15,966 research outputs found
X-ray Line Emitting Objects in XMM-Newton Observations: the Tip of the Iceberg
We present preliminary results from a novel search for X-ray Line Emitting
Objects (XLEOs) in XMM-Newton images. Three sources have been detected in a
test-run analysis of 13 XMM-Newton observations. The three objects found are
most likely extremely absorbed AGN characterized by a column density
NH~10^24cm^-2. Their redshift has been directly determined from the X-ray data,
by interpreting the detected emission line as the 6.4 keV Fe line. The measured
equivalent width of the X-ray line is, in all three cases, several keV. This
pilot study demonstrates the success of our search method and implies that a
large sample of XLEOs can be obtained from the public XMM-Newton data archive.Comment: 10 pages, 3 figures, accepted for publication in ApJ Letter
A Hard Medium Survey with ASCA. IV: the Radio-Loud Type 2 QSO AXJ0843+294 2
We discuss the X-ray, optical and radio properties of AX J0843+2942, a high
luminosity Type 2 AGN found in the ASCA Hard Serendipitous Survey. The X-ray
spectrum is best described by an absorbed power-law model with photon index of
Gamma = 1.72 (+0.3 -0.6) and intrinsic absorbing column density of NH = 1.44
(+0.33 -0.52) x 10E23 cm-2. The intrinsic luminosity in the 0.5-10 keV energy
band is ~ 3x10E45 erg s-1, well within the range of quasar luminosities. AX
J0843+2942, positionally coincident with the core of a triple and strong (S_1.4
GHz ~ 1 Jy; P_1.4 GHz ~ 9 x 10E33 erg s-1 Hz-1) radio source, is
spectroscopically identified with a Narrow Line object (intrinsic FWHM of all
the permitted emission lines <= 1200 km s-1) at z=0.398, having line features
and ratios typical of Seyfert-2 like objects. The high X-ray luminosity,
coupled with the high intrinsic absorption, the optical spectral properties and
the radio power, allow us to propose AX J0843+2942 as a Radio-Loud "Type 2
QSO". A discussion of the SED of this object is presented here together with a
comparison with the SED of Ultra Luminous Infrared Galaxies, other "Type 2 QSO"
candidates from the literature, and "normal" Radio-Quiet and Radio-Loud QSOs.Comment: 10 pages, 7 figures, Latex manuscript, Accepted for publication in
Ast ronomy and Astrophysic
Heavily obscured AGN in the local Universe
We present here a new powerful diagnostic plot to select heavily obscured AGN
in the local universe by combining infrared (Spitzer, IRAS) and X-ray (XMM)
information. On the basis of this plot, we selected a sample of X-ray obscured
sources in the 2XMM catalogue and found seven newly discovered Compton-thick
AGN candidates.Comment: 2 pages, 2 figures, To appear in refereed Proceedings of "X-ray
Astronomy 2009: Present Status, Multi-Wavelength Approach and Future
Perspectives", Bologna, Italy, September 7-11, 2009, AIP, eds. A. Comastri,
M. Cappi, and L. Angelin
Cu-catalyzed Si-NWS grown on “carbon paper” as anodes for Li-ion cells
The very high theoretical capacity of the silicon (4200mAh/g more than 10 times larger than graphite), environmental-friendly, abundant and low-cost, makes it a potential candidate to replace graphite in high energy density Li-ion batteries. As a drawback, silicon suffers from huge volume changes (300%) on alloying and dealloying with Li, leading a structural deformation that induces disruption. The use of nanostructured silicon materials has been shown to be an effective way to avoid this mechanical degradation of the active material. In this paper the synthesis of silicon nanowires, grown on a highly porous 3D-like carbon paper substrate by CVD using Cu as the catalyst, is presented. The use of carbon paper allows to achieve remarkable loadings of active material (2-5 mg/cm2) and, consequently, high capacity densities. The silicon electrode was investigated both morphologically and electrochemically. To improve the electrochemical performance various strategies have been carried out. It was observed that a very slow first cycle (C/40), which helps the formation of a stable solid electrolyte interphase on the silicon surface, improves the performance of the cells; nevertheless, their cycle life has been found not fully satisfactory. Morphological analysis of the Si-NWs electrodes before and after cycling showed the presence of a dense silicon layer below the nanowires which could reduce the electrical contact between the active material and the substrate
The structure of the X-ray absorber in Mrk 915 revealed by Swift
In this paper we present the results obtained with a monitoring programme (23
days long) performed with Swift-XRT on the local Seyfert galaxy Mrk 915. The
light-curve analysis shows a significant count rate variation (about a factor
of 2-3) on a time-scale of a few days, while the X-ray colours show a change in
the spectral curvature below 2 keV and the presence of two main spectral
states. From the spectral analysis we find that the observed variations can be
explained by the change of the intrinsic nuclear power (about a factor of 1.5)
coupled with a change of the properties of an ionized absorber. The quality of
