373 research outputs found
AGN in the XMM-Newton first-light image as probes for the interstellar medium in the LMC
The XMM-Newton first-light image revealed X-ray point sources which show
heavily absorbed power-law spectra. The spectral indices and the probable
identification of a radio counterpart for the brightest source suggest AGN
shining through the interstellar gas of the Large Magellanic Cloud (LMC). The
column densities derived from the X-ray spectra in combination with HI
measurements will allow to draw conclusions on HI to H_2 ratios in the LMC and
compare these with values found for the galactic plane.Comment: 4 pages, LaTex, 4 figures, Accepted for publication in A&A Letter
Deep ROSAT Surveys & the contribution of AGNs to the soft X-ray background
The ROSAT Deep Surveys in the Lockman Hole have revealed that AGNs are the main contributors (~75%) to the soft X-ray background in the 1–2 keV band. Using new optical/infrared and radio observations we have obtained a nearly complete identification (93%) of the 91 X-ray sources down to a limiting flux of 1.2·10^(–15) erg cm^(–2) s^(–1) in the 0.5–2.0 keV band. We present the optical colors and the emission line properties of our AGNs in comparison with other X-ray selected AGN samples. Furthermore we discuss the fraction of red AGNs found in the ROSAT Deep Surveys. From the ROSAT Deep Surveys we see no evidence for a new class of X-ray bright galaxies, which significantly contributes to the soft X-ray background
BeppoSAX observations of low-energy spectral features in AGN
The combination of the broad band coverage and moderate spectral resolution
of the LECS and MECS instruments on-board BeppoSAX allow the spectra of AGN to
be studied in unprecedented detail down to 0.1 keV. We describe the calibration
and the performance of the LECS and report on observations of low-energy
absorption features in the spectra of both a low (MCG-6-30-15) and a high
luminosity (3C 273) AGN. These features provide important diagnostics on the
location and nature of the material surrounding the AGN. A comparison of LECS
and ASCA/SIS low energy performance is also presented in the case of 3C 273.Comment: 5 pages. To appear in symposium proceedings: The Active X-Ray Sky,
Rome, October 199
Purely gravito-magnetic vacuum space-times
It is shown that there are no vacuum space-times (with or without
cosmological constant) for which the Weyl-tensor is purely gravito-magnetic
with respect to a normal and timelike congruence of observers.Comment: 4 page
The harmonic power spectrum of the soft X-ray background I. The data analysis
Fluctuations of the soft X-ray background are investigated using harmonic
analysis. A section of the ROSAT All-Sky Survey around the north galactic pole
is used. The flux distribution is expanded into a set of harmonic functions and
the power spectrum is determined. Several subsamples of the RASS have been used
and the spectra for different regions and energies are presented. The effects
of the data binning in pixels are assessed and taken into account. The spectra
of the analyzed samples reflect both small scale effects generated by strong
discrete sources and the large scale gradients of the XRB distribution. Our
results show that the power spectrum technique can be effectively used to
investigate anisotropy of the XRB at various scales. This statistics will
become a useful tool in the investigation of various XRB components.Comment: 12 pages, A&A accepte
Rotating dust solutions of Einstein's equations with 3-dimensional symmetry groups, Part 3: All Killing fields linearly independent of u^{\alpha} and w^{\alpha}
This is the third and last part of a series of 3 papers. Using the same
method and the same coordinates as in parts 1 and 2, rotating dust solutions of
Einstein's equations are investigated that possess 3-dimensional symmetry
groups, under the assumption that each of the Killing vectors is linearly
independent of velocity and rotation at every point
of the spacetime region under consideration. The Killing fields are found and
the Killing equations are solved for the components of the metric tensor in
every case that arises. No progress was made with the Einstein equations in any
of the cases, and no previously known solutions were identified. A brief
overview of literature on solutions with rotating sources is given.Comment: One missing piece, signaled after eq. (10.7), is added after (10.21).
List of corrections: In (3.7) wrong subscript in vorticity; In (3.10) wrong
subscript in last term of g_{23}; In (4.23) wrong formulae for g_{12} and
g_{22}; In (7.17) missing factor in velocity; In (7.18) one wrong factor in
g_{22}; In (10.9) factor in vorticity; In (10.15) - (10.20) y_0 = 0; In
(10.20) wrong second term in y. The rewriting typos did not influence result
X-ray emission from the Sculptor galaxy NGC 300
We report here the results of a full analysis of all the ROSAT PSPC spectral
imaging observations and all the ROSAT HRI high resolution imaging observations
of the very nearby (D=2.1 Mpc) Sculptor galaxy, NGC 300. Many point sources are
detected within the field, several of them showing evidence for variability,
and we present full source lists detailing their X-ray properties, and attempt
to classify them on the basis of their temporal, spectral and multi-wavelength
characteristics. A black hole X-ray binary candidate, a supersoft source and
several supernova remnants and HII regions are detected in X-rays, as is
unresolved, possibly diffuse emission, accounting for perhaps 20% of the total
NGC 300 X-ray (0.1-2.4 keV) luminosity (5.8 10e38 erg/s). We compare the X-ray
source luminosity distribution of NGC 300 with that of other nearby galaxies,
and we also compare NGC 300 with its Sculptor neighbours, concluding that it is
a quite an unremarkable system, showing no unusual X-ray (or other
multi-wavelength) properties. It may be one of the best examples of a
completely typical normal quiescent late-type spiral galaxy.Comment: 12 pages, latex file, 7 compressed postscript figures, to appear in
A&
Recent progress constraining the nuclear equation of state from astrophysics and heavy ion reactions
The quest for the nuclear equation of state (EoS) at high densities and/or
extreme isospin is one of the longstanding problems of nuclear physics. Ab
initio calculations for the nuclear many-body problem make predictions for the
density and isospin dependence of the EoS far away from the saturation point of
nuclear matter. On the other hand, in recent years substantial progress has
been mode to constrain the EoS both, from the astrophysical side and from
accelerator based experiments. Heavy ion experiments support a soft EoS at
moderate densities while recent neutron star observations require a ``stiff''
high density behavior. Both constraints are discussed and shown to be in
agreement with the predictions from many-body theory.Comment: Invited talk given at NPA III, Dresden, Germany, March 200
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