1,198 research outputs found
Multiwavelength study of Cygnus A III. Evidence for relic lobe plasma
We study the particle energy distribution in the cocoon surrounding Cygnus A,
using radio images between 151 MHz and 15 GHz and a 200 ks Chandra ACIS-I
image. We show that the excess low frequency emission in the the lobe further
from Earth cannot be explained by absorption or excess adiabatic expansion of
the lobe or a combination of both. We show that this excess emission is
consistent with emission from a relic counterlobe and a relic counterjet that
are being re-energized by compression from the current lobe. We detect hints of
a relic hotspot at the end of the relic X-ray jet in the more distant lobe. We
do not detect relic emission in the lobe nearer to Earth as expected from light
travel-time effects assuming intrinsic symmetry. We determine that the duration
of the previous jet activity phase was slightly less than that of the current
jet-active phase. Further, we explain some features observed at 5 and 15 GHz as
due to the presence of a relic jet.Comment: Accepted for publication with MNRAS, 10 pages with 10 figure
Cosmology with Varying Constants
The idea of possible time or space variations of the `fundamental' constants
of nature, although not new, is only now beginning to be actively considered by
large numbers of researchers in the particle physics, cosmology and
astrophysics communities. This revival is mostly due to the claims of possible
detection of such variations, in various different contexts and by several
groups. Here, I present the current theoretical motivations and expectations
for such variations, review the current observational status, and discuss the
impact of a possible confirmation of these results in our views of cosmology
and physics as a whole.Comment: 14 pages, no figures. Essay to appear in Phil. Trans. Roy. Soc. Lond.
A Triennial Series (Christmas 2002 Issue
X-ray line tomography of AGN-induced motion in clusters of galaxies
The thermal broadening of emission lines of heavy ions is small enough such
that Doppler shifts due to bulk motions may be detected with the next
generation of X-ray observatories. This opens up the possibility to study gas
velocities in the intra-cluster medium. Here we study the effect of bulk
motions induced by a central active galactic nucleus (AGN) on the emission
lines around the FeXXV complex. We have modelled the evolution of AGN-induced
bubbles in a realistic cosmological framework and studied the resulting FeXXV
line profiles. We found that in clusters with AGN feedback, motions induced by
the inflation of bubbles and their buoyant rise lead to distinct features in
the iron emission lines that are detectable with a spectral resolution of about
10 eV. These observations will help to determine the mechanical energy that
resides in the bubbles and thereby the kinetic luminosity of the AGN.Comment: to appear in Ap
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