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Register a new userStudies of Air Showers above 10^18 eV with the CHICOS Array
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CHICOS (California HIgh school Cosmic ray ObServatory) is presently an array of more than 140 detectors distributed over a large area (~400 km^2) of southern California, and will consist of 180 detectors at 90 locations in the near future. These sites, located at area schools, are equipped with computerized data acquisition and automatic nightly data transfer (via internet) to our Caltech lab. The installed sites make up the largest currently operating ground array for ultra-high energy cosmic ray research in the northern hemisphere. The goal of CHICOS is to provide data related to the flux and distribution of arrival directions for ultra-high energy cosmic rays. We have performed detailed Monte-Carlo calculations to determine the density and arrival-time distribution of charged particles in extensive air showers for the CHICOS array. Calculations were performed for proton primaries with energies 10^18 to 10^21 eV and zenith angles out to 50 degrees. We have developed novel parameterizations for both distributions as functions of distance from the shower axis, primary energy, and incident zenith angle. These parameterizations are used in aperture calculations and reconstruction of shower data, enabling preliminary analysis of ultra-high energy shower data from CHICOS.
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In this paper, we present results obtained from the measurements of radio emission at frequency of 32 MHz with energy more than 10$^{19}$ eV. Generalized formula that describe lateral distribution and depends on main characteristic of the air showers: energy E$_0$ and depth of maximum X$_{max}$ was derived. The formula has a good agreement with data at average and large distances from shower axis. Employing the ratio of radio emission amplitude at distances 175 m and 725 m we determined the depth of maximum X$_{max}$ for air shower with energy 3.7$cdot$10$^{19}$ eV, which in our case is equal to X$_{max}$ = 769$pm$34g$cdot$cm$^{-2}$.
The energy reconstruction of extensive air showers measured with the LOFAR Radboud Air Shower Array (LORA) is presented in detail. LORA is a particle detector array located in the center of the LOFAR radio telescope in the Netherlands. The aim of this work is to provide an accurate and independent energy measurement for the air showers measured through their radio signal with the LOFAR antennas. The energy reconstruction is performed using a parameterized relation between the measured shower size and the cosmic-ray energy obtained from air shower simulations. In order to illustrate the capabilities of LORA, the all-particle cosmic-ray energy spectrum has been reconstructed, assuming that cosmic rays are composed only of protons or iron nuclei in the energy range between $sim2times10^{16}$ and $2times10^{18}$ eV. The results are compatible with literature values and a changing mass composition in the transition region from a galactic to an extragalactic origin of cosmic rays.
We present the results of the search for ultra-high-energy photons with nine years of data from the Telescope Array surface detector. A multivariate classifier is built upon 16 reconstructed parameters of the extensive air shower. These parameters are related to the curvature and the width of the shower front, the steepness of the lateral distribution function, and the timing parameters of the waveforms sensitive to the shower muon content. A total number of two photon candidates found in the search is fully compatible with the expected background. The $95%,$CL limits on the diffuse flux of the photons with energies greater than $10^{18.0}$, $10^{18.5}$, $10^{19.0}$, $10^{19.5}$ and $10^{20.0}$ eV are set at the level of $0.067$, $0.012$, $0.0036$, $0.0013$, $0.0013~mbox{km}^{-2}mbox{yr}^{-1}mbox{sr}^{-1}$ correspondingly.
A search for ultra-high energy photons with energies above 1 EeV is performed using nine years of data collected by the Pierre Auger Observatory in hybrid operation mode. An unprecedented separation power between photon and hadron primaries is achieved by combining measurements of the longitudinal air-shower development with the particle content at ground measured by the fluorescence and surface detectors, respectively. Only three photon candidates at energies 1 - 2 EeV are found, which is compatible with the expected hadron-induced background. Upper limits on the integral flux of ultra-high energy photons of 0.038, 0.010, 0.009, 0.008 and 0.007 km$^{-2}$ sr$^{-1}$ yr$^{-1}$ are derived at 95% C.L. for energy thresholds of 1, 2, 3, 5 and 10 EeV. These limits bound the fractions of photons in the all-particle integral flux below 0.14%, 0.17%, 0.42%, 0.86% and 2.9%. For the first time the photon fraction at EeV energies is constrained at the sub-percent level. The improved limits are below the flux of diffuse photons predicted by some astrophysical scenarios for cosmogenic photon production. The new results rule-out the early top-down models $-$ in which ultra-high energy cosmic rays are produced by, e.g., the decay of super-massive particles $-$ and challenge the most recent super-heavy dark matter models.
This paper presents the set of measurements of ultra-high energy air shower radio emission at frequency 32 MHz in period of 2008-2012. The showers are selected by geomagnetic and azimuth angles and then by the energy in three intervals: 3*10^16 3*10^17 eV, 3*10^17 6*10^17 eV and 6*10^17 5*10^18 eV. In each energy interval average lateral distribution function using mathematically averaged data from antennas with different directions are plotted. In the paper, using experimental data the dependence of radio signal averaged amplitude from geomagnetic angle, the shower axis distance and the energy are determined. Depth of maximum of cosmic ray showers Xmax for the given energy range is evaluated. The evaluation is made according QGSJET model calculations and average lateral distribution function shape.
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