10,023 research outputs found
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
Metal distribution in sloshing galaxy clusters: the case of A496
We report results from a detailed study of the sloshing gas in the core of
A496. We detect the low temperature/entropy spiral feature found in several
cores, we also find that conduction between the gas in the spiral and the
ambient medium must be suppressed by more than one order of magnitude with
respect to Spitzer conductivity. Intriguingly, while the gas in the spiral
features a higher metal abundance than the surrounding medium, it follows the
entropy vs metal abundance relation defined by gas lying outside the spiral.
The most plausible explanation for this behavior is that the low entropy metal
rich plasma uplifted through the cluster atmosphere by sloshing, suffers little
heating or mixing with the ambient medium. While sloshing appears to be capable
of uplifting significant amounts of gas, the limited heat exchange and mixing
between gas in and outside the spiral implies that this mechanism is not at all
effective in: 1) permanently redistributing metals within the core region and
2) heating up the coolest and densest gas, thereby providing little or no
contribution to staving of catastrophic cooling in cool cores.Comment: Accepted for publication on A&
Non-equilibrium dynamics of the Bose-Hubbard model: A projection operator approach
We study the phase diagram and non-equilibrium dynamics, both subsequent to a
sudden quench of the hopping amplitude and during a ramp
with ramp time , of the Bose-Hubbard model at zero temperature using a
projection operator formalism which allows us to incorporate the effects of
quantum fluctuations beyond mean-field approximations in the strong coupling
regime. Our formalism yields a phase diagram which provides a near exact match
with quantum Monte Carlo results in three dimensions. We also compute the
residual energy , the superfluid order parameter , the equal-time
order parameter correlation function , and the wavefunction overlap
which yields the defect formation probability during non-equilibrium
dynamics of the model. We find that , , and do not exhibit the
expected universal scaling. We explain this absence of universality and show
that our results compare well with recent experiments.Comment: Replaced with the accepted version, added one figure. 4 pages, 4
figures, to appear in Phys. Rev. Let
Renormalization flow for unrooted forests on a triangular lattice
We compute in small temperature expansion the two-loop renormalization
constants and the three-loop coefficient of the beta-function, that is the
first non-universal term, for the sigma-model with O(N) invariance on the
triangular lattice at N=-1. The partition function of the corresponding
Grassmann theory is, for negative temperature, the generating function of
unrooted forests on such a lattice, where the temperature acts as a chemical
potential for the number of trees in the forest. To evaluate Feynman diagrams
we extend the coordinate space method to the triangular lattice.Comment: 26 pages, 4 figure
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