42 research outputs found
Time-Domain Measurement of Broadband Coherent Cherenkov Radiation
We report on further analysis of coherent microwave Cherenkov impulses
emitted via the Askaryan mechanism from high-energy electromagnetic showers
produced at the Stanford Linear Accelerator Center (SLAC). In this report, the
time-domain based analysis of the measurements made with a broadband (nominally
1-18 GHz) log periodic dipole array antenna is described. The theory of a
transmit-receive antenna system based on time-dependent effective height
operator is summarized and applied to fully characterize the measurement
antenna system and to reconstruct the electric field induced via the Askaryan
process. The observed radiation intensity and phase as functions of frequency
were found to agree with expectations from 0.75-11.5 GHz within experimental
errors on the normalized electric field magnitude and the relative phase; 0.039
microV/MHz/TeV and 17 deg, respectively. This is the first time this agreement
has been observed over such a broad bandwidth, and the first measurement of the
relative phase variation of an Askaryan pulse. The importance of validation of
the Askaryan mechanism is significant since it is viewed as the most promising
way to detect cosmogenic neutrino fluxes at E > 10^15 eV.Comment: 10 pages, 9 figures, accepted by Phys. Rev.
Prospects for GMRT to Observe Radio Waves from UHE Particles Interacting with the Moon
Ultra high energy (UHE) particles of cosmic origin impact the lunar regolith
and produce radio signals through Askaryan effect, signals that can be detected
by Earth based radio telescopes. We calculate the expected sensitivity for
observation of such events at the Giant Metrewave Radio Telescope (GMRT), both
for UHE cosmic rays (CR) and UHE neutrino interactions. We find that for 30
days of observation time a significant number of detectable events is expected
above eV for UHECR or neutrino fluxes close to the current limits.
Null detection over a period of 30 days will lower the experimental bounds on
UHE particle fluxes by magnitudes competitive to both present and future
experiments at the very highest energies.Comment: 21 pages, 9 figure
Experimental Limit on the Cosmic Diffuse Ultra-high Energy Neutrino Flux
We report results from 120 hours of livetime with the Goldstone Lunar
Ultra-high energy neutrino Experiment (GLUE). The experiment searches for <10
ns microwave pulses from the lunar regolith, appearing in coincidence at two
large radio telescopes separated by 22 km and linked by optical fiber. Such
pulses would arise from subsurface electromagnetic cascades induced by
interactions of >= 100 EeV neutrinos in the lunar regolith. No candidates are
yet seen, and the implied limits constrain several current models for
ultra-high energy neutrino fluxes.Comment: 4 pages, 4 figures, revtex4 style. New intro section, Fig. 2, Fig 4;
in final PRL revie
Determining neutrino absorption spectra at Ultra-High Energies
A very efficient method to measure the flux of Ultra-high energy (UHE)
neutrinos is through the detection of radio waves which are emitted by the
particle shower in the lunar regolith. The highest acceptance is reached for
radio waves in the frequency band of 100-200 MHz which can be measured with
modern radio telescopes. In this work we investigate the sensitivity of this
detection method to structures in the UHE neutrino spectrum caused by their
absorption on the low-energy relic anti-neutrino background through the Z-boson
resonance. The position of the absorption peak is sensitive to the neutrino
mass and the redshift of the source. A new generation of low-frequency digital
radio telescopes will provide excellent detection capabilities for measuring
these radio pulses, thus making our consideration here very timely.Comment: 7 figures, submitted to JCAP revision: References updated and minor
changes in tex
Detection of Five New RRATs at 111 MHz
Results of 111-MHz monitoring observations carried out on the Big Scanning
Antenna of the Pushchino Radio Astronomy Observatory during September 1-28,
2015 are presented. Fifty-four pulsating sources were detected at declinations
. Forty-seven of these are known pulsars, five are new
sources, and two are previously discovered transients. Estimates of the peak
flux densities and dispersion measures are presented or all these sources.Comment: published in Astronomy Report, translated by Yandex translator with
correction of scientific lexis, 8 pages, 2 figures, 3 table
On the Spectral Index of Distant Radio Galaxies
The problems of using the spectral index of radio galaxies in various tests,
in particular, in selecting distant radio sources are considered. The history
of the question of choosing a criterion of searching for distant radio galaxies
based on the spectral index is presented. For a new catalog of 2442 radio
galaxies constructed from NED, SDSS, and CATS data, an analytical form of the
sp ectral index.redshift relation has been determined for the first time. The
spectral index.angular size and spectral index.flux density diagrams have also
been constructed. Peculiarities of the distribution of sources on these
diagrams are discussed.Comment: 7 pages,5 figure
Observation of the Askaryan Effect: Coherent Microwave Cherenkov Emission from Charge Asymmetry in High Energy Particle Cascades
We present the first direct experimental evidence for the charge excess in
high energy particle showers predicted nearly 40 years ago by Askaryan. We
directed bremsstrahlung photons from picosecond pulses of 28.5 GeV electrons at
the SLAC Final Focus Test Beam facility into a 3.5 ton silica sand target,
producing electromagnetic showers several meters long. A series of antennas
spanning 0.3 to 6 GHz were used to detect strong, sub-nanosecond radio
frequency pulses produced whenever a shower was present. The measured electric
field strengths are consistent with a completely coherent radiation process.
The pulses show 100% linear polarization, consistent with the expectations of
Cherenkov radiation. The field strength versus depth closely follows the
expected particle number density profile of the cascade, consistent with
emission from excess charge distributed along the shower. These measurements
therefore provide strong support for experiments designed to detect high energy
cosmic rays and neutrinos via coherent radio emission from their cascades.Comment: 10 pages, 4 figures. Submitted to Phys. Rev. Let
Observations of the Askaryan Effect in Ice
We report on the first observations of the Askaryan effect in ice: coherent
impulsive radio Cherenkov radiation from the charge asymmetry in an
electromagnetic (EM) shower. Such radiation has been observed in silica sand
and rock salt, but this is the first direct observation from an EM shower in
ice. These measurements are important since the majority of experiments to date
that rely on the effect for ultra-high energy neutrino detection are being
performed using ice as the target medium. As part of the complete validation
process for the Antarctic Impulsive Transient Antenna (ANITA) experiment, we
performed an experiment at the Stanford Linear Accelerator Center (SLAC) in
June 2006 using a 7.5 metric ton ice target, yielding results fully consistent
with theoretical expectations.Comment: 4 pages, 5 figures, minor correction