2,129 research outputs found
The Fate of Intracluster Radio Plasma
Radio plasma injected by active radio galaxies into clusters of galaxies
quickly becomes invisible due to radiative losses of the relativistic
electrons. In this talk, the fate of radio plasma and its role for the galaxy
cluster is discussed: buoyancy removes it from the central regions and allows
to transfer its energy into the ambient gas. The remaining low energy electron
populations are still able to emit a low luminosity glow of observable
radiation via synchrotron-self Comptonized emission. Shock waves in the ambient
gas can re-ignite the radio emission.Comment: Invited Talk at `Matter and Energy in Clusters of Galaxies', Taipei
2002, 8 pages, 6 figures, uses newpasp.sty (includued
IMS EXPERIENCE IN ADVANCED CHECKOUT
Relates strengths and weaknesses of Marketron Retailer System gained through recent in-store experiences.Marketing,
Reconstruction of signals with unknown spectra in information field theory with parameter uncertainty
The optimal reconstruction of cosmic metric perturbations and other signals
requires knowledge of their power spectra and other parameters. If these are
not known a priori, they have to be measured simultaneously from the same data
used for the signal reconstruction. We formulate the general problem of signal
inference in the presence of unknown parameters within the framework of
information field theory. We develop a generic parameter uncertainty
renormalized estimation (PURE) technique and address the problem of
reconstructing Gaussian signals with unknown power-spectrum with five different
approaches: (i) separate maximum-a-posteriori power spectrum measurement and
subsequent reconstruction, (ii) maximum-a-posteriori power reconstruction with
marginalized power-spectrum, (iii) maximizing the joint posterior of signal and
spectrum, (iv) guessing the spectrum from the variance in the Wiener filter
map, and (v) renormalization flow analysis of the field theoretical problem
providing the PURE filter. In all cases, the reconstruction can be described or
approximated as Wiener filter operations with assumed signal spectra derived
from the data according to the same recipe, but with differing coefficients.
All of these filters, except the renormalized one, exhibit a perception
threshold in case of a Jeffreys prior for the unknown spectrum. Data modes,
with variance below this threshold do not affect the signal reconstruction at
all. Filter (iv) seems to be similar to the so called Karhune-Loeve and
Feldman-Kaiser-Peacock estimators for galaxy power spectra used in cosmology,
which therefore should also exhibit a marginal perception threshold if
correctly implemented. We present statistical performance tests and show that
the PURE filter is superior to the others.Comment: 21 pages, 5 figures, accepted by PR
On the equipartition of thermal and non-thermal energy in clusters of galaxies
Clusters of galaxies are revealing themselves as powerful sources of non
thermal radiation in a wide range of wavelengths. In order to account for these
multifrequency observations equipartition of cosmic rays (CRs) with the thermal
gas in clusters of galaxies is often invoked. This condition might suggest a
dynamical role played by cosmic rays in the virialization of these large scale
structures and is now testable through gamma ray observations. We show here, in
the specific case of the Coma and Virgo clusters, for which upper limits on the
gamma ray emission exist, that equipartition implies gamma ray fluxes that are
close or even in excess of the EGRET limit, depending on the adopted model of
CR injection. We use this bound to limit the validity of the equipartition
condition. We also show that, contrary to what claimed in previous
calculations, the equipartition assumption implies gamma ray fluxes in the TeV
range which can be detectable even by currently operating gamma ray
observatories if the injection cosmic ray spectrum is flatter than .Comment: 20 pages + 2 figures. To appear in the Astrophysical Journa
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