157 research outputs found
Dethinning Extensive Air Shower Simulations
We describe a method for restoring information lost during statistical
thinning in extensive air shower simulations. By converting weighted particles
from thinned simulations to swarms of particles with similar characteristics,
we obtain a result that is essentially identical to the thinned shower, and
which is very similar to non-thinned simulations of showers. We call this
method dethinning. Using non-thinned showers on a large scale is impossible
because of unrealistic CPU time requirements, but with thinned showers that
have been dethinned, it is possible to carry out large-scale simulation studies
of the detector response for ultra-high energy cosmic ray surface arrays. The
dethinning method is described in detail and comparisons are presented with
parent thinned showers and with non-thinned showers
Using Fractal Dimensionality in the Search for Source Models of Ultra-High Energy Cosmic Rays
Although the existence of cosmic rays with energies extending well above
eV has been confirmed, their origin remains one of the most important
questions in astro-particle physics today. Several source models have been
proposed for the observed set of Ultra High Energy Cosmic Rays (UHECRs). Yet
none of these models have been conclusively identified as corresponding with
all of the available data. One possible way of achieving a global test of
anisotropy is through the measurement of the information dimension, , of the arrival directions of a sample of events. is a measure
of the intrinsic heterogeneity of a data sample. We will show how this method
can be used to take into account the extreme asymmetric angular resolution and
the highly irregular aperture of a monocular air-fluorescence detector. We will
then use a simulated, isotropic event sample to show how this method can be
used to place upper limits on any number of source models with no statistical
penalty.Comment: LaTeX, 23 pages, 41 figure
A Measurement of Time-Averaged Aerosol Optical Depth using Air-Showers Observed in Stereo by HiRes
Air fluorescence measurements of cosmic ray energy must be corrected for
attenuation of the atmosphere. In this paper we show that the air-showers
themselves can yield a measurement of the aerosol attenuation in terms of
optical depth, time-averaged over extended periods. Although the technique
lacks statistical power to make the critical hourly measurements that only
specialized active instruments can achieve, we note the technique does not
depend on absolute calibration of the detector hardware, and requires no
additional equipment beyond the fluorescence detectors that observe the air
showers. This paper describes the technique, and presents results based on
analysis of 1258 air-showers observed in stereo by the High Resolution Fly's
Eye over a four year span.Comment: 7 pages, 3 figures, accepted for publication by Astroparticle Physics
Journa
Search for Global Dipole Enhancements in the HiRes-I Monocular Data above 10^{18.5} eV
Several proposed source models for Ultra-High Energy Cosmic Rays (UHECRs)
consist of dipole distributions oriented towards major astrophysical landmarks
such as the galactic center, M87, or Centaurus A. We use a comparison between
real data and simulated data to show that the HiRes-I monocular data for
energies above 10^{18.5} eV is, in fact, consistent with an isotropic source
model. We then explore methods to quantify our sensitivity to dipole source
models oriented towards the Galactic Center, M87, and Centaurus A.Comment: 17 pages, 31 figure
Observation of the Ankle and Evidence for a High-Energy Break in the Cosmic Ray Spectrum
We have measured the cosmic ray spectrum at energies above eV using
the two air fluorescence detectors of the High Resolution Fly's Eye experiment
operating in monocular mode. We describe the detector, PMT and atmospheric
calibrations, and the analysis techniques for the two detectors. We fit the
spectrum to models describing galactic and extragalactic sources. Our measured
spectrum gives an observation of a feature known as the ``ankle'' near eV, and strong evidence for a suppression near eV.Comment: 14 pages, 9 figures. To appear in Physics Letters B. Accepted versio
Ultra-High Energy Cosmic Ray Probes of Large Scale Structure and Magnetic Fields
We study signatures of a structured universe in the multi-pole moments,
auto-correlation function, and cluster statistics of ultra-high energy cosmic
rays above 10^19 eV. We compare scenarios where the sources are distributed
homogeneously or according to the baryon density distribution obtained from a
cosmological large scale structure simulation. The influence of extragalactic
magnetic fields is studied by comparing the case of negligible fields with
