9,635 research outputs found
VLA Polarimetry of Two Extended Radio Galaxies
Multi-wavelength VLA observations of two extended radio galaxies, 0235-197
and 1203+043 are presented. There is some evidence from earlier studies that
these two sources exhibit low frequency (<1 GHz) variability. This work shows
that both sources have linear polarizations, if any, below the detection limits
at 320 MHz, so we cannot explain the variability as being due to instrumental
polarization effects as has been suggested for 3C159. Refractive scintillation
may be the cause of the variability in 0235-197. This would require the
existence of a bright, compact component in one of the hot spots seen in these
observations. This is not implausible but the resolution of this observational
program is insufficent to address that question. The radio source 1203+043
lacks any bright compact component thereby ruling out a refractive
scintillation mechanism for its variability. Consequently, it is possible that
claims of variability in this source are spurious. However, the 320 MHz VLA
observations show that 1203+043 has an `X'-shaped radio structure. This is a
rare morphology for the brightness distribution of a radio galaxy; the
implications of this are examined.Comment: 8 pages, plain tex, accepted by Astronomy and Astrophysics,
Supplement Serie
Geo-neutrinos
We review a new interdisciplinary field between Geology and Physics: the
study of the Earth's geo-neutrino flux. We describe competing models for the
composition of the Earth, present geological insights into the make up of the
continental and oceanic crust, those parts of the Earth that concentrate Th and
U, the heat producing elements, and provide details of the regional settings in
the continents and oceans where operating and planned detectors are sited.
Details are presented for the only two operating detectors that are capable of
measuring the Earth's geo-neutrinos flux: Borexino and KamLAND; results
achieved to date are presented, along with their impacts on geophysical and
geochemical models of the Earth. Finally, future planned experiments are
highlighted
Radio polarimetry of compact steep spectrum sources at sub-arcsecond resolution
Aims - We report new Very Large Array polarimetric observations of Compact
Steep-Spectrum (CSS) sources at 8.4, 15, and 23GHz. Methods - Using
multi-frequency VLA observations we have derived sub-arcsecond resolution
images of the total intensity, polarisation, and rotation measure (RM)
distributions. Results heading - We present multi-frequency VLA polarisation
observations of CSS sources. About half of the sources are point-like even at
the resolution of about 0.1x0.1 arcseconds. The remaining sources have double
or triple structure. Low values for the percentage of polarised emission in CSS
sources is confirmed. On the average, quasars are more polarised than galaxies.
A wide range of RM values have been measured. There are clear indications of
very large RMs up to 5\,585 rad m**(-2). CSS galaxies are characterized by RM
values that are larger than CSS quasars. The majority of the objects show very
large values of RM. Conclusions - The available data on sub-arcsecond-scale
rest-frame RM estimates for CSS sources show that these have a wide range of
values extending up to about 36,000 rad m**(-2). RM estimates indicate an
overall density of the magneto-ionic medium larger than classical radio
sources.Comment: Accepted for publication by Astronomy & Astrophysic
Geoneutrinos and reactor antineutrinos at SNO+
In the heart of the Creighton Mine near Sudbury (Canada), the SNO+ detector
is foreseen to observe almost in equal proportion electron antineutrinos
produced by U and Th in the Earth and by nuclear reactors. SNO+ will be the
first long baseline experiment to measure a reactor signal dominated by CANDU
cores (55\% of the total reactor signal), which generally burn natural
uranium. Approximately 18\% of the total geoneutrino signal is generated by the
U and Th present in the rocks of the Huronian Supergroup-Sudbury Basin: the
60\% uncertainty on the signal produced by this lithologic unit plays a crucial
role on the discrimination power on the mantle signal as well as on the
geoneutrino spectral shape reconstruction, which can in principle provide a
direct measurement of the Th/U ratio in the Earth.Comment: 7 pages including 2 figures and 1 table, in XIV International
Conference on Topics in Astroparticle and Underground Physics (TAUP 2015) IOP
Publishing , published on Journal of Physics: Conference Series 718 (2016)
06200
Radio asymmetry in 3C99
The N-galaxy 3C99, a Compact Steep-spectrum Source showing a triple
asymmetric structure, has been observed with several arrays of radio telescopes
at sub-arcsecond resolution. New images from MERLIN, European VLBI Network and
the Very Long Baseline Array show that the source components detected in the
central region of 3C99 have steep spectral indices, making it difficult to
determine which of them is the core. The asymmetric radio structure of 3C99 is
explained using the Scheuer-Baldwin continuous streaming model with a rather
large difference in the interstellar medium density on the two sides of the
central region. The age of 3C99 has been estimated; the source is found younger
than 10^6 years.Comment: 18 pages, plain tex, plus 8 figures, accepted by A&
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