653 research outputs found
Effect of multiple reusing of simulated air showers in detector simulations
The study of high energy cosmic rays requires detailed Monte Carlo
simulations of both, extensive air showers and the detectors involved in their
detection. In particular, the energy calibration of several experiments is
obtained from simulations. Also, in composition studies simulations play a
fundamental role because the primary mass is determined by comparing
experimental with simulated data. At the highest energies the detailed
simulation of air showers is very costly in processing time and disk space due
to the large number of secondary particles generated in interactions with the
atmosphere. Therefore, in order to increase the statistics, it is quite common
to recycle single showers many times to simulate the detector response. As a
result, the events of the Monte Carlo samples generated in this way are not
fully independent. In this work we study the artificial effects introduced by
the multiple use of single air showers for the detector simulations. In
particular, we study in detail the effects introduced by the repetitions in the
kernel density estimators which are frequently used in composition studies.Comment: 15 pages and 4 figure
SGARFACE: A Novel Detector For Microsecond Gamma Ray Bursts
The Short GAmma Ray Front Air Cherenkov Experiment (SGARFACE) is operated at
the Whipple Observatory utilizing the Whipple 10m gamma-ray telescope. SGARFACE
is sensitive to gamma-ray bursts of more than 100MeV with durations from 100ns
to 35us and provides a fluence sensitivity as low as 0.8 gamma-rays per m^2
above 200MeV (0.05 gamma-rays per m^2 above 2GeV) and allows to record the
burst time structure.Comment: 29 pages, 14 figures, accepted for publication in Astroparticle
Physic
Cosmic ray acceleration at supergalactic accretion shocks: a new upper energy limit due to a finite shock extension
Accretion flows onto supergalactic-scale structures are accompanied with
large spatial scale shock waves. These shocks were postulated as possible
sources of ultra-high energy cosmic rays. The highest particle energies were
expected for perpendicular shock configuration in the so-called "Jokipii
diffusion limit", involving weakly turbulent conditions in the large-scale
magnetic field imbedded in the accreting plasma. For such configuration we
discuss the process limiting the highest energy that particles can obtain in
the first-order Fermi acceleration process due to finite shock extensions to
the sides, along and across the mean magnetic field. Cosmic ray outflow along
the shock structure can substantially lower (below ~10^18 eV for protons) the
upper particle energy limit for conditions considered for supergalactic shocks.Comment: A&A, accepte
Cosmic-Ray Events as Background in Imaging Atmospheric Cherenkov Telescopes
The dominant background for observations of gamma-rays in the energy region
above 50 GeV with Imaging Atmospheric Cherenkov telescopes are cosmic-ray
events. The images of most of the cosmic ray showers look significantly
different from those of gamma-rays and are therefore easily discriminated.