the data prevents us from firmly establishing if the spectral variation is due
to a change in the ionization state and/or in the covering factor of the
absorbing medium. The latter scenario would imply a clumpy structure of the
ionized medium. By combining the information provided by the light curve and
the spectral analyses, we can derive some constraints on the location of the
absorber under the hypotheses of either homogeneous or clumpy medium. In both
cases, we find that the absorber should be located inside the outer edge of an
extended torus and, in particular, under the clumpy hypothesis, it should be
located near, or just outside, to the broad emission line region.Comment: 8 pages, 6 figures, 1 table. Accepted for publication on MNRA
Free-carrier screening of polarization fields in wurtzite GaN/InGaN laser structures
The free-carrier screening of macroscopic polarization fields in wurtzite
GaN/InGaN quantum wells lasers is investigated via a self-consistent
tight-binding approach. We show that the high carrier concentrations found
experimentally in nitride laser structures effectively screen the built-in
spontaneous and piezoelectric polarization fields, thus inducing a
``field-free'' band profile. Our results explain some heretofore puzzling
experimental data on nitride lasers, such as the unusually high lasing
excitation thresholds and emission blue-shifts for increasing excitation
levels.Comment: RevTeX 4 pages, 4 figure
XMM-Newton and NuSTAR joint observations of Mrk 915: a deep look into the X-ray properties
We report on the X-ray monitoring programme (covering slightly more than 11
days) carried out jointly by XMM-Newton and NuSTAR on the intermediate Seyfert
galaxy Mrk 915. The light curves extracted in different energy ranges show a
variation in intensity but not a significant change in spectral shape. The
X-ray spectra reveal the presence of a two-phase warm absorber: a fully
covering mildly ionized structure [log xi/(erg cm/s)~2.3, NH~1.3x10^21 cm-2]
and a partial covering (~90 per cent) lower ionized one [log xi/(erg cm/s)~0.6,
NH~2x10^22 cm-2]. A reflection component from distant matter is also present.
Finally, a high-column density (NH~1.5x10^23 cm-2) distribution of neutral
matter covering a small fraction of the central region is observed, almost
constant, in all observations. Main driver of the variations observed between
the datasets is a decrease in the intrinsic emission by a factor of ~1.5.
Slight variations in the partial covering ionized absorber are detected, while
the data are consistent with no variation of the total covering absorber. The
most likely interpretation of the present data locates this complex absorber
closer to the central source than the narrow line region, possibly in the broad
line region, in the innermost part of the torus, or in between. The neutral
obscurer may either be part of this same stratified structure or associated
with the walls of the torus, grazed by (and partially intercepting) the line of
sight.Comment: 14 pages, 10 figures, 4 tables. Accepted for publication in MNRA
Eating Habits of Professional Firefighters: Comparison With National Guidelines and Impact Healthy Eating Promotion Program.
Firefighters' eating habits may be an additional risk factor for metabolic diseases. We assessed eating habits of firefighters, compared them with national guidelines, and evaluated the impact of a prevention program.
Twenty-eight professional firefighters from a Swiss airport benefited from a healthy-eating program. Food intake, eating behavior, and anthropometric data were collected at baseline and 1-year follow-up using an electronic food record, questionnaires, and bio-impedance.
Participants had unbalanced diets with low-quality food choices associated with low intakes of fibers and micronutrients compared with national guidelines. Intervention did not impact eating habits or anthropometrics data at the group level, but changes were measured in sub-groups. Main reported barriers for healthy eating were lack of motivation, prioritization, or time.
Intensive and culturally tailored prevention interventions targeting nutritional behaviors are needed at the individual, group, and organizational levels
Visualization of Coherent Destruction of Tunneling in an Optical Double Well System
We report on a direct visualization of coherent destruction of tunneling
(CDT) of light waves in a double well system which provides an optical analog
of quantum CDT as originally proposed by Grossmann, Dittrich, Jung, and Hanggi
[Phys. Rev. Lett. {\bf 67}, 516 (1991)]. The driven double well, realized by
two periodically-curved waveguides in an Er:Yb-doped glass, is designed so that
spatial light propagation exactly mimics the coherent space-time dynamics of
matter waves in a driven double-well potential governed by the Schr\"{o}dinger
equation. The fluorescence of Er ions is exploited to image the spatial
evolution of light in the two wells, clearly demonstrating suppression of light
tunneling for special ratios between frequency and amplitude of the driving
field.Comment: final versio
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