576 research outputs found
Comparison of the moments of the X(max) distribution predicted by different cosmic ray shower simulation models
In this paper we study the depth at which a cosmic ray shower reaches its maximum (Xmax) as predicted by Monte Carlo simulation. The use of Xmax in the determination of the primary particle mass can only be done by comparing the measured values with simulation predictions. For this reason it is important to study the differences between the available simulation models. We have done a study of the first and second moments of the X max distribution using the Corsika and Conex programs. The study was done with high statistics in the energy range from 1017 to 10 20.4 eV. We focus our analysis in the different implementations of the hadronic interaction models Sibyll2.1 and QGSJetII in Corsika and Conex. We show that the predictions of the «Xmax» and RMS(X max) depend slightly on the combination of simulation program and hadronic interaction model. Although these differences are small, they are not negligible in some cases (up to 5 g/cm2 for the worse case) and they should be considered as a systematic uncertainty of the model predictions for «Xmax» and RMS(Xmax). We have included a table with the suggested systematic uncertainties for the model predictions. Finally, we present a parametrization of the Xmax distribution as a function of mass and energy according to the models Sibyll2.1 and QGSJetII, and showed an example of its application to obtain the predicted Xmax distributions from cosmic ray propagation models. © 2013 Elsevier B.V. All rights reserved.Carlos Jose Todero Peixoto, Vitor de Souza, Jose Alfredo Bellid
Monte Carlo Performance Studies for the Site Selection of the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) represents the next generation of
ground-based instruments for very-high-energy (VHE) gamma-ray astronomy, aimed
at improving on the sensitivity of current-generation experiments by an order
of magnitude and providing coverage over four decades of energy. The current
CTA design consists of two arrays of tens of imaging atmospheric Cherenkov
telescopes, comprising Small, Medium and Large-Sized Telescopes, with one array
located in each of the Northern and Southern Hemispheres. To study the effect
of the site choice on the overall \gls{cta} performance and support the site
evaluation process, detailed Monte Carlo simulations have been performed. These
results show the impact of different site-related attributes such as altitude,
night-sky background and local geomagnetic field on CTA performance for the
observation of VHE gamma rays.Comment: 34 pages, 11 figures, Accepted for publication in AP
The Pierre Auger Observatory III: Other Astrophysical Observations
Astrophysical observations of ultra-high-energy cosmic rays with the Pierre
Auger ObservatoryComment: Contributions to the 32nd International Cosmic Ray Conference,
Beijing, China, August 201
Operations of and Future Plans for the Pierre Auger Observatory
Technical reports on operations and features of the Pierre Auger Observatory,
including ongoing and planned enhancements and the status of the future
northern hemisphere portion of the Observatory. Contributions to the 31st
International Cosmic Ray Conference, Lodz, Poland, July 2009.Comment: Contributions to the 31st ICRC, Lodz, Poland, July 200
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
Measurement of the Depth of Maximum of Extensive Air Showers above 10^18 eV
We describe the measurement of the depth of maximum, Xmax, of the
longitudinal development of air showers induced by cosmic rays. Almost four
thousand events above 10^18 eV observed by the fluorescence detector of the
Pierre Auger Observatory in coincidence with at least one surface detector
station are selected for the analysis. The average shower maximum was found to
evolve with energy at a rate of (106 +35/-21) g/cm^2/decade below 10^(18.24 +/-
0.05) eV and (24 +/- 3) g/cm^2/decade above this energy. The measured
shower-to-shower fluctuations decrease from about 55 to 26 g/cm^2. The
interpretation of these results in terms of the cosmic ray mass composition is
briefly discussed.Comment: Accepted for publication by PR
Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory
The Pierre Auger Collaboration has reported evidence for anisotropy in the
distribution of arrival directions of the cosmic rays with energies
eV. These show a correlation with the distribution
of nearby extragalactic objects, including an apparent excess around the
direction of Centaurus A. If the particles responsible for these excesses at
are heavy nuclei with charge , the proton component of the
sources should lead to excesses in the same regions at energies . We here
report the lack of anisotropies in these directions at energies above
(for illustrative values of ). If the anisotropies
above are due to nuclei with charge , and under reasonable
assumptions about the acceleration process, these observations imply stringent
constraints on the allowed proton fraction at the lower energies
A search for point sources of EeV photons
Measurements of air showers made using the hybrid technique developed with
the fluorescence and surface detectors of the Pierre Auger Observatory allow a
sensitive search for point sources of EeV photons anywhere in the exposed sky.
A multivariate analysis reduces the background of hadronic cosmic rays. The
search is sensitive to a declination band from -85{\deg} to +20{\deg}, in an
energy range from 10^17.3 eV to 10^18.5 eV. No photon point source has been
detected. An upper limit on the photon flux has been derived for every
direction. The mean value of the energy flux limit that results from this,
assuming a photon spectral index of -2, is 0.06 eV cm^-2 s^-1, and no celestial
direction exceeds 0.25 eV cm^-2 s^-1. These upper limits constrain scenarios in
which EeV cosmic ray protons are emitted by non-transient sources in the
Galaxy.Comment: 28 pages, 10 figures, accepted for publication in The Astrophysical
Journa
Azimuthal asymmetry in the risetime of the surface detector signals of the Pierre Auger Observatory
The azimuthal asymmetry in the risetime of signals in Auger surface detector
stations is a source of information on shower development. The azimuthal
asymmetry is due to a combination of the longitudinal evolution of the shower
and geometrical effects related to the angles of incidence of the particles
into the detectors. The magnitude of the effect depends upon the zenith angle
and state of development of the shower and thus provides a novel observable,
, sensitive to the mass composition of cosmic rays
above eV. By comparing measurements with predictions from
shower simulations, we find for both of our adopted models of hadronic physics
(QGSJETII-04 and EPOS-LHC) an indication that the mean cosmic-ray mass
increases slowly with energy, as has been inferred from other studies. However,
the mass estimates are dependent on the shower model and on the range of
distance from the shower core selected. Thus the method has uncovered further
deficiencies in our understanding of shower modelling that must be resolved
before the mass composition can be inferred from .Comment: Replaced with published version. Added journal reference and DO
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