2,609 research outputs found
Editorial: Embodied cognition over the lifespan. Theoretical issues and implications for applied settings
The editorial introduces The Special Topic on Embodied Cognition over the Lifespan and in Applied Settings. The Topic aimed at gathering evidence on the role of EC in development, adulthood, and aging, and to shed light on the applied fields benefiting from this approach
The contribution of AGN to the X-ray background: the effect of iron features
The contribution of the iron emission line, commonly detected in the X-ray
spectra of Seyfert (Sey) galaxies, to the cosmic X-ray background (XRB)
spectrum is evaluated in the framework of the XRB synthesis models based on AGN
unification schemes. To derive the mean line properties, we have carried out a
search in the literature covering a sample of about 70 AGN. When adopting line
parameters in agreement with the observations, it turns out that the maximum
contribution of the iron line to the XRB is less than 7% at a few keV. This is
still below the present uncertainties in the XRB spectrum measurements.Comment: 21 LaTeX pages with 5 Postscript figures. Accepted for publication in
New Astronom
Time-delay in a multi-channel formalism
We reexamine the time-delay formalism of Wigner, Eisenbud and Smith, which
was developed to analyze both elastic and inelastic resonances. An error in the
paper of Smith has propagated through the literature. We correct this error and
show how the results of Eisenbud and Smith are related. We also comment on some
recent time-delay studies, based on Smith's erroneous interpretation of the
Eisenbud result.Comment: 4 pages, no figure
Inverse Compton X-rays from the radio galaxy 3C 219
We report the results from a Chandra observation of the powerful nearby
(z=0.1744) radio galaxy 3C 219. We find evidence for non-thermal X-ray emission
from the radio lobes which fits fairly well with a combination of inverse
Compton scattering of Cosmic Microwave Background radiation and of nuclear
photons with the relativistic electrons in the lobes. The comparison between
radio synchrotron and IC emission yields a magnetic field strength
significantly lower (about a factor 3) than that calculated under minimum
energy conditions; the source energetics is then dominated by the relativistic
particles.Comment: 5 pages, 2 color figures, Accepted for publication in MNRAS pink
page
The resolved fraction of the Cosmic X-ray Background
We present the X-ray source number counts in two energy bands (0.5-2 and 2-10
keV) from a very large source sample: we combine data of six different surveys,
both shallow wide field and deep pencil beam, performed with three different
satellites (ROSAT, Chandra and XMM-Newton). The sample covers with good
statistics the largest possible flux range so far: [2.4*10^-17 - 10^-11] cgs in
the soft band and [2.1*10^-16 - 8*10^{-12}]cgs in the hard band. Integrating
the flux distributions over this range and taking into account the (small)
contribution of the brightest sources we derive the flux density generated by
discrete sources in both bands. After a critical review of the literature
values of the total Cosmic X--Ray Background (CXB) we conclude that, with the
present data, the 94.3%, and 88.8% of the soft and hard CXB can be ascribed to
discrete source emission. If we extrapolate the analytical form of the Log
N--Log S distribution beyond the flux limit of our catalog in the soft band we
find that the flux from discrete sources at ~3*10^-18 cgs is consistent with
the entire CXB, whereas in the hard band it accounts for only 93% of the total
CXB at most, hinting for a faint and obscured population to arise at even
fainter fluxes.Comment: Accepted for publication in Ap
The 2-10 keV luminosity as a Star Formation Rate indicator
Radio and far infrared luminosities of star-forming galaxies follow a tight linear relation. Making use of ASCA and BeppoSAX observations of a well-defined sample of nearby star-forming galaxies, we argue that tight linear relations hold between the X-ray, radio and far infrared luminosities. The effect of intrinsic absorption is investigated taking NGC3256 as a test case. It is suggested that the hard X-ray emission is directly related to the Star Formation Rate. Star formation processes may also account for most of the 2-10 keV emission from LLAGNs of lower X-ray luminosities (for the same FIR and radio luminosity). Deep Chandra observations of a sample of radio-selected star-forming galaxies in the Hubble Deep Field North show that the same relation holds also at high (0.2< z< 1.3) redshift. The X-ray/radio relations also allow a derivation of X-ray number counts up to very faint fluxes from the radio Log N-Log S, which is consistent with current limits and models. Thus the contribution of star-forming galaxies to the X-ray background can be estimated
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