1,198 research outputs found
Minimal prospects for radio detection of extensive air showers in the atmosphere of Jupiter
One possible approach for detecting ultra-high-energy cosmic rays and
neutrinos is to search for radio emission from extensive air showers created
when they interact in the atmosphere of Jupiter, effectively utilizing Jupiter
as a particle detector. We investigate the potential of this approach. For
searches with current or planned radio telescopes we find that the effective
area for detection of cosmic rays is substantial (~3*10^7 km^2), but the
acceptance angle is so small that the typical geometric aperture (~10^3 km^2
sr) is less than that of existing terrestrial detectors, and cosmic rays also
cannot be detected below an extremely high threshold energy (~10^23 eV). The
geometric aperture for neutrinos is slightly larger, and greater sensitivity
can be achieved with a radio detector on a Jupiter-orbiting satellite, but in
neither case is this sufficient to constitute a practical detection technique.
Exploitation of the large surface area of Jupiter for detecting
ultra-high-energy particles remains a long-term prospect that will require a
different technique, such as orbital fluorescence detection.Comment: 15 pages, 15 figures, 2 tables, accepted for publication in Ap
Sleep Analytics and Online Selective Anomaly Detection
We introduce a new problem, the Online Selective Anomaly Detection (OSAD), to
model a specific scenario emerging from research in sleep science. Scientists
have segmented sleep into several stages and stage two is characterized by two
patterns (or anomalies) in the EEG time series recorded on sleep subjects.
These two patterns are sleep spindle (SS) and K-complex. The OSAD problem was
introduced to design a residual system, where all anomalies (known and unknown)
are detected but the system only triggers an alarm when non-SS anomalies
appear. The solution of the OSAD problem required us to combine techniques from
both machine learning and control theory. Experiments on data from real
subjects attest to the effectiveness of our approach.Comment: Submitted to 20th ACM SIGKDD Conference on Knowledge Discovery and
Data Mining 201
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
A method for high precision reconstruction of air shower Xmax using two-dimensional radio intensity profiles
The mass composition of cosmic rays contains important clues about their
origin. Accurate measurements are needed to resolve long-standing issues such
as the transition from Galactic to extragalactic origin, and the nature of the
cutoff observed at the highest energies. Composition can be studied by
measuring the atmospheric depth of the shower maximum Xmax of air showers
generated by high-energy cosmic rays hitting the Earth's atmosphere. We present
a new method to reconstruct Xmax based on radio measurements. The radio
emission mechanism of air showers is a complex process that creates an
asymmetric intensity pattern on the ground. The shape of this pattern strongly
depends on the longitudinal development of the shower. We reconstruct Xmax by
fitting two-dimensional intensity profiles, simulated with CoREAS, to data from
the LOFAR radio telescope. In the dense LOFAR core, air showers are detected by
hundreds of antennas simultaneously. The simulations fit the data very well,
indicating that the radiation mechanism is now well-understood. The typical
uncertainty on the reconstruction of Xmax for LOFAR showers is 17 g/cm^2.Comment: 12 pages, 10 figures, submitted to Phys. Rev.
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
Cosmic Ray Physics with the LOFAR Radio Telescope
The LOFAR radio telescope is able to measure the radio emission from cosmic
ray induced air showers with hundreds of individual antennas. This allows for
precision testing of the emission mechanisms for the radio signal as well as
determination of the depth of shower maximum , the shower observable
most sensitive to the mass of the primary cosmic ray, to better than 20
g/cm. With a densely instrumented circular area of roughly 320 m, LOFAR
is targeting for cosmic ray astrophysics in the energy range -
eV. In this contribution we give an overview of the status, recent
results, and future plans of cosmic ray detection with the LOFAR radio
telescope.Comment: Proceedings of the 26th Extended European Cosmic Ray Symposium
(ECRS), Barnaul/Belokurikha, 201
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