius of 10-20 . This plasma could be the
warm upper layer of the accretion disk. On the contrary the hot corona has a
more photon-starved geometry. The high temperature ( 100 eV) of the
soft-photon field entering and cooling it favors a localization of the hot
corona in the inner flow. This soft-photon field could be part of the
comptonised emission produced by the warm plasma. In this framework, the change
in the geometry (i.e. ) could explain most of the observed flux and
spectral variability.Comment: 19 pages, 14 figures. Accepted for publication in A&
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