59 research outputs found
VLBI observations of jupiter with the initial test station of LOFAR and the nancay decametric array
AIMS: To demonstrate and test the capability of the next generation of
low-frequency radio telescopes to perform high resolution observations across
intra-continental baselines. Jupiter's strong burst emission is used to perform
broadband full signal cross-correlations on time intervals of up to hundreds of
milliseconds. METHODS: Broadband VLBI observations at about 20 MHz on a
baseline of ~50000 wavelengths were performed to achieve arcsecond angular
resolution. LOFAR's Initial Test Station (LOFAR/ITS, The Netherlands) and the
Nancay Decametric Array (NDA, France) digitize the measured electric field with
12 bit and 14 bit in a 40 MHz baseband. The fine structure in Jupiter's signal
was used for data synchronization prior to correlation on the time-series data.
RESULTS: Strong emission from Jupiter was detected during snapshots of a few
seconds and detailed features down to microsecond time-scales were identified
in dynamic spectra. Correlations of Jupiter's burst emission returned strong
fringes on 1 ms time-scales over channels as narrow as a hundred kilohertz
bandwidth. CONCLUSIONS: Long baseline interferometry is confirmed at low
frequencies, in spite of phase shifts introduced by variations in ionospheric
propagation characteristics. Phase coherence was preserved over tens to
hundreds of milliseconds with a baseline of ~700 km. No significant variation
with time was found in the correlations and an estimate for the fringe
visibility of 1, suggested that the source was not resolved. The upper limit on
the source region size of Jupiter Io-B S-bursts corresponds to an angular
resolution of ~3 arcsec. Adding remote stations to the LOFAR network at
baselines up to thousand kilometers will provide 10 times higher resolution
down to an arcsecond.Comment: 6 pages, 4 figures. Nigl, A., Zarka, P., Kuijpers, J., Falcke, H.,
Baehren, L., VLBI observations of Jupiter with the Initial Test Station of
LOFAR and the Nancay Decametric Array, A&A, 471, 1099-1104, accepted on
31/05/200
Decay time of type III solar bursts observed at kilometric wavelengths
Type III bursts were observed between 3.5 MHz and 50 kHz by the University of Michigan radio astronomy experiment aboard the OGO-5 satellite.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43731/1/11207_2004_Article_BF00156186.pd
Geomagnetic origin of the radio emission from cosmic ray induced air showers observed by CODALEMA
The new setup of the CODALEMA experiment installed at the Radio Observatory
in Nancay, France, is described. It includes broadband active dipole antennas
and an extended and upgraded particle detector array. The latter gives access
to the air shower energy, allowing us to compute the efficiency of the radio
array as a function of energy. We also observe a large asymmetry in counting
rates between showers coming from the North and the South in spite of the
symmetry of the detector. The observed asymmetry can be interpreted as a
signature of the geomagnetic origin of the air shower radio emission. A simple
linear dependence of the electric field with respect to vxB is used which
reproduces the angular dependencies of the number of radio events and their
electric polarity.Comment: 9 pages, 15 figures, 1 tabl
Quasi-periodic acceleration of electrons by a plasmoid-driven shock in the solar atmosphere
Cosmic rays and solar energetic particles may be accelerated to relativistic
energies by shock waves in astrophysical plasmas. On the Sun,
shocks and particle acceleration are often associated with the eruption
of magnetized plasmoids, called coronal mass ejections (CMEs).
However, the physical relationship between CMEs and shock particle
acceleration is not well understood. Here, we use extreme ultraviolet,
radio and white-light imaging of a solar eruptive event on 22 September
2011 to show that a CME-induced shock (Alfvén Mach number 2:4+0:7
-0:8) was coincident with a coronal wave and an intense metric radio burst
generated by intermittent acceleration of electrons to kinetic energies
of 2{46 keV (0.1{0.4 c). Our observations show that plasmoid-driven
quasi-perpendicular shocks are capable of producing quasi-periodic acceleration
of electrons, an effect consistent with a turbulent or rippled
plasma shock surface
Characterization and nutritional value of precooked products of kiwicha grains (Amaranthus caudatus)
Auroral Processes at the Giant Planets: Energy Deposition, Emission Mechanisms, Morphology and Spectra
The influence of the amount and the origin of calcium carbonates on the isotopically exchangeable phosphate in calcareous soils
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