fields expected to be produced along large scale shocks with a maximal strength
consistent with observations. We confirm that strongly magnetized observers
would predict considerable anisotropy on large scales, which is already in
conflict with current data. In the best fit scenario only the sources are
strongly magnetized, although deflection can still be considerable, of order 20
degrees up to 10^20 eV, and a pronounced GZK cutoff is predicted. We then
discuss signatures for future large scale full-sky detectors such as the Pierre
Auger and EUSO projects. Auto-correlations are sensitive to the source density
only if magnetic fields do not significantly affect propagation. In contrast,
for a weakly magnetized observer, degree scale auto-correlations below a
certain level indicate magnetized discrete sources. It may be difficult even
for next generation experiments to distinguish between structured and
unstructured source distributions.Comment: 17 revtex pages, 29 ps figures, published version with minor changes,
see http://link.aps.org/abstract/PRD/v70/e04300
A Likelihood Method for Measuring the Ultrahigh Energy Cosmic Ray Composition
Air fluorescence detectors traditionally determine the dominant chemical
composit ion of the ultrahigh energy cosmic ray flux by comparing the averaged
slant depth of the shower maximum, , as a function of energy to the
slant depths expect ed for various hypothesized primaries. In this paper, we
present a method to make a direct measurement of the expected mean number of
protons and iron by comparing the shap es of the expected
distributions to the distribution for data. The advantages of this method
includes the use of information of the full distribution and its ability to
calculate a flux for various cosmic ray compositi ons. The same method can be
expanded to marginalize uncertainties due to choice of spectra, hadronic models
and atmospheric parameters. We demonstrate the technique with independent
simulated data samples from a parent sample of protons and iron. We accurately
predict the number of protons and iron in the parent sample and show that the
uncertainties are meaningful.Comment: 11 figures, 22 pages, accepted by Astroparticle Physic
Alternative Methods to Finding Patterns in HiRes Stereo Data
In this paper Ultra High Energy Cosmic Rays UHECRs data observed by the HiRes
fluorescence detector in stereo mode is analyzed to search for events in the
sky with an arrival direction lying on a great circle. Such structure is known
as the arc structure. The arc structure is expected when the charged cosmic
rays pass through the galactic magnetic field. The arcs searched for could
represent a broad or a small scale anisotropy depending on the proposed source
model for the UHECRs. The Arcs in this paper are looked for using Hough
transform were Hough transform is a technique used to looking for patterns in
images. No statistically significant arcs were found in this study
The surface detector array of the Telescope Array experiment
The Telescope Array (TA) experiment, located in the western desert of
Utah,USA, is designed for observation of extensive air showers from extremely
high energy cosmic rays. The experiment has a surface detector array surrounded
by three fluorescence detectors to enable simultaneous detection of shower
particles at ground level and fluorescence photons along the shower track. The
TA surface detectors and fluorescence detectors started full hybrid observation
in March, 2008. In this article we describe the design and technical features
of the TA surface detector.Comment: 32 pages, 17 figure
New air fluorescence detectors employed in the Telescope Array experiment
Since 2007, the Telescope Array (TA) experiment, based in Utah, USA, has been
observing ultra high energy cosmic rays to understand their origins. The
experiment involves a surface detector (SD) array and three fluorescence
detector (FD) stations. FD stations, installed surrounding the SD array,
measure the air fluorescence light emitted from extensive air showers (EASs)
for precise determination of their energies and species. The detectors employed
at one of the three FD stations were relocated from the High Resolution Fly's
Eye experiment. At the other two stations, newly designed detectors were
constructed for the TA experiment. An FD consists of a primary mirror and a
camera equipped with photomultiplier tubes. To obtain the EAS parameters with
high accuracies, understanding the FD optical characteristics is important. In
this paper, we report the characteristics and installation of new FDs and the
performances of the FD components. The results of the monitored mirror
reflectance during the observation time are also described in this report.Comment: 44 pages, 23 figures, submitted to NIM-
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