1,367 research outputs found
A Bayesian Approach to Comparing Cosmic Ray Energy Spectra
A common problem in ultra-high energy cosmic ray physics is the comparison of
energy spectra. The question is whether the spectra from two experiments or two
regions of the sky agree within their statistical and systematic uncertainties.
We develop a method to directly compare energy spectra for ultra-high energy
cosmic rays from two different regions of the sky in the same experiment
without reliance on agreement with a theoretical model of the energy spectra.
The consistency between the two spectra is expressed in terms of a Bayes
factor, defined here as the ratio of the likelihood of the two-parent source
hypothesis to the likelihood of the one-parent source hypothesis. Unlike other
methods, for example chi^2 tests, the Bayes factor allows for the calculation
of the posterior odds ratio and correctly accounts for non-Gaussian
uncertainties. The latter is particularly important at the highest energies,
where the number of events is very small.Comment: 22 pages, 10 figures, accepted for publication in Ap
Techniques for measuring atmospheric aerosols at the High Resolution Fly's Eye experiment
We describe several techniques developed by the High Resolution Fly's Eye
experiment for measuring aerosol vertical optical depth, aerosol horizontal
attenuation length, and aerosol phase function. The techniques are based on
measurements of side-scattered light generated by a steerable ultraviolet laser
and collected by an optical detector designed to measure fluorescence light
from cosmic-ray air showers. We also present a technique to cross-check the
aerosol optical depth measurement using air showers observed in stereo. These
methods can be used by future air fluorescence experiments.Comment: Accepted for publication in Astroparticle Physics Journal 16 pages, 9
figure
EDGE: a code to calculate diffusion of cosmic-ray electrons and their gamma-ray emission
The positron excess measured by PAMELA and AMS can only be explained if there
is one or several sources injecting them. Moreover, at the highest energies, it
requires the presence of nearby (hundreds of parsecs) and middle age
(maximum of hundreds of kyr) source. Pulsars, as factories of electrons
and positrons, are one of the proposed candidates to explain the origin of this
excess. To calculate the contribution of these sources to the electron and
positron flux at the Earth, we developed EDGE (Electron Diffusion and Gamma
rays to the Earth), a code to treat diffusion of electrons and compute their
diffusion from a central source with a flexible injection spectrum. We can
derive the source's gamma-ray spectrum, spatial extension, the all-electron
density in space and the electron and positron flux reaching the Earth. We
present in this contribution the fundamentals of the code and study how
different parameters affect the gamma-ray spectrum of a source and the electron
flux measured at the Earth.Comment: Presented at the 35th International Cosmic Ray Conference (ICRC2017),
Bexco, Busan, Kore
Atmospheric Calorimetry above 10 eV: Shooting Lasers at the Pierre Auger Cosmic-Ray Observatory
The Pierre Auger Cosmic-Ray Observatory uses the earth's atmosphere as a
calorimeter to measure extensive air-showers created by particles of
astrophysical origin. Some of these particles carry joules of energy. At these
extreme energies, test beams are not available in the conventional sense. Yet
understanding the energy response of the observatory is important. For example,
the propagation distance of the highest energy cosmic-rays through the cosmic
microwave background radiation (CMBR) is predicted to be strong function of
energy. This paper will discuss recently reported results from the observatory
and the use of calibrated pulsed UV laser "test-beams" that simulate the
optical signatures of ultra-high energy cosmic rays. The status of the much
larger 200,000 km companion detector planned for the northern hemisphere
will also be outlined.Comment: 6 pages, 11 figures XIII International Conference on Calorimetry in
High Energy Physic
Atmospheric aerosols at the Pierre Auger Observatory and environmental implications
The Pierre Auger Observatory detects the highest energy cosmic rays.
Calorimetric measurements of extensive air showers induced by cosmic rays are
performed with a fluorescence detector. Thus, one of the main challenges is the
atmospheric monitoring, especially for aerosols in suspension in the
atmosphere. Several methods are described which have been developed to measure
the aerosol optical depth profile and aerosol phase function, using lasers and
other light sources as recorded by the fluorescence detector. The origin of
atmospheric aerosols traveling through the Auger site is also presented,
highlighting the effect of surrounding areas to atmospheric properties. In the
aim to extend the Pierre Auger Observatory to an atmospheric research platform,
a discussion about a collaborative project is presented.Comment: Regular Article, 16 pages, 12 figure
Study of Small-Scale Anisotropy of Ultrahigh Energy Cosmic Rays Observed in Stereo by HiRes
The High Resolution Fly's Eye (HiRes) experiment is an air fluorescence
detector which, operating in stereo mode, has a typical angular resolution of
0.6 degrees and is sensitive to cosmic rays with energies above 10^18 eV. HiRes
is thus an excellent instrument for the study of the arrival directions of
ultrahigh energy cosmic rays. We present the results of a search for
anisotropies in the distribution of arrival directions on small scales (<5
degrees) and at the highest energies (>10^19 eV). The search is based on data
recorded between 1999 December and 2004 January, with a total of 271 events
above 10^19 eV. No small-scale anisotropy is found, and the strongest
clustering found in the HiRes stereo data is consistent at the 52% level with
the null hypothesis of isotropically distributed arrival directions.Comment: 4 pages, 3 figures. Matches accepted ApJL versio
Comparison of the Ultra-High Energy Cosmic Ray Flux Observed by AGASA, HiRes and Auger
The current measurements of the cosmic ray energy spectrum at ultra-high
energies ( eV) are characterized by large systematic errors
and poor statistics. In addition, the experimental results of the two
experiments with the largest published data sets, AGASA and HiRes, appear to be
inconsistent with each other, with AGASA seeing an unabated continuation of the
energy spectrum even at energies beyond the GZK cutoff energy at
eV. Given the importance of the related astrophysical questions regarding the
unknown origin of these highly energetic particles, it is crucial that the
extent to which these measurements disagree be well understood. Here we
evaluate the consistency of the two measurements for the first time with a
model-independent method that accounts for the large statistical and systematic
errors of current measurements. We further compare the AGASA and HiRes spectra
with the recently presented Auger spectrum. The method directly compares two
measurements, bypassing the introduction of theoretical models for the shape of
the energy spectrum. The inconsistency between the observations is expressed in
terms of a Bayes Factor, a standard statistic defined as the ratio of a
separate parent source hypothesis to a single parent source hypothesis.
Application to the data shows that the two-parent hypothesis is disfavored. We
expand the method to allow comparisons between an experimental flux and that
predicted by any model.Comment: accepted by Phys. Rev.
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