201 research outputs found
Composition of Primary Cosmic-Ray Nuclei at High Energies
The TRACER instrument (``Transition Radiation Array for Cosmic Energetic
Radiation'') has been developed for direct measurements of the heavier primary
cosmic-ray nuclei at high energies. The instrument had a successful
long-duration balloon flight in Antarctica in 2003. The detector system and
measurement process are described, details of the data analysis are discussed,
and the individual energy spectra of the elements O, Ne, Mg, Si, S, Ar, Ca, and
Fe (nuclear charge Z=8 to 26) are presented. The large geometric factor of
TRACER and the use of a transition radiation detector make it possible to
determine the spectra up to energies in excess of 10 eV per particle. A
power-law fit to the individual energy spectra above 20 GeV per amu exhibits
nearly the same spectral index ( 2.65 0.05) for all elements,
without noticeable dependence on the elemental charge Z.Comment: Accepted for publication in the Astrophysical Journal (3-Jan-08), 37
pages, 15 figure
Large scale cosmic-ray anisotropy with KASCADE
The results of an analysis of the large scale anisotropy of cosmic rays in
the PeV range are presented. The Rayleigh formalism is applied to the right
ascension distribution of extensive air showers measured by the KASCADE
experiment.The data set contains about 10^8 extensive air showers in the energy
range from 0.7 to 6 PeV. No hints for anisotropy are visible in the right
ascension distributions in this energy range. This accounts for all showers as
well as for subsets containing showers induced by predominantly light
respectively heavy primary particles. Upper flux limits for Rayleigh amplitudes
are determined to be between 10^-3 at 0.7 PeV and 10^-2 at 6 PeV primary
energy.Comment: accepted by The Astrophysical Journa
Primary Proton Spectrum of Cosmic Rays measured with Single Hadrons
The flux of cosmic-ray induced single hadrons near sea level has been
measured with the large hadron calorimeter of the KASCADE experiment. The
measurement corroborates former results obtained with detectors of smaller size
if the enlarged veto of the 304 m^2 calorimeter surface is encounted for. The
program CORSIKA/QGSJET is used to compute the cosmic-ray flux above the
atmosphere. Between E_0=300 GeV and 1 PeV the primary proton spectrum can be
described with a power law parametrized as
dJ/dE_0=(0.15+-0.03)*E_0^{-2.78+-0.03} m^-2 s^-1 sr^-1 TeV^-1. In the TeV
region the proton flux compares well with the results from recent measurements
of direct experiments.Comment: 13 pages, accepted by Astrophysical Journa
Nonextensive thermal sources of cosmic rays?
The energy spectrum of cosmic rays (CR) exhibits power-like behavior with a
very characteristic "knee" structure. We consider a possibility that such a
spectrum could be generated by some specific nonstatistical temperature
fluctuations in the source of CR with the "knee" structure reflecting an abrupt
change of the pattern of such fluctuations. This would result in a generalized
nonextensive statistical model for the production of CR. The possible physical
mechanisms leading to these effects are discussed together with the resulting
chemical composition of the CR, which follows the experimentally observed
abundance of nuclei.Comment: 16 pages, 3 figures, rewritten and updated version, to be published
in Centr. Eur. J. Phy
Optimized Trigger for Ultra-High-Energy Cosmic-Ray and Neutrino Observations with the Low Frequency Radio Array
When an ultra-high energy neutrino or cosmic ray strikes the Lunar surface a
radio-frequency pulse is emitted. We plan to use the LOFAR radio telescope to
detect these pulses. In this work we propose an efficient trigger
implementation for LOFAR optimized for the observation of short radio pulses.Comment: Submitted to Nuclear Instruments and Methods in Physics Research
Section
Ultrahigh Energy Cosmic Rays: The state of the art before the Auger Observatory
In this review we discuss the important progress made in recent years towards
understanding the experimental data on cosmic rays with energies \agt 10^{19}
eV. We begin with a brief survey of the available data, including a description
of the energy spectrum, mass composition, and arrival directions. At this point
we also give a short overview of experimental techniques. After that, we
introduce the fundamentals of acceleration and propagation in order to discuss
the conjectured nearby cosmic ray sources. We then turn to theoretical notions
of physics beyond the Standard Model where we consider both exotic primaries
and exotic physical laws. Particular attention is given to the role that
TeV-scale gravity could play in addressing the origin of the highest energy
cosmic rays. In the final part of the review we discuss the potential of future
cosmic ray experiments for the discovery of tiny black holes that should be
produced in the Earth's atmosphere if TeV-scale gravity is realized in Nature.Comment: Final version. To be published in Int. J. Mod. Phys.
A study on the sharp knee and fine structures of cosmic ray spectra
The paper investigates the overall and detailed features of cosmic ray (CR)
spectra in the knee region using the scenario of nuclei-photon interactions
around the acceleration sources. Young supernova remnants can be the physical
realities of such kind of CR acceleration sites. The results show that the
model can well explain the following problems simultaneously with one set of
source parameters: the knee of CR spectra and the sharpness of the knee, the
detailed irregular structures of CR spectra, the so-called "component B" of
Galactic CRs, and the electron/positron excesses reported by recent
observations. The coherent explanation serves as evidence that at least a
portion of CRs might be accelerated at the sources similar to young supernova
remnants, and one set of source parameters indicates that this portion mainly
comes from standard sources or from a single source.Comment: 13 pages, 4 figures, accepted for publication in SCIENCE CHINA
Physics, Mechanics & Astronomy
Radio Emission Reveals Inner Meter-Scale Structure of Negative Lightning Leader Steps
We use the Low Frequency Array (LOFAR) to probe the dynamics of the stepping process of negatively charged plasma channels (negative leaders) in a lightning discharge. We observe that at each step of a leader, multiple pulses of vhf (30-80 MHz) radiation are emitted in short-duration bursts (<10 mu s). This is evidence for streamer formation during corona flashes that occur with each leader step, which has not been observed before in natural lightning and it could help explain x-ray emission from lightning leaders, as x rays from laboratory leaders tend to be associated with corona flashes. Surprisingly, we find that the stepping length is very similar to what was observed near the ground, however with a stepping time that is considerably larger, which as yet is not understood. These results will help to improve lightning propagation models, and eventually lightning protection models.</p
Search for cosmic-ray point sources with KASCADE
A survey of the northern hemisphere for astrophysical point sources with
continuous emission of high-energy cosmic rays is presented. Around 47 Mio
extensive air showers with primary energies above 300 TeV measured by
the KASCADE detector field are selected for this analysis. Besides the sky
survey, a search for signal excess in the region of the galactic plane and of
selected point source candidates has been performed. There is no evidence for
any significant excess. This is valid for an analysis of all recorded showers
as well as for a data set enhanced in gamma-ray induced showers. An upper flux
limit of around ms for a steady point source
that transits the zenith is obtained. Additionally, the distribution of the
arrival directions of extensive air showers with energies above 80 PeV were
studied by an autocorrelation analysis.Comment: accepted by The Astrophysical Journa
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