318 research outputs found
Study of contamination of liquid oxygen by gaseous nitrogen First quarterly report, 1 Jul. - 30 Sep. 1964
Analytical model development for contamination study of liquid oxygen by gaseous nitroge
SMAUG: a new technique for the deprojection of galaxy clusters
This paper presents a new technique for reconstructing the spatial
distributions of hydrogen, temperature and metal abundance of a galaxy cluster.
These quantities are worked out from the X-ray spectrum, modeled starting from
few analytical functions describing their spatial distributions. These
functions depend upon some parameters, determined by fitting the model to the
observed spectrum. We have implemented this technique as a new model in the
XSPEC software analysis package. We describe the details of the method, and
apply it to work out the structure of the cluster A1795. We combine the
observation of three satellites, exploiting the high spatial resolution of
Chandra for the cluster core, the wide collecting area of XMM-Newton for the
intermediate regions and the large field of view of Beppo-SAX for the outer
regions. We also test the validity and precision of our method by i) comparing
its results with those from a geometrical deprojection, ii) examining the
spectral residuals at different radii of the cluster and iii) reprojecting the
unfolded profiles and comparing them directly to the measured quantities. Our
analytical method yields the parameters defining the spatial functions directly
from the spectra. Their explicit knowledge allows a straightforward derivation
of other indirect physical quantities like the gravitating mass, as well as a
fast and easy estimate of the profiles uncertainties.Comment: 24 pages, 11 figures, 3 tables; emulateapj; accepted for publication
in the Astrophysical Journa
Study of contamination of liquid oxygen by gaseous nitrogen third quarterly progress report, 1 jan. - 31 mar. 1965
Contamination of liquid oxygen by gaseous nitroge
Radiative cooling, heating and thermal conduction in M87
The crisis of the standard cooling flow model brought about by Chandra and
XMM-Newton observations of galaxy clusters, has led to the development of
several models which explore different heating processes in order to assess if
they can quench the cooling flow. Among the most appealing mechanisms are
thermal conduction and heating through buoyant gas deposited in the ICM by
AGNs. We combine Virgo/M87 observations of three satellites (Chandra,
XMM-Newton and Beppo-SAX) to inspect the dynamics of the ICM in the center of
the cluster. Using the spectral deprojection technique, we derive the physical
quantities describing the ICM and determine the extra-heating needed to balance
the cooling flow assuming that thermal conduction operates at a fixed fraction
of the Spitzer value. We assume that the extra-heating is due to buoyant gas
and we fit the data using the model developed by Ruszkowski and Begelman
(2002). We derive a scale radius for the model of kpc, which is
comparable with the M87 AGN jet extension, and a required luminosity of the AGN
of a erg s, which is comparable to the observed AGN
luminosity. We discuss a scenario where the buoyant bubbles are filled of
relativistic particles and magnetic field responsible for the radio emission in
M87. The AGN is supposed to be intermittent and to inject populations of
buoyant bubbles through a succession of outbursts. We also study the X-ray cool
component detected in the radio lobes and suggest that it is structured in
blobs which are tied to the radio buoyant bubbles.Comment: 25 pages, 10 figures and 2 tables. Accepted for publication in Ap
The serendipituous discovery of a short-period eclipsing polar in 2XMMp
We report the serendipituous discovery of the new eclipsing polar 2XMMp
J131223.4+173659. Its striking X-ray light curve attracted immediate interest
when we were visually inspecting the source products of the 2XMMp catalogue.
This light curve revealed its likely nature as a magnetic cataclysmic variable
of AM Herculis (or polar) type with an orbital period of ~92 min, which was
confirmed by follow-up optical spectroscopy and photometry. 2XMMp
J131223.4+173659 probably has a one-pole accretion geometry. It joins the group
of now nine objects that show no evidence of a soft component in their X-ray
spectra despite being in a high accretion state, thus escaping ROSAT/EUVE
detection. We discuss the likely accretion scenario, the system parameters, and
the spectral energy distribution.Comment: Accepted for publication in A&
On the Nature of Feedback Heating in Cooling Flow Clusters
We study the feedback between heating and cooling of the intra-cluster medium
(ICM) in cooling flow (CF) galaxies and clusters. We adopt the popular view
that the heating is due to an active galactic nucleus (AGN), i.e. a central
black hole accreting mass and launching jets and/or winds. We propose that the
feedback occurs with the entire cool inner region (r <~ 5-30 kpc), where the
non-linear over-dense blobs of gas with a density contrast >~2 cool fast and
are removed from the ICM before experiencing the next major AGN heating event.
We term this scenario "cold-feedback". Some of these blobs cool and sink toward
the central black hole, while others might form stars and cold molecular
clouds. We derive the conditions under which the dense blobs formed by
perturbations might cool to low temperatures (T <~ 10^4 K), and feed the black
hole. The main conditions are found to be: (1) An over-dense blob must be
prevented from reaching an equilibrium position in the ICM: therefore it has to
cool fast, and the density profile of the ambient gas should be shallow; (2)
Non-linear perturbations are required: they might have chiefly formed by
previous AGN activity; (3) The cooling time of these non-linear perturbations
should be short relative to few times the typical interval between successive
AGN outbursts. (4) The blobs should be magnetically disconnected from their
surroundings, in order not to be evaporated by thermal conduction.Comment: Replaced wiht the version accepted by the Ap
Is the gas in cooling-flows multi-phase?
Employing XMM-Newton EPIC data we perform a detailed comparison between
different spectral models to test whether the gas in cooling-flows is
multi-phase or not. Our findings all point in the same direction, namely that
gas in cooling-flows does not show the wide distribution of temperatures
expected from standard multi-phase models. This result has profound
implications for cooling-flow models. Firstly, the large absorption column
depths inferred by previous analysis of cooling-flow spectra are most likely an
artifact following from the application of an incorrect spectral model to the
data. Secondly, the mass deposition and mass flow are likely to be much smaller
than previously thought. Last, but perhaps not least, the term "cooling-flow"
cluster is probably no longer appropriate, as it describes a phenomenon of
smaller entity and impact than previously thought. We propose to substitute it
with that of "cool-core" cluster. The latter definition is less ambitious than
the first, as it reflects only an observational fact rather than an inferred
physical property, the flow, but has the undeniable advantage of being firmer.Comment: To appear in Ap
Detailed diagnostics of an X-ray flare in the single giant HR 9024
We analyze a 96 ks Chandra/HETGS observation of the single G-type giant HR
9024. The high flux allows us to examine spectral line and continuum
diagnostics at high temporal resolution, to derive plasma parameters. A
time-dependent 1D hydrodynamic model of a loop with half-length cm (), cross-section radius
cm, with a heat pulse of 15 ks and ~erg cm s
deposited at the loop footpoints, satisfactorily reproduces the observed
evolution of temperature and emission measure, derived from the analysis of the
strong continuum emission. For the first time we can compare predictions from
the hydrodynamic model with single spectral features, other than with global
spectral properties. We find that the model closely matches the observed line
emission, especially for the hot ( K) plasma emission of the FeXXV
complex at \AA. The model loop has and aspect
ratio as typically derived for flares observed in active stellar
coronae, suggesting that the underlying physics is the same for these very
dynamic and extreme phenomena in stellar coronae independently on stellar
parameters and evolutionary stage.Comment: 26 pages. Accepted for publication on the Astrophysical Journa
AGN effect on cooling flow dynamics
We analyzed the feedback of AGN jets on cooling flow clusters using
three-dimensional AMR hydrodynamic simulations. We studied the interaction of
the jet with the intracluster medium and creation of low X-ray emission
cavities (Bubbles) in cluster plasma. The distribution of energy input by the
jet into the system was quantified in its different forms, i.e. internal,
kinetic and potential. We find that the energy associated with the bubbles, (pV
+ gamma pV/(gamma-1)), accounts for less than 10 percent of the jet energy.Comment: "Accepted for publication in Astrophysics & Space Science
Are Radio AGN Powered by Accretion or Black Hole Spin?
We compare accretion and black hole spin as potential energy sources for
outbursts from AGN in brightest cluster galaxies (BCGs). Based on our adopted
spin model, we find that the distribution of AGN power estimated from X-ray
cavities is consistent with a broad range of both spin parameter and accretion
rate. Sufficient quantities of molecular gas are available in most BCGs to
power their AGN by accretion alone. However, we find no correlation between AGN
power and molecular gas mass over the range of jet power considered here. For a
given AGN power, the BCG's gas mass and accretion efficiency, defined as the
fraction of the available cold molecular gas that is required to power the AGN,
both vary by more than two orders of magnitude. Most of the molecular gas in
BCGs is apparently consumed by star formation or is driven out of the nucleus
by the AGN before it reaches the nuclear black hole. Bondi accretion from hot
atmospheres is generally unable to fuel powerful AGN, unless their black holes
are more massive than their bulge luminosities imply. We identify several
powerful AGN that reside in relatively gas-poor galaxies, indicating an
unusually efficient mode of accretion, or that their AGN are powered by another
mechanism. If these systems are powered primarily by black hole spin, rather
than by accretion, spin must also be tapped efficiently in some systems, i.e.,
, or their black hole masses must be substantially
larger than the values implied by their bulge luminosities. We constrain the
(model dependent) accretion rate at the transition from radiatively inefficient
to radiatively efficient accretion flows to be a few percent of the Eddington
rate, a value that is consistent with other estimates.Comment: Accepted for Publication in ApJ, January 2011, 21 pages, 4 figures;
One new data point added to figures; clarifications and minor corrections in
response to referee repor
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