4,324 research outputs found
Detection of a relic X-ray jet in Cygnus A
We present a 200 ks Chandra ACIS-I image of Cygnus A, and discuss a long
linear feature seen in its counterlobe. This feature has a non-thermal spectrum
and lies on the line connecting the brighter hotspot on the approaching side
and the nucleus. We therefore conclude that this feature is (or was) a jet.
However, the outer part of this X-ray jet does not trace the current counterjet
observed in radio. No X-ray counterpart is observed on the jet side. Using
light-travel time effects we conclude that this X-ray 50 kpc linear feature is
a relic jet that contains enough low-energy plasma (gamma ~ 10^3) to
inverse-Compton scatter cosmic microwave background photons, producing emission
in the X-rays.Comment: 4 pages. Proceedings of "High Energy Phenomena in Relativistic
Outflows", held in Dublin, Ireland, September 24-28, 200
Multiwavelength study of Cygnus A IV. Proper motion and location of the nucleus
Context. Cygnus A, as the nearest powerful FR II radio galaxy, plays an
important role in understanding jets and their impact on the surrounding
intracluster medium. Aims. To explain why the nucleus is observed superposed
onto the eastern lobe rather than in between the two lobes, and why the jet and
counterjet are non-colinear. Methods. We made a comparative study of the radio
images at different frequencies of Cygnus A, in combination with the published
results on the radial velocities in the Cygnus A cluster. Results. From the
morphology of the inner lobes we conclude that the lobes are not interacting
with one another, but are well separated, even at low radio frequencies. We
explain the location of the nucleus as the result of the proper motion of the
galaxy through the cluster. The required proper motion is of the same order of
magnitude as the radial velocity offset of Cygnus A with the sub-cluster it
belongs to. The proper motion of the galaxy through the cluster likely also
explains the non-co-linearity of the jet and counterjet.Comment: Accepted for publication in A&A, 8 pages, 4 figure
The radio luminosity function of radio-loud quasars from the 7C Redshift Survey
We present a complete sample of 24 radio-loud quasars (RLQs) from the new 7C
Redshift Survey. Every quasar with a low-frequency (151 MHz) radio flux-density
S_151 > 0.5 Jy in two regions of the sky covering 0.013 sr is included; 23 of
these have sufficient extended flux to meet the selection criteria, 18 of these
have steep radio spectra (hereafter denoted as SSQs). The key advantage of this
sample over most samples of RLQs is the lack of an optical magnitude limit. By
combining the 7C and 3CRR samples, we have investigated the properties of RLQs
as a function of redshift z and radio luminosity L_151.
We derive the radio luminosity function (RLF) of RLQs and find that the data
are well fitted by a single power-law with slope alpha_1=1.9. We find that
there must be a break in the RLQ RLF at log_10(L_151 / W Hz^-1 sr^-1) < 27, in
order for the models to be consistent with the 7C and 6C source counts. The
z-dependence of the RLF follows a one-tailed gaussian which peaks at z=1.7. We
find no evidence for a decline in the co-moving space density of RLQs at higher
redshifts.
A positive correlation between the radio and optical luminosities of SSQs is
observed, confirming a result of Serjeant et al. (1998). We are able to rule
out this correlation being due to selection effects or biases in our combined
sample. The radio-optical correlation and best-fit model RLF enable us to
estimate the distribution of optical magnitudes of quasars in samples selected
at low radio frequencies. We conclude that for samples with S_151 < 1 Jy one
must use optical data significantly deeper than the POSS-I limit (R approx 20),
in order to avoid severe incompleteness.Comment: 28 pages with 13 figures. To appear in MNRA
The 6C** Sample and the Highest Redshift Radio Galaxies
We present a new radio sample, 6C** designed to find radio galaxies at z > 4
and discuss some of its near-infrared imaging follow-up results.Comment: 2 pages, 2 figures, to appear in proceedings of 'Multi-wavelength AGN
surveys', Cozumel, 200
Inverse Compton X-rays from Giant Radio Galaxies at z~1
We report XMM-Newton observations of three FR II radio galaxies at redshifts
between 0.85 and 1.34, which show extended diffuse X-ray emission within the
radio lobes, likely due to inverse-Compton up-scattering of the cosmic
microwave background. Under this assumption, through spectrum-fitting together
with archival VLA radio observations, we derive an independent estimate of the
magnetic field in the radio lobes of 3C 469.1 and compare it with the
equipartition value. We find concordance between these two estimates as long as
the turnover in the energy distribution of the particles occurs at a Lorentz
factor in excess of ~ 250. We determine the total energy in relativistic
particles in the radio emitting lobes of all three sources to range between
3e59 and 8e59 erg. The nuclei of these X-ray sources are heavily-absorbed
powerful AGN.Comment: 5 pages, 7 figures, 2 tables. Accepted for publication in MNRA
On the uncertain future of the volumetric 3D display paradigm.
Volumetric displays permit electronically processed images to be depicted within a transparent physical volume and enable a range of cues to depth to be inherently associated with image content. Further, images can be viewed directly by multiple simultaneous observers who are able to change vantage positions in a natural way. On the basis of research to date, we assume that the technologies needed to implement useful volumetric displays able to support translucent image formation are available and so primarily focus on other issues that have impeded the broad commercialization and application of this display paradigm. This is of particular relevance given the recent resurgence of interest in developing commercially viable, general purpose, volumetric systems. We particularly consider image and display characteristics, usability issues and identify several advantageous attributes that need to be exploited in order to effectively capitalize on this display modality.N/
Two-gap superconductivity with line nodes in CsCaFeAsF
We report the results of a muon-spin rotation (SR) experiment to
determine the superconducting ground state of the iron-based superconductor
CsCaFeAsF with K. This compound is
related to the fully-gapped superconductor CaCsFeAs, but here the
Ca-containing spacer layer is replaced with one containing CaF. The
temperature evolution of the penetration depth strongly suggests the presence
of line nodes and is best modelled by a system consisting of both an - and a
-wave gap. We also find a potentially magnetic phase which appears below
K but does not appear to compete with the superconductivity. This
compound contains the largest alkali atom in this family of superconductors and
our results yield a value for the in-plane penetration depth of
nm.Comment: 6 pages, 2 figure
Magnetic Monopole Noise
Magnetic monopoles are hypothetical elementary particles exhibiting quantized
magnetic charge and quantized magnetic flux . A classic proposal for detecting such magnetic charges is to measure the
quantized jump in magnetic flux threading the loop of a superconducting
quantum interference device (SQUID) when a monopole passes through it.
Naturally, with the theoretical discovery that a plasma of emergent magnetic
charges should exist in several lanthanide-pyrochlore magnetic insulators,
including DyTiO, this SQUID technique was proposed for their direct
detection. Experimentally, this has proven extremely challenging because of the
high number density, and the generation-recombination (GR) fluctuations, of the
monopole plasma. Recently, however, theoretical advances have allowed the
spectral density of magnetic-flux noise due to GR
fluctuations of magnetic charge pairs to be determined. These
theories present a sequence of strikingly clear predictions for the
magnetic-flux noise signature of emergent magnetic monopoles. Here we report
development of a high-sensitivity, SQUID based flux-noise spectrometer, and
consequent measurements of the frequency and temperature dependence of
for DyTiO samples. Virtually all the elements
of predicted for a magnetic monopole plasma, including the
existence of intense magnetization noise and its characteristic frequency and
temperature dependence, are detected directly. Moreover, comparisons of
simulated and measured correlation functions of the magnetic-flux
noise imply that the motion of magnetic charges is strongly
correlated because traversal of the same trajectory by two magnetic charges of
same sign is forbidden
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