However, a small fraction of events seems to be indistinguishable from
gamma-rays. This constitutes an irreducible background to the observation of
high-energy gamma-ray sources, and limits the sensitivity achievable with a
given instrument. Here, a Monte Carlo study of gamma-like cosmic-ray events is
presented. The nature of gamma-like cosmic-ray events, the shower particles
that are responsible for the gamma-like appearance, and the dependence of these
results on the choice of the hadronic interaction model are investigated. Most
of the gamma-like cosmic ray events are characterised by the production of
high-energy pi0's early in the shower development which dump most of the shower
energy into electromagnetic sub-showers. Also Cherenkov light from single muons
can mimic gamma-rays in close-by pairs of telescopes. Differences of up to 25%
in the collection area for gamma-like proton showers between QGSJet/FLUKA and
Sibyll/FLUKA simulations have been found.Comment: Accepted by Journal of Astroparticle Physic
Using {\sc top-c} for Commodity Parallel Computing in Cosmic Ray Physics Simulations
{\sc top-c} (Task Oriented Parallel C) is a freely available package for
parallel computing. It is designed to be easy to learn and to have good
tolerance for the high latencies that are common in commodity networks of
computers. It has been successfully used in a wide range of examples, providing
linear speedup with the number of computers. A brief overview of {\sc top-c} is
provided, along with recent experience with cosmic ray physics simulations.Comment: Talk to be presented at the XI International Symposium on Very High
Energy Cosmic Ray Interaction
Ultra-high energy cosmic rays may come from clustered sources
Clustering of cosmic-ray sources affects the flux observed beyond the cutoff
imposed by the cosmic microwave background and may be important in interpreting
the AGASA, Fly's Eye, and HiRes data. The standard deviation, sigma, in the
predicted number, N, of events above 10^{20} eV is sigma/N = 0.9(r_0/10
Mpc)^{0.9}, where r_0 is the unknown scale length of the correlation function
(r_0 = 10 Mpc for field galaxies). Future experiments will allow the
determination of r_0 through the detection of anisotropies in arrival
directions of ~ 10^{20} eV cosmic-rays over angular scales of Theta ~ r_0/30
Mpc.Comment: Accepted for publication in Astrophysical Journa
Two-Dimensional particle-in-cell simulations of the nonresonant, cosmic-ray driven instability in SNR shocks
In supernova remnants, the nonlinear amplification of magnetic fields
upstream of collisionless shocks is essential for the acceleration of cosmic
rays to the energy of the "knee" at 10^{15.5}eV. A nonresonant instability
driven by the cosmic ray current is thought to be responsible for this effect.
We perform two-dimensional, particle-in-cell simulations of this instability.
We observe an initial growth of circularly polarized non-propagating magnetic
waves as predicted in linear theory. It is demonstrated that in some cases the
magnetic energy density in the growing waves, can grow to at least 10 times its
initial value. We find no evidence of competing modes, nor of significant
modification by thermal effects. At late times we observe saturation of the
instability in the simulation, but the mechanism responsible is an artefact of
the periodic boundary conditions and has no counterpart in the supernova-shock
scenario.Comment: 18 pages, 6 figures, accepted for publication in Ap
Neutrino initiated cascades at mid and high altitudes in the atmosphere
High energy neutrinos play a very important role for the understanding of the
origin and propagation of ultra high energy cosmic rays (UHECR). They can be
produced as a consequence of the hadronic interactions suffered by the cosmic
rays in the acceleration regions, as by products of the propagation of the
UHECR in the radiation background and as a main product of the decay of super
heavy relic particles. A new era of very large exposure space observatories, of
which the JEM-EUSO mission is a prime example, is on the horizon which opens
the possibility of neutrino detection in the highest energy region of the
spectrum. In the present work we use a combination of the PYTHIA interaction
code with the CONEX shower simulation package in order to produce fast
one-dimensional simulations of neutrino initiated showers in air. We make a
detail study of the structure of the corresponding longitudinal profiles, but
focus our physical analysis mainly on the development of showers at mid and
high altitudes, where they can be an interesting target for space fluorescence
observatories.Comment: To appear in Astroparticle Physic
The energy spectrum observed by the AGASA experiment and the spatial distribution of the sources of ultra-high energy cosmic rays
Seven and a half years of continuous monitoring of giant air showers
triggered by ultra high-energy cosmic rays have been recently summarized by the
AGASA collaboration. The resulting energy spectrum indicates clearly that the
cosmic ray spectrum extends well beyond the Greisen-Zatsepin-Kuzmin (GZK)
cut-off at eV. Furthermore, despite the small number
statistics involved, some structure in the spectrum may be emerging. Using
numerical simulations, it is demonstrated in the present work that these
features are consistent with a spatial distribution of sources that follows the
distribution of luminous matter in the local Universe. Therefore, from this
point of view, there is no need for a second high-energy component of cosmic
rays dominating the spectrum beyond the GZK cut-off.Comment: 14 pages, 4 figures, Astrophys. J. Letters (submitted
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