1,485 research outputs found
Analytic calculation of radio emission from parametrized extensive air showers:A tool to extract shower parameters
The radio intensity and polarization footprint of a cosmic-ray induced extensive air shower is determined by the time-dependent structure of the current distribution residing in the plasma cloud at the shower front. In turn, the time dependence of the integrated charge-current distribution in the plasma cloud, the longitudinal shower structure, is determined by interesting physics which one would like to extract, such as the location and multiplicity of the primary cosmic-ray collision or the values of electric fields in the atmosphere during thunderstorms. To extract the structure of a shower from its footprint requires solving a complicated inverse problem. For this purposewe have developed a code that semianalytically calculates the radio footprint of an extensive air shower given an arbitrary longitudinal structure. This code can be used in an optimization procedure to extract the optimal longitudinal shower structure given a radio footprint. On the basis of air-shower universality we propose a simple parametrization of the structure of the plasma cloud. This parametrization is based on the results of Monte Carlo shower simulations. Deriving the parametrization also teaches which aspects of the plasma cloud are important for understanding the features seen in the radio-emission footprint. The calculated radio footprints are compared with microscopic CoREAS simulations
Discrete Wirtinger-based inequality and its application
In this paper, we derive a new inequality, which encompasses the discrete Jensen inequality. The new inequality is applied to analyze stability of linear discrete systems with an interval time-varying delay and a less conservative stability condition is obtained. Two numerical examples are given to show the effectiveness of the obtained stability condition
Polarized radio emission from extensive air showers measured with LOFAR
We present LOFAR measurements of radio emission from extensive air showers.
We find that this emission is strongly polarized, with a median degree of
polarization of nearly , and that the angle between the polarization
direction of the electric field and the Lorentz force acting on the particles,
depends on the observer location in the shower plane. This can be understood as
a superposition of the radially polarized charge-excess emission mechanism,
first proposed by Askaryan and the geomagnetic emission mechanism proposed by
Kahn and Lerche. We calculate the relative strengths of both contributions, as
quantified by the charge-excess fraction, for individual air showers. We
find that the measured charge-excess fraction is higher for air showers
arriving from closer to the zenith. Furthermore, the measured charge-excess
fraction also increases with increasing observer distance from the air shower
symmetry axis. The measured values range from for very
inclined air showers at to for almost
vertical showers at . Both dependencies are in qualitative
agreement with theoretical predictions.Comment: 22 pages, 14 figures, accepted for publication in JCA
The radio emission pattern of air showers as measured with LOFAR - a tool for the reconstruction of the energy and the shower maximum
The pattern of the radio emission of air showers is finely sampled with the
Low-Frequency ARray (LOFAR). A set of 382 measured air showers is used to test
a fast, analytic parameterization of the distribution of pulse powers. Using
this parameterization we are able to reconstruct the shower axis and give
estimators for the energy of the air shower as well as the distance to the
shower maximum.Comment: 15 pages, 10 figures, accepted for publication in JCA
Calibration of the LOFAR low-band antennas using the Galaxy and a model of the signal chain
The LOw-Frequency ARray (LOFAR) is used to make precise measurements of radio
emission from extensive air showers, yielding information about the primary
cosmic ray. Interpreting the measured data requires an absolute and
frequency-dependent calibration of the LOFAR system response. This is
particularly important for spectral analyses, because the shape of the detected
signal holds information about the shower development. We revisit the
calibration of the LOFAR antennas in the range of 30 - 80 MHz. Using the
Galactic emission and a detailed model of the LOFAR signal chain, we find an
improved calibration that provides an absolute energy scale and allows for the
study of frequency-dependent features in measured signals. With the new
calibration, systematic uncertainties of 13% are reached, and comparisons of
the spectral shape of calibrated data with simulations show promising
agreement.Comment: 23 pages, 10 figure
Realtime processing of LOFAR data for the detection of nano-second pulses from the Moon
The low flux of the ultra-high energy cosmic rays (UHECR) at the highest
energies provides a challenge to answer the long standing question about their
origin and nature. Even lower fluxes of neutrinos with energies above
eV are predicted in certain Grand-Unifying-Theories (GUTs) and e.g.\ models for
super-heavy dark matter (SHDM). The significant increase in detector volume
required to detect these particles can be achieved by searching for the
nano-second radio pulses that are emitted when a particle interacts in Earth's
moon with current and future radio telescopes.
In this contribution we present the design of an online analysis and trigger
pipeline for the detection of nano-second pulses with the LOFAR radio
telescope. The most important steps of the processing pipeline are digital
focusing of the antennas towards the Moon, correction of the signal for
ionospheric dispersion, and synthesis of the time-domain signal from the
polyphased-filtered signal in frequency domain. The implementation of the
pipeline on a GPU/CPU cluster will be discussed together with the computing
performance of the prototype.Comment: Proceedings of the 22nd International Conference on Computing in High
Energy and Nuclear Physics (CHEP2016), US